RECYCLED PET IN FINLAND –

what to do with it?

Valeria Poliakova

Department of Business administration,

Media and Technology

Arcada

Department of Business administration, Media and Technology

Industrial Management

Helsinki 2008

DEGREE THESIS

Arcada – University of applied sciences

Degree Programme: Industrial Management

Identification number: 6322

Author: Valeria Poliakova

Title: RECYCLED PET IN FINLAND – what to do with it?

Supervisor: Mikael Paronen

Commissioned by: Marianne Holmberg

Abstract:

The growing threat of oil coming to an end and the limited capacity of landfills make plastic

recycling a promising alternative for landfilling. The increasing price of plastics makes recycling of

expensive and middle-price plastics economically attractive. Polyethylene terephthalate (PET) is a

middle-price plastic readily available on the Finnish market due to an implemented PET bottles

return system.

The questions considered in the present work is how should returned PET bottles be treated, and

how does then properties of polyethylene terephthalate (PET) and recycled polyethylene

terephthalate (RPET) differ. A system of PET recycling is considered as an extension of Finnish

PET bottles return system.

The work was conducted by examining existing information on PET recycling and applying it to

Finnish circumstances. Existing literature considering recycling in Germany and USA was studied

and information available in the internet collected. Interviews with local recyclers and involved

authorities were conducted.

As a result of the analysis of information available the conclusion has been made that the best

treatment method for PET bottles is back-to-bottles recycling. While all properties of PET are

affected by recycling, a noticeable change might occur in mechanical strength, color, transparency

and odor. The results apply to RPET obtained through Finnish bottles return system.

Keywords: Waste management, PET recycling

Number of pages: 103 (without attachments)

Language: English

Date of acceptance: 23.09.2008

Table of Contents

LIST OF FIGURES AND TABLES ............................................................................. 6

ABBREVATIONS ........................................................................................................ 8

1 INTRODUCTION ................................................................................................... 11

1.1 Background ....................................................................................................... 12

2 Recycling system ..................................................................................................... 16

2.1 Technical considerations ................................................................................... 16

2.2 Economical consideration .................................................................................. 17

2.3 Ecological considerations .................................................................................. 20

2.4 Normative and legal considerations ................................................................... 21

2.5 Recycling in Finland ......................................................................................... 23

3 PET and RPET - Overview ...................................................................................... 25

3.1 PET ................................................................................................................... 25

3.1.1 Production .................................................................................................. 25

3.1.2 Processing .................................................................................................. 28

3.1.3 Properties ................................................................................................... 34

3.1.4 Products ..................................................................................................... 44

3.2 RPET ................................................................................................................ 46

3.2.1 Production .................................................................................................. 46

3.2.2 Re-Processing ............................................................................................. 46

3.2.3 Properties ................................................................................................... 51

3.2.4 Products ..................................................................................................... 52

4 From material to product .......................................................................................... 61

4.1 Correlation between polymer properties, polymer characteristics and processing parameters ............................................................................................................... 61

4.1.1 Characteristics of polymer .......................................................................... 63

Molecular weight ................................................................................................ 64

Chemical structure of a polymer molecule ........................................................... 69

Polymer morphology ........................................................................................... 69

Co-polymers and blends ...................................................................................... 71

Additives ............................................................................................................. 71

4.1.2 Processing parameters ................................................................................ 73

4.2 Typical challenges in PET recycling .................................................................. 79

4.2.1 Degradation ................................................................................................ 79

4.2.1.1 Hydrolysis ........................................................................................... 80

4.2.1.2 Thermal degradation ............................................................................ 80

4.2.1.3 Mechanical degradation ....................................................................... 80

4.2.2 Contamination ............................................................................................ 80

4.2.3 Thermal history .......................................................................................... 85

5 Applications for RPET ............................................................................................. 88

5.1 Systematic approach .......................................................................................... 88

5.2 Comparing specifications to requirements ......................................................... 90

5.3 The most similar to PET plastics ....................................................................... 95

6 CONCLUSION ........................................................................................................ 99

6.1 FUTURE DEVELOPMENTS ......................................................................... 100

7 AKNOWLEDGEMENTS ...................................................................................... 101

8 REFERENCES ...................................................................................................... 102

9 Appendices ............................................................................................................ 115

9.1 Types of pelletizers ......................................................................................... 115

9.2 Techniques of measuring molecular weight ..................................................... 119

9.3 PET and market ............................................................................................... 125

9.3.1 Plastic manufacturers ................................................................................ 125

9.3.1.1 PET Manufacturers (representatives in Finland) ................................. 125

9.3.1.2 Others (representatives in Europe) ..................................................... 126

9.3.2 Plastic distributors (operating in Finland) ................................................. 128

9.3.3 Manufacturers of semi-finished products .................................................. 130

9.3.3.1 Companies, processing PET ............................................................... 130

9.3.3.2 Potential PET processors.................................................................... 131

9.3.4 Examples of equipment suppliers for the recycling ................................... 133

Potential applications for RPET ............................................................................ 134

LIST OF FIGURES AND TABLES

Figure 1 Waste recovery options [7] ............................................................................ 13

Figure 2 Stages of a plastic item production and use, and plastic waste utilization ...... 21

Figure 3 Circulation of RPET in Finland ..................................................................... 23

Figure 4 Chemical structure of the repeating unit of PET molecule [19] ...................... 25

Figure 5 Process of PET production [20] ..................................................................... 26

Figure 6 Schematic sketch of an extruder [28] ............................................................. 30

Figure 7 The schematic sketch of a vent type molding machine [36] ........................... 32

Figure 8 Tensile strength of PET and selected materials .............................................. 35

Figure 9 Elongation at break of PET and selected materials ........................................ 36

Figure 10 Tensile modulus of elasticity of PET and selected materials ........................ 37

Figure 11 Maximum short service temperature of PET and selected materials ............. 39

Figure 12 Water absorption (24h) of PET and selected materials ................................. 40

Figure 13 Permeability of water vapor in PET film and selected materials* ................ 42

Figure 14 Permeability of CO2 in PET film and selected materials* ............................ 42

Figure 15 Price fluctuation of PET over a period from April, 2006 to April, 2008 [50] 44

Figure 16 Applications of PET in Europe, 1999 [37] .................................................. 45

Figure 17 Price of RPET and selected polymers .......................................................... 51

Figure 18 Outlets for recovered PET in Europe [58] .................................................... 54

Figure 19 The rucksack and the hat made of recycled PET [60] .................................. 54

Figure 20 The carpet, the umbrella and the mouse pad made of recycled PET [60]...... 55

Figure 21 The pontoone-boat based on PET bottles [68] ............................................. 56

Figure 22 The bottle made of RPET [69]..................................................................... 57

Figure 23 RPET brush and bag [70] ............................................................................ 57

Figure 24 The plant-watering vessel made of PET bottle [71, 72] ................................ 58

Figure 25 The bottle-filter made of PET bottle [73] ..................................................... 58

Figure 26 The blurring screen made of parts of PET bottles [74] ................................. 59

Figure 27 The lamp decoration made of parts of PET bottles [74] ............................... 59

Figure 28 The bags and containers made of RPET [75] ............................................... 60

Figure 29 The factors affecting the properties of a polymer ......................................... 62

Figure 30 The relation between processing parameters, characteristics of a polymer and

properties of a polymer ........................................................................................ 63

Figure 31 Influence of characteristics of polymer on its properties .............................. 64

Figure 32 Dependence of mechanical properties on the molecular weight of a polymer

[76] ..................................................................................................................... 64

Figure 33 Schematic plot of a molecular weight distribution with average molecular

weights [76] ........................................................................................................ 68

Figure 34 Effect of stabilizers (phosphite P-1 and phenolic antioxidant AO-1) on

molecular weight of RPET [81] ........................................................................... 73

Figure 35 Linear growth rate of spherulites in PET as a function of temperature at

pressure of 1 bar [78] .......................................................................................... 76

Figure 36 Age pyramid of respondents ........................................................................ 84

Figure 37 The effect of recycling on relation of characteristics of polymer, processing

parameters and polymer properties ...................................................................... 86

Figure 38 Schematic representation of optimal profile for PET sheet .......................... 93

Figure 39 Optimal profile for PET sheet...................................................................... 94

Figure 40 Plot of molecular weight distribution obtained by SEC [3] ........................ 121

Figure 41 A plot of dependence of viscosity on concentration [3].............................. 122

Table 1 Bond energy of the bonds found in PET molecule .......................................... 13

Table 2 Stages of a plastic item production from raw material and from recycled

material ............................................................................................................... 19

Table 3 The drying conditions for PET ....................................................................... 29

Table 4 Intrinsic viscosity values of different PET resin grades ................................... 41

Table 5 Properties of crystalline and amorphous structures ......................................... 70

Table 6 Properties of PET sheets produced by different manufacturers ....................... 91

Table 7 Plastics which one or few properties have value similar to PET property value ±

5 % ..................................................................................................................... 96

Table 8 Rank of the most similar to PET plastic .......................................................... 98

ABBREVATIONS

AA Acetaldehyde

ABS Acrylonitrile polybutadiene styrene

ASA AN/AN elastomers/ styrene

ETFE Ethylene/ Tetrafluoroethylene copolymer

EVOH Ethylene Vinyl Alcohol

FDA Food and Drug Administration

FEP Tetrafluoroethylene/ hexafluoropropylene copolymer

IV Intrinsic Viscosity

OPP Oriented Polypropylene Film

PA 11 Polyamide 11

PA 6 Polyamide 6

PA 66 Polyamide 66

PAE Polyaryl ether

PAS Polyaryl sulfone

PB Polybutene-1

PBT Polybutylene terephthalate

PC Polycarbonate

PCTFE Polychlorotrifluoroethylene

PDAP Polydiallyphthalate (GF) molding compound

PEN Polyethylene naphthalate

PES Polyether sulfone

PET Polyethylene terephthalate

PETG Glycol-modified polyethylene terephthalate

PETN Naphthalate-modified polyethylene terephthalate

PF Phenol/formaldehyde

PI Polyimide molding

PMMA Polymethyl methacrylate

POM Polyacetal

PP Polypropylene

PPE Polyphenylene ether modified

PPS Polyphenylene sulfide

PS Polystyrene

PSU Polysulfone

PTFE Polytetrafluoroethylene

PVC-P Plasticized PVC

PVC-U Rigid PVC

PVK Polyvinyl carbazole

RPET Recycled polyethylene terephthalate

SAN Styrene/ Acrylonytril copolymer

SB Styrene/ Polybutadiene

SEC Size Exclusion Chromatography

SI Silicone resin

Tg Glass-transition temperature

Tm Melting temperature

TEKES Teknologian ja innovaatioiden kehittämiskeskus

TPA Terephtalatic acid

UF Urea/formaldehyde

UP Unsaturated polyester

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1 INTRODUCTION

With an increasing amount and variety of goods produced, waste management becomes

a timely and important topic. In the year 2005, there were 354 900 tonnes of plastic

packaging used in Finland. Out of this packaging 72 % (254 800 tonnes) were reused.

Out of residuary 100 100 tonnes, 15 % were recycled, which is 7.5 % less than the EU

target for recycling of plastic waste in 2008 [1].

The reuse of packaging means that a material was not altered by any processing, unlike

recycling, which implies that a material was re-processed. For instance, if after one use

a plastic bottle − one type of plastic packaging − was washed and re-filled with

contents, it was re-used. If, on the contrary, it was re-melted and extruded into another

bottle, it said to be recycled. A bottle that is recycled after one use is called a single

serve bottle, while bottle reused after one use is called a refillable bottle. The term

“recovery” refers to all kinds of waste treatment where energy or material is recovered

from a process.

The use of term “waste” is ambiguous when plastic packaging is considered. In

everyday language waste is something out of use. From a consumer point of view, used

plastic bottle is waste, while from a recycler point of view it is a resource. According to

[2], packaging waste is “out of use packaging before possible recovery”.

In Finland the producer or importer of alcohol-containing and non-alcoholic drink- and

beverage- packaging has to pay a tax for almost all of the packaging it produces/

imports. Since the year 2005 the tax for the single serve packaging has been 8.5 cents –

17 cents/ liter, if a package can be recovered in the existing system or 51 cents/liter, if

not. Refillable packaging has not been the subject to taxation. In the beginning of 2008

the tax for single serve recyclable packaging was removed, so that an increase in the

amount of recyclable plastic waste is expected [3].

Plastic bottles are one of the most common types of recyclable plastic packaging. Most

plastic bottles in the recycling system are bottles made of PET plastic. The plastic

bottles are produced from small test tube like-looking bottles, preforms.

According to an article in Talouselämä [4], the production goal of Preformia Oy, the

only company in Finland producing preforms for PET-bottles, is 200 millions preforms

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a year. Assuming that all the bottles will stay on the domestic market, the amount of

plastic waste potentially available after the use of those bottles is 8 000 tonnes of clean

PET, given that an average weight of a plastic bottle is 40 g [5]. The actual amount of

PET bottles will be higher, as the bottles are produced also from imported preforms.

The bottles are different in color and used in different ways, so a grade of plastic waste

varies. What are those grades, how to treat different grades of PET plastic waste, and

what are the differences between PET and recycled PET (RPET) – are the main

questions discussed in this document.

The document in hand is a bachelor degree thesis. The conclusions of the work are

based on the analysis of extensive literature available on the topic. Sources of

information include text-books, professional magazines’ articles, newspapers’ reviews,

corporate web-pages, on-line databases, personal communications and a questionnaire.

The work addresses either a plastic manufacturer or a designer, considering RPET

plastic for an existing application or a producer of RPET, looking for possible

applications of the plastic. An idea behind is to provide the manufacturer, the designer

or the producer with sufficient information about RPET plastic in order to promote use

of RPET and to give some ideas about possible utilization of the material.

The document includes five chapters. Background information presented in the first

chapter gives and an overview of recovery methods and chapter 2 derives the best

recycling method for PET bottles. Chapter 3 gives an overview of PET and RPET

material; in chapter 4 factors affecting the quality of PET and RPET are investigated,

while in chapter 5 some ideas of applicability of RPET are given. IEEE style is for

referencing throughout the document [6].

1.1 Background

Recovery of waste is an alternative for waste disposal. A simplified scheme for plastic

recovery options is presented on figure 1 [7]:

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Recovery

Material Recycling

Energy Recovery

Composting

Feedstock Recycling

Same application

New application

Mechanical Recycling

Figure 1 Waste recovery options [7]

Composting is mostly applicable for biological waste, so it is not considered in this

work.

Energy recovery is a method to recover the energy content of plastic. It is based on the

fact that plastic is made of crude oil and therefore can be used as fuel.

The energy content of PET is 24 MJ/kg [8], value close to the heat content of the “soft

coal” (24-32 MJ/kg). The energy value recovered when burning PET can be calculated

using the algorithm described in [9] and the values for bond energy given in table 1.

Table 1 Bond energy of the bonds found in PET molecule

Bond Amount in PET molecule

Bond energy (kJ/mol)

C – H 8 412

C – C 6 348

C – O 4 360

C = C 3 518 (benzene)

C = O 2 743

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The calculation is not performed in this work, as for PET bottles recommended

recovery process is recycling [10] for reasons discussed in chapter 2.

Not only energy, but also material can be recovered from waste. The process is called

material recycling. Two types of material recycling are mechanical recycling and

feedstock recycling.

The principle of feedstock recycling is breakdown of a polymer into molecules, which

are lately separated from impurities and used as raw materials such as gas and oil.

Breakdown of molecules is achieved by thermal decomposition of molecules commonly

assisted by chemical substances.

Thermal decomposition is a process when the temperature of a polymer is increased so

that the flexibility of chains rises and they eventually break. For the chains containing

oxygen (like in case of PET), decomposition starts at high rate already at 300 ˚C [11].

The process can be catalyzed with oxygen, alcohols, metal ions, or water.

If oxygen accelerates the degradation of a polymer in a melt so that decomposition

temperature can be reduced by about 150 ˚C, the process is called oxidation; when

water is added to breakdown a polycondenced polymer –the name used is hydrolysis.

Feed stock recycling method that is usually used with PET is solvolysis. Solvolysis is

degradation of PET obtained by using alcohols or water. Three different alternatives of

solvolysis can be found as industrial methods: glycolysis (boiling glycol), methanolysis

(methanol) or hydrolysis (water). The description of these processes is available in the

literature [12, 13].

Mechanical recycling is a method of recovery a material from waste by means of

mechanical processing. In order to be recycled, PET bottles have to be collected from a

store and baled. The actual recycling process refers to sorting bottles, separating bottles

from waste, few stages of washing and drying the bottles, grinding the bottles to flakes

and pelletizing of flakes. The flakes can also be sold as raw material prior to pelletizing.

Very often the recycling process is extended so that pellets or flakes are immediately

processed into a plastic product. This product can serve the same purpose as a recycled

one (the same application), or satisfy a new need (a new application).

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PET bottles, either single serve or refillable after the last use, are usually mechanically

recycled. Reasons behind this choice and challenges of mechanical recycling are

considered in chapter two.

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2 RECYCLING SYSTEM

2.1 Technical considerations

Nowadays, when the humankind is threatened by the possible end of limited natural

resources like oil and gas, recycling can be viewed as salvation. When material is

recycled a new portion of raw martial is not taken from the depths of the earth.

As it was mentioned in 1.1, plastic waste can be recycled for a new application, the

same application, or as feedstock.

Post-consumer plastic, or plastic considered as waste by a consumer, can be

conventionally divided into four categories (see list below). Single-grade plastic refers

to plastic of one type, while mixed-grade means mixture of different plastic types.

1. Single-grade production and processing scarp and surplus raw material

2. Single-grade post-consumer commercial waste

3. Mixed-grade post-consumer commercial waste

4. Household waste and agricultural plastic waste

The first category has the best recycling possibilities: the cleaner and more

homogeneous plastic is within the grade, the higher is its possibility to be mechanically

recycled into a useful product and to compete with a virgin material [13].

Single-grade post consumer plastic already has the substantial level of contamination,

but can still be recycled for the same application or for a new application, depending on

the level of contamination, collecting practices and history of products [13].

The best waste treatment option for mixed-grade post-consumer commercial and

domestic plastic is energy-recovery or feed-stock recycling [13].

The last option is to dump plastic in a properly-organized landfill, what is undesirable,

due to the limited available space and the long biological rate of degradation of plastics.

So, technically speaking, the best recycling option for PET bottles is mechanical

recycling.

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Whether PET is recycled for a new or the same application is defined by a history of a

plastic and its contamination. During its lifetime PET bottles are exposed to oxygen,

humidity, wear, and various processing [13]. The history of a bottle has an influence on

its properties, so recycling for the same application might be impossible, as plastic do

not satisfy the initial specifications any more. There are methods to upgrade deteriorated

quality of plastic, like compounding or blending it with other plastic, using additives or

mixing it with virgin plastic. Some mechanical processes can be also utilized to improve

the quality of a recyclate. Another technical challenge for mechanical recycling is

contamination. The effect of the plastic history and contamination on a recycling

process is considered in chapter 4.

2.2 Economical consideration

When considering viability of recycling, economical benefits play an important role. A

company that recycles plastics participates in market activities according to market

rules. It means, that apart of struggling to survive and success on the market, it faces

some additional challenges like

• varying quantity of incoming raw material

• varying quality of incoming material

• deterioration of quality of recycled material comparing to virgin one

• conformity to standards (not only the a final product, but also a manufacturing

process, monitoring, etc…see ISO 9000)

• public attitude for recycled products

In practice it means that a company has to deal with a high level of uncertainty, as it is

difficult, if not impossible, to predict amount of post-consumer plastic available for use

at a certain time and quality of recyclate. Recyclate quality heavily depends on the

previous history of plastics and methods of collection [13].

Apart of uncertainty, a company has to solve the problem of deterioration of recyclate

quality, what often means increase in equipment and qualified labor cost.

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According to the managing director of Muovix, Mika Surakka, conformation to

standards is a rock on the way of a recycling company. When dealing with an undefined

source of material, following standards is challenging. In many cases conformity to

standards means for a company a lack of freedom to chose what product to bring to the

market.

Public attitude is an important factor in defining success of a product on the market.

While some tendencies toward change in attitude do exist, still, majority of consumers

would not pay more or even the same for a recycled product. The evidences of change

in attitude can be found in a change of focus of companies (a strategic goal of Neste Oil

Oy “is to make the company a world’s leader in biodiesel production”), in the focus of

researchers in the “green” topics (fuel cell research, etc), in the media, in the

entertaining industry (“Inconvenient truth” movie), etc. The change in attitude is

expected to induce a change in consumer behavior, such as conscious purchases of

“green” energy or a recycled product. The change is slow, and until consumers change

there habits, a recycling company faces a challenge to promote its goods.

One should not forget about competitors –possible competitors for a company making

products from recycled plastic are manufacturers of the same product from

corresponding virgin plastics, manufacturers of the same product from other virgin

plastics and other recycling companies producing this product. In the case when

recycled plastic is utilized for some other but original product, the conventional material

for the new product would compete with recycled plastic (for example, if recycled

plastic is used for profiles that were originally made from impregnated wood, plastic

will compete with wood).

In most of the cases, a plastic can be recycled for the same application only if one or

few of quality-enhancing methods are used (additives, vacuum, etc). These methods

impose an additional cost on recycling, and thus add to the price of a final product. If

the increment in the price makes a product incompetent on the market, a plastic should

be recycled to a product with lower quality requirements, so that no additional quality

enhancement is needed.

Life-time costs of a product made of raw material and a product made of recycled

material are presented in table 2

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Table 2 Stages of a plastic item production from raw material and from recycled

material

Production from raw material Production from recycled plastic

Raw material

Oil well operations Collecting

Crude oil transport Sorting

Oil refining Grinding

Naphtha production Washing

Resin production Drying

Pelletizing Pelletizing

Processing Processing

Packaging Packaging

Transportation Transportation

Disposal Disposal � Collecting

Some of the stages are the same for both sequences (they are italic in the table). Other

stages are exclusive for each production. The difference in the prices of pristine and

recycled plastics arises from the difference in those exclusive stages. The necessity to

sort post-consumer plastic or to use sophisticated washing processes increases the cost

of plastic recycling and can make production unviable [13].

Production from RPET is economically viable if the cost of collecting the bottles,

sorting, grinding, washing, drying, and processing the plastic is less than sum of costs of

raw material (oil), oil well operations, crude oil transport, oil refining, naphtha

production, resin production, and processing and disposal of PET.

In cost estimation of production from pristine PET some intangible “costs” of oil

refining such as pollution of the environment and the opportunity cost of oil

consumption for resin production should be estimated as precise as possible.

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Profitability of recycling can be increased if a government encourages conservation of

resources or landfill space by economical instruments (Economic instruments for

encouraging plastic recycling are discussed by Brandrup et all in chapters 1.3 -1.4 [13]).

2.3 Ecological considerations

Once more figure 2 illustrates the process of plastic item production, product use and

energy recovery.

Pelletizing, processing, packaging and transportation stages are the same, whether

recycled or pristine polymer is used for making a product (compare the box on the top

with the box of Option 2). Assuming, that energy requirements of RPET and PET

processing are similar, the production of resin is the only stage that is not needed when

the recycled polymer is used instead of virgin one. Since a polycondensation reaction is

endothermic, energy required for polymerization will be wasted, if the product is

landfilled after one use (option 1). If, instead of landfilling, plastic is recovered as

material, energy will be required for numerous processing stages like collecting of

bottles, washing, grinding, etc… (option 2). Following this logic, recycling is viable

from the ecological point of view only if energy required for recycling of plastic

(collecting of bottles, sorting, grinding, washing, and drying) is less than energy

required for polymerization of plastic. That is why, for example, the recycling of

contaminated mixed film is not ecologically viable [13].

On the other hand, washing, grinding and re-processing are partially avoided if the

polymer is recovered as energy or as feedstock material after the first use. So, if

substantial washing, sorting and re-processing is required to make a quality product

from RPET, energy recovery or feedstock recycling options are the most viable

recovery methods.

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Option 1 (when material and its energy content is wasted)

• Disposal (landfill)

• Resin production

• Pelletizing

• Processing

• Packaging

• Transportation

Option 2 (when material is recovered as material, i.e. mechanically recycled)

• Collecting

• Sorting

• Grinding

• Washing

• Drying

• Pelletizing

• Processing

• Packaging

• Transportation

• Disposal/ � Collecting

Option 3 (when material recovered as energy)

• Collecting

• Grinding / Washing / Drying (optional)

• Combusting

• Disposal of aches

USE OF A PLASTIC PRODUCT

Figure 2 Stages of a plastic item production and use, and plastic waste utilization

2.4 Normative and legal considerations

According to the EU legislation [14], in sustainable waste management waste

prevention is the first option, recycling /energy recovery - second option and landfilling

–the last, undesirable one. Local governments are encouraged to implement the

sustainable waste management. There are financing programs to assist companies

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utilizing waste as a raw material (for example, maximum 5-year-long gradually

descending financial aid granted for waste management and energy recovering

companies).

As was mentioned before, one of the challenges of a recycling company is conformity

to standards. Not only the quality of a product, but also raw material, research and

development, manufacturing processes and internal logistics –are all subject for the

standardization [13]. Because of the standards, a manufacturer is not free to choose an

application and has to restrict raw material to clean plastic of a known origin.

If RPET is considered for an application that might be in contact with food, a plastic

manufacturer should consult product safety requirements of EC Directive 2002/72/EC

[15, 16].

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2.5 Recycling in Finland

Circulation of RPET starts and ends in a recovery company, if the plastic is not

disposed after regular use (see figure 3).

Packers Hartwall Sinebrychoff

Importers from abroad

Shops CityMarket

Transport companies L&T

Collection points

Recovery companies Preformia, Muovix

PALPA’s responsibilities

SUM’s responsibilities

users

Figure 3 Circulation of RPET in Finland

The biggest producer of RPET in Finland is Preformia Oy, manufacturer of PET

preforms with content of recycled material up to 50 %. Preformia’s partner on the

market is the distributor of PET and RPET in Finland, Kauko-Telko Oy. The biggest

clients of Preformia Oy are Finn Spring Oy and Bull Berry Oy [17].

Preforms can be processed into bottles right after the process of preforms production or

before the bottles are filled with contents. Beverage companies and breweries that

produce bottles from preforms themselves are classified as packing companies.

Sinebrychoff Oy and Hartwall Oy are examples of those.

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According to the Finnish law, packing companies and importers of plastic packaging

(including bottles) are responsible for its disposal.

In order to facilitate the transfer of used packaging back to packers, some controlling

and organizational units are founded by the packers and the importers.

PYR (Pakkausalan Ympäristörekisteri) is the supervising organization for several

producer organizations. Other functions of PYR are statistics compilation, collection of

recovery fees, registration of new members (packers and importers), reporting to

governmental environmental organizations and the informative function [18].

Each producer organization is responsible for certain types of recyclable packaging and

promotion of sustainable packaging use and disposal.

The producer organization for plastics is Suomen Uusiomuovi OY (SUM), promoting

the recycling of plastic in Finland. SUM has a contract with a number of plastic

recyclers and transportation firms. At the moment this work was concluded, one of the

partner companies, Muovix Oy, was launching the project regarding PET recycling at

its factory in Salo, Finalnd.

Palpa (Suomen Palautuspakkaus Oy) coordinates the activities within the recycling

system together with Ekopulloyhdistys.

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3 PET AND RPET - OVERVIEW

3.1 PET

3.1.1 Production

The chemical formula of PET is (-(C6H4)-CO-O-CH2-CH2-CO-O-)n and a repeating unit

is presented on figure 4:

Figure 4 Chemical structure of the repeating unit of PET molecule [19]

PET polymer is produced in two steps:

The first step is an esterification reaction, where terephtalatic acid reacts with ethylene

glycol to produce bis-hydroxyethyl terephthalate (bis-HET) and water (see figure 5).

Alternatively, PET is produced by a trans-esterification reaction, where demethyl

terephthalate reacts with ethylene glycol to produce bis-hydroxyethyl terephthalate (bis-

HET) and methanol. During the reaction the temperature has to be 258-263 ˚C and the

gauge pressure should be below 1.7 bar

The second step is a polycondensation reaction, which results in PET polymer as the

main product and ethylene glycol as the by-product.

The conditions for the polycondensation reaction are following:

− the temperature higher than melting temperature (260 -265 ˚C), but lower than the

temperature, when a fast decomposition starts (300 ˚C)

− the time of reaction is minimum 2 hours

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Ethylene glycol (EG) is to be removed from the reaction as quickly as possible, so that

the equilibrium is driven towards the polycondensation reaction, what is essential

especially near the end of the reaction. Removal of EG is achieved with vacuum and

continuous mixing of a melt. Removed ED can be reused in the esterification reaction

[20].

P

olycondensation reaction

+

p (< 1,7 atm, gauge), t (258-263 ’C) PET + EG

H2O (product of reaction)

bis-hydroxyethyl terephatalate (bis-HET)

terephtalatic acid (TPA) –low roxity (1,4 benzenedicarboxylic acid, C6H4(COOH)2, M = 166, 14 g/mol

ethylene glycol (EG) – toxic (ethane – 1,2 diol, HOCH2CH2OH)

+

Figure 5 Process of PET production [20]

Before continuing, few concepts should be explained. The molecular weight, the degree

of polymerization and intrinsic viscosity are definitions used frequently with regard to

polymers.

In the text of this document the molecular weight of polymer implies the molecular

weight of one polymer molecule. An issue of variations of weight of molecules in a

polymer sample, the molecular weight distribution and techniques for measuring the

molecular weight are discussed in 4.1.1.1. Units of the molecular weight are g/mol. The

degree of polymerization is closely related to the molecular weigh of a polymer. The

degree of polymerization shows how many monomers constitute a polymer molecule

and is unitless. Intrinsic viscosity is directly proportional to the molecular weight of a

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polymer. Its units are dL/g, what is the reciprocal of the concentration unit. The

description of molecular weight measuring techniques utilizing intrinsic viscosity of a

polymer can be found in attachment 2.

The molecular weight determines dramatically possible applications of a polymer. In

order to use PET for production of a fibre, its degree of polymerization should be

around 14 000 – 20 000 [20].

Increasing intrinsic viscosity

Intrinsic viscosity, or shortly IV, is often used as an indicator of the molecular weight of

the plastic. Different grades of PET are defined by different IV value.

The polymer used for production of fibre should have intrinsic viscosity (IV) of 0.5 -

0.65. Bottle-grade PET has minimum IV of 0.72 [20].

Most of the companies are looking for methods to increase IV, despite the existing

information that higher than 1.1 IV tends to revert back to the lower IV during

“ordinary” processing [21].

To produce PET with IV 0.72 and higher the mixture should be polycondensated using

melt-stirred autoclaves (IV 0.6) and special heavy-duty reactors (IV up till 0.85) [20].

As some producers claim, by solid state polycondensation (SSP) it is possible to

increase IV of PET up to 1.2 [22].

PET should be crystallized prior to SSP process to avoid sticking it to a reactor. The

polymer is crystallized at 180 -235 ˚C till its density is around 1.3 g/c3. The temperature

of SSP reaction is close to the temperature that was used for crystallization or slightly

higher. During SSP reaction volatile products of the reaction are removed with the inert

gas, nitrogen [23]. Removal of the products shifts the balance of the reaction and the

molecular weight of PET increases.

Other IV increasing processes based on the solid state polycondensation are Stehning

process [24], and Schmalbach-Lubeca Supercycle [25].

During the polycondensation reaction of PET the formation of free acetaldehyde occurs,

what increases the total level of acetaldehyde in a final product. Above certain limits of

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concentration acetaldehyde can diffuse in a content of a final product, altering its taste

and aroma. SSP reaction decreases the level of free acetaldehyde in the polymer (see

details in 4.2.1) [23, 26].

3.1.2 Processing

PET, as most of the plastics, can be processed in various ways. Here is the short

overview of techniques used for PET processing.

Drying

PET pellets are produced by a polymerization process, what implies that under

sufficiently high temperature and presence of water the reaction can be reversed with

PET precursors, ethylene glycol and terephtalatic acid formed, i.e. hydrolytic

degradation can occur.

As PET is subject to the hydrolytic degradation, the raw material should be stored in a

dry place after polymerization.

In most of the cases, nevertheless, to prevent hydrolysis an appropriate drying process

should be applied.

Generally, plastics can be dried mechanically, thermally or by combination of both. In

case of PET the mechanical drying does not produce sufficient results, so PET is to be

dried thermally [27].

PET is dried inside of a hopper dryer (more sophisticated dehumidifier can be used

[19]), where hot air is pumped over the resin to remove moisture while flowing through

it. After that hot air leaves the hopper from the top and moves through an after-cooler (it

is easier to remove moisture from cold air than from hot) and later through a desiccant

bed (filled, for example, with silica). Dried air is then heated up again and the process is

repeated [28, 29]. Re-utilizing of the extracted heat could decrease the operating cost.

Drying time for the pellets is 4 h, for the regrind - 5-6 h. In [21] it is said, that every

four hours of additional heating would require a reduction of the drying temperature by

10 ˚C. If the portion of amorphous material in a feedstock is more than 40 %, the drying

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becomes problematic, as at 75 ˚C amorphous PET starts soften and forms clumps of

material sticking to the equipment and eventually depolymerizing. To avoid those

problems PET can be crystallized prior to the drying in a crystallizer (a drying hopper

with agitator), what takes 5-10 min at a temperature of 130 – 150 ˚C.

Table 3 The drying conditions for PET

Temperature 140 – 160 ̊ C (crystalline) [29]

150 – 180 ˚C (crystalline) [21]

Dew pointi - 32 [19]

Time 5-6 hours

Final moisture content 0.1 % [13, 29]

0.04 % [19, 21]

Extrusion

Extrusion is a “continuous shaping of plastic material by forcing it, as a melt, by

pressure through a die” [30]. A clear and detailed description of extruder components

and working principles of an extruder can be found in [30].

This document includes the overview of the processes relevant to processing of PET.

The general structure of an extruder is shown below [28]:

i The dew point is the temperature to which a given parcel of air must be cooled, at constant barometric

pressure, for water vapor to condense into water [31].

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Figure 6 Schematic sketch of an extruder [28]

First, the polymer is introduced to the hopper. Through the feedthroat the material is fed

to the barrel, where it moves toward the die with the help of the screw. The polymer

melts inside of the barrel by means of friction, by external heating or by combination of

both.

Possible impurities in the melt are removed by filters. Filters are protected by the rigid

case of breaker plate. The clean melt is pumped to the die, which shape depends on a

final product. The end result of extrusion process is usually a sheet, a tube, a film or a

pellet.

There are at least three zones in the screw – the feed zone (solids conveying zone), the

transition zone (melting zone) and the metering zone (pressurizing zone). The functions

of those zones are different and conditions (temperature and pressure) vary for different

plastics.

There are two kinds of extruders with regard to ratio of length of the screw (L) to its

diameter (D) [32]:

− A long screw extruder (L/D = 20:1 – 35:1). Approximately 70 % of the heat is

produced by friction, so an external heating source is needed.

− An adiabatic extruder (L/D = 10:1 – 15:1). Melting is a result of friction.

Another classification of extruders involves amount of screws they have. There are two

types of extruders we will be concerned with:

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− The first, a single screw extruder either with a smooth internals of the barrel

(conventional) or with grooves in the feed zone (grooved feed extruder)

− The second is a twin screw extruder which is perfect for mixing and compounding

of polymers. The twin screw extruder can have co-rotating or counter-rotating

screws which are intermeshing or not [33].

The single-screw extruder is a less-costly option, but screw wear is higher with

recyclate, so hardened steel or a special coating should be used.

The extruder diameter is measured by the barrel’s inner diameter. The usual rate of

screw rotation is 20 – 200 rpm [34].

Injection Molding

Injection molding and extrusion processes are rather similar at the feeding end, but

differences appear as a nozzle is approached. Both extruder and injection molding

machine have similar zones, although their length and functioning are different. At the

front end of a machine, where an extruder has die, an injection molding machine has a

nozzle, through which a melt is supplied to a mold.

As it was mentioned, PET pellets have to be dried prior to processing, so either a

preliminary drier is mounted on the top of an injection molding machine, or a vent type

molding machine is used. The efficiency of the process often requires the external drier

to be large, what increases power consumption and space requirements. The external

drying can be avoided by use of the vent type molding machine, where moisture is

driven off during the melting cycle.

The vent type injection molding machine (see figure 7) has the first and the second

stage of the melt moving along the screw. Humid pellets are fed to the hopper and

melted in the feeding zone due to shear and compression. After the feeding zone with

deep grooves the melt passes to the metering zone with shallow grooves, followed by

second stage of the screw with deep grooves again. The difference of groove depth

between first and second stage causes the difference in pressure, what, in turn, causes

vaporization of the moisture content of the melt. The moisture is removed through the

vent with assistance of the vacuum pump. Whereas this type of injection molding

machines is rather suitable for crystallized dried PET, it is inappropriate for non-

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crystallized granules, as they have a tendency to soften and form a clump at the feeding

zone [35].

Figure 7 The schematic sketch of a vent type molding machine [36]

Stretch blow molding

The quality of PET affects dramatically the quality of RPET. In Finland, the only

organized way to collect RPET is the collection of plastic PET bottles. Following

paragraphs explain the production technique of plastic bottles.

The process of bottle production includes the following steps:

1. Drying of pellets

2. Injection molding of preforms

3. Heating of preforms

4. Stretch-blow molding of preforms

PET pellets are dried, either in an oven or using an autoloader and a hopper drier

(optionally an additional dehumidifier can be used to achieve superior quality of the

pellets) [19]. PET pellets are dried inside the hopper by hot dry air. Hot moisture air

afterwards is cooled down and passed through a desiccant bed, after what the loop is

repeated [28].

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Dried pellets are loaded into an injection molding machine, avoiding as much as

possible the contact of pellets with ambient air.

After preforms are produced by injection molding they can either be directly shaped

into bottles (in this case step 3 is avoided), or cooled down, stored and processed again

when needed.

During the stretch-blow molding process highly-pressurized air is blown into preforms

and bottles are formed. The set of equipment for this step would include a stretch blow

molding machine, a blow mold, an air compressor, and an air purifier, if required [19].

Sometimes, when few types of plastic are processed together or colorants are added to

the polymer, blending is needed. Blending is preferred prior to drying. If different

grades of PET are to be blended, it is recommended, that the plastics have virtually the

same IV value within range 0.1. Blending increases homogeneity what results in better

processability and reduced scrap rates [29].

In some cases additives are used to enhance properties of PET. The mixture of additives

and the polymer should be also homogenized prior to processing.

Thermoforming

Another process potentially utilized for production of articles from PET and RPET is

thermoforming.

The thermoforming is a process, where a sheet made of polymer is shaped into an end-

use product by heat and/or pressure.

A thermoforming process consists of five stages: heating, forming, cooling, trimming

and sealing. Each of theses stages should be strictly controlled in order to achieve the

desired quality. In the beginning of the process the polymer is heated up to 120-150 ˚C,

thereafter a sheet is formed into a final product and cooled. The final shape to the

product is given by trimming or cutting redundant parts. Out of four sealing methods –

heat, sonic, radio frequency and UV –sonic sealing is recommended as the most suitable

for PET.

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Amorphous PET suits perfectly for vacuum forming, where molding occurs fast, as the

warm-up time for it is short and no pre-drying is needed. The shrinkage is small and

uniform.

It is also possible to crystallize amorphous PET by thermoforming. After vacuum

forming, without removing it from a mold, a piece is warmed up to the temperature of

150 ˚C or higher. During the crystallization the piece shrinks about 2%, the material

changes from transparent to milky-white and its density rises, due to dense packing of

polymer chains in crystallites [32].

3.1.3 Properties

Once a polymer is polymerized and processed to a certain shape, the properties of a

plastic are defined. This chapter will be devoted to investigating different properties of

PET plastic [37, 38, 39, 40, and 41] and comparing it with other plastics. All the

properties are given for pure PET.

1. Trade names

There are various names used for PET by different companies. At the moment the work

was performed PET could be found under the following trade names:

Rynite® PET, Impet®, Arnite ®, LIGHTER ™, Terom®, PermaClear®, EcoClear®,

NUDECPET ™

2. Density / Particle density

The density of PET is 1370 kg/m3 in its amorphous form and 1515 kg/m3 when it is

crystalline [40]

3. Bulk Density

Instead of density, for porous and granular material bulk density is often defined. In

contrast to density, bulk density or apparent density depends on the way a material is

packed. It is defined as “weight per unit volume of material” [42] and is measured by

placing granular material inside of a cylinder and dividing the weight of particles in the

cylinder by its volume. Bulk density does not consider the actual volume of particles,

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but includes the volume of air between particles, so can be altered by compacting

granular material. Bulk density of PET pellets is around 800 kg/m3.

4. Tensile strength (σt)

Tensile strength is a measure of stress that is needed to break a sample (tensile strength

at break) or to deform a sample (tensile strength at yield point). It is an important

characteristic for a polymer that has to be stretched.

According to various sources, tensile strength of PET is 47 -75 MPa [37, 39]. Tensile

strength at a yield limit is 56 MPa. The number is determined by the tensile test

performed at a test speed of 50 mm/min [37].

51.7 70.5 94

+ 10% + 50 % + 100%

42.3

- 10% - 50 %

23.5

PET 47 N/mm2

PS PM-MA e/tfe

PVC-U POM PA 11 PC PPE PSU PAE

SAN PA 6 PA 66 PPS PAS

ABS

PEHD PP PB SB PVK PTFE FEP PCTFE PBT ASA

- 100%

0

PELD EVA PVC-P PIB

Figure 8 Tensile strength of PET and selected materials

5. Elongation at yield limit

Elongation of PET at yield point is 3.8 %, when determined at a test speed of 50

mm/min [37].

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5. Elongation at break

Elongation at break shows, how many times a polymer sample is its own length when it

breaks. According to [39], PET can expand from 50 to 300 % of its original length.

According to [41] elongation at break is 600 %.

192.5 262.5 350

+ 10% + 50 % + 100%

157.2

- 10% - 50 %

87.5

PET 175 % (average)

PA 66

PVC-P PA 6

PB FEP PA 12

PCTFE

PC

- 100%

0

PMP PVC-U PS SAN ABS SB ASA PMMA POM PBT PPE PSU PPS PAS PES PAE PF UF MF UP PI

PELD PEHD EVA PP PMP PA 11

Figure 9 Elongation at break of PET and selected materials

6. Tensile modulus

Tensile modulus is given as a ratio of tensile stress to corresponding strain. On a stress-

strain curve it is expressed by the gradient of the linear part of the curve. Tensile

modulus of PET is 2800-3100 MPa [39].

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3410 4650 6200

+ 10% + 50 % + 100%

2790

- 10% - 50 %

1550

PET 3100 N/mm2

PS PPS

PVK

PF MF SI

PM-MA POM

PVC-U SB ABS ASA PCTFE PA 66 PA 12 PC PBT PPE PSU PAS PES PAE

- 100%

0

PELD PEHD EVA PB PP PMP PTFE FEP E/TFE PA 6 PA 11

UF UP PDAP PI

Figure 10 Tensile modulus of elasticity of PET and selected materials

7. Flexural yield strength

In some sources [38], flexural strength is defined as a measure of stiffness, of how well

a material resist bending. Flexural yield strength of PET is 80 MPa [37].

8. Charpy impact strength

Impact strength is the indication of material “toughness”. The test is based on the

amount of energy lost during a pendulum hitting a specimen. In the case of PET the

specimen doesn’t break [37].

Charpy notch test is similar to Charpy impact strength test with only the specimen being

notched (“V” cut in the specimen). Impact strength of PET defined by Charpy notch test

is 3.8 kJ/m2 [37].

9. Glass transition temperature

The glass transition temperature of PET is 75 ˚C [29] (or 82 °C [19]). That means that

at temperatures higher that amorphous PET begins to soften and become rubbery, what

makes amorphous PET unsuitable for some application, where dimensional stability at

elevated temperatures is important (electronics, automotives, etc). Nevertheless, some

additives can substantially increase the glass transition temperature of PET, increasing

the range of its applications [29].

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It should be noted that not all plastics behave in a similar way at glass transition

temperature. In partially crystalline plastics only an amorphous part undergoes glass

transition.

10. Best orientation temperature

Once warmed up for sufficient temperature, PET molecules can be orientated by

stretching, what dramatically increases tensile strength, impact strength, chemical

resistance and barrier properties. Stretching is applied for PET bottles in stretch blow

molding. PET molecules are oriented the best at 105 °C [19].

11. Melting point

Melting point exists only for crystalline polymers, because amorphous polymers do not

have structured arrangements of molecules that can be decoupled when sufficient heat is

supplied to them. The melting point of crystalline portions of PET is 248 ˚C [37] or 260

°C [39]. Melting point and glass transition temperature are terms used to define the

important temperatures, at which a structural change occurs in polymers. In the case of

partially crystalline PET, at glass transition temperature it softens up insignificantly, due

to softening of its amorphous regions. The drastic change occurs at melting point, when

the solid polymer becomes liquid.

12. Utilization temperature

PET can be utilized at temperatures above -20 °C, but below 100 °C [39].

13. Maximum service temperature

The maximum temperature at what PET can be utilized for prolonged period is 100 °C

[41]. The maximum short service temperature is 200 °C [39] or 225 °C [41]. According

to figure 11, short service temperature of PET is close to those of PA 66 and E/TFE.

39(135)

220 300 400

+ 10% + 50 % + 100%

180

- 10% - 50 %

100

PET 200 ˚C

e/tfe pdap

FEP PTFE PPS PAS PES SI

PI

PA-66 PSU UP

PMP PP PB PVK PCTFE PA 6 PA 11 PA 12 PC PBT PPE PAE PF MF

- 100%

0

LDPE EVA PIB PVC-U PVC-P PS SAN SB ABS ASA PMMA UF

Figure 11 Maximum short service temperature of PET and selected materials

14. Heat deflection temperature

Heat deflection temperature (HDT) is a temperature at which a standard specimen

deflects a certain distance under a specified load [43]. Under the load of 1.8 MPa HDT

for PET is in the range of 60 – 240 °C [41].

15. Vicat B

Vicat softening temperature is a temperature at which a flat-ended loaded needle

penetrated a polymer specimen to the depth of 1 mm [43]. For Vicat B test the load is

50 N. PET has Vicat softening temperature of 170 °C [37].

16. Thermal conductivity

Thermal conductivity of PET is 0.24 W/m*K [39].

17. Linear expansion coefficient (α)

The linear expansion coefficient is defined as change in original length of a specimen

per one Kelvin. The linear expansion coefficient of PET is 7×10−5/K [39].

18. Specific heat (c)

The specific heat or specific heat capacity expresses the amount of energy a sample of 1

kg requires for it temperature to increase by 1 Kelvin. For PET this value is 1.05

kJ/kg.K [39].

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19. Water absorption

PET is hygroscopic, i.e. it absorbs water from the surroundings. According to [39], in

24 hours PET would absorb 0.3 % of its dry weight (see figure 12). On saturation PET

will absorb 0.47 – 0.50 % of its dry weight [41]

0.33 0.45 0.6

+ 10% + 50 % + 100%

0.27

- 10% - 50 %

0.15

PET 0.30 %

SB PA-11 ABS PI

PVC-P PES MF

PVC-P UF

-

PVC-U PMMA POM PA 12 PC PAE SI SAN PDAP UP

- 100%

0

PELD PEHD PP PB PIB PMP PS PVK E/TFE PBT PPE PSU PPS

PA 6 PA 66 PAS PF

PTFE FEP PCTFE

Figure 12 Water absorption (24h) of PET and selected materials

20. Crystallinity

Polymerized and, in most of the cases, extruded PET is amorphous, while molding

grade PET is crystalline.

21. IV

One of the most important characteristic of a resin is intrinsic viscosity (IV), which is

dependent on the length of a polymer chain: the longer the chain, the higher the IV. IV

values of different grades are compiled in table 4.

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Table 4 Intrinsic viscosity values of different PET resin grades

Grade IV value (dL/g) Molecular weight (degree of polymerization)

Reference

Fiber grade 0.5 – 0.65 14 000 – 19 000 [13, 28]

Film grade 0.65 N/A [28]

Bottle grade 0.76 – 0.85 24 000 – 28 000 [13, 28]

Industrial materials grade (Binding tape, engineering plastic wire, etc…)

0.85 – 1.10 N/A [22]

Construction materials grade (PET panel, high intensity sheet, etc…)

0.85 – 1.20 N/A [22]

22. UV-resistance

PET resistance for UV-light is considered as fair (options: good/fair/poor) [44].

23. Chemical resistance

Chemical resistance of PET for acids, alkalis and solvents is good [45].

24. Resistance to micro-organisms

PET is very resistant to micro-organisms and is not bio-degradable [46].

25. Barrier properties

The rate of oxygen ingress is 2 ppm in 40 days (untreated) [47], the relative loss rate

of CO2 retention is 1.5 to 2.0% /week [48]. The rate of water vapor permeation is

0.6 g / cm2 day [39].

*On the graphs below in brackets the temperature in ˚C and film thickness in µm is given

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0.66 0.9 1.2

+ 10% + 50 % + 100%

0.54

- 10% - 50 %

0.3

PET 0.6 g/cm2 day

ctfe (40; 25)

PP (25 ;40) HDPE (25 ;40)

LDPE (23;100) PP (30;40)

e/tfe (23;25)

PA 12 (25;25)*

- 100%

0

-

PVC-U (20;40) PVC-P (20;40) PS (25;50) E/CTFE (23;25) PVF (23;25) PA 6 (25;25) PA 66 (25;25) PA 11 (25;25) PC (23;25) PSU (23;25) PI (23;25)

Figure 13 Permeability of water vapor in PET film and selected materials*

227 405 540

+ 10% + 50 % + 100%

243

- 10% - 50 %

135

PET 270 cm3/m2 day bar

-

-

CTFE (40 ;25)

-

PVC-U (20;40, unstretched) PA 6 (25;25) PA 66 (25;25)

- 100%

0

PVC-U (20;40, stretched)*

PP (25 ;40) LDPE (23;100) HDPE (25 ;40) PVC-P (20;40) PS (25;50) E/CTFE (23;25) PVF (23;25) PA 11 (25;25) PC (23;25) PSU (23;25) PI (23;25)

Figure 14 Permeability of CO2 in PET film and selected materials*

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26. Copolymers

Addition of other monomer (mostly cyclohexane dimethanol) to the backbone of PET

instead of ethylene glycol disturbs the crystallinity, so that the co-polymer melts at

lower temperature. A decrease in melting temperature is useful for injection molding

processing, but disturbed crystallinity can be undesirable for the applications, where

dimensional and mechanical stability is important [28].

For bottle grade PET the small amount of cyclohexane dimethanol or other co-monomer

is often added not to prevent crystallization, but to slow it down. As a result bottles can

be produced by stretch blow molding (SBM), have good transparency and barrier

properties [28].

27. Additives

Antimony trioxide (Sb2O3) is often used as a catalyst in production of PET. Potentially,

toxic antimony can migrate from PET bottles to bottled water, but according to the

investigation made by Swiss Federal Office of Public Health, the level of migrated

antimony was well below the allowed maximal level [28]. Other additives that are often

used with PET are durability enhancer phosphite P-1 or P-2 and phenolic antioxidant

AO-1.

28. Alloys (blends)

In 1996 recycling PET industry experienced a crisis, caused by the high level of

production of virgin PET resin in 1995, and, as a result, a drop in the demand for

recycled PET in 1996. According to research results [49] during the crises in 1996

mainly the companies dealing with PET composites and alloys had competitive power

on the market.

A very common alloy of PC and PET (50-80 % PET) can be 25-30 % less expensive

while showing similar performance to virgin ABS [49].

Generally, blends require the perfect dispersion of one material in another as well as the

use of compartibilizers, what makes the production of blends expensive and often

unbeneficial with recycled plastics [49].

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29. Price

The price of packaging grade PET varies through a year, increasing at a summer time

and dropping down during winter months. In April, 2004 the price of PET was 1260 €/

ton [50].

Figure 15 Price fluctuation of PET over a period from April, 2006 to April, 2008 [50]

3.1.4 Products

In the world and in Europe in particular PET is mostly used for production of bottles for

beverages and mineral water and for engineering applications (see figure 16).

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Applications of PET in Europe, 1999

41%

34%

9%

6%

10%Beveragedrinks

Mineral waterdrinks

Foodcontainers

Sheets

other

Figure 16 Applications of PET in Europe, 1999 [37]

In Finland plastics are mostly used for packaging [51]:

Use of plastics (Finland) 500 000 tonnes/ year

• Building 24 %

• Packaging 40 %

• Electrics and electronics 6 %

• Clothes and shoes 6 %

• Agriculture 6 %

• Furniture 5 %

• Medical industry 4 %

• Automotive 3 %

• Domestic goods 2 %

• Machinery parts 2 %

• Toys, sport equipment 1 %

• Others 1 %

Particularly, according to the Handbook of plastics [37], transparent and flexible

amorphous PET (PET-A), is used in the following applications:

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− textile fibers

− preforms for bottles for beverages, water, food, and cosmetics

− packaging films (area, where PET competes with polyamides)

− adaptors

− grave candles

Crystalline PET (PET-C) is more similar to polybutylene terephthalate (PBT) than to

amorphous PET. PET-C is more rigid and heat resistant than PBT and requires a

warmer mould in injection molding. Both PET-C and PBT are mostly used in the

electronics industry [37, 52].

3.2 RPET

3.2.1 Production

The substance of recycling is utilization of existing material instead of virgin resources.

Consequently, RPET can not be produced, but rather PET should be collected after

usage. Technically, PET plastic becomes RPET at the moment it exits re-processing

unit like an extruder or an injection molding machine. Nevertheless, in practice the

name RPET is used when referring to the secondary raw material originated from PET

plastic, whether it is grinded flakes or extruded pellets.

3.2.2 Re-Processing

The term “recycling” implies that a material being reprocessed. Therefore, in this

document processing is referred to when virgin PET is considered, while re-processing

includes all the processes RPET undergoes.

There are different stages PET plastic goes through before actual reprocessing. After

being collected it should be transported, grinded to flakes, washed, dried, and

compacted into bags for further transportation.

What happens to the flakes depends on the application. RPET intended for striping,

fibers, film and sheet is reprocessed in an extruder, which can also be used for

laminating applications. Pelletizing and possible blending with additives also utilizes an

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extrusion process. For bottle preforms production an injection molding process is

employed [29].

Extrusion and injection molding processes do not substantially differ, whether RPET is

used or PET. Nevertheless, an expected quality drop of RPET emphasizes the

importance of filtering, pelletizing and IV-increasing equipment.

Grinding

Grinding is a process of size reduction. Before going through the extrusion/ injection

molding process, bottles have to be grinded and washed. The grinding increases the

surface area of a plastic, enhancing contact between a plastic and a washing liquid.

Machines used for grinding are called “shredders” or “granulators”, and the output

material of these machines is “grains” or “flakes”.

The shape and the size of the grains (flakes) depends on

• the geometry of the grind

• a granulator used

• the hole diameter of the screen plate

• the state of granulator knives

[13]

In further discussion of the topic, the result of grinding activities is called flake.

Pelletizing

In most of the cases commercially-available PET polymer is in pellets. The diameter of

pellets is around 3 mm and they are round in shape.

The shape of RPET feedstock depends on the treatment method of incoming plastic. If

bottles or other material to be treated were only grinded, then the output material is

flakes, flat pieces of plastic of undefined shape. If the material underwent the whole

recycling process, was re-melted, extruded and pelletized –then the output material is

pellets, similar to PET pellets.

Pellets are used for the following reasons [53]:

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− pelletized plastic can be mixed with additives and other plastics

− pellets are uniform unlike flakes, what provides homogeneous mixing and heating

during the process

Pelletizing is an important step performed to prepare a plastic for injection molding or

for other processing. There are two main categories of pelletizers: cold cutting and hot

face cutting systems that can be further divided into types:

− Cold cutting system (pellets are cut from a solidified polymer)

o Strand pelletizer

o Dicer

− Hot face cutting system (pellets are cut as a molten polymer exits the die)

o Water ring pelletizer

o Air pelletizer

o Underwater pelletizer

o Centrifugal force pelletizer

[53]

The advantages, the disadvantages and the operational principles of mentioned

pelletizers can be found in attachment 1 of this document.

Filtering

In the melt filtration flakes are melted and the molten mass moves through one of few

screens. The screens with various wire meshes filter out impurities of different sizes.

The overall level of contaminants (aluminum, glass, paper, etc) should not exceed 100

ppm (0.01 % by weight) [13].

A set of screen filters is called a screen pack and it is usually supported by a breaker

plate – a perforated plate placed at the end of metering zone to protect the screen pack

and the die from foreign particles. The clogged screen pack often causes back pressure

in the melt, resulting in the flow of the melt in the reverse direction. Too restrictive die

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is another back pressure causing factor. There are two kinds of filter systems-

continuous and discontinuous. In the continuous system a change of the clogged filter

takes place without or with minor interruption with an extrusion process, while in the

discontinuous models a filter should be changed manually or mechanically, what

disturbs the process [13].

Contamination of RPET items is the reason for increased importance of filtering

equipment. The type of the filter used depends heavily on the type of contamination.

Increasing IV of RPET

The importance of IV has being mentioned earlier in 3.1.1. Methods to increase IV are

especially important, when considering recycling, as IV tends to drop during the

recycling process.

One method to increase IV is SSP, described in 3.1.1. This method is costly and not

readily used for recycling of plastics.

Fortunately, there are technologies that produce the high-quality PET resin without SSP.

A simplified scheme of the process is shown bellow:

Sorting � Washing � Grinding � Crystallization � Drying � Extrusion � Cooling

� Pelletizing

What follows is a review of the technologies utilized by different companies to produce

high-quality RPET without SSP

This review is done using the information presented at Plastic Technologies web site

[54], as well as collecting information from the web sites of mentioned companies.

Browsing the literature written about PET recycling revealed that there are some

characteristic problems such as

• the moisture content of PET causes hydrolysis in the melt and, eventually, a

chains scission

• the feeding of the flakes is problematic due to their inconsistency and

heterogeneity

• discoloration

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• the overall degradation of PET quality

There are few solutions available on the market to deal with the mentioned problems.

Some companies offer bottle-to-bottle solutions, others – the solution for recycling PET

into pellets, finished or semi-finished goods (sheets, fibres).

For example, the Italian company Sorema has patented the whole chain of equipment

for Ecopet process, which includes bottle sorting, washing, wet grinding, intensive

washing at 76 – 100 ˚C, crystallizing, drying and extrusion with a modified twin-screw

extruder with multiple vacuum vents. The process is promised to raise IV from 0.75 to

0.8 without using SSP.

Another company, Erema, introduced the Vacurema method, what raises IV of a stock

from 0.76 to 0.8. In the process pre-dried and crystallized RPET flakes are fed to a high

temperature, high-vacuum reactor (densifier), where they are dried and de-contaminated

from the volatile matters. After that the flakes are continuously fed to a single-screw

extruder, still under vacuum conditions. The output material of both companies is

approved by FDA [54].

A new invention of Erema saves time and energy. It is a combined system, a

crystallizer-dryer-shredder unit, where RPET resin is dried and crystallized only by heat

produced by the rotating knives of the shredder. The whole system operates under high

vacuum, and the crystallized polymer fed from the shredder-compactor to an extruder

proceeds trough a backflushing (continuous) screen. The extruder is a 35:1 L/D extruder

with two vacuum vents and a specially designed screw. The use of a melt pump helps to

keep pressure fluctuations at a die to ±0.2 bar [55].

One more solution for recycling of PET is provided by Kreyenborg Group, the producer

of infrared heaters suitable for PET drying and crystallizing. The heaters dry and

crystallize the flakes using selected IR waves, after what the flakes proceed under

vacuum to a densifier and then to a vacuum-vented twin-screw extruder. The IV is said

to rise from 0.78 to 0.79.

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3.2.3 Properties

There is little or no information found about properties of RPET. A possible reason for

that is non-defined nature of the material, where the treatment history and possible

contaminants are unknown.

The price of recycled PET, as obtained in a personal communication with

representatives of Kauko-Telko Oy, is noticeably below the price of virgin PET (see

figure 17).

Transparent granules cost around 975 €/ton, while transparent flakes are 775 €/ton and

colored flakes 550 €/ton.

1386 1890 2520

+ 10% + 50 % + 100%

1134

- 10% - 50 %

630

PET 1260 €

HD-PE, LD-PE, PP

ABS

PVC RPET (gran, bright) RPET (flakes, bright)

- 100%

0

RPET (flake, color)

PC POM PMMA PA 6 PA 66 PBT

Figure 17 Price of RPET and selected polymers

The change of properties of RPET comparing to properties of PET becomes an

important issue, when one is considering RPET for one’s applications. The properties of

RPET flakes and pellets have hardly been published, but some analytical considerations

about the change of properties are done in chapter 4 of this work.

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3.2.4 Products

In Europe, USA and other parts of the world PET is very popular also in recycled form.

Products made of RPET are encountered in everyday life.

The following section of the document introduces the various uses of RPET all over the

world.

USA

According to “Best Practices and Industry Standards in PET bottle recycling” [56],

there are 5 main groups of products RPET can be used for:

1. plastic stripping

2. fibers products (brush bristles, carpets, fleeces, textile fiber like “EcoSpun”)

3. bottles and containers

a. de-polymerization (feed-stock recycling)

b. multi-layer or laminated (when the last layer of container is made of

virgin material)

c. full-contact (direct recycling)

4. sheet and film applications (thermoforming applications)

5. engineered resins (reinforced components for the automobiles), often in

combination with glass fibers

So, translating possibilities into applications, RPET is used for [56]

• belts

• blankets

• boat hulls

• business cards

• caps

• car parts

• carpets

• egg containers

• furniture

• insulation

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• landfill liners

• paintbrush bristles

• pillows

• recycling bins

• sails

• stuffing for ski jackets, cushions, mattresses, sleeping bags

• tennis ball cans

• welcome mats

Recycled PET, containing up to 30 % glass fiber and minerals as reinforcement, is used

in automotive industry as [49]

• grille opening reinforcing panels (Ford)

• headlamp brackets

• exterior car door escutcheonsii

• automotive window hardware

• roof racks

• arm for chairs

The alloy of RPET and PC (5:5 -8:2) is used for [49]

• automotive applications (bumpers, grilles, wheel covers, body panels, electrical

and electronic compounds)

• power tools

• consumer items (office machines and cartridges for copying machines)

In the construction industry unsaturated polyester resin based on recycled PET is used

in polymer concrete that is strong, durable and has a fast curing time [57].

ii Escutcheon is an ornamental or protective plate [88].

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Europe

In Europe recycled PET is used for fiber production, as a packaging material and for

some other applications (see figure 18).

Figure 18 Outlets for recovered PET in Europe [58]

About 70% of all recycled PET is used to produce fibres (2003). The flakes made out of

recycled bottles are spun into strands. The thickness (usually 5 -150 mm) and the length

of the fibres determine a final application. The fibers of larger diameter are used to stuff

anoraks, sleeping bags and soft toys. The fibres with smaller diameters are used for

sweatshirts, jackets and scarves. The amount of recycled material in these fabrics is

close to 100 % and one “polar” fleece jacket “consumes” 25 PET bottles [59].

Figure 19 The rucksack and the hat made of recycled PET [60]

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Figure 20 The carpet, the umbrella and the mouse pad made of recycled PET [60]

About 9 % of recycled PET is used for the production of egg containers and other

preformed plastic food containers, as well as containers for cosmetics and household

products [59].

Among other applications of recycled PET the most significant are:

- computer and automotive parts produced by injection molding from engineering

resiniii

- shoe liners, webbing, geotextilesiv [59]

With the development of new technologies more and more PET is recycled into food

contact applications. Huhtamaki Oyj, a global company whose headquarters are situated

in Espoo, Finland, has recently announced producing thermoformed food packaging for

salads, containing 40 – 70% of recycled PET [62].

Finland

In Finland there are not so many direct uses of recycled PET, but some solitary

examples of PET use exist:

iii PET modified in a certain way, so that it is not used for bulk production, but for production of special

items

iv Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate,

filter, reinforce, protect, or drain [61]

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− Muovix Oy produces profile-products such as pillars, posts, plastic boards,

agricultural and other customer commodities using a mixture of post-consumer

plastics [63].

− Preformia Oy uses recycled content to produce preforms for new bottles, utilizing

30 % of clear RPET to mix it with the virgin material [64].

− In large stores, such as IKEA, some products made out of recycled PET can be

found. Examples of the products are the IKEA PS BÖLSÖ table-board that is made

in Poland and sold in IKEA and the TEPPAS plastic box.

Some projects of utilizing a recycled plastic in general and PET in particular are going

on all the time. An example is the project initiated by TEKES of investigating the

possibilities of recycled PET to attenuate sound [65]. The current status of the project is

unknown, as the responsible person did not respond to the inquiry.

Sustainability is a fashionable concept at the moment, what reflects also in research

topics. For example, in the thesis work of Anne Salminen, a former student of South-

Karelia polytechnic, the use of recycled plastics (PP, PE and PET) in jewellery

manufacturing is considered and implemented [66].

Designers all over the world used RPET and re-used PET in their works. Some of the

examples are presented below [67]

Figure 21 The pontoone-boat based on PET bottles [68]

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Figure 22 The bottle made of RPET [69]

Figure 23 RPET brush and bag [70]

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Figure 24 The plant-watering vessel made of PET bottle [71, 72]

Figure 25 The bottle-filter made of PET bottle [73]

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Figure 26 The blurring screen made of parts of PET bottles [74]

Figure 27 The lamp decoration made of parts of PET bottles [74]

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Figure 28 The bags and containers made of RPET [75]

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4 FROM MATERIAL TO PRODUCT

One objective of the following chapter is revealing relationship between polymer

characteristic and polymer properties. Another objective is clarifying how processing

affects polymer properties. As the relations discussed in the chapter applies in the most

cases to both PET and RPET, “the polymer” is used to refer to either of these plastics.

The typical challenges in the recycling process are presented in the second half of the

chapter.

The discussion of polymer properties in most of the cases refers to the properties of a

final product made of polymer. Quality is considered from a manufacturer point of view

– as the set of properties allowing a manufacturer to maximize the value of a product for

a customer while minimizing the manufacturing cost. Degradation of quality then

means deterioration of certain properties of the polymer resulting in the decrease of the

product value or the increase of the manufacturing cost.

4.1 Correlation between polymer properties, polyme r

characteristics and processing parameters

Mechanical, chemical, thermal, electrical, and optical properties are specific for a given

product. Rheological properties, on the contrary, are properties of a polymer melt. The

properties of the polymer, referred to in this document, imply the properties of a plastic

product and of a polymer melt.

There are much more factors affecting the properties of a polymer than one might think.

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Properties

Characteristics of polymer itself

External factors and thermal history

Processing parameters

Quality degradation

Figure 29 The factors affecting the properties of a polymer

The factors affecting the properties of a polymer can be divided into three groups:

The first group is represented by characteristics of a polymer, typical features of a

polymer inherent in it from the moment of polymerization.

The second group is processing parameters such as processing temperature, time and

pressure.

The third group is composed of the factors that can not be controlled by a producer of a

processor of a polymer. These factors are weather, wear, sun light, oxygen, humidity,

etc…

The elements presented in figure 29 are interrelated. Detailed interrelation between

polymer characteristics, processing parameters and properties are presented in figure 30.

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Rheological properties

Mechanical properties

Thermal properties

Optical properties

Additives Molecular weight

Co-polymers Arrangement of the molecules

contaminants

time of shear

shear rate pressure in melt

processing temperature

homogenity of mass

grinding/ pelletizing

pumping vacuum drying filtering extruding

moisture content

crystallizing

shape of input material

Throughput capacity

cooling time

Chemical properties

Figure 30 The relation between processing parameters, characteristics of a polymer

and properties of a polymer

The rest of the chapter is devoted to explaining the details presented in figures 29 and

30.

4.1.1 Characteristics of polymer

First, the properties of a polymer depend on the inherent characteristic of a polymer,

what is the molecular weight, the chemical structure of molecules, the polymer

morphology, additives or co-polymers possibly used in the production of the polymer.

Figure 31 represents this dependence schematically:

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Rheological properties (viscosity, melt flow, etc…)

Mechanical properties (tensile strength, modulus of elasticity, etc...)

Thermal properties (melting temperature, glass transition, etc…)

Optical properties (color, refraction, etc...)

Additives Molecular weight

Co-polymers Arrangement of the molecules

Chemical properties (taste, aroma)

Figure 31 Influence of characteristics of polymer on its properties

Molecular weight

The importance of a molecular weight for the quality of a final product can be

understood thought the fact that there is a direct dependence between the molecular

weight and the properties of a polymer [40, 76].

Molecular weight and mechanical properties

Until certain limit, mechanical strength and stiffness increase with the increasing

molecular weight.

Figure 32 Dependence of mechanical properties on the molecular weight of a polymer

[76]

According to [77], an increase in the molecular weight enhances tensile strength and

impact strength and improves stress fracture and weather durability.

Molecular weight

Mechan

ical

streng

th,

stiffness

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Molecular weight and thermal properties

As was already mentioned in the third chapter, thermal degradation of PET starts at 300

˚C, glass transition region for it is 75 – 82 ˚C and the best temperature to orient

molecules is around 105 ˚C. See the box below

Glass transition (Tg) = 72-82 °C

Orientation temperature = 105 °C

Suitable temperature for drying = 160 °C [19]

Melting temperature (Tm) = 260 °C

Degradation temperature <300 °C

The dependence of glass transition and melting temperatures on a molecular weight is

an example of a limiting-property relationship [78]. That means that Tg and Tm increase

with increase in the molecular weight, but at a certain point (Tg∞) an increase in the

molecular weight almost does not affect anymore Tg or Tm. This dependence can be

expressed with the Fox-Flory equation [78]

Tg = Tg∞ - (K/Mn), where

K is the constant for a given polymer.

Molecular weight and rheological properties

It is worth noticing that the temperature at which a solid polymer becomes liquid

increases with the increasing molecular weight. In contrast, the temperature, at which

the degradation of a polymer starts, decreases with the increasing molecular weight

[76].

The higher the molecular weight, the more viscous a polymer melt is [77]. This property

is widely used in the estimation of the molecular weight using melt flow index (MFI).

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The molecular weight also affects the behavior of a polymer melt at different share

ratesv. The higher the molecular weight of polymer, the lower is the critical shear rate at

which a shear thinning behavior will occur [40]. The shear thinning means that the

viscosity of a polymer melt decreases with an increase of a shear rate in contrast to

behavior of Newtonian fluids, the viscosity of which does not depend on a shear rate.

Molecular weight average and molecular weight distribution

It is not common that polymers molecules have the same molecular weight (like in the

case of a monodispersed polymer). More often there is some variation in the length of

the chains and, consequently, their molecular weight. To deal with those variations, an

average molecular weight is used, or, to be more precise, different averages like a

number average, a weight average and a viscosity average molecular weight. The most

important difference between the number average and the weight average molecular

weight is that in the weight average calculations the contribution of each group of

molecules (molecules with similar weights) is taken into consideration, so that the

weight average would be sufficiently close to the weigh of the most of molecules.

An average molecular weight can be:

Mn = Number average molecular weight

Mw = Weight average molecular weight

Mv = Viscosity average molecular weight

It is possible to calculate these three averages, knowing the amount of molecules with

different molecular masses in a sample. The molecular weight of each molecule in a

sample (Mi) and the amount of molecules with similar molecular weights (Ni) is

possible to define using Size Exclusion Chromatography (SEC). The description of this

and other techniques of measuring a molecular weight is presented in the attachment 2

at the end of this document.

v Shear rate is “velocity gradient measured across the diameter of a fluid-flow channel, be it a pipe,

annulus or other shape” [80].

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So the number average molecular weight (Mn) is equal to

Mn = ∑M iNi / Ni , where

M i is the molecular weight of a polymer molecule

Ni is the amount of polymer molecules with the molecular weight M i

To calculate the weight average molecular weight the weight fraction is to be obtained

Wi = MiNi / ∑ MiNi

and the weight average is then

Mw = ∑WiM i

At last, to calculate the viscosity average molecular weight the following formula

should be used [76]:

Mv = (∑miM iα+1/ ∑mi)

1/α

where mi is equal to the weight of all molecules with the molecular weight Mi (mi =

NiM i) and αααα is a material dependent parameter, which relates intrinsic viscosity [ηηηη] to

the viscosity-average molecular weight [76]. This relation is called the Mark–Houwink

equation (or Mark–Houwink–Sakurada equation), which is

[η] = KMvα

The values for K and for αααα are given in tables and defined for various polymer-solvent

systems.

Instead of a molecular weight, a molecular weight distribution is often referred to. The

schematic plot of a molecular weight distribution with different average molecular

weights is shown in figure 33.

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Figure 33 Schematic plot of a molecular weight distribution with average molecular

weights [76]

A narrow molecular weight distribution enhances impact strength, improves stress

fracture durability and gloss. The polymers with wider molecular weight distribution

have better flow characteristics under pressure [77].

The measure of the width of a molecular weight distribution is called polydispersity

index, PI. PI is equal to the ratio Mw/Mn. Influence of PI on polymer properties is

explained in literature [76]:

A polymer with the narrow molecular weight distribution has PI = 1, what means that

most of the molecules have the length close to an average, what, in turn, leads to higher

impact strength.

The wider molecular weight distribution yields PI > 1, what means that the majority of

the molecules are long with some short ones. The short molecules act as lubricants so

that a melt fracture is less likely to occur [76]. On the other hand, crystallization

happens slower with the longer molecules.

The description of the molecular weights of polymer can be concluded with two more

definitions: Mc – is the critical molecular weight that is the minimum polymer chain

length necessary for the formation of stable entanglements, and Me – is the molecular

weight between entanglements. Mc ≈ 2 Me [78].

Molecualr weight

Cha

in leng

th distribution

Viscosity average

Weight average

Number average

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Different techniques of measuring different molecular weights can be found in the

attachment 2 for this document.

Chemical structure of a polymer molecule

The second factor that polymer properties depend on is a structure of a polymer

molecule. By the structure of a molecule here is meant the configuration of a polymer

chain (tacticity and cis- trans- isomers). This configuration is defined by the

polymerization process and can not be altered without altering primary bonds [40] and

conformation of the chain, what is rotation of the chain components relatively each

other. Since neither primary bonds, nor conformation of the chain is affected by

mechanical recycling, they are not dealt with within this work.

Polymer morphology

The properties of a polymer are dependent on a large extend on degree of crystallinity,

orientation of molecules and entanglements.

Whether a polymer will be crystalline or amorphous in its solid state is defined by the

chemical structure of the polymer [78], the polymerization and other possible

processing it went trough [13].

Sources claim that the pellets of PET produced by bulk polymerizing are uncrystallized

and transparent [35].

Thermoplastic PET during the solidification process can become either amorphous

(through quenching), or semi-crystalline.

The rule of thumb is that the structure of PET depends on the transition phase from a

melt to a solid, during which the following can occur:

1. Fast cooling (quenching), when the melt is cooled so fast that the molecules do

not have time to arrange themselves to an ordered structure, i.e. to crystallize.

The structure of PET plastic in this case is amorphous.

2. Under its melting temperature, PET resin cools down slowly, so that semi-

crystalline structure is formed [9].

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PET is one of few plastics that might be used in its amorphous or semi-amorphous

(semi-crystalline) form.

The table 5 below summarizes the differences that arise in the polymer due to its

crystallinity.

Table 5 Properties of crystalline and amorphous structures

Comparative point

Crystalline Amorphous

Description Dense ”ordered” structure, where molecules are tightly aligned. The extent of aligned regions might vary [38].

Molecules are not organized, but construct a “spaghetti”-like mass [38].

Properties “+”

High thermal resistance

Stability at a dynamic loading

Stiffness

High tensile strength

Good barrier properties (for gases and water vapor)

Good chemical resistance

Higher density

“-“

High processing- and post-processing shrinkage

Higher processing temperatures

Susceptibility for stress fracture

Low friction coefficient

“+”

Good dimensional precision during processing

Stability at a static loading

Flexibility

Good toughness

Clearness (homopolymers)

Small linear heat expansion coefficient

“-“

Strength dependence on the temperature

Thermal dimensional instability

Instability at dynamic loading

Low extension possibility

Poor chemical resistance

Poor wear resistance

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Reaction for heat Remain solid until the melting point is reached, then become flowing liquids

Have a broad softening range. Soften on addition of heat, once the glass transition temperature is reached.

Best manufacturing processes

Where its crystallinity is enhanced by orientation

Vacuum forming (thermoforming)

Products Fibres, strapping, film, oriented sheet and stretch blow molded bottles

Packaging, textile fibres, bottle preforms, sheets

In a melt viscosity increases with increased entanglement, and the strong entanglements

of long molecules is a reason for the high strength and toughness of the polymer and for

the stickiness of its melt [13].

Orientation in a polymer is a reason for anisotropyvi . Tensile strength, elastic modulus

and impact strength are better in the direction of orientation than in non-oriented

direction.

The orientation of molecules also affects the optical properties of a polymer [77].

The value of the refractive index, n, depends on the degree of orientation and the

direction of the orientation of the molecules within a polymer [79].

Co-polymers and blends

Co-polymers affect significantly properties of PET. Co-polymers added to the backbone

of PET alter crystallinity and has an effect on the melting temperature. The possibilities

the co-polymerization of PET offers for the manufacturer are extensive and constitute

an entire investigation topic by itself. The effect of co-polymers on the properties of

PET or RPET is out of the scope of the present work.

Additives

Additives and the possibilities they present to PET recycling are considered in this work

only shortly.

vi the difference in polymer properties when measured along different axis of the material

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As recommended by the Clean Washington Centre [29], the following additives can be

used to alter certain properties of a plastic:

• Glass or other fibres to provide stiffness, strength, and/or electrical properties

• Nucleators to control the level of crystallinity

• Impact modifiers to impart toughness

• Flame retardant additives to meet product safety requirements

• Mineral fillers to stiffen, provide dimensional stability

• Heat and/or light stabilizers

• Lubricants for improved processing

• Antistats to minimize the development of static charge

• Liquid color or color concentrate

The list of additives and their properties can be also found on pages 11-13 in the

Wellman design guide [38].

Citing the information given in “Recycling and recovery of plastics” [81], an increased

phosphite concentration would improve the melt and color stability, while the more

recent papers recommend as the best stabilizer for PET a combination of phosphite P-1

with a small proportion of phenolic antioxidant AO-1. Figure 34 shows that stabilized

PET provides better conservation of molecular weight comparing to unstabilized one

and containing only phosphite P-1 [81].

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Stabilization of PET bottle material

0

5000

10000

15000

20000

25000

30000

0 1 2 3 4 5

Number of extrusions

Mol

ecul

ar w

eigh

t (M

)

reference

0.30 % P-1

0.30 % AO-1/P-1 (1/4)

Figure 34 Effect of stabilizers (phosphite P-1 and phenolic antioxidant AO-1) on

molecular weight of RPET [81]

4.1.2 Processing parameters

The effect of characteristics of a polymer on its properties has being considered in 4.1.1.

Processing parameters constitute the second group of the factors affecting the properties

of a polymer (see figure 30). While the characteristics of a polymer are mostly inherent

to the polymer from the moment of polymerization, the processing parameters can be

altered in a manufacturing process. An overview of processing methods was given in

the chapter 3. This sub-chapter is devoted to explanation of effects of equipment and

processing parameters on RPET and PET properties.

Effect of injection molding on IV, tensile strength, acetaldehyde level

One of the challenges a recycler of RPET is facing is deterioration of the properties of

RPET compared with PET. If no IV increasing methods are used, the quality of RPET

during repeating injection molding is expected to drop. The vendors of a vent type

molding machine for RPET flakes claim that in a molded product the drop of IV is 10 %

or lower and the decrease in tensile strength is 3-4 % or lower [36].

Additionally, the increase in acetaldehyde level can be expected due to melting and re-

melting of the polymer (see 4.2.1 for more details). For example, the initial

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acetaldehyde level of pellets of 3 ppm can rise up to 13 ppm in preforms during an

injection molding process with the barrel temperature of 285 ˚C and the melt residue

time of 108 s [82]. It is said that the items intended to be in contact with food should not

have an acetaldehyde level higher than a few ppm [83].

Effect of extrusion parameters:

− Type of the extruder affects melting temperature, pressure distribution,

throughput capacity

For the material to move inside of the barrel during processing there should be a friction

between the plastic and the barrel surface. The friction results in pressure what in a

conventional single screw extruder is mostly generated in the metering zone (at the end)

[33]. One of the ways to increase the friction is to make grooves at the surface of the

barrel. This idea is implemented in a grooved feed extruder. To prevent the excess

pressure the grooved zone should be no longer than 3.5 D (see 3.1.2 for details). In the

grooved feed extruder the pressure is mainly generated in the feed (the solid conveying)

zone, resulting in higher productivity, higher melt stability and pressure invariance [33].

The disadvantages include the higher wear of the screw.

In the metering zone the characteristics of the screw affect productivity. It has been

concluded [33] that for Newtonian fluids the screw with shallow channels should be

used for a restrictive die and the screw with deep channels should be used for a less

restrictive die to achieve the best productivity.

In devolatilization machines the screw has an extra devolatilization section after the

feed and melting sections. The fluctuation of capacities in the different zones of the

screw produces the pulsation. The variations in a melt flow can also be caused by filter

screen changes and differences in melt pressure these changes cause. A melt pump is

recommendable to achieve a stable melt flow [84]. A filter is to be placed upstream of

the pump to avoid damage of the pump.

The extruder output per screw rotation depends on a screen pack condition, die back

pressure, polymer viscosity and bulk density [34]. For the grooved feed extruder the

bulk density of feedstock is particularly important, as is affects pressure build-up and,

consequently, the behavior of the melt throughout the process.

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Generally, a conventional single screw extruder is more suitable for processing of re-

grind. The disadvantages are a much smaller throughput capacity (comparing to

grooved feed) and the high dependency on a die resistance (backpressure). A filter

should be chosen with caution and discontinuous models are not recommended [84].

Processing of regrind in a twin-screw extruder is also possible. The size of the particles

influences the processing time, which is longer for the bigger particles. Preheating of

equipment and the high temperature of the barrel at the feed zone ensure the throughout

melting of the plastic. A low throughput rate and/or special screw geometry can assist

the melting [84].

A co-rotating twin screw extruder is particularly suitable for PET re-processing. The

most probable reason is a larger free surface created by two screws what helps

devolatilization, as stated in literature [84].

There is also a possibility to use an extruder with a gravimetric extrusion control, but as

it used mainly for the dimensional control of a product and for the material management

(compounding, additives) - it is not considered in the present work. (Read more [34])

− Speed of the extruder affects homogeneity of the mass and shear rate

The rotational speed of an extruder screw affects homogeneity of the mass and a shear

rate. Too high shear rate during the process can be the reason for mechanical

degradation (see 4.2.1).

− Cooling affects degree of crystallinity, processability

During the crystallization the heat of crystallization should be conducted out of a

material for the crystallization process to continue [79]. Sufficient cooling should also

be provided for the feeding zone of an extruder to ensure high friction inside the barrel

[33].

Slow cooling of the polymer melt leads to the formation of coarse crystals resulting in

reduced clarity and impact strength [29].

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− Temperatures affects degree of crystallinity, orientation, acetaldehyde level

Temperature and cooling time are two main factors affecting crystallinity. Fast cooling

of the polymer results in an amorphous structure, while gradual cooling from melting

temperature enhances crystallinity.

At Tm and Tg crystallization rates are equal to zero, so the maximum crystallization rate

is somewhere in between those two values. The temperature, at which the crystallization

rate is maximal, depends on a molecular weight, but this relation is not linear as for high

molecular weights the rate of crystallization decreases [78].

The diagram, describing the crystallization process of PET and showing the dependence

of crystallinity formation on temperature, is presented in figure 35 [78]

0

20

40

60

80

100

120

140

160

180

120 130 140 150 160 170 175 180 190 200 210 220

Crystallization temperature (˚C)

Line

ar g

row

th r

ate

(nm

s-1

)

Figure 35 Linear growth rate of spherulitesvii in PET as a function of temperature at

pressure of 1 bar [78]

Apart of crystallinity, the processing temperature also affects the level of acetaldehyde

in a final product (see details in 4.2.1). The level of acetaldehyde can be minimized by

processing the resin at the lowest possible temperature, residence time and shear heating

[21].

vii spherulites are spherical semi-crystalline regions inside non-branched linear polymers [80]

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− Pump affects pressure stability

A gear pump can be employed to achieve a pulsefree and surgefree melt at a die at

constant pressure [34]. The pump can substitute completely the metering function of the

screw or supplement metering.

The advantages of the pump are stabilizing of pressure with minor affect on the polymer

(thermal regulation of the pump is needed), the reduction of “slip” effect in a single

screw extruder (when the die resistance creates back-flow), and even the increase in

energy efficiency of the process in some cases. The pump is placed after the screw and

the filters, but before the dies [34].

Effect of grinding on melting temperature, throughput capacity, and melt flow

The main difference between flakes and pellets is their shape and, as a result, amount of

air per volume unit. For pellets this amount is minimal, while flakes have 65-80 % of air

per volume unit. That difference in reflected in the bulk density of pellets that is almost

twice higher than the bulk density of flakes.

The variation in shape and size of flakes presents a problem for the RPET recycling

process, as inconsistent feedstock has variations in the melting temperature and the melt

flow.

The problem with too big flakes is slow melting, clogging of the screen pack, and

decrease in the throughput of an extruder. Small flakes, on the contrary, melt too

quickly, what can result in the thermal degradation of the melt [34].

The size of flakes influences the amount conveyed per screw rotation. For small

extruders the flake size should not be bigger than the flightviii depth on the screw [84].

viii depth of the thread of the screw. See [30].

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Effect of pelletizing on the shape of pellets

An overview of pelletizer types is given in the attachment 1. An internet search revealed

that a recommended pelletizer for PET resin is an underwater pelletizer [more reading

85]. Additionally, a vibrating conveyor can be used to prevent the sticking of pellets.

Effect of drying on molecular weight and color

The importance of the drying can be understood by knowing the fact that the inadequate

drying of polymer causes 60 % of injection molding-related problems in PET

processing [29].

The moisture level of dried PET should be between 0.04 % and 0.1 % [19, 29] and this

level should be kept during the whole processing. Loss of IV during the processing

should be less than 0.04. To achieve that PET should be dried at 138 – 160 ˚C using

dehumidified air with the dew pointix under -32 ˚C. The temperature higher than 160 ˚C

can cause the hydrolytic degradation and the discoloration of the polymer [28].

Effect of filtering on pressure distribution in melt, throughput capacity

A filtration is an important stage in processing PET and especially in re-processing

RPET. Impurities in the melt of re-processed plastic burden the filtration system.

A clogged screen pack affects the pressure distribution in the melt and causes back

pressure [13]. A screen pack condition is one of the factors the extruder output per

screw rotation depends on [34].

ix The dew point is the temperature to which a given parcel of air must be cooled, at constant barometric

pressure, for water vapor to condense into water [31].

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The number and type of filters influence the cost of recycling process, so that the need

for additional filter screens can make the process economically unviable.

Effect of vacuum on IV

Vacuum at any stage of the manufacturing process affects the intrinsic viscosity of the

resin. To achieve the sufficient quality of the polymer, the vacuum should be retained

during the whole process (drying � pelletizing).

4.2 Typical challenges in PET recycling

While certain problems like degradation of the quality of the polymer are common for

both PET and RPET processors, there are some challenges that are more likely to be

faced by RPET manufacturers. Two of those challenges – contamination and affect of

heat history – are considered in this work.

4.2.1 Degradation

Three main types of degradation that can occur in PET are hydrolytic, thermal and

mechanical degradation. The consequences of degradation are discoloration, reduction

in the molecular weight, formation of cross-links and acetaldehyde. The last one is

especially undesirable for food contact applications such as food containers, films and

bottles. When acetaldehyde (AA) is trapped in PET, it can diffuse into a food altering its

taste and aroma. That is especially important in production of PET bottles for bottled

water, what is almost tasteless by itself and the fruity taste of acetaldehyde is very

noticeable.

An acetaldehyde level can be measured in bottles or preforms using the ground parison

(GPAA) and headspace (HSAA) methods [86]. The total level of acetaldehyde is

composed of two components: free or residual AA and generated AA. Free AA is

formed during the polymerization process and can be measured in pellets. Apart of free

AA, precursors of AA such as species containing vinyl end groups are also formed

80(135)

during the polymerization stage. Those species can react in the process of re-melting

PET/RPET pellets, forming generated AA [82].

The level of AA in PET/RPET plastic can be decreased by altering processing

conditions (decreasing melting temperature, residence time and shear heating). SSP

decreases the level of free AA [82].

4.2.1.1 Hydrolysis

PET is a hygroscopic material, what means that it absorbs water from the surroundings.

This fact causes problems in processing the polymer, as PET is susceptible to hydrolytic

degradation. PET is produced by a polycondensation polymerization reaction, what is

reversible. De-polymerization reaction starts in the melt on the addition of heat [28, 29].

4.2.1.2 Thermal degradation

Thermal degradation leads to a main chain scission (decrease in a molecular weight) or

a side-chain scission (breakage of weak bonds in different chain segments).

The covalent C-C bond with the bond energy 348 kJ/mol can be broken by a lower

energy input, if the bond is weakened by the presence of impurities like metal ions and

the influence of neighboring atoms. A decomposition temperature for most of the

polymers is around 400 ˚C. If a polymer chain is heterogeneous, i.e. contains oxygen

atoms or aromatic rings, like in the case of PET, decomposition starts already at around

300 ˚C [13].

4.2.1.3 Mechanical degradation

Mechanical degradation is a mechanical scission of polymer chains. In a molten state

the polymer chains can break if the melt is subjected to a very high shear rate during the

processing. In a solid state the reason for stress-induces degradation can be such stages

of mechanical processing of the polymer as grinding, machining, stretching, etc [40].

4.2.2 Contamination

In the recycling process of RPET contamination is an important factor affecting the

whole recycling process. The contamination can be of two types: physical (macro- or

micro level) or chemical. The physical macro level contamination is easily removable

81(135)

dirt, fragments of foreign materials (glass, paper) or other plastics. This contamination

is usually removed by mechanical separation and washing processes. Physical micro

level impurities include ink residues, glues and other adhesives. Those of the micro

level impurities that can not be removed by a conventional washing process will

decrease chances of RPET to be recycled into a usable product. Chemical contamination

arises from the use of PET bottles as the storage for liquid fuels, medicines or toxic

substances. Chemically contaminated bottles are usually impossible to recycle into

direct food contact applications [19].

In an attempt to define the most significant contaminants for the recycling process of

RPET two points of view was considered. First, a manufacturer of products from

recycled plastics was interviewed. Second point of view was obtained by inspecting the

web-page of the governmental organization establishing standards for RPET recycling.

According to Mika Surakka, the president of Muovix, the following contaminants are

not a problem if their content is not higher than 10 %:

− paper and cardboard

− tape

− insulators

− metal-inserts (pieces smaller than pin-head)

− soft metals (copper, aluminum)

In contrast, the following materials cause problems in the RPET recycling process:

− hazardous waste

− food leftovers

− sand and gravel

− glass fiber

− wood

− rubber

The main source of RPET in Finland at the moment is bottles, so mainly the

contaminants originated from the use of bottles represents the interest for the research.

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According to PALPA, a Finnish organization responsible for bottle collection, the

following contaminants will not prevent RPET to be processed into bottles [87]:

− Transparent or light-blue PETGx and PETNxi (max. 5 %)

− plasma-treated bottles (surface treatment, max. 5 %)

− PP and HDPE closure material

− EVA and PE closure gasket

− paper, OPPxii and PE etiquette (lable)

− water-soluble glue and recyclable HotMeltxiii

− printing ink on a label

− price-tags

The following materials are allowed, if RPET is to be processed into fibres:

− colored PET bottles

− surface-treated bottles (for example Glaskinxiv, Plasmax)

− scavengersxv, acetaldehyde blockers, UV-stabilizers

− barrier materials in multi-layer bottles (such as MXD6xvi, PHAExvii , etc)

− PET closures

− PET etiquettes (labels)

x PETG is Glycol-modified PET

xi PETN is Naphthalate-modified PET

xii OPP stands for Oriented Polypropylene Film

xiii HotMelt is a brand of adhesives

xiv Glaskin and Plasmax are trade names for silicon-oxide coating systems

xv Scavenger is a type of additive, chemical that consumes or renders inactive the impurities in a mixture

[88]

xvi MXD6 is crystalline polyamide resine used as barrier material

xvii PHAE stands for polyhydroxyaminoether, another barrier material

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The materials mentioned in the following list are the contaminants that prevent the

recycling of PET (according to PALPA)

− bottles made of PP, PE or PVC

− PENxviii -bottles

− metallic pigment

− EVOHxix

− other than PET, PP, HDPE, steel or aluminum closure material

− closure gaskets made of any other material than PET, PP and HDPE

− etiquettes (labels) made of any other material than

− other than in list one and two mentioned glues PET, OPP, PE and paper

− other additional components of PET bottles

Undefined contaminants originated from so called user contents of a bottle constitute

one of the most problematic classes of the contaminants. According to a questionnaire*

conducted for the purposes of this work substances that can be found in PET bottle vary

greatly. 30 respondents were asked what substances do they store or place into a PET

bottle.

− water was named by 21 respondent

− juice received 12 answers

− small metal items, oil for cooking, and ash from smoking each got 5 answers

− strong alcohol or sand were chosen by 4 people

− used motor oil – by 3

− home-made beer (kotikalja), sugar, gasoline, mead (sima), milk, sport drink, wine,

tea, fertilizer for plants, small paper pieces, soil, seeds, parts of the plant –options

each got 2 answers

xviii PEN is polyethylene naphthalate

xix EVOH is Ethylene Vinyl Alcohol Polymer used as barrier resin

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− paint, oil after frying, engine lubricant, animal food, nails, cappuccino, diesel, salad

dressing, developer and fixer for photography , beer, honey, insects, ketchup,

mustard, Fairy, window cleaner – each was chosen by one person.

*The questionnaire was conducted among 20-65 year-old people, mainly teachers, students and artists.

The total amount of respondents was 30. The respondents were allowed to choose more than one option.

The age pyramid of the respondents is presented in figure 36

0%

20%

40%

60%

80%

100%

Man Woman

Age pyramid of respondents

< 40

30-40

20-30

< 20

Figure 36 Age pyramid of respondents

The investigation of the effect of contaminants on properties of RPET is a separate

research topic in itself.

A literature search reveals that the effect of contamination on a recycling process is

significant. The problems caused by contamination can be combined into 4 groups:

− degradation of inferior properties: contaminants affect mechanical, thermal and

chemical properties, causing a decrease in mechanical strength, change in odor,

thermal stability, etc…

− surface defects: contaminants migrated to a surface to cause surface defects

− inconsistency: contaminants act as nucleators, causing uncontrolled crystallization

− equipment failure: contaminants clog equipment or otherwise damage it [29].

There are few examples of contamination-caused degradation:

As the studies were conducted on plastic films, a nitrocellulose printing ink binder was

the reason for yellow-brown marks in a recycled application; degradation products of

some additives (lubricants, antistatic agents and stearates) caused a recyclate film

discoloration and odors and the residues of a degraded polymer in a recyclate were the

85(135)

reason for poorer UV-resistance, accelerated further degradation and odors of a recycled

product [13].

Pigment particles can induce thermal degradation and act as nucleators, initiating

uncontrolled crystallization.

4.2.3 Thermal history

Thermal history of a polymer is the amount of times a polymer was re-melted or

otherwise thermally processed. The effect of thermal history on the quality of a

recyclate is difficult to investigate, as the proportion of a recycled material in the raw

material of a bottle is not accessible after the first recycling. Preformia uses up to 50 %

of recycled PET in production of new bottles, but after few cycles it is not possible to

define the content of the recyclate in the new bottle.

Information is available that the molecular weight of RPET resin decreases with an

increasing number of extrusions. After five extrusions the molecular weight is 65 % of

the original (see figure 34).

Another effect of reprocessing RPET is an increase in generated acetaldehyde level (see

details in 4.2.1)

Intermediate conclusion

After considering the effect of different factors on the properties of PET and RPET –

the question should be answered “How do the properties of PET change due to the

recycling?”

Figure 37 defines which of the factors affecting properties of PET are altered by the

recycling (comparing to figure 30 factors affected typed in bold).

It can be noticed that all the characteristics of the polymer and some processing

parameters are affected by the recycling. The scheme also illustrates higher load on the

equipment used for the recycling.

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Rheological properties

Mechanical properties

Thermal properties

Optical properties

Additives Molecular weight

Co-polymers Arrangement of the molecules

contaminants

time of shear

shear rate pressure in melt

processing temperature

homogenity of mass

grinding/ pelletizing

pumping vacuum drying filtering extruding

moisture content

crystallizing

shape of input material

Throughput capacity

cooling time

Chemical properties

Figure 37 The effect of recycling on relation of characteristics of polymer, processing

parameters and polymer properties

One of the most significant effects of the recycling is the decrease in the molecular

weight of RPET, usually indicated by the reduction of IV. Reasons for IV drop include

hydrolytic degradation of the plastic caused by improper drying of the plastic,

mechanical degradation of RPET caused by the grinding and the excessive screw

rotational speed, thermal degradation caused by the excessive heating, the

heterogeneous bulk density and the presence of contaminants in the feedstock.

Possible consequences of the decrease of the molecular weight are the reduction of

mechanical strength and stiffness.

Possible positive effects are the diminution of the melting temperature and better flow

characteristics of the melt.

The second effect of the recycling is the change in crystallinity of a final product.

Contamination and the heterogeneous bulk density of the feedstock might affect the

melt flow and, as a result, the arrangement of the molecules in the cooled plastic. Inc

residues can start uncontrolled crystallization, acting as nucleators, while bigger

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particles can disrupt the orientating of long molecules, and disturb formation of

entanglements.

The disruption of entanglement would lead to the decrease in strength, toughness and

viscosity. The disturbed crystallinity of the polymer can result in the increased

transparency of a final product. Nevertheless, separate particles of impurities can cause

surface defects.

Other possible effects of contamination on the quality of a recycled product include

random discoloration, graying or yellowing of the plastic, odor, poorer UV-resistance,

increased surface tension.

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5 APPLICATIONS FOR RPET

An overview of the applications of RPET was made in 3.2.4. The chapter 5 presents

some ideas on what materials can be substituted with RPET.

5.1 Systematic approach

The next chapter is intended for a manufacturer contemplating the use of RPET instead

of PET or some other plastic. General guidelines presented should help one to conclude,

whether it is feasible or not to utilize RPET for an existing product.

The idea of the systematic approach is in a systematic analysis of the feasibility of use

of RPET by answering questions.

The more negative answers will be recorded for the questions presented, the more

feasible the use of RPET for a product is.

The approach considers the appropriateness in two dimensions: the first are different

aspects of recycling (economical, ecological, technical and legal), and the second is life

span of a product from the raw material to the disposal.

The following questions are meant to be answered with the product in mind.

Questions

Part 1: Economical aspect

1. Is the material used at the moment cheap?

2. Is the manufacturing method of the product expensive?

3. Does it require secondary processing?

4. Does the manufacturing process of the product require some extra drying,

cooling, custom processing?

5. Is this product irregularly shaped?

6. Is the producer responsible for the disposal of the product?

7. Does it require special treatment at disposal (hazard)?

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8. Does it have an image of “luxury” product?

□

The more negative answers are recorded, the more feasible the use of RPET for this

product from the economical point of view.

If most of the answers were YES, the use of recycled material will be costly. What price

level the product has?

Part 2: Technical aspect

1. Should the product float on the water surface (for not hollow items)?

2. Are there strict optical requirements for the product?

3. Should the product resist a high stress?

4. Should it have a perfectly smooth surface?

5. Does it have to be used under - 20 °C?

6. Does it have to be flexible at room temperature?

7. Is it used with food or drink?

8. Is it used as a container for medicine?

9. Should it keep its shape when in contact with boiling water?

10. Are there any obstacles to use the drying equipment (see 3.1.2 and 4.1.2) like

absence of equipment, not sufficient floor space, etc?

11. Does this product have any other special requirement you can think about?

□

The more negative answers are recorded, the more feasible the use of RPET is for this

application from the technical point of view.

Every YES for the preceding questions might be a reason not to use RPET for product

manufacturing.

Part 3: Ecological aspect

1. If hazardous chemicals are used for the manufacturing of the product at the

moment, would the use of them still be necessary with RPET?

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2. Is energy consumption for production of this product low?

3. Is it difficult/ impossible to recycle the product?

4. Is it true, that consumers of the product are not concerned with environmental

friendliness of the product?

The more negative answers are recorded the more probable the use of RPET will

improve the image of the product, make it more “environmental-friendly”.

The more YES-answers are recorded, the more probable that the substitution of utilized

plastic with RPET is not feasible from the environmental point of view.

“+” of the method

A systematic approach

Technical, economical and ecological points of view are considered

Easy to use

“-“ of the method

Gives some ideas, but no answers

5.2 Comparing specifications to requirements

This method allows a user to compare RPET to other plastics. The method is easy in

principal: the user compares properties of different plastics to the specification of

desired products. The expected outcome of the method is the comparison of

appropriateness of RPET and another material as the feedstock for a product.

Obtaining the data

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To clarify the method an example is presented. A manufacturer of plastic sheet from

PET wants to know, whether RPET will be worse, equally good or better raw material

for this product.

The first step is to define the desired specifications for the product. The manufacturer

has specifications of its own product. Nevertheless, it is recommended to obtain the

specifications for the same product produced by a few manufacturers. In the present

work product specifications are obtained from Finnish manufacturers like Fluorotech,

Aikolon, and Foiltek (see attachment 3). Only PET homopolymer is considered.

Table 6 Properties of PET sheets produced by different manufacturers

Property Fluorotech (PET)

Aikolon (PET)

Foiltek (PETA)

Density (g/cm3) 1,37 1,39 1,34

Friction coefficient 0,22 0,2 N/A

Water absorption (%) 0,2 0,16 N/A

Tensile strength at yield (Mpa) 74 90 59

Elongation at break (%) >20 20 No break

Elastic modulus (Mpa) 3000 3400 2420

Flexural strength (Mpa) 125 N/A 86

Charpy impact strength (kJ/m2) No break N/A No break

Charpy notched (kJ/m2) >4 N/A N/A

Ball indentation (Mpa) 130 N/A 117

Rockwell Hardness M/R scale N/A 96 / N/A N/A / 111

Service temperature range (‘C) -20 - +100 -20 - +100 N/A - +60

Short time heat resistance (‘C) 170 160 N/A

Coefficient of linear thermal expansion (*10-5)

7-8 N/A <6

Melting point (‘C) 255 255 N/A

Heat conduction (W/’Km) 0,21 0.29 N/A

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Dissipation factor

50 Hz

1 MHz

0, 019

0.004

N/A

Specific resistivity (Ohm/cm) 4*1016 1016 N/A

Surface resistance (Ohm) 5*1012 10115 N/A

Electric breakdown strength (kV/mm) >70 50 N/A

Light transmission (%) N/A N/A 89

Refractive index N/A N/A 1,576

To visualize the appropriateness of RPET for a sheet application an optimal profile

should be built. The rules for the profile building are the following (see figure 38):

− each property is represented on its own axis (in figure 38 five properties are chosen,

so the pattern has five axes. The properties chosen should be relevant for the

product)

− each axis has its own scale, starting at the origin

− the scale of the axis should be chosen so that all the values found in specification for

corresponding property can be placed on it

− values are represented on the axis with dots or other symbols

− values obtained from the specifications should be plotted to the axes by placing the

dot to the corresponding place on the axis, according to the scale

− the dots that are closest to origin and the most distant from origin should be marked

out (green dots in figure 38). Those marked values are significant ones. Other dots

can be ignored.

− the dots on the axes should be connected by two continuous lines –one line

connecting all closest to origin dots and another connecting dots that are the most

distant from origin

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− the distance between two dots on each axis represents the set of values optimal for

each property. For example, the distance between dots A2 and A1 in figure 38

represents that tensile strength values region A2-A1 is optimal, i.e. most of

commercially available PET sheets will have value of tensile strength within this

region.

− the area between outer and inner lines represents the profile of the product – set of

properties optimal for the product, according to market specifications

Figure 38 Schematic representation of optimal profile for PET sheet

If all the aforementioned steps are performed with values obtained from specifications

of three Finnish manufacturers (table 6), the following profile should appear:

Electric breakdown

strength (kV/mm)

Elongation at break

(%)

Flexural strength (MPa)

Service temperature ˚C

F1

F2

A1

A2

B2

C2

C1

D2

D1

B1

Tensile strength (MPa)

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Figure 39 Optimal profile for PET sheet

Once the optimal profile for a PET sheet is build, values corresponding to properties of

RPET are to be placed on the respective axes.

The final judgment should be made of appropriateness of RPET for the product. If the

values of the properties of RPET are within the optimal profile for a PET sheet (red area

in figure 39), then RPET is an equally good material as PET for manufacturing of a

sheet. Each value of property outside of optimal profile should be considered separately

to define the effect it makes on the product. For example, if elongation at break of

RPET is 4 %, while according to optimal profile it should be 20 %, the manufacturer

should consider what effect this difference makes on the sheet. If the difference in

values does not affect the sheet, RPET still can be used for it.

Unfortunately, at the moment there is no sufficient information available on properties

of RPET. The method can not be used without specifications of RPET.

“+” of the method

Visual

Each parameter in the specification can be evaluated separately

Elongation at break (%)

Flexural strength (MPa)

Service temperature ‘C

Electric breakdown strength (kV/mm)

70

50

90

59

86

125 +60

+100

Tensile strength (MPa)

20

70

-20

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Limiting values for different properties are visible

The more axis (properties) are chosen, the more precise will be evaluation

“-“ of the method

Specifications of RPET are needed

The conclusion can be difficult to make

Scaling might be difficult

Relevance of properties chosen as axis affects the accuracy of evaluation

5.3 The most similar to PET plastics

In this approach PET was compared to other plastics. The data for comparison was

taken from the datasheet found in Material Science of Polymers for Engineers [39].

The idea of comparison is to find what plastics have the properties most similar to PET

and what those properties are. The original idea was to perform this comparison for

RPET, but the properties of RPET were not available at the moment the work was

performed. Therefore, comparison was done for PET, so that the method can be tested

and the relevancy of the results evaluated.

The idea was to find what plastics have properties similar to PET. It was done by

comparing the numerical values of properties of selected plastics to the properties of

PET. The plastic was given one point of similarity, if the numerical value of its specific

property was equal to the corresponding value of PET or was within ± 5 % range. The

range was chosen relatively small to limit the amount of plastics getting similarity

points up to 3-7. In case the value of selected plastic was presented as a range, the

plastic was given the similarity point if any of the values from the range satisfied the

original criterion.

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Example of tensile strength is given for clarification. Tensile strength of PET, according

to the tables used [39], is 47 N/mm2. Therefore, any plastic with tensile strength value

equal to 47 N/mm2 or within range of [44.65 N/mm2 to 49.35 N/mm2] will be given one

similarity point. In this way, PS, ABS, E/TFE, PDAP and SI each got one similarity

point.

The results of the similarity points’ collection are presented in table 7. Assumed values

for RPET are based on the conclusions made in the chapter four.

Table 7 Plastics which one or few properties have value similar to PET property value

± 5 %

Comparison point Value for PET Range Polymers within range

Density 1.37 g/cm3 [1.3015 - 1.4385] PVC-U, PVC-P, POM, PBT, PPS, PAS, PES, PI

Tensile strength 47 N/mm2 [44.65 – 49.35] PS, ABS, E/TFE, PDAP, SI

Elongation at break*

175 % [166.25 – 183.75] PCTFE, PA 66

Tensile modulus of elasticity

3100 N/mm2 [2945 – 3255] PS, POM, PMMA

Ball indentation value

200 10-s-value [190-210] PMMA, PVK, RPET

Notched impact strength

4 kJ/m2 [3.8 – 4.2] PB, PBT, RPET

Water absorption (24 h)

0.30 % [0.285 – 0.315] PVC-U, PVC-P, SAN, ABS, PMMA, PA 11, PF, PDAP, SB

Service temperature

(max, short time)

200 ˚C [190 – 210] PA 66, PSU, UP, PDAP, RPET

Service temperature

(max, continuous)

100 ˚C [95 – 105 ] PP, POM, PA 6, PBT, RPET

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Service temperature

(min, continuous)

- 20 ˚C [-19 - 21] PVC-U, SAN, SB, PP, RPET

HDT

(Viscat 5 kg)

188 ˚C [178.6 – 197.4] PVK, PA 6, PBT,

Coefficient of linear expansion

70 * K-1*106 [66.5 – 73.5] PVC-U, PS, SB, PMMA, PC, ABS

Thermal conductivity

0.24 W/mK [0.228 – 0.252] POM, PTFE, FEP, E/TFE, PA 66, PA 11, PPE

Specific heat 1.05 kJ/ kgK [0.998 – 1.102] PVC-P, PTFE, PES

Dielectric constant

(50 Hz)

4 [3.8 – 4.2] SB, ABS, ASA, PMMA, PA 6, PAS, SI, RPET

Dissipation factor

(50 Hz)

2* 10-3 [1.9 – 2.1] PBT, PI, RPET

Dielectric strength 500 kV/25 µm [475 – 525] PS, SAN, SB, PVK, PTFE, FEP, PCTFE, PBT, PPE, RPET

Water vapor permeability

0.6 g/cm2 day [0.57 – 0.63] E/TFE

H2 permeability 1500 cm3/m2 day bar

[1425 – 1575] PA 6

* when the value in the datasheet [39] was given as a range of values (like for elongation at break 50-300

%), the average value was taken, that is 50 + (300-50)/2 = 175 %

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After counting similarity points for each of selected plastics the table 8 was compiled:

Table 8 Rank of the most similar to PET plastic

Similarity points Plastics

8 RPET

6 PBT

5 PMMA, SB

4 PA 6, PVC-P, POM, PS, ABS

3 PVC-U, E/TFE, PDAP, PCTFE, PA 66, PVK, SAN, PTFE, FEP

2 PAS, PES, PI, SI, PA 11, PC, PPE, PP

1 UP, PSU, PF, PB, PPS

According to the made comparison, RPET, PBT and PMMA have properties most

similar to properties of PET.

The properties of RPET were assumed, so no evaluation of accuracy of results can be

made. The properties of PBT are known to be similar to the properties of PET, as their

names imply (both are terephtalates). Applications of PET and PBT in the electronic

industry are very similar. Applications of PMMA are glass replacement, fibers, yarn,

etc. While PET could be used for some of those applications, the price of PET is

significantly lower.

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6 CONCLUSION

Mechanical recycling is the best recovery method for PET bottles, because the

organized collection of PET bottles in Finland provides a recycler with a sufficiently

clean, homogeneous, and stable stream of raw material. A less homogenous stream of

bottles with presence of plastics like PP and HDPE and other physical contamination

might be better viewed as a stock for energy recovery. The best waste treatment method

for heavily chemically contaminated PET bottles is, most probably, feedstock recycling.

Another reason for preferred mechanical recycling of PET bottles is the volume of the

raw material available. The amount of PET bottles available for recovery do not provide

a sufficient stock for the feedstock recycling technology, neither justifies an investment

in equipment needed for an energy recovery facility.

The properties of PET and RPET are difficult to compare, as no sufficient information

is available on the properties of RPET. The stable numerical values for properties of

RPET would be difficult to obtain, as those values vary with variations in the quality of

stream of PET bottles available for recovery. It is generally believed that mechanical

strength of RPET is lower than of PET due to decrease in the molecular weight.

Theoretically, decrease in the molecular weight can be minimized, if RPET is washed

and properly dried. Main reasons for decrease in molecular weight are thermal

degradation catalyzed by presence of contamination or hydrolytic degradation caused by

presence of water.

Apart of different mechanical properties, an item made of RPET might be expected to

have surface defects caused by contamination. On the other hand, contaminants in

RPET can disturb the crystallinity, which results in increased transparency of RPET.

An overview of RPET applications revealed that in Europe RPET is mainly used for

fiber production. Virgin PET also can be used for fiber production, but is mainly used

for bottles, as quality requirement for the plastic for bottle production is higher. In

Europe, RPET is used for fibers and not for bottles, as quality of RPET collected in

Europe is not suitable for bottle production. Applications of RPET in USA and even in

Europe can not be compared to possible applications of RPET in Finland, as collection

systems are very different. Finland is one of a few countries, where PET bottles can be

returned upon monetary incentive. The method of collection reflects greatly in the grade

of plastic waste collected. Clean PET bottles are a valuable resource, rather than waste.

100(135)

PET bottles obtained through the Finnish return system have the best grounds to be

recycled into bottles and be used in applications PET is used in.

Other applications of RPET can be thought of by comparing the properties of RPET to

the properties of other plastics. A comparison of different plastic shows, that PBT and

PMMA have the closest properties to the properties of PET. The price of PMMA and

PBT is at least twice of PET price. RPET is less expensive than PET. Comparison of

properties of RPET to properties of other plastics can result in finding economically

interesting alternatives for expensive plastics.

6.1 FUTURE DEVELOPMENTS

The energy content of PET is close to that of soft coal, which makes it a candidate for

successful energy recovery. The topic might be worth investigating at this moment,

when the project of building waste burning facility is Helsinki has started.

Another practical work might be done on investigation of properties of RPET

comparing to properties of virgin PET. The work can be expanded to a general

correlation between properties of virgin and recycled material.

One more possible investigation topic is an effect of additives on the quality of RPET.

Most of the available on the market grades of PET contain some kind of additives,

which effect on quality of RPET after repeating reprocessing is practically unknown.

The process of recycling is altered by presence of contamination in the material stream.

The investigation can be made on the effect of different contaminants on a recycling

process and quality of the final resin. Washing costs can substitute up to 30 % of the

final processing cost of recycled plastic [13] so by defining the effect of contaminants

on the quality of RPET, the need for excessive washing can be rethought.

101(135)

7 AKNOWLEDGEMENTS

I would like to express my sincere gratitude to my supervisor, Mikael Paronen for his

time, persistence, inexhaustible enthusiasm and priceless comments.

I would also like to thank Erland Nyroth for his help and patience in answering all

possible questions.

I extend my sincere thanks to my teachers, Mathew Vihtonen and Henry Ericsson for

their advices and comments.

I would like to thank separately my teacher Mariann Holmberg for her invaluable help

and understanding.

I have no words to thank my Mum and my friends, Jaui, Cecilia, Laura, Rasmus for

their support during my work. My separate and warmest thanks go to Joni for his

presence and help.

I would like to express my gratitude to Vesa Kärhä for initiating this project and

supplying me with the idea.

I also want to thank John Ekholm and Janne Halminen for provided information and

motivation to finalize this work.

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9 APPENDICES

9.1 Types of pelletizers

There are two main categories of pelletizers: cold cutting and hot face cutting systems

that can be further divided into several types [1].

Cold cutting system

The two components of a cold cutting system are a die and a cutting chamber.

There are two kinds of the cold cutting systems: dicers and strand pelletizers.

− Dicer

In a dicer a molten polymer exits trough ribbon dies or a roll mill. The resulting

continuous “sausage” of polymer is solidified and cut into pellets or cubes.

The advantages:

Accumulated expertise of the subject

Accurate method

Production rate 18 200 kg/hour

The disadvantages:

Noise emission

Reduced knives life

− Strand pelletizer

En extruder is employed to force a molten polymer through a die to produce strands.

Thereafter the strands are cooled by air or water. The strands are also dried, if water was

used as a cooling medium. Solidified and dried strands are cut into pellets.

The advantages:

Experience

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Inexpensiveness

Ease in operation

The disadvantages:

Dropping of strand when drawn through the cooling medium due to the poor

melt strength (PET)

Production rate around 6 800 kg/ hr

Extra space needed for the cooling

Reduced knifes life

Hot face cutting system

In a hot face cutting system pellets are cut as a melt exits a die. The components of the

system are a die, a cutting chamber, motor-driven rotating blades, and a drying

compartment. The die is heated by oil or electricity and has uniform-diameter extrusion

holes. As pellets exit the die, they are cut by the rotating blades and driven away by the

centrifugal force to the cooling media. There are three types of hot face systems

differentiated by the cooling medium: air pelletizer, water ring pelletizer and underwater

pelletizer.

− Air pelletizer

Air pelletizers are recommended for the polymers that are sensitive for heat. Pellets are

cut and fast cooled (quenched) by air in the cutting chamber and further cooled by

circulating air.

The advantages:

Decreased wear of the blades

Minimum heat is used to heat the die

Inexpensive cooling medium

The disadvantages:

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Cutting rate 5 000 kg/hour

− Water ring (water spray) pelletizer

This method is not suitable for polymers with low melt viscosity. In a water ring

pelletizer a molten polymer is cut by the rotating blades and the pellets are thrown with

the water stream to rotate in the cutting chamber. After the pellets are quenched, the

water-pellets slurry is additionally cooled and discharged to the centrifugal drier.

The advantages:

Longer blades life

Cutting rate 13 600 kg/hour

− Underwater pelletizer

In this pelletizer water is conveyed directly to the die, so as pellets are cut they are

driven away to the dryer by the stream of hot water. At the dryer water and the pellets

are separated so that water can be cooled and reused.

The advantages:

Longer blades life

Cutting rate is 27 000 kg/hour

Can be used with low viscosity and sticky polymers

Low noise emission

The disadvantages:

The special die with heat distribution and isolation is needed

The water has to be heated to the maximum temperature

− Centrifugal force pelletizer

In this pelletizer the minimum heat is needed at the die and the pellets are cut from a

molten polymer. The polymer is forced to the die holes by rotating the die and

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appearing strands are thrown to the cutting blades (which are usually also rotating at a

low speed). After the pellets are cut, they are cooled by water spray and dried.

[1] Modern Plastics Encyclopedia Handbook, edited by Modern Plastics Magazine,

McGraw-Hill, Inc., 1994

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9.2 Techniques of measuring molecular weight

1. Methods, based on the difference in the osmotic pressures

a. membrane osmometry

The method is based on the chemical potential difference of a dilute polymer solution

and a pure solvent separated by a semipermeable membrane (usually made of cellulose

or its derivatives), what results in the transport of the pure solvent trough the membrane

to the solution and increase in the solution level. The osmotic pressure is calculated

using the difference in levels, after what the number average molecular weight is

calculated utilizing the existing formula [1]. The time consumption and the performance

of the membrane are the disadvantages of this method, while the accuracy for the high

molecular-weight polymers is an advantage.

b. vapor-pressure osmometry

This method is more suitable for lower molecular-weight polymers and based on the

fact that the vapor pressure of a solvent is lowers if a polymer is added to the solvent.

The formula to realize that dependence is the following [1]:

lim c�

0 (∆p/c) = - (p10V10)/Mn

c = concentration

p10 = the vapor pressure of the pure solvent

V10 = the molar volume of the pure solvent

Mn = number average molecular weight

Nevertheless, in practice instead of pressure differences, concentration induced

temperature differences are measured.

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2. Methods, based on the light-scattering

Some light-scattering methods, like the Zimm method can be used to determinate the

molecular weight of unknown polymer [1].

In this method Mw is found utilizing the Zimm equation [2]:

KC/R(θ) = 1/(Mw*P(θ)) + 2A2С

K = is a function of refractive index, n0, of a pure solvent; of a specific refraction

increment, v, of a dilute polymer solution and the wavelength of the incident light in

vacuum

C = sample concentration

Mw = weight average molecular weight

R(θ) = Rayleigh ratio

P(θ) = particle scattering function

A2 = the second virial coefficient of solution

Principles of LALS detector for measuring molecular weigh are based on the Zimm

equation.

3. Methods, based on the chromatography

One of the inexpensive and fast techniques is size exclusion chromatography (SEC) or

gel permeation chromatography.

A polymer dissolved in a solvent (for instance tetrahydrofyran, THF) is shot through a

column (spirally coined tube) filled with the porous gel beads of a crosslinked polymer.

Longer molecular chains slide (elute) faster through the column, as they do not get

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trapped into the pores of the beads as often as short chains. As a result, a graph similar

to the one bellow is formed (see figure 40).

Figure 40 Plot of molecular weight distribution obtained by SEC [3]

The molecular weigh of molecules on SEC plot is growing from the right to the left due

to the fact that molecules with the highest molecular weight will be the fastest ones to

elute through the column, so they appear first.

Polystyrene gels are used for the investigation of nonpolar polymers in nonpolar

solvents, porous glass gels are used for more polar systems.

The elution is performed under pressure, so results can be obtained in few minutes and

only a few milligrams of the polymer is required for the testing.

The drawback of the method is dependence of results on the shape of polymer, so that

two polymers with the same mass but different shapes show different results.

Experiments show, nevertheless, quite precise measurements for most of the polymers

[4].

4. Methods, based on the viscosity measurements

a. Intrinsic viscosity measurements

Another method used for a routine molecular weight determination is the method based

on viscosity measurements. For these measurements Ostwald-Feske or Ubbelohde

capillary viscometers can be used. The Ubbelohde viscometer is preferable, as it has a

pressure equilibration arm, what ensures that the measurements are not affected by the

pressure under the capillary [1, 5]. The calculations are based on the time it takes for a

polymer solution or a pure solvent to flow through the capillary.

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First, the relative viscosity, ŋrel is found what is

ŋrel = efflux time of solution / efflux time of the solvent = t soln/t solvent

Second, change in viscosity upon the addition of a polymer is found, what is specific

viscosity, ŋsp

ŋsp = (tsoln – t solvent)/ t solvent

As specific and relative viscosities depend on the concentration of the solution, they are

divided by the concentration, to find reduced viscosity, ŋred

ŋred = ŋsp/c

If now ŋred is plotted against the concentration, the picture would look something like

that

Figure 41 A plot of dependence of viscosity on concentration [3]

The intercept of the graph and the y-axis will be intrinsic viscosity, [ŋ], or the viscosity

at 0-level concentration (that is not really obtainable in real life).

[ŋ] = limc�

0 (ŋsp/c)

Another way to find intrinsic viscosity is to find the interception of the graph of

ln(relative viscosity)/concentration plotted against the concentration, so that

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[ŋ] = limc�

0 (ln ŋrel/c)

The units of intrinsic viscosity are reciprocal of concentration units, or dL/g (most

commonly used).

After intrinsic viscosity is found, the Mark-Houwink equation can be used

[η] = KMvα

Both K and α constants are specific for a given polymer, a solvent and a temperature. It

should be noted that if intrinsic viscosity of a polymer are measured in different

solvents (so that the polymer chains take different configuration in those solvents), the

results can be very different [1, 3]

b. MFI/FRR measurements

Although the MFI/FRR measurements do not determine the molecular weight directly,

some considerations can be made.

Material flow index (MFI) depends on viscosity –the higher the viscosity, the smaller

MFI is. Viscosity linearly depends on a molecular weight. So, out of two polymers

having different MFI one having lower MFI has higher molecular weight.

Measurements of MFI are easy and inexpensive and conducted by measuring the

amount (in grams) of a polymer extruded through an orifice under the force of a

weighted piston [6].

Flow rate ratio (FRR), in turn, gives the picture of the distribution of molecular weight:

the smaller the ratio, the wider the distribution [7].

[1] J. E. Fried, Polymer Science and Technology, 2nd revised ed, Prentice Hall, 2002,

pp 112-123

[2] Viscotek, “GPS Theory: Light Scattering Detector”, [company web-site], accessed

20.06.2008, http://www.viscotek.com/the-gpc-ls.aspx

124(135)

[3] The University of Southern Mississippi, Macrogalleria, “Size exclusion

chromatography” [university’s page], accessed 16.05.2007

http://pslc.ws/mactest/level3.htm

[4] P. Atkins, J. de Paula, Atkins’ Physical Chemistry, Seventh Edition, Oxford, 2002,

ISBN 0-19-879285-9, p747

[5] P. Russo, “Intrinsic Viscosity”, [doc document], 2007, accessed 31.05.2007

macro.lsu.edu/HowTo/IntrinsicVisc.doc

[6] “Wellman design guide”, [pdf design guide], Feb 1995, accessed 21.5.08

http://www.wellmaninc.com/ContentStore/ERDesign/designguide.pdf

[7] V. Kurri, T. Malén, R.Sandell, and M.Virtanen, Muovitekniikan perusteet, 3.

tarkestettu painos, Hakapaino Oy, 2002, , ISBN 952-13-1584-9, p 40

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9.3 PET and market

The time the survey was conducted is 7-12 of May, 2007.

9.3.1 Plastic manufacturers

This section presents companies involved in manufacturing of PET plastic under

different trade names. Distributor companiee importing PET to Finland are also

presented.

9.3.1.1 PET Manufacturers (representatives in Finla nd)

DuPont (Espoo)

(http://www2.dupont.com/Automotive/en_US/products_services/engineeringPlastics/ryn

itePET.html)

This giant in the polymer world produces almost all possible polymers. Rynite® PET is

an engineering resin available form DuPont that is used, among others, in the

automotive industry and recommended for its stiffness, thermal and dimensional

stability and high gloss. (Datasheets available)

Ticona (Tuusula)

(http://www.ticona.com/index.htm)

A global company with representatives in Finland, among other resins produces Impet®

PET (unfilled IV 0.68), which, supplemented by different additives, is suitable for

automotive applications. Datasheets are available limitedly.

Advansa (through distributor)

(http://www.advansa.com/)

“Europe polyester leader”

The company has units in Turkey and Spain. It produces PET, PBT, PEN, PBN and

polyester intermediates (DTM).

The products are available in Finland through distributors (Distpol)

There are following applications for PET homopolymer

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IV Luster Application

0.62 Superbright Films

0.63 Bright Nonwovens

Superbright Film

0.64 Semidull, bright, Nonwovens

superbright POY spinning (pre-oriented yarn)

Bright, Superbright Industrial yarn

0.65 Fulldull POY spinning

Semidull Nonwovens

0.66 Semidull Nonwovens

0.76 Superbright Industrial (engineering polymers)

9.3.1.2 Others (representatives in Europe)

• Artenius (Turkey, Spain, Portugal, Italy, Greece, UK)

• Belpak (Belarus)

(http://opencity.narod.ru/predpri/belpak.html)

Producing PET preforms and granules approved for applications in contact with food

• Catalana de Polimers (Spain)

• DSM Engineering Plastics (through distributors)

(http://www.dsm.com/en_US/html/dep/home_dep.htm)

Trade name of PET plastic is Arnite ®. Data availability is restricted

• Eastman Chemical (Netherlands, UK)

(http://www.eastman.com/)

It is said to be the biggest PET producer for packaging

• Elana (Poland)

• Equipolymers (Italy, Germany)

(http://www.equipolymers.com/index.htm)

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Produces copolymers (with MEG) of PET for food and thermoforming applications

Datasheets are available for trade name LIGHTER ™

• Europlast (Russia)

(http://www.europlast.ru/eng/)

Produces PET preforms and polymer cups

• Invista (Germany)

(http://www.invista.com/page_whois_index_en.shtml)

Headquarters in USA, a producer of fiber and polymers

• Italpet Preform (Italy)

• M&G group (Italy)

(http://www.mgpolymers.com/Default.htm)

Produces homo- and copolymers of PET resin, high viscosity homopolymer PET

intended for industrial foams and food trays and containers and high melt point

homopolymer designed for dual-ovenable tray applications (IV = 0.95)

• Cray Valley Iberica (Spain)

• Mogilevkhimvolokno JSC (Belarus)

(http://www.khimvolokno.by/en/aboutus.asp)

Produces PET mainly for fibers and yarn, also geotextiles

• Neo Group (Lithuania)

• Novapet (Spain)

• PET processors (UK)

(http://www.petuk.com/)

Specializes in enhancing crystallinity and molecular weight in semi-crystalline

thermoplastics (IV up to 1.25). Range of materials from PET to LCP (liquid crystal

polymer)

• Orion Global PET (subsidiary of Thai Indorama PET in Lithuania)

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(http://www.indoramapolymers.com/company-profile.htm)

A company produces PET polymer (and copolymer) of different IV, preforms and

bottles. Datasheets are available.

• Sibur-PETF (Russia)

(http://www.sibur.ru/eng/articles/tverpet-z.shtml)

A company, producing bottle granulate among other products.

• SK Eurochem (subsidiary of Korean SK Chemicals in Poland)

(http://www.skchemicals.com/english/company/AboutEuro.asp)

• Slovensky Hodvab (Slovakia)

(http://www.slovhodvab.sk/hodvab_en.html)

Produces preforms, filaments, technical fibres and PET chips

• Tegral Fibres (France)

• Terom (Romania)

Producer of Terom® PET

• Wellman (Netherlands)

(http://www.wellmaninc.com/)

Produces PermaClear® resin and EcoClear® resin from recycled stock (10 %) for food

applications. Datasheets are available.

9.3.2 Plastic distributors (operating in Finland)

Ashland Finland

(http://www.ashland.com/products_services/plastics.asp)

An international company, one of areas of interest is distribution of plastic materials.

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Aspokem

(http://www.aspokem.com/introduction/index.html)

A company with headquarters in Helsinki, a distributor of industrial chemicals, car

chemicals and plastic raw materials. Mainly works in B-to-B sector.

Bang and Bonsomer

(http://www.bangbonsomer.com/)

A distributor of chemical raw materials. Polyester resin was found from the list of

products.

Brenntag Nordic

(http://www.brenntag-nordic.com/en/)

A distributor of chemicals with representatives in all 4 Nordic countries.

Distrupol

(http://www.distrupol.com/en/)

Distribution, sales, marketing and application of thermoplastic polymers and

elastomers. Very user-friendly site.

Etra

(http://www.etratrading.fi/epm_eng.php)

A supplier of engineering plastics, who also provides design services. Datasheets are

available.

Resin Express Nordik Ab (RESINEX)

(http://www.resinexpress.com/home/en/default.asp)

A global distributor of plastics, rubber, and chemical raw materials.

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Kauko-Telko Oy

(www.telkogroup.com)

The company, operating in Finland, Sweden, Denmark, Russia, Estonia, Latvia,

Lithuania and Poland. Both PET and RPET are available through this company.

9.3.3 Manufacturers of semi-finished products

This section presents manufactures of semi-finished products. Some of them process

PET, so they are listed as potential RPET processors. Others do not process PET, but

could use it according to their products profile.

9.3.3.1 Companies, processing PET

Aikolon (Oulu)

(http://www.aikolon.fi/)

A Finnish company designing, machining and selling semi- or finished products.

At the moment delivers sheets and bars from unfilled and additives containing PET.

Datasheets are available.

OY Fluorotech (Vantaa)

(http://www.fluorotech.fi/index.htm)

A company specializing on sales of plastic tubing applications and technical plastics. At

the moment sheets, round bars and tubes made out of PET are available. (Datasheets are

available)

Foiltek (Vantaa)

(http://www.foiltek.fi/index.html)

Produces and processes plastic sheets (including PET) for such applications as shops

storefronts, shelves and cases, roofs, covers for automatic vending machines, sport

equipment and protection masks. Trade name for the PET resin is NUDECPET ™. The

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example of prices can be found here (http://www.foiltek.fi/hinnasto_muovilevyt.pdf).

Datasheets are available.

Optinova Ab (Godby)

(http://www.optinova.fi/index.pbs)

A company specializes on medical tubing, but also has capabilities to extrude

thermoplastics (including PET).

Thermoplast Oy (Helsinki)

(http://www.kpfilms.com/en/index.asp)

This global company produces wide range of applications from plastics including PET

films and other packaging.

Vink Finland OY (Finland)

(http://www.vink.fi/)

This global company has department in Finland, producing sheets, pipes, rods, films, etc

also from PET.

9.3.3.2 Potential PET processors

Christian Berner OY (Vantaa)

(http://www.cboy.com/index.htm)

The company operating in the Nordic countries (Finland, Sweden, Norway, Denmark),

and supplying equipment and semi-finished applications from the technical plastics

(sheets, tubes, films, etc). PET at the moment is not present in the range of supplies.

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Fodesko Oy (Lehmo)

(https://www.fodesco.fi/)

Producing sheets and special application for the plastic industry. Range of processed

plastics is unknown.

KalusteMuovi Virtala Oy (Lahti)

(http://www.kalustemuovi.fi/)

Producing plastic sheets, no PET in use at the moment.

KWH Plast Oy (Jakobstad)

(http://www.kwhplast.com/Default.aspx?id=451920)

Producing film and sheets. PET is not used at the moment.

Muoviura (Riihimöki)

(http://www.muoviura.fi/English/index.htm)

A wholesaler and a subcontractor. At the moment it sales sheets, rods, tubes and films

from different thermoplastic (PET is not included) and providing design and second-

stage treatment (vacuum molding, thermoforming).

Perlos Oyj Lehmonharju Plant (Joensuu)

(http://www.perlos.com/index.asp?id=02a23ea5a2d54f0d953870ef2c2c26cc)

Designs and manufacture products for the electronics and telecommunication industries.

Renau Ab Oy (Vantaa)

(http://www.rehau.fi/yritys/index/index.shtml)

The company providing the polymer-based solutions for construction-, automotive-, and

industrial applications.

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Oy Toppi Ab (Espoo)

(http://www.toppi.fi/)

The web page is unavailable

9.3.4 Examples of equipment suppliers for the recyc ling

This section is focused on companies producing the equipment for recycling of PET.

Erema (Austria)

(http://www.erema.com/en/42/)

The company supplies patented VACUREMA technology to process post-consumer

PET plastic into pellets or finished material (fibre, striping, sheets). The technology is

claimed to increase IV of RPET.

Kreyenborg Group (Germany)

(http://www.kreyenborg.com/en/kreyenborg/index.php)

A supplier for the components and systems for plastic industries and recycling. PET

solution is infrared dryer for the flakes or the pellets.

Luigi Bandera SpA (Italy)

(http://www.luigibandera.com/index3.html)

Among other products, the company provides the solutions for the recycling, i.e. high-

vacuum venting PET recycling system

Sorema (Italy)

(http://www.sorema.it/)

A partner for plastic recycling. The provider of solutions for recycling companies, like

patented Ecopet line for PET recycling.

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Potential applications for RPET

1. Water-pipe or water-conduit (on the roofs, from the roofs) out of bi-axially

oriented plastics

The idea of using recycled PET in water pipes came from the similarity of the shape of

a PET bottle and a pipe and the fact that a few bottles of the same diameter and removed

upper- and bottom parts can be easily connected into a pipe (one of those was in use at

the summer cottage of the author for a few years).

On an industrial extend, pipes can be extruded from recycled PET or mixture of RPET

with other plastics. At the moment HDPE pipes are extruded [1].

2. Insulating concrete forms

PS and PU are the most common expanded plastics, PP and PE can also be expanded.

According to [2], recycled PET can also be used together with branched PET to produce

extended PET plastic (content of recycled PET 25 -75 %) usable in various applications

such as trays, food containers, oil resistant packages, insulation and so on (more items

can be found in the description of the invention).

One possible application for the foam plastic would be to use it in stay-in-place

Insulating Concrete Forms (ICFs). ICFs are the forms made of composition of extended

plastic or wooden chips and concrete to build concrete walls and similar constructions.

According to [3], “those forms should be constructed of rigid foam plastic meeting the

requirements of ASTM C 578, a composite of cement and foam insulation, a composite

of cement and wood chips or other approved material…” The stay-in-place forms are

performing heat-, sound- and air insulating function (Read more about Insulating

Concrete Forms http://www.forms.org/index.php?act=technicallibrary and in

Wikipedia).

3. Insulation

At K 2007, the international plastic fair held in Dusseldorf in October, 2007, the

American company DOW presented its insulation material under tradename of

SAFETOUCH ™ made of PET that claimed to outperform conventionally used

fiberglass-based insulation [4].

4. Lining in between casing (steel or metal) and concrete, so that a casing would

not stick to concrete (an idea of Poliakov V.N, construction engineer)

135(135)

5. In the greenhouse –water-interminable layer that is placed before the layer of

soil (idea of Poliakov V.N, construction engineer)

6. Flower pots

7. The wetting surface of PET can be utilized in applications which have to be

painted.

8. Water absorption – property can be utilized in applications where non-slip

property is important (rainy conditions, under-water conditions). Examples are

inside swimming shoes, soles for diving slippers, a non-slippery bottom

layer for shower, outdoor carpets.

[1] Plastic Pipe Institute, [institute’s web site], accessed 11.07.2007,

http://www.plasticpipe.org/

[2] United States Patent 5391582, “Poly(ethylene terephthalate) foams comprising

recycled plastic and methods relating thereto”, [on-line free patent], 02.21.1995,

accessed 11.07.2007, http://www.freepatentsonline.com/5391582.html

[3] U.S. Department of Housing and Urban development, “Prescriptive methods for

connecting cold-formed steel framing to insulating concrete form walls in residential

construction”, [pdf document] February 2003, accessed 11.07.2007,

http://www.huduser.org/Publications/PDF/pm_for_steel_framing.pdf (pdf)

[4] DOW, [corporate web site], accessed 21.05.2008;

http://building.dow.com/styrofoam/na/safetouch/main.htm