Plastics Recovery and

Recycling

Summary

Statistics

Waste recovery routes

1. Mechanical recycling

2. Feedstock recycling

3. Energy recovery

Plastics Waste Recovery - Europe

UK Recycling of Plastic Bottles (+

Non-Bottle Packaging) (Recoup.org)

UK Plastic Bottles Statistics (Recoup.org: figures for 2010)

Plastic

bottles

(tonnes)

Non-bottle rigid

plastic packaging

(tonnes)

Total

(tonnes)

Bring 47,265 5,141 52,406

Kerbside 233,832 71,223 306,055

TOTAL 281,097 76,364 357,461

For plastic bottles, 281,097 tonnes were recycled out of ~580,000 tonnes consumption, giving a recycling rate of ~48.5% (2010), compared with ~46%

(2009), ~39% (2008)

For non-bottle rigid plastic packaging, 76,364 tonnes were recycled out of ~500,000600,000 tonnes giving a recycling rate ~12-15%

N.B. (a) ~11% of household waste is plastic, ~40% of which is plastic bottles

(b) 25 recycled PET bottles can be used to make an adult fleece jacket

(c) Plastic packaging uses ~2% of all crude oil produced

EU Plastics Recycling/Recovery (Plastics The facts 2011, PlasticsEurope.co.uk)

Waste Management Routes

Waste Management Routes

Three main potential recovery routes

1. Mechanical recycling

2. Feedstock recycling

3. Energy recovery

Mechanical Recycling

Most potential since low energy consumption and original energy of synthesis is conserved

1. In-plant recycling

Has always been carried out as part of good housekeeping and waste minimisation

Regrind (plastic from runners, sprue, off-specification products, etc.) is blended with virgin plastic in relatively small proportions.

2. Post-consumer recycling (PCW)

Degraded and contaminated, so a bigger challenge

(a) Homogeneous material can be recycled similarly to in-plant regrind, except it needs decontamination

(b) Co-mingled post-consumer waste commonly contains multiple incompatible polymers

Injection Moulding Machine

Mould showing Sprue and Runners

Recycling Homogeneous PCW

(Post-Consumer Waste) Typical sequence (Figure 3.8)

1. Primary grinding

2. Air classifier (to eliminate paper and other lightweight materials)

3. Hydrocyclone (to eliminate metals and other dense materials)

4. Secondary grinding

5. Washing

6. Melt filtration by extrusion (final purification)

7. Final extrusion compounding can now include additives

Need to keep processing to a minimum to minimise degradation

Recycling Homogeneous PCW

Problem Materials

Multilayer packaging (e.g. PET sandwiching a nylon layer for beer container)

Composite items

Highly contaminated items

Highly pigmented or filled polymers

Different grades (particularly molecular weight) of the same polymer (N.B. MFI)

Non-recognisable plastic items

Minor amounts of specific polymers

Co-mingled PCW

Historically some co-mingled PCW has been reprocessed using standard extrusion, injection

moulding etc., but, due to imperfections, just in

thick cross-sections to minimise the effect on

mechanical performance, e.g. Plaswood - plastic

lumber, road markers, etc.

Several new processes have been attempted to produce higher quality (value) material, without

separation procedures. These are just at the

experimental stage, not commercial.

Examples of Plastic Lumber

Co-mingled PCW Potential New Processing Techniques

NewPlast Intensive mixing in a cylindrical drum, rotating at high speed. It is claimed that HDPE, LDPE, PP, PET and PVC can be mixed this way to give a material with a higher stiffness than LDPE and retaining significant ductility

Solid State Shear Extrusion Pulverisation unsorted PCW is subjected to high shear and pressure, which would normally melt the plastics. In this process rapid heat removal is required to prevent melting, so that the polymer mix is transformed into a uniform powder. It is claimed that powders produced from mixes of PET, PS and PVC are homogeneous with no segregation detected on blending

Revitalisation Plastics get modified during the original processing and during

the lifetime of the component

The additives and stabilisers added when first manufactured are consumed during processing and use so the end-of-life plastic is not necessarily re-usable

Table 3.3 illustrates some problems of reprocessing Appropriate revitalisation requires knowledge of: (a) Effects of previous life cycles

(b) Material characterisation methods

(c) Performance requirements and service life of new product

(d) Processing and compounding techniques

To date, conventional additives have been used, but manufacturers are developing new products specifically for plastics revitalisation

Blends

Blending is common in virgin plastics e.g. high proportions of poyolefins are sold

as blends

(N.B. blends are physical mixtures of

chains of different polymers, not to be

confused with copolymers, which consist

of chains each containing more than one

type of monomer)

Blending and Compatibisation Miscible blends homogeneous mix down to

molecular level can use law of mixtures to estimate properties but there are few miscible polymer pairs (e.g. PS and PPO)

Immiscible blends heterogeneous normally mechanical properties are inferior to either component however sometimes they can be compatibilised, commonly using a block copolymer e.g. poly(styrene ethylene)

Compatibilisers generally increase ductility and impact properties, but reduce stiffness and heat resistance

Fig 3.10 shows electron micrograph of immiscible

PET in PP and a PET/PP blend compatibilised

with PP-MAH (maleic anhydride grafted onto PP).

In Fig.(b) there is a finer dispersion of PET

domains and improved adhesion.

Environmental Aspects of Additives

Although plastics have a reputation for causing environmental problems, it is the

additives that are more significant than the

polymer

See Table 3.4 for some of these problems

Environmental Aspects of Additives

Case Study of Mechanical Recycling (www.closedlooprecycling.co.uk)

Closed Loop Recycling set up in Dagenham June 2008

Capacity ~35,000 tonnes per annum of waste bottles (November 2013 - they announced that due to the

demand for more bottles, capacity is to be increased

to 55,000 tonnes.)

Now producing food grade plastics and other side products

In November 2011, annual production ~11,000 tonnes of rPET and ~6,000 tonnes of rHDPE

Summary of Process For details see: http://www.closedlooprecycling.co.uk/information/our-

plant-process-technology

Bottles go through numerous stages of cleaning (trommel, electromagnet, eddy current separator, air classifier) and

optical sorting machines separate them into 6 types followed

by manual sorting.

Bottles are granulated, air classified, and cleaned in a weak solution of hot caustic soda and sink-float separated in water

Decontamination of PET in caustic soda removes thin surface layer and finally it is colour and laser sorted and sold as flake

Decontamination of HDPE is by treating flake at high temperature (~200oC) and low pressure. Then it is extruded

filtered and pelletised.

Mechanical Recycling

Summing up

Although technical problems can usually be solved, it is not always economically

viable

Generally slightly inferior properties

Progress needs improvements in separation, cleaning and purifying

More confidence in recycled materials is needed for designers

Feedstock Recycling

Involves breaking down polymers to monomers or petroleum feedstock

Can obtain virgin grade material, but requires energy to de-polymerise and re-polymerise.

Mostly just at the development or pilot plant stage due to large investment required (capital and operation costs)

Two types of process -

(1) Chemical depolymerisation

(2) Thermal depolymerisation

Chemical Depolymerisation

(Solvolysis)

This works for most condensation (step reaction) polymers (e.g. PET, nylon) since

the chemical polymerisation reactions can

be reversed

Needs fairly pure material

Hence potential for well defined recycling stream (e.g. PET bottles)

Thermal Decomposition

(Thermolysis) This is appropriate for most free radical (chain

reaction) polymers (e.g. PE, PP, PS, PVC)

Can be used with mixed plastics or composites (releases the fibres)

3 major techniques-

(1) Pyrolysis heat plastics in the absence of air produces synthetic crude oil and combustible gases

(2) Gasification heat plastics in a controlled oxygen environment producing gases such as H2 and CO

(3) Hydrogenation heat plastics at high pressure in hydrogen, producing petrochemical feedstock

Example of Pyrolysis Pilot Plant

BP have built a pilot pyrolysis plant in Grangemouth

It was designed to process 400 tonnes per annum

From data collected from this plant they have estimated that to be viable a plant would need to

process at least ~25,000 tonnes per annum

Needs high hydrocarbon input and low PVC content since pyrolysis yields hydrochloric acid

or chloride salts and potentially toxic dioxins

Plastics Recovery and Recycling Concluding Comments

(1) Energy Recovery

Plastics retain a high calorific value similar to oil and gas (~40GJ/tonne) and so can be burnt to release this energy

Preferable to landfilling as a last alternative

Control of emissions is possible, but there is a social acceptance barrier to overcome

(2) Environmentally Degradable Polymers

Very small market at present, but hope they can be developed using renewable resources

Making synthetic biodegradable material is probably a waste of resources better to concentrate on recycling

(3) Applications for Recycled Plastics

Driven by economics and legislation

Important factors are reliable quality, comparable price to virgin material, reliable supply

Designers will require standards to be specified