polyethylene (pe)

Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302

ROLE OF ADDITIVES IN LINEAR LOW DENSITY POLYETHYLENE (LLDPE) FILMS

Project Report (2013-14)

By

Mr. Kamal Batra, Integrated M.Sc. (4th Year)

Department of Chemistry Indian Institute of Technology Kharagpur

Kharagpur, West Bengal -721302


POLYETHYLENE

~ (CH2 – CH2) n ~

Introduction

The word polyethylene means: “repeating units of ethylene”. These invisibly tiny

parts of ethylene (monomer) are the building blocks for polyethylene during

production.

Polyethylene (PE) is a Thermoplastic polymer, which can be melted to a liquid and

remoulded as it returns to a solid state.

The recommended scientific name polyethene is systematically derived from the scientific name of the monomer. The IUPAC name of polyethylene is poly (methylene). The general formula for ethene (ethylene) is C2H4. PE is chemically synthesized from molecules that contain long chains of ethylene monomer. It can be produced through radical polymerization, anionic addition polymerization, ion coordination polymerization or cationic addition polymerization. This is because ethene does not have any substituent groups that influence the stability of the propagation head of the polymer. Each of these methods results in a different type of polyethylene.

Brief History

• 1898, von Pechmann' produced a white substance from an ethereal solution of diazomethane on standing.

• In 1900, Bamberger and Tschirner analyzed a similar product, found it to have the formula (CH2) n and termed it ‘polymethylene’. The reaction can be considered to be fundamentally. n (CH 2) N = N

• In 1930, another condensation method was investigated by Carothers and co-

workers. They reacted decamethylene dibromide with sodium in a Wurtz-type reaction but found it difficult to obtain polymers with molecular weights above 1300.

~~n (CH 2) n~~ + n N2

n-Br (CH 2)10Br + 2n Na ~~ (CH 2)10n~~ + 2n Na-Br


ROUTES TO POLYETHYLENE

POLYETHYLENE POLYMERIZATION REACTION & TECHNIQUES • Polymerization A reaction in which polymer chain is formed by combining large number of small molecules called “Monomers”. • Polymerization reaction steps: 1. Initiation The trick to get the reaction started is to use a catalyst, initiator or promoter. I I* I* + M I-M* 2. Propagation The new radical formed in the first step reacts with another monomer molecule to give a new larger radical. This chain growth continues until propagation is terminated. I-M*+ M I-M-M* I-M*+ Mn I-Mn-M* 3. Termination Mechanism to stop the propagation -Dispropagation--Recombination---Chain transfer.

From Naphtha

Steam Cracking

Polymerization

Polyethylene

Ethylene

From Natural Gas

Natural Gas Separation

Ethane/Propane

Steam Cracking

Polymerization

Polyethylene

Ethylene

From Molasses

Ethyl Alcohol

Polyethylene

Dehydration

Ethylene

Polymerization

Fermentation


Industrial Techniques to Synthesis Polyethylene

1. High Pressure Polymerization

Ethylene Polyethylene

Pressure: 1000-3000 atm,

Temperature: 80-300ºC,

(At high temperature much higher pressure is required to obtain the desired product. The

reactions will occur faster and lower molecular weight products are obtained. It might

appear that better results are obtained at lower reaction temperatures. Also in this reaction

the side reactions leading to branching can be reduced).

Initiator: Benzoyl peroxide, Azodi-IsoButyroNitrile (AIBN) or oxygen. (By injecting initiator into the reaction mixture at various points in the reactor it is possible to vary polymer characteristics such as branching, molecular weight, molecular weight distribution independent of each other)

The mechanism is carried out by Free Radical Mechanism.

Continuous process By continuously passing reactants through narrow bore tubes or through stirred reactors. Batch process By adding the raw material in a autoclave. Characteristics of free radical mechanism

High exothermic reaction (As at elevated temperature employed other reactions can occur leading to formation of

o Hydrogen o Methane o Graphite)

Critical dependence on monomer concentration

(Rate of reaction of radical with monomer is much greater with higher monomer concentration).

2. Low Pressure Polymerization (a) The Ziegler-Natta Process

Ziegler-Natta catalysts: TiCl4 and Al (C2H5)3

The basic steps followed in this process are:


• Ethylene and Catalyst are taken in a reactor.

• Reaction temperature is below 100oC in absence of oxygen and water (Both reduce

effectiveness of catalyst).

• Catalyst remains suspended and polymer precipitates to form slurry which

thickens as reaction proceeds.

• Reactants discharged to a catalyst decomposition vessel.

• Catalyst destroyed by action of ethanol, water and caustic alkali.

• The polymer is recovered from the solvent.

(b) The Phillips Process

• Ethylene dissolved in hydrocarbon solvent such as cyclohexane at temperature

130-160oC and pressure (1.4-3.5 MPa).

• Solvent used to dissolve polymer as it is formed (doesn’t participates in reaction).

• Catalyst: CrO3 (5%) on a finely divided Si-Al catalyst (75-90%)

• Gas-Liquid mix flashed-off to separate gas & catalyst is removed from liquid.

• Polymer removed from solvent by flashing-off solvent or by precipitation cooling.

• The polymer produced by this process has MFI varying from 0.2 to 600

• Oxygen, Acetylene, Nitrogen and Chlorine acts as a catalyst poison.

Final polymer formed has MFI- 0.2-5

High density (0.96) Molecular weight (depend on temperature and pressure) (High temperature and low pressure yield less molecular Weight).

(c) Standard Oil Company (Indiana) Process

• Temperature: 230-270oC

• Pressure: 40-80 atm

• Catalyst: MoO (Molybdenum Oxide)

• Hydrocarbon solvent

• Promoters: Sodium and Calcium as metal or hydrides.

The petrochemical complex at GAIL, Pata has two manufacturing units which uses the technology from Mitsui chemicals, Japan and Novacor chemicals, Canada. Both the plants are based on the Ziegler-Natta process.

There are THREE different processes developed for low pressure PE polymerization

are as follows :

I. Solution Process

Both catalyst and resulting polymer remain dissolved in a solvent that must be

removed to isolate the polymer.

Polymerization reaction takes place in a CSTR (Continuous Stirred Tank Reactor).


The solution process is particularly suited to the production of high quality LLDPE

film resin based on octene-1 co-monomer.

Additionally, these processes are known for very short reactor residence times thus

allowing them significant flexibility in producing wide product slate in short

production cycle.

One disadvantage inherent to solution processes is their higher investment cost.

II. Slurry Process

Catalyst and polymer formed during production remains suspended in a liquid

medium but never dissolving.

Polymerization reaction takes place in CSTR or tubular reactor.

This process dedicated to the production of MDPE and HDPE resin above certain

minimum density.

This process dominated globally, especially with respect to quality and performance

of broad MWD resins for blow Moulding and pipe applications.

And an inherent limitation to produce low density material because of polymer

solubility problem in reactor.

III. Gas Phase Process

No solvent is used.

Ethylene monomer and supported catalyst are blown into the reactor.

Polymerization reaction takes place in fluidized bed reactor.

The process offers the capability of producing both LLDPE and HDPE resins.

Classification

Polyethylene is classified into several different categories based mostly on its density

and branching. The mechanical properties of PE depend significantly on variables such

as the extent and type of branching, the crystal structure and the molecular weight.

With regard to sold volumes, the most important polyethylene grades are HDPE, LLDPE

and LDPE.


High density polyethylene (HDPE) Medium density polyethylene (MDPE) Linear low density polyethylene (LLDPE) Metallocene Linear low density polyethylene (mLLDPE) Low density polyethylene (LDPE)

HDPE is defined by a density of greater or equal to 0.941 g/cm3. HDPE has a low degree of branching and thus stronger intermolecular forces and tensile strength. HDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. The lack of branching is ensured by an appropriate choice of catalyst (for example, chromium catalysts or Ziegler-Natta catalysts) and reaction conditions.

HDPE is used in products and packaging such as hard hats, milk jugs, detergent bottles, margarine tubs, garbage containers and water pipes. One third of all toys are manufactured from HDPE. MDPE is defined by a density range of 0.926–0.940 g/cm3. MDPE can be produced by chromium/silica catalysts, Ziegler-Natta catalysts or metallocene catalysts. MDPE has good shock and drop resistance properties. It also is less notch sensitive than HDPE, stress cracking resistance is better than HDPE. MDPE is typically used in gas pipes and fittings, sacks, shrink film, packaging film, carrier bags and screw closures. LLDPE is defined by a density range of 0.915–0.925 g/cm3. LLDPE is a substantially linear polymer with significant numbers of short branches, commonly made by copolymerization of ethylene with short-chain alpha-olefins (for example, 1-butene, 1-hexene and 1-octene). PRODUCTION METHODS • LLDPE is produced using a low pressure in either gas phase reactor or solution

process. • The production of LLDPE is initiated by transition metal catalyst particularly

Ziegler or Philips type catalyst. • Usually octene is the co-polymer in solution phase while butene and octene are co-

polymerized with ethylene in gas phase reactor. • The LLDPE resin produced in gas phase reactor is in granular form and may be

sold as granules or processed into pellets. • The raw LLDPE is mixed with additives to produce various grades which can be

compounded, extrude and chopped into pellets for sale.


PHYSICAL CHARACTERISTICS LLDPE has higher tensile strength than LDPE, It exhibits higher impact and puncture resistance than LDPE. Lower thickness (gauge) films can be blown, compared with LDPE, Better environmental stress cracking resistance but is not as easy to process.

LLDPE is used in packaging, particularly film for bags and sheets. Cable covering, toys, lids, buckets, containers and pipe. While other applications are available, LLDPE is used predominantly in film applications due to its toughness, flexibility and relative transparency. Product examples range from agricultural films, saran wrap, and bubble wrap, to multilayer and composite films.

mLLDPE or Metallocene LLDPE is LLDPE manufactured using metallocene catalysts rather than other types of catalysts. Metallocene LLDPE resin is quite different to regular LLDPE resin & two should not be confused.

The production of regular LLDPE materials with traditional Ziegler-Natta catalyst

yield LLDPE resin with broad molecular weight distribution and non uniform co

monomer distribution.

mLLDPE on other hand posses much narrow molecular weight distribution and

much more homogeneous co monomer incorporation and this translate to superior

strength, elongation, impact and optical properties.

For instance, metallocene LLDPEs are well known for their outstanding puncture

resistance and clarity.

Production Methods and Physical Characteristics

A metallocene catalyst is a compound consisting of two cyclopentadienyl anion (Cp

which is C5H5-) bound to transition metal centre (M) in the oxidation state II.

The transition metal M is preferably zirconium, hafnium or titanium most

preferably zirconium.


This type of compound serves as an excellent catalyst for polyethylene since the flat

cyclopentadienyl anions act as “clamshell” restricting unfettered access of ethylene

to the active metal catalyst site.

It has been found that metallocene catalyst have the ability of producing

polyethylene having much narrower MWD and much more homogeneous co

monomer incorporation.

LDPE is defined by a density range of 0.910–0.925 g/cm3. LDPE has a high degree of short and long chain branching, which means that the chains do not pack into the crystal structure as well. It has, therefore, less strong intermolecular forces as the instantaneous-dipole induced-dipole attraction is less. This results in a lower tensile strength and increased ductility. LDPE is created by free radical polymerization. The high degree of branching with long chains gives molten LDPE unique and desirable flow properties.

lLDPE is used for both rigid containers and plastic film applications such as plastic bags, dispensing bottles, cable insulation and film wrap.

SCHEMATIC MOLECULAR STRUCTURE AND PROPERTIES [A] HDPE

[B] MDPE

[C] LLDPE [D] LDPE

Relation between basic properties and application properties of Polyethylene

HDPE MDPE LLDPE LDPE

Density, g/cm3 0.941-0.960 0.926-0.940 0.915-0.925 0.910-0.925

Crystallinity, % 80-90 55-75 55 50-65

Melting temp. oC 130 - 125 115

Yield strength, MPa 20-40 - 8-45 4-16


ROLE OF ADDITIVES IN LINEAR LOW DENSITY POLYETHYLENE (LLDPE) FILMS

Additives Polymer additives are materials designed to enhance or upgrade the performance or Capabilities of base polymers to achieve the optimal properties for a specific application. MASTERBATCH LLDPE

Master batch may be prepared using LLDPE as the “carrier” for a wide variety of colorants and additives.

Master batch are concentrates of polymer additives that are used in manufacture of wide range of moulded, extruded and fabricated articles.

Designed to enhance or upgrade the performance or capabilities of base polymers to achieve the optimal properties for a specific application.

Important examples of LLDPE master batches are:

Antioxidants Masterbatches

used to prevent thermal degradation inhibit ‘oxidation’ (i.e. degradation) Cheap’ insurance for multiple pass materials.

Antioxidants are generally divided into primary and secondary categories. Each category has a specific function in polymer stabilization. Primary Antioxidants (or Chain terminating) They consist mainly of hindered phenols and hindered aromatic amines. They scavenge and destroy the chain propagating peroxy and alkoxy radicals

before they can react with the polymer. Primary antioxidants [AH] work as radical scavengers [R*] by the following

mechanism: R* + AH RH +A* The phenol radical [A*] can cause polymer degradation but is kept from doing so by the hindered physical structure of the primary antioxidant. Primary A/Os are added to the polymer to protect against degradation during the service life of the finished product. Amines cause staining whereas phenolics are colorless. The concentration of primary antioxidants are kept in the range of 0.02 - 1 % above

this they facilitate oxidation. The amine antioxidants are generally more powerful than the hindered phenols.

This is due to acyclic process which the amine antioxidant undergoes in which a nitroxyl radical is regenerated and consumes more radicals.


Secondary Antioxidants (or Hydro peroxide decomposers) Organic molecules consisting of phosphates and lower molecular weight hindered

phenols. Generally, the lower the molecular weight, the better the performance They are added to the resin to reduce color formation and to provide processing stability during the pelletization and extrusion/Moulding processes. Secondary A/Os [P(OR)3] decompose hydroperoxides [ROOH] to form stable

alcohols [ROH] by the following mechanism: ROOH + P (OR) 3 ROH + O=P (OR)3

Thioesters perform a role similar to that of secondary A/Os in that, they decompose the hydro peroxides into alcohols and other nonreactive species.

But they also have a synergistic effect with primary A/Os, especially with the high molecular weight, hindered phenol type of primary A/O. Note: The particular method by which the thioesters decompose hydroperoxide radicals is not well known but is theorized to be similar to that of the secondary A/Os.

The Antioxidants used by GAIL are - IRGANOX 1010 (Primary) - IRGAFOS 168 (Secondary) - Dilaurylthiopropionate (Secondary) In conclusion, A certain minimum amount of

A/Os is necessary in most polyolefins to stabilize and protect the polymers from autoxidative degradation.


UV LIGHT STABILIZERS Light stabilizers can be added to plastics to protect them from the degradative

effects of exposure to sun and weather. Polyolefin's are susceptible to attack by ultraviolet light, oxygen, moisture, and heat

resulting in polymer brittleness, surface crazing, color change and product failure. There are three major classes of light stabilizers: 1. UV ABSORBERS Typical examples are Benzophenones and Benzotriazoles. These are low cost, effective stabilizers that function by the absorption of UV light. They are effective for short-term exposures.


2. NICKEL QUENCHERS They are Energy Transfer Agents that function by “Quenching” : The excited state of carbonyl groups formed during photo-oxidation and Also through the decomposition of hydroperoxides. These types of stabilizers are not in wide use since they contain heavy metal, impart color to the final product, and are not as effective as the HALS.

3. HINDERED AMINE LIGHT STABILIZERS (HALS) They are the most effective of the light stabilizers for polyolefins. Available in a wide range of molecular weights and structures suitable for almost

any application. They can also perform as long-term thermal stabilizers (HATS). They function by “trapping” free radicals formed during the photo-oxidation

process. The UV stabilizer used by GAIL is Chemassorb 944.

Some of the more significant new product development trends in antioxidants include the following:

(1) A new phosphite secondary antioxidant, based on butyl ethyl propane diol, reputedly yields high activity, solubility, and hydrolytic stability in a range of polymers.

(2) Lactone stabilizers (derivatives of the benzofuranone family) are claimed to stop the autoxidation process before its starts. They can interrupt the autoxidation cycle earlier than phenolic and phosphite type stabilizers. These additives are claimed to provide some thermal protection to inert atmospheres, whereas traditional antioxidants are only effective in the presence of oxygen.

(3) Multifunctional antioxidants combine the functionality of both primary and secondary antioxidants in one compound. These materials have only recently become available.


(4) Hydroxylamines act as both primary and secondary antioxidants. They are capable of scavenging carbon-centered radicals.

(5) Antioxidants in the form of liquids and pellets are challenging the powder form. Advantages include low dusting, improved safety, and lower cost. (6) A new antioxidant based on butyl ethyl propane diol is claimed to have high

efficiency and solubility to allow lower concentration levels. It is also claimed to provide improved hydrolytic stability.

Anti-block Masterbatches

They are used to prevent blocking of plastic films. Blocking where adjacent film

“stick” together and make film separation or they block the smooth surfaces and ease the take-off process in films.

It is thought that blocking of adjacent film layers occurs due to the presence of Van der Waal’s forces between the amorphous regions of the polymer. These forces increase with reduced distance between the two layers, thereby increasing blocking when two layers are pressed together.

Another possible reason for blocking is the presence of low molecular weight species (such as oligomers), which tend to migrate to the surface of the film.

Criteria used in selection of an Anti-blocking agent: Particle Size Distribution

Affects both the level of anti-block performance and the physical properties of the final film

Surface Area Measured in m2/gms. Affects the coefficient of friction of the film and level of wear on equipment.


Specific Gravity Density

Indicates the relative weight of the product. Measures the mass/volume ratio. Affects the quality of the film. Table1. Commercially Important Inorganic Anti blocks: Natural Silica (DE) Silicon Dioxide (SiO2) – Mined Talc Magnesium Silicate - Mined Synthetic Silica Silicon Dioxide – Manufactured Calcium Carbonate Calcium Carbonate (CaCO3) - Mined Ceramic Spheres Alumina-silicate ceramic - Manufactured

World LLDPE Film Market Trends Around the world, LLDPE blown film resin, masterbatch and compound producers see a number of trends in the marketplace, as film producers vie to gain market share. These trends are: • Higher clarity films • Lower costs • Higher film strength • Thinner films. Winning In the LLDPE Film Market Using Optibloc 10 or 25 as the antiblock in your film formulation can help you develop products for today’s changing LLDPE film market, with the demands for higher clarity, lower cost, stronger films and thinner films. Optibloc Talc-Based Antiblocks When high clarity and low haze are needed in polyethylene films, one of the Optibloc talc-based products is the best choice. They are used around the world by major resin and film producers. Optibloc talcs are coated, which results in excellent dispersion in the film, reducing the presence of gel particles. Coating also gives low absorption of film additives. • Optibloc 10 and 25 Antiblocks With the smaller particle size, 2.5 microns, and cleanest top size, 90% less than 10 microns, Optibloc 10 is the choice for highest clarity and lowest haze, or when thinner films are being produced. Optibloc 25 is slightly larger, with a median particle size of 4.0 microns, and a top size of 25microns. In some formulations it will give slightlyless clarity, but provides better antiblocking. It is lower in cost than Optibloc 10. Film Clarity The clarity and haze of a film is affected by two factors: • The refractive indexes of the antiblock and the polymer


•The particle size distribution achieved for the antiblock in the film. This is determined by the antiblock’s average particle size, its top size, or size of the largest particles, and how well it disperses in the film. • Refractive Index and Film Clarity Refractive Index is a measure of how much a ray of light is bent when it hits a material. The better the clarity that can be achieved. Material Refractive Index Polyethylene 1.51 – 1.54 Talc 1.56 Optibloc 1.54 Synthetic Silica 1.46 Diatomaceous Earth 1.45 • Particle Size and Film Clarity The second factor affecting film clarity is the size of the antiblock particles in the film. When choosing the antiblock particle size to use, there can be a trade-off between clarity and antiblocking effectiveness. Very fine particles will give a very clear film, but if the particles are too small, the antiblocking will be poor. Very large particles will give very high blocking resistance, but the clarity will be poor. The right particle size and particle size distribution is necessary to give the right balance of clarity and antiblock effectiveness. High Film Strength Antiblock particle top size is also important to maximizing the strength of films. As is true for all plastics, the presence of large, oversized particles is detrimental to strength. These particles can either be in the antiblock to begin with, or can result when the antiblock is not well dispersed in the formulation. Very large particles form points of weakness in plastics. When a stress is applied – the piece is hit – the large particles concentrate the stress, and form a path for failure. When the break occurs, it is often brittle. Thinner Films The combination of small particle size, controlled top size and high aspect ratio of Optibloc Antiblocks can produce high clarity films with higher strength. This allows the “down gauging” –the production of thinner films with the strength of the original, thicker film. Lower Costs In addition to the lower cost in use, Optibloc talcs can produce additional savings from their lower abrasivity and low additive interactions. Low Abrasivity Abrasion caused by the antiblock can be a “hidden cost” factor in masterbatch and film production. Abrasive additives cause wear of expensive dies, screw elements, barrels, cutting blades, and other equipment that comes in contact with the mixture. Abrasion can

This close match aids the development of high clarity and low haze in LLDPE films using Optibloc.


be correlated to the hardness of the particles. Hardness is described using the Moh’s Hardness scale, where talc is defined as a hardness of 1 and diamond, a hardness of 10. It is a logarithmic, not a linear scale; minerals with higher Moh’s values are much more abrasive than the simple numbers might imply. Optibloc High Clarity Antiblocks Help– • Help you make higher clarity films • Refractive Index closer to LLDPE’s • Clean top size • Surface treated for best dispersion • Help you lower film costs • Lower purchase price • High efficiency • Combining to give low cost in use • Low additive interaction, which reduces • Melt fracture film losses • Low abrasion of process equipment • Ability to add directly during resin manufacture • Ability to make higher concentration masterbatches • Masterbatch and powder shelf life not shortened by moisture absorption • Talc is inherently hydrophobic • Help you make stronger films • Platy, high aspect ratio talc particles increase tensile strength • Clean top size improves impact strength • Help you make thinner films • Get the tensile strength and impact strength of thicker films Anti-static Masterbatches

They are used to dissipate static electricity from the surface of plastic products.

Thus facilitating the production and conversion process and or reducing dust

accumulation.

During processing, polymers can accumulate static charge on their surface due to

Shear-generating production equipment. This can hinder production operations &

degrade final intended use of the polymer. It can also pose serious fire hazard in

solvent-based applications.

Anti-Static Additive is an ideal solution to eliminate static charge accumulation on

surfaces.


TYPES OF ANTISTATS: General types of antistats are used in polyethylene: glycerol monostearate (GMS), ethoxylated fatty acid amines. Glycerolmonostearate (GMS)

The reaction between glycerine and fatty acids yields mono-, di- and tri- substituted esters.

The monoester portion acts as an antistat. Although heat stable to 600 °F, and FDA

compliant at any level, GMS is less efficient than ethoxylated fatty acid amines and

diethanolamides in polyethylene and polypropylene. GMS is typically used as an in-process

antistat to reduce static and dust buildup.GMSimparts short term antistatic properties to

LDPE and LLDPE films (typically 1-2 months).

Ethoxylatedfatty Acidamines

Amines used as antistats are typically ethoxylated tertiary fatty acid amines. The fatty acid

composition of amine antistats will vary depending upon the type feedstock. The fatty acid

composition influences migration rates of the antistat within the polymer matrix.It imparts

longer term antistatic properties to LDPE and LLDPE films

• Amine antistats have limited FDA compliance. • Amine antistats have lower heat stability than GMS and can cause some skin irritation. • Amine antistats are more efficient than GMS, enabling their use in applications which specify conditioning at 50% relative humidity. • Amine antistats should not be used in electronic packaging where exposure to polycarbonate components may occur. Polycarbonate, when exposed to ethoxylated amines, tends to exhibit crazing.


Slip Masterbatches

They are used to modify the coefficient of friction of LLDPE plastic film. The

addition level of slip masterbatch depend on film type, thickness and the require slip

effect. The coefficient of friction rapidly decreases during the first day after

extrusion and level out to a constant value after 2-3 days.

Erucamide is more stable so it should be preferred. For processing temperature

above 220oC . Effectiveness of slip agent is enhanced when in combination with anti-

blocking additives. Maximum storage time is 6 months.

Slip Master batches also helps in speeding up the film production and ensures

the product quality.

Major type of slip agents include: Fatty acid amides, Fatty acid esters, Metallic

stearates, Waxes, Fluorocarbons, Graphite. Erucamide and Oleomide are most

commonly used.

Processing Aid Masterbatches

They are used at an addition rate of 1-2% to eliminate the surface defect, reduce

power consumption, facilitate output increase and plate out on die surface.

• Polymer Processing aids are used to ease the melt processing of the material.

• They reduce the melt viscosity and hence reduce the shear forces generated

during the processing.

• PPA used by GAIL is Calcium Stearate.


Colorants

Most plastic components are colored by techniques in which the coloring system is

dispersed throughout the polymer. Generally speaking, colorants are divided into

two major types: Dyes and Pigments.

Dyes are soluble, generally organic, coloring system that produces transparent

colors.

Pigments are dispersed insoluble solids that produce opaque colors.

Pigments are the most widely used. The most widely used colors are white (TiO2)

And black (carbon black).

Fillers Fillers are the materials added to the polymer to achieve the synergistic properties of both polymers and the fillers.

Fillers when added in appropriate concentration; improves the mechanical properties of the material and often reduces the cost of the material.

Fillers are of two types: a) Particulate b) Fibres a) Particulate

Particulate fillers are added to the material while processing and they acts as the stress concentrators within the material.

The better the dispersion of the particles better will be the properties of the composite.

Better the adhesion between the particles and the matrix, better will be its load bearing capacity

Common examples are Silica, CaCO3, Carbon black, etc.

b) Fibres The property of fibre reinforced composites depends upon the aspect ratio of the

reinforcing fibre. Fibres bear the load similar to that in particulate composite. Common examples are Glass fibres, Polyester, Kevlar etc.

Blown film extrusion

The manufacture of plastic film for products such as shopping bags and continuous sheeting is achieved using a blown film line.

This process is the same as a regular extrusion process up until the die. The die is an upright cylinder with an annular opening similar to a pipe extrusion die. The opening diameter can be a few centimetres to more than three metres across. The molten plastic is pulled upwards from the die by a pair of nip rolls high above the die (4 metres to 20 metres

http://en.m.wikipedia.org/wiki/Plastic_film

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or more depending on the amount of cooling required). Changing the speed of these nip rollers will change the gauge (wall thickness) of the film. Around the die sits a cooling ring that blows air onto the film tube as it travels past. The air flow cools the film as it travels upwards. In the centre of the die is an air outlet trough which compressed air can be forced into the inside of the extruded cylindrical profile, adjusting the bubble volume. This expands the extruded circular cross section by some ratio (a multiple of the die diameter). This ratio, called the blowup ratio can be below unity to 8 and indicates how the bubble diameter compares to the die diameter. The nip rolls flatten the bubble into a double layer of film whose width (layflat) is equal to half the circumference of the bubble. This film can then be slit, spooled, printed on or cut into shapes and heat sealed into bags or other items.

An advantage of blown film extrusion over traditional film extrusion is that in the latter there are edges where there can be quality (thickness) variations.

Blown film extruders require limited amounts of compressed air for two operations:

1) To increase the film width by adding air inside the bubble. Once the bubble is inflated, no additional air is required. The air is trapped inside, and with the help of the top nip rolls and cooling air, shapes the plastic tube to the desired width and film thickness. The volume of air required initially depends highly on the size of the machine and width to be extruded. As this is only required at the start of a production run, flow rate is to be considered as insignificant.

2) To apply pressure on the nip rolls, these need to be held together so that the film can be pulled up. It is important that even and regulated pressure is used to ensure proper thickness control. The pressure required can be adjusted by an air pressure regulator attached to the machine. The incoming pressure needs to be more than 6 bar. Ideally a compressor, with more than 8 bar but less than 11 bar, is used in conjunction with a regulator to maintain the pressure. As the application is only to apply pressure, any air loss is only through leakage. As per ISO standards, 0.1l/connection/hr is the maximum allowable leakage for pneumatics. There are about 36 connections in an average blown film extruder. So a leakage rate of 3.6l/hour (0.06l/min) could be expected. This is also very low for any industrial compressor

During the production of Blown Film it is necessary to 'trim' the edge of the blown film in order to achieve the required sale dimensions. This "edge trim" has been successfully transferred automatically to an on-line or off-line recycling system for many years. The recycled edge trim is then reprocessed into a "pellet" which can then be used back into the main film production. This recycling process has made blown film production a very efficient operation


The major parameters that control the quality of blown film are:-

- Die Design - Efficiency of cooling ring with reference to volume and angle of contact. - Control of frost-line - Control of neck, a long neck for HM-HDPE, - Right temperature of the film at the nip-rollers by adjusting the height from the die

so that the creases are ironed out. - Exact centering of the nip-rollers with reference to the die. - Efficient winding.

The following formula is used for selection of a Die for a particular Lay-flat width:- Die size = D = 2(LFW)/(BR) Where,

- D- Diameter of Die Orifice - BR-Blow-up ratio

- LFR- Lay-flat width.

LAB SCALE FILM PLANT

Significance: To study the processing behaviour, quality of film and to compare it with co-producer’s equivalent grades for continual improvement in film grades.

Uses: To make film sample for evaluation of its properties, to check the processing behavior and effect of additives in PE film grades.

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• Important Film Parameters:

(a) Dart Impact strength (b) Tensile properties (c) Tear strength (d)Coefficient of friction (e) Hot tack strength (f)Heat seal strength (g) Haze (h) Gloss

The resin properties and the processing variables influence the final film properties.

Dart Impact strength

Tear Tester

Use – Measure average force required to propagate tearing in flexible packaging material.

Significance- Evaluating the suitability of film in packaging film.

Impact strength of film is determined by measuring the loss in kinetic energy of a free falling dart as it penetrates a film specimen.

Impact strength is indication of the balance of film properties in both the direction.

Universal Tensile Machine

Tensile strength and elongation of film is measured using a tensile test machine. Film samples must be tested in the direction of maximum orientation and in the cross direction. Tensile properties are another indication of the mechanical strength and toughness of the film.

Use – Measure the tensile and flexural properties of the material.

Significance- Vital property for product design and indicates the suitability of the material for end use application.


Haze

Haze is the cloudy appearance of an otherwise transparent specimen caused by light scattered from within the specimen or from its surface.

Percentage of transmitted light which is passing through a specimen deviates from incident beam by forward scattering.

It is generally accepted that if the amount of transmitted light is deviated more than 2.5 degree from the incident beam the light flux is considered to be haze.

Haze caused by surface imperfection density changes.

Procedure: The test is conducted by taking four different consecutive reading nad measuring photocell output.

T1- specimen and light trap out of position, reflectance standard in position.

T2- specimen and reflectance in position, light trap out of position.

T3-light trap in position, specimen and reflectance standard out of position.

T4- light and specimen trap in position, reflectance standard out of position.

Total transmittance Tt = T2/T1

Diffuse transmittance Td = [T4-T3(T2/T1)]/T1

Haze percentage = Td/ Tt *100

Significance and use of Haze clarity meter: Measures percentage haze, clarity & transmittance of films. Evaluation of optical properties of films.

Gloss

Gloss is defined as the relative reflectance factor of a specimen at the specular direction.

Method – Light beam is directed towards the specimen at a specified angle and the light reflected by the specimen is collect and measured. All the gloss values are based on primary reference standard i.e. A highly polished black glass with gloss value of 100.

As the angle of incidence increase gloss value of the surface also increase.


Slip Tester (Co-efficient of friction)

Significance- Measure the static and dynamic coefficient of friction of films.

Important parameter for evaluating the machinability of films on machine like FFS, printing etc.

Testing of Film grades

1. E20AN009

(Linear Low Density Polyethylene for Blown Film Extrusion)

Application: E20AN009 is recommended for lamination and cling film applications. It has excellent processability with optimum combination of mechanical and optical properties. It does not contain slip and antiblock additive.

* Typical characteristics of the product given purely as a guide. Mechanical/Optical properties were determined on 40 micron film made with 2.0mm die gap and BUR: 2.2

Processing Guidelines:

Barrel temperature: 170 - 2000C

Blow up ratio: 2.0 to 2.25

Die gap: 1.8 to 2.2

Packaging & Storage:

E20AN009 is available in natural colour/pellet form in 25 kg strong bags made of woven fabric. The product should be stored in dry conditions at temperature below 50oC and protected from UV light.


2. F20S009

Linear Low Density Polyethylene for Blown Film Extrusion

Typical Applications: It is recommended for general purpose, heavy duty and liquid packaging in laminated / non-laminated film applications. It has excellent processability with optimum combination of mechanical, optical and sealing characteristics.

F20S009 is optimally stabilized with antioxidants, slip additive, antiblocking agent and processing aid.

* Typical characteristics of the product given purely as a guide. Mechanical/Optical properties were determined on 40 micron film made with 2.0mm die gap and BUR: 2.2

Processing Guidelines:

Barrel temperature: 170 - 2000C

Blow up ratio: 2.0 to 2.25

Die gap: 1.8 to 2.2

Packaging & Storage: F20S009 is available in natural colour/pellet form in 25 kg strong bags made of woven fabric. The product should be stored in dry conditions at temperature below 50oC and protected from UV light.

polyethylene (pe)

Engineering

radical polymerization

polymerization reaction

polyethylene pe

synthesis polyethylene

reaction mixture

reaction proceeds

iit kharagpur

low pressure polymerization