Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 1
ROLE OF ADDITIVES IN LINEAR LOW DENSITY
POLYETHYLENE (LLDPE) FILMS
Project Report (2013-14)
Mr. Kamal Batra, Integrated M.Sc. (4th Year)
Department of Chemistry
Indian Institute of Technology Kharagpur
Kharagpur, West Bengal -721302
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 2
~ (CH2 – CH2)n ~
The word polyethylene means: “repeating units of ethylene”. These invisibly tiny
parts of ethylene (monomer) are the building blocks for polyethylene during
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.
• 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
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
~~n (CH 2)n~~ + n N2
n-Br (CH 2)10Br + 2n Na ~~ (CH 2)10n~~ + 2n Na-Br
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ROUTES TO POLYETHYLENE
POLYETHYLENE POLYMERIZATION REACTION & TECHNIQUES
A reaction in which polymer chain is formed by combining large number of small molecules
• Polymerization reaction steps:
The trick to get the reaction started is to use a catalyst, initiator or promoter.
I* + M I-M*
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*
Mechanism to stop the propagation
From Natural Gas
Natural Gas Separation
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 4
Industrial Techniques to Synthesis Polyethylene
1. High Pressure Polymerization
Pressure: 1000-3000 atm,
(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.
By continuously passing reactants through narrow bore tubes or through stirred reactors.
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
Critical dependence on monomer concentration
(Rate of reaction of radical with monomer is much greater with higher monomer
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:
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• 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
High density (0.96)
Molecular weight (depend on temperature and pressure)
(High temperature and low pressure yield less molecular
(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).
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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
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
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.
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
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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
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).
• LLDPE is produced using a low pressure in either gas phase reactor or solution
• 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.
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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
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
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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
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
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ROLE OF ADDITIVES IN LINEAR LOW DENSITY POLYETHYLENE
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.
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:
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
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.
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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)
A certain minimum amount of
A/Os is necessary in most
polyolefins to stabilize and
protect the polymers from
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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
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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
They can also perform as long-term thermal stabilizers (HATS).
They function by “trapping” free radicals formed during the photo-oxidation
The UV stabilizer used by GAIL is Chemassorb 944.
Some of the more significant new product development trends in antioxidants include the
(1) A new phosphite secondary antioxidant, based on butyl ethyl propane diol,
reputedly yields high activity, solubility, and hydrolytic stability in a range of
(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
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(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.
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
Measured in m2/gms. Affects the coefficient of friction of the film and level of wear
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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
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.
The clarity and haze of a film is affected by two factors:
• The refractive indexes of the antiblock and the polymer
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•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
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.
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.
In addition to the lower cost in use, Optibloc talcs can produce additional savings from
their lower abrasivity and low additive interactions.
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
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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
They are used to dissipate static electricity from the surface of plastic products.
Thus facilitating the production and conversion process and or reducing dust
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
Anti-Static Additive is an ideal solution to eliminate static charge accumulation on
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TYPES OF ANTISTATS:
General types of antistats are used in polyethylene: glycerol monostearate (GMS),
ethoxylated fatty acid amines.
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).
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.
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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
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.
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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
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 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
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
Better the adhesion between the particles and the matrix, better will be its load
Common examples are Silica, CaCO3, Carbon black, etc.
The property of fibre reinforced composites depends upon the aspect ratio of the
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
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 21
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
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
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 22
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)
- 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.
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 23
• 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
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
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.
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 24
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 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.
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 25
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
Testing of Film grades
(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
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.
Kamal Batra, 4th Year Integrated Master of Science, IIT Kharagpur-721302 Page 26
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
* 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
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.