EGE UNIVERSITYChemical Engineering Department

Che 438: PROCESSES IN POLYMER TECHNOLOGY

Polyolefin Based Film Manufacturing Processes and

Biodegradable Films

Prepared by;Merve AYVAZİsmail Bahadır KARA

CONTENT OF PRESENTATION

Properties of polypropylene Polymerization reactions Usage areas Film manufacturing methods Corona Treatment Biodegradable films Recycling

General Information about PP?

PP is a strong, lightweight thermoplastic polymer. First discovered in Italy by Cullio Natta in 1957. A methyl group is attached to the carbon atom in structure.

Similar to polyethylene, polypropylene belongs to the group of polyolefin's.

A polyolefin is a polymer produced from an alkene with the general formula CnH2n as a monomer.

The chemical structure of monomer

Differences Between PP and PE?

• Because of PE and PP are in polyolefin group, they have similarities in their properties such as:

-in solution behavior and

-in their electrical properties.• Exhibition of CH3 group in PP change the chemical

properties of polymer in some ways such as:

- Increase in the crystalline melting point. Melting point of most regular PP is some 50 oC higher than regular PE .

-PP is less stable than PE to the influence of oxygen because tertiary carbon in PP provides a site for oxidation. It results with degradation from UV radiation.

What is Isotactic Polymer?

Most significant effect of CH3 group is making different tacticity.

Most commercial polypropylene is isotactic form. Since all CH3 groups are gathered on one side of the molecule.

Greater the amount of isotactic material, the greater:

-crystallinity -greater the softening point

-stiffness, modulus -tensile strength, hardness

CH3 CH3

Isotactic form of PP

CH3 CH3 CH3

Types of Polypropylene There are two general types of polypropylene:

-Homopolymer

-Block Copolymer Homopolymer: A polymer is a large molecule composed of

repeating structural units typically connected by covalent bonds. Block copolymer: A polymer derived from two (or more)

monomeric species, as opposed to a homopolymer where only one monomer is used.

-Copolymerization is the method that is used to chemically synthesize a copolymer.

-The comonomer used is typically ethylene.

Types of PP Addition of ethylene as comonomer increases homopolymers

low temperature impact strength. Hence comonomer decreases the polymer crystallinity and

makes the polymer more transparent. Which it is preferred in film manufacturing.

PP

monomer

PE

monomer

Two or more homopolymer subunits linked by covalent bonds

Characteristics of Polypropylene Low density: 0.9 g/cm3

Good mechanical stability High rigidity and hardness Good heat forming stability Very good chemical stability Good hot water stability (hydrolysis resistance) Low moisture absorption Very good dielectric insulating behavior Non-toxic, Inflammable and Inexpensive

Properties creates disadvantages: Damage from stress corrosion in outdoor applications Inadequate impact resistance at temperatures below 0ºC PP is unsuitable for sliding functions

Additives used for PP

1) Fillers: Talk and Calcium carbonate for stiffness, impact strength, thermal resistance, brighter color.

2) Rubbers: Butyl rubber for reducing the brittleness.

3) Pigments: Higher processing temperature and less resistance to oxidation, pigment selection is important.

4) Carbon black and ultra-violet absorbers: Hindered amine and nickel to improve resistance to ultra violet

5) Antioxidants: They are normally added to prevent polymer degradation

6) Nucleating agents

USAGE AREAS

Such usage areas are ;

Films for packaging, Textiles (e.g. ropes, thermal underwear and carpets), Stationery*

Plastic parts and reusable containers of various types, Laboratory equipment, Automotive components

*Stationery=kırtasiye malzemesi

Polymerization Reaction

Polymerization of propylene takes place either in -Gas phase; fluidized bed-Liquid phase; slurry

In the fluidized-bed process •The monomer flows through perforated distribution plate at the reactor bottom.

•Rapid gas circulation ensures fluidization and heat removal.

•Unreacted polymer is separated from the polymer particles at the top of the reactor and recycled.•A modification uses a second reactor connected in series to perform copolymerization.

Polymerization Reaction

In slurry process• Process run in loop reactors with two stirred tank reactors in

series• The reaction is carried out in hexane/heptane heavy diluents.• Polymerization reaction takes place in boiling solvent.• At last step the slurry is flashed and volatiles are recycled to

the process. • The polymer is purged and dried before pelletization.• A gas phase reactor can be added for block copolymer

production.

Primary Gas Phase Reactor Copolymer Gas Phase Reactor

Monomer Comonomer Ethylene

Catalyts

Dispatch

Film Production Processes

1.Blown Film Process

2.Flat Film Process

Blown Film Process

The first blown film was patented in 1938 in the United States

The first successful plastics film was based on regenerated

cellulose. Lower melt temperature (air cooling) Film thickness variations are kept at 10% The film widths are in the range of 100 mm to 7 m according to die

and extruder widths and the film thickness is in the range of 6 μm to 250 μm

Slow cooling cause less gloss more clear film The capital investment and output are less Materials: LDPE, LLDPE, HDPE, Modified PE, PVC, Nylon

EXTRUDER

Film can be compose of number of layers. Each layer is produced by different extruders. So number of layers is equal to number of extruders in the process.

Screw Design Single screw extruders supplied a flow of molten polymer to the

die which extrudes a thin walled tube.

L/D ratios of the screws are in the range of 15-25 to 1.

Screws has feed, compression and metering zone.

The dept of the metering zone depended on the shear sensitivity of the polymer.

More shear sensitive polymers are processed with deeper metering zone and lower screw speeds.

Breaker Plate and Screen Pack Made of stainless steel Placed between the extruder and die in order to generate back

pressure and hence to improve mixing in the screw. It will also out put impurities in the melt before they reach die They may cause punctures in the blowing stage.

Breaker Plate and Screen Pack The screen pack surprisingly does not eliminate gels of lightly

crosslinked or very high molecular weight polymer. This cause faults in film which calls as fish eyes.

The life of screen pack depends on the polymer used. The life of screen pack is several weeks for LDPE and 12 hours for PVC which is thermally unstable.

This process often involves stopping the line and separating die from extruder in order to remove screen pack. Systems are available which do not necessitate extruder shut down.

Blown Film Dies

Blown Film Dies

Dies are usually heated with electrical resistance to prevent heat lost. Temperature of the each layer are kept in the die.

The aim in the die temperature control is to maintain the die uniformly at a temperature close to the temperature of the melt.

Sometimes outer layer is heated in the die to improve surface finishing by further softening of the outer layer.

Cooling Rings Cooling increased by directing a flow of air from the cooling ring

on the out side of the bubble. This is called external cooling. The ring sits on the top of the film die with a thermal insulation

layer between it and hot die. Non-uniform air flow gives rise to variations in the film

thickness. Inlets should direct air into the ring either in radial or

perpendicular direction to the plane of the ring. Air flows over baffles in the ring.

Bubble Guides and Collapsing Frame

Between cooling ring and the top nip, bubble guide may be placed to reduce sideways movement of the bubble. These are often horizontal metal bars and easily to accommodate different diameter bubbles.

Collapsing frame is fitted to guide the bubble from its cylindrical shape to layflat sheet at nips.

Film Thickness Measurement for Bubble

Film thickness is measured by electronic control system and data is send to the control room.

Web Transport Film is transport from nip-roll to winding by series of freely

rotating flat metal rolls. Speed of the rolls are adjusted according to the seed in winding unit. The film thickness and tension is controlled by automatic systems along this transportation.

Winding

Finally film is wounded in real form on a cardbore. Then it is going to part in slices in different lengths.

Flat Film Process

Higher melt temperature (water cooling) Fast cooling forms outstanding optical clarity and gloss High capital investment and high output Film thickness variations are kept at 5% Materials: Polypropylene, polyester, nylon Biaxially oriented (BOPP) and uniaxially oriented (CPP) films

are produced by this method. BOPP film could not be streched at the end of the production,

but CPP could be streched.

PP is preferred in Flat Process Melt temperature of PP ranges between 215-230 oC

In Flat Process, PP is rapidly cooled from the melt to give low level of crystallinity. Consequently, clear and glossy film is formed.

To use PP in Blown Process water should be used instead of air for cooling of extruded melt.

Biaxially Oriented Polypropylene Film

Film compose of three layers. corona

Copolymer + Antiblock masterbatch 1 , satellite 1

Homopolymer Antistatic / Slip Masterbatch

Terpolymer + Antiblock masterbatch 1 ,

satellite 1

18 18

Heat Sealing Property With Terpolymer Heat sealing property is ability to stick of edges of packing

films to each other.

Terpolymer layers have heat sealing property at 130C. To achieve this property some additives are used.

Copolymer does not have heat sealing property so it does not stick on each other.

Protection of Ink By Upper Layer Ink is applied on the middle layer. The upper layer protects

the ink from destruction and maintain high gloss on the printed surface.

corona

Copolymer + Antiblock masterbatch 1 , satellite 1

Homopolymer Antistatic / Slip Masterbatch

Terpolymer + Antiblock masterbatch 1 , satellite 1

18

Steps of the Production Process

http://www.polinas.com/page.php?pageID=4&langID=trThis is a continuous process as one line,

Weighting and Mixing Extrusion Molding and Chill Roll Orientation Corona Winding

Weighting and Mixing Raw materials pass through the metal detector to grab the

possible metal particles. Then they sent to the raw material weighing hopper.

Weighing hopper is small 0.2m3 tank. After the weighing, the material is sent to the mixing hopper.

Mixing hopper is a conical device with a rotating large diameter screw. This agitating system makes the chip like raw material smooth

Automatic control system sends them to the extrusion step regularly.

Extrusion There are three extruders in the system; one main (for

middle layer) and two satellite extruders.

The screw speed & torque are very important parameters to control. If the screw speed is more than determined by control system the film thickness increases.

Also the temperature profile along the length of the screw and the metering rate are controlled.

All these parameters are adjusted by the computerized control with the set values.

Extrusion

The melting is achieved at temperature of 230C. That is supplied by electrical heaters on extruder body.

The main extruder is water cooled.

There’s an air cooling system for the other two satellite extruders.

Film Die The homogenised melt extracted from the extruder is filtered. The melt coming from the extruders are fed in the die just

above the die.

Die, has three holes in it where homopolymer from the main extruder enters into the middle and satellite layers into the other two holes. So they flow into the die as three layers of melt.

Chill Roll It is a wide, horizontal,

cylindrical device which cools the film by cooling water inside of the roll.

Film that comes from the die flows onto the chill roll continuously to maintain homogeneous cooling.

The speed of the whole system is adjusted according to the CR speed.

Air used to take the dirt from

the outer surface of film. System blows

high pressurized air so that the film

sticks to the surface of chill roll

homogeneously without any bubble forming.

Rapid cooling increases the gloss of film

Orientation Process-MDO At MDO the film is stretched up to the 5-6 times of its original

length in machine direction. The stretching is provided by the rolls which are turning in different speeds.

The pre-heating rolls are heated up to 104-112 C by oil flowing in the channels, which flows in the rotating rolls. After the film is heated, it is stretched in the machine direction.

Orientation Process-TDO TDO is basically a large oven in which the film is heated up to 150-

160 C. At the entrance of TDO the film is gripped from its edges by the clips, which are perfectly synchronized. The film is stretched in transverse direction up to 9-12 times of its original width as the clips are travelling along a diverging rail system. This step is applied just for BOPP.

Corona Treatment

Most plastics, such as PE and PP, have low surface tension which causing them to be non-receptive to bonding with printing inks, coatings, and adhesives.

Although results are invisible to the naked eye, surface treating modifies surfaces to improve adhesion.

Corona treatment is also suitable for the treatment of injection and blow molded parts.

Corona Application Corona discharge equipment consists of a high-frequency power

generator, a high-voltage transformer, a stationary electrode, and a treater ground roll.

Standard utility electrical power is converted into higher frequency power. The treater station applies this power through ceramic or metal electrodes over an air gap onto the material’s surface.

The effects of corona treatment diminish over time. Therefore many surfaces will require a second corona treatment at the time they are printed.

Atmospheric Plasma Atmospheric plasma is very similar to corona but there are a

few differences between them. Both systems use one or more high voltage electrodes which

positively charge the surrounding air ion particles. However in atmospheric plasma systems, the bonding rate of

oxygen molecules to a polymer 100 times more. That cause higher ion bombardment and higher surface quality.

Flame Plasma Flame plasma treaters generate more heat than other treating

processes.

Materials treated through this method tend to have a longer shelf-life.

Flame plasma occurs when flammable gas and surrounding air are combusted together into an intense blue flame.

Objects’ surfaces are polarized from the flame plasma affecting the distribution of the surface’s electrons in an oxidation form.

AFM topographic images for (a) untreated,

(b) 2s and corona treated PP films.

(a) Rough surface with granular structures and presents some orientation, which results from manufacturing process. Contact angle is 90° between water and film .

(b) Remarkable changes in the morphology as small droplets. Atomic oxygen formed in corona discharge, in air, reacts with PP chains and forms oxidized polar groups on the surface. Contact angle is 54° between water and film .

Results of Corona Treatment Corona discharge treatment of PP films leads to the

incorporation of various chemical groups containing oxygen, mainly C=O, into the films.

As a result, the surface wettability by water (polar liquid) increases (contact angle decreases), which is the reason for the improvement of adhesion performance of polymer.

Winding and Slitting The film is wounded after

corona treatment in the original length. Then it would be sliced in the length and width of costumer desired.

Metallized Film BOPP film durability is increased against the water vapor and sun

light by using metalizing process.

Process takes place in vacuum chamber. Under high vacuum, an aluminum wire is firstly vaporized in a boat.

Aliminium vapor condensed on film as extremely thin layer

The film passes through several rollersto adjust tension and cool

Preparation of Printing Films Packaging is the science, art and technology of enclosing or

protecting products for distribution, storage, sale, and use. For printing of package film; most suitable and chosen

method is flexography. Flexography is also used at a wide range in food packaging. After the flexographic printing operation, printed product

must be endurance by lamination process. Methods that combine two or more webs by bonding them

together are called as lamination process.

Process of Flexographic Film Printer

Flexographic plates: Created by analog and digital plate making processes

Plate Cylinder: It keeps the flexo plates. Transfer ink to film Impression Cylinder: Apply pressure to film between plate cylinder

and impression cylinder. After the film has been printed, it is fed through overhead tunnel

dryer to remove solvents or water. The finished product is then rewound onto a roll or is fed through

the cutter.

Ink Roller: Transfer ink to the anilox roll

Anilox Roller: Gives uniform thickness to ink on plate cylinder

Process of Flexographic Film Printer

Biodegradable Films

Biodegradation is degradation caused by biological activity, particularly by enzyme action leading to significant changes in the material’s chemical structure.

Currently available degradable plastic materials can be broken down into two main groups:

1. Polyester Polymers

2. Synergistic and Hybrid Polymers

Biodegradable Polyester Polymers Biodegradable polyesters which do not contain six-carbon rings

are known as aliphatic polyesters. They react with moisture at elevated temperatures. This process, called chemical hydrolysis, reduces higher

molecular weight polymer to much smaller hydrocarbon compounds.

The resulting molecules can then be absorbed by microorganisms and metabolized for energy.

Aliphatic polyesters however have poor physical and mechanical properties like strength, flexibility, heat resistance.

Biodegradable Polyester Polymers Some common biodegradable polyester polymers in commercial

use include examples of; Poly(caprolactone) (PCL),

Poly(glycolic acid) (PGA) and Poly(lactic acid) (PLA).

PCL PGA

Biodegradable Polyester PolymersRaw material used in film making is: Poly(lactic acid) (PLA)PLA: -Made from fermented sugars extracted primarily from food

crops such as corn or sugarcane. -Then resulting monomer polymerized in the presence of metalcatalyst to form high molecular weight.

Synergistic and Hybrid Polymers

Mixtures of oil-based and naturally occurring polymers

When mixed, there is intimate contact between the two polymer chains so as to create a homogenous single phase. In other words, once mixed they could not be mechanically separated.

A good example of a commercial, synergistic, biodegradable material is Thermoplastic Starch (TPS).

RECYCLE Resin identification code:

Manufacturers of PP based films, use the waste films in production.

The edge trims and the films are blended and melted with extruder and finally converted to the polypropylene granules again after

According to the film type produced, these recycled PP granules are used less than 15 % of the original raw materials

CONTENT OF PRESENTATION

Properties of polypropylene Polymerization reactions Usage areas Film manufacturing methods Corona Treatment Biodegradable films Recycling

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