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Polymer an Insight in to the learning topicsPolymer an Insight in to the learning topicsClassification of polymers:

Thermoplastics- PE, PS, PVC, PTFE, ABS, PMMA, Synthetic Rubber Thermosetting plastics - properties and industrial applications properties and industrial applications of Bakelite, Melamine Resin, Epoxy Resin, Polyurethane (PU), of Bakelite, Melamine Resin, Epoxy Resin, Polyurethane (PU), Polyamide (nylon Series), Polyester (PET), PC, Silicon PolymerPolyamide (nylon Series), Polyester (PET), PC, Silicon Polymer

Moulding of plastics into articles: Compression,Compression, injection,injection, transfer and extrusion methodstransfer and extrusion methods.Conducting polymers: Properties and applications Biodegradable polymers Properties and applications

A word polymer is a combination of two Greek words, “Poly” means “many” and “Meros” meaning “parts or units”.

A polymer is a large molecule of which is formed by repeated linking of the small molecules called “monomers”.

n(CH2-CH2) (-CH2-CH2-)n ethylene polyethylene

The number of repeating units in the chains of which a polymer is made up is called degree of a polymerization (n).

Polymers with high degree of polymerization are called the “High Polymer”, and those with low degree of polymerization are called “Oligopolymers”.

High polymers have very high molecular mass (10000 to 1000000 u) and are called macromolecules.

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CH2 CH23 CH2 CH23

Degree of Polymerization (P) = M/m;

Where, M= Mass of Polymer; m = mass of monomeric unit

PolymerisationPolymerisation

polyethylenepolyethyleneEthyleneEthylene

Degree of polymerisation (P) = 3Degree of polymerisation (P) = 3

Mass of this polymer M = (28 x 3) = 84Da

A macromolecule may consist of monomer of identical or different chemical structure and accordingly they are called Homopolymers or copolymers (or Heteropolymers).

A A A A … Homopolymers

A A B A … Copolymers

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Tacticity- Plane representation of polypropylene polymerTacticity- Plane representation of polypropylene polymer

CH2 C CH2 C CH2 C CH2

H

CH3

H

CH3

H

CH3

C CH2 CH

CH3

H

CH3

CH2 C CH2 C CH2 C CH2

H

CH3

H

CH3

CH3

HC CH2 C

H

CH3H

CH3

CH2 C CH2 C CH2 C CH2

H

CH3

CH3

H

CH3

HC CH2 C

H

CH3

H

CH3

1. Isotactic polymers1. Isotactic polymers

Functional groups on the Functional groups on the same sidesame side of the main carbon of the main carbon skeletonskeleton

2. Syndiotactic polymers2. Syndiotactic polymers

Functional groups arranged Functional groups arranged in the in the alternate fashionalternate fashion of the of the main carbon skeletonmain carbon skeleton

3.Atactic polymers3.Atactic polymers

Functional groups arranged Functional groups arranged in a in a random mannerrandom manner around around the main carbon skeletonthe main carbon skeleton

Polymers can be linear, branched or cross-linked. The monomer may be arranged in the chain at random or regularly.

(LINEAR POLYMER) A A A A … … B B B

A A A A A A

A A A A A

A A A

(BRANCHED POLYMER)

A A

A A A

A A A A A A

A A A

A A A A A A

(CROSS-LINKED POLYMER)

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Functionality Functionality

HO C CH2

ONH2

OH CH2 CH C OHO

NH2

OH CH2 CH C OHO

NH2

HO C CH2

ONH2

Ex. SerineEx. Serine

Glycine

The The number of reactive sitesnumber of reactive sites present in a monomer is called functionality present in a monomer is called functionality

Linear chain polymer is formed if the functionality of the monomer is only two (Bifunctional)

Ex. Glycine

1.1.

2.2.

Cross linked chain polymer is formed if the functionality of the monomer is more than two (multifunctional)

Classification of PolymersClassification based on Source 1. Natural polymers E.g., Proteins, Cellulose, Starch, Rubber

2. Semi-synthetic polymers E.g., Cellulose derivatives - Cellulose acetate

(Rayon)

3. Synthetic polymers E.g., Buna-S, Buna-R, Nylon, Polythene,

Polyester.

Classification based on Structure1. Linear polymers consist of long and straight chains. E.g., Polyvinyl chloride

2. Branched chain polymers contain linear chains having some branches, e.g., low density polymer.

3. Cross-linked or Network polymers formed from bi-functional and tri-functional monomers and contain

strong covalent bonds e.g. bakelite, melamine,

Classification based on Molecular Forces 1. Elastomers eg. Buna-S, Buna-N, neoprene 2. Fibers eg. Polyesters, Polyamides. 3. Thermoplastic polymers eg. Polythene, Polystyrene, PVC. 4. Thermosetting polymers eg. Bakelite, urea-formaldelyde resins

Order of strength :-Thermosetting > Fibres > Thermoplastics >

Elastomers

Classification based on mode of Polymerization 1. Addition polymers formed by the repeated addition of monomer molecules

possessing double or triple bonds n(CH2=CH2) -(CH2 -CH2 )- Ethylene polyethylene

2. Condensation polymers formed by repeated condensation reaction between two

different bi-functional or tri-functional monomeric units. eg. terylene (dacron), nylon 6, 6, nylon 6.

n(H2N(CH2)6 NH2) + n(HOOC(CH2)4COOH) [-NH(CH2)6NHCO(CH2)4CO-]n +

nH2O (Nylon 6:6)

Polymerization is of two types;

Addition or chain polymerization Condensation polymer

1. Free radical mechanism:- Alkenes or dienes and their derivatives are polymerized in the presence of a free radical generating initiator (catalyst) like benzoyl peroxide, acetyl peroxide, t-bu peroxide, etc.

This process involves in 3 steps – a) Chain initiation step - addition of phenyl free radical formed by the

peroxide to the ethene double bond ,thereby forming a larger radical.

b) Chain propagation step - repetition of this sequence with new and bigger radicals.

c) Chain terminating step - the product radical thus formed reacts with another radical to form the polymerized product. Some of polymers formed by this process are-Polytetrafluroethene (Teflon), Polyacrylonitrile, Polyethylene, etc.

In addition polymers , the polymer is formed from the monomer, without the loss of any material, and the product is the exact multiple of the original monomeric molecule.

CH2=CH2 -CH2-CH2- POLYMERIZATION (-CH2-CH2-)n Ethylene monomer Molecular Rearrangement Polyethylene

Addition polymerization proceeds by the initial formation of some reactive species such as free radicals or ions and by the addition of the reactive species to the other molecule, with the regeneration of the reactive feature.

Chain polymerization occur in three steps:-

•Chain initiation step•Chain propagation step•Chain termination step

In chain initiation step, a free radical is first generated as a result of physical or chemical effect, which is responsible for the further continuation of the chain polymerization

The primary free radical react with the double bond of an unexcited monomer molecule and adds to it forming a new radical capable of further interaction with the initial monomers.

The most common termination processes are Radical Combination and Disproportionate. These reactions are illustrated by the following equations.

In condensation polymerization, the chain growth is accompanied by the elimination of small molecules. The molecules are in the form of the water molecule H2O ; methanol molecule CH3OH ,etc.

Step Growth polymerization:- It involves a repetitive

condensation reaction between two bi-functional monomers.

Eg. Formation of Nylon 6,6 nHOOC(CH2)4COOH + nH2N(CH2)6 NH2 553K

[-N-(CH2) 6-N-

C(CH2)4-C-]n

H O

O

High pressure

Nylon6,6

Copolymerisation:- is a polymerization reaction in which a mixture

of more than one monomeric species is allowed to polymerize and form

a copolymer. For example, a mixture of 1, 3 – butadiene and styrene can form a copolymer.

Examples of Daily Use Polymers

Plastics Plastics are high molecular weight organic materials

which can be moulded into any desired shape by the application of heat and pressure in the presence of catalyst.

Constituents of plastics:1. Resins 2. Plasticizers3. Fillers or Extenders4. Lubricants5. Stabilizers6. Pigments7. Anti-oxidants8. Catalysts or Accelerators

Resins: They are basic binding materials and hold the constituents

together. They are generally linear polymers with low molecular weight

to enhance fusibility and mouldability.It is then converted into crosslinked form during moulding in

the presence of a catalyst.E.g. Thermoplastic resins and thermosetting resins.

Plasticizers: They improve flow for processing by reducing the

intermolecular force of attractionE.g. Dioctylphthalate, oleate and organic phosphates

Fillers: They increase the tensile and compressive strength of

plastics. They also reduce the shrinkage during setting of the plastics.E.g. Mica, quartz, limestone, acrylics

Lubricants: They makes the moulding process easier and also provide glossy

finish to the final product.E.g. Waxes, oils and soaps

Stabilizers: They increase the thermal stability during processing.E.g. Stearates of lead, barium and cadmium.

Pigments: They provide colours to the plasticsTiO2, ZnO – White; Cr2O3 – Green, Carbon black – black, Red lead -

RedAnti-oxidants: They protect against oxidative degradationE.g. Phenyl p-napthyl amine, diphenyl p-phenylene diamine

Catalysts: They are added to accelerate the polymerization of fusible resin into

cross-linked infusible form especially for thermosetting plastics.E.g. H2O2, benzoyl peroxide

These are linear or slightly branched long chain polymers, which can be softened on heating & reversibly hardened on cooling repeatedly.

Their hardness is a temporary property & varies with temperature.

It can be reprocessed, so sometimes also referred as green plastics.

Definition

Thermoplastics possess weak intermolecular forces(e.g. Van der Waal) & don’t have crosslinks.

Structure

Cellulose derivatives- 1) Cellulose acetate- Cellulose nitrate

Polyethenic/vinyl resins- 2) Polyethylene- 3) Polypropylene- 4) Polyvinyl acetate- 5) Polyvinyl chloride- 6) Polystyrene- 7) Teflon- 8) Acrylic- 9) Polysulfone- 10) Polyester

Examples

There are mainly two types of polythene:Low density polythene(density range of

0.910–0.940 g/cm3):It is obtained by the polymerisation of ethene under high pressure of 1000-2000 atm at a temperature of 350-570 K in the presence of traces of oxygen or a peroxide initiator.

It is created by free radical polymerization.

Polyethylene(PE)/Polythene

Properties:1.High degree of short and long chain

branching.2.intermolecular forces is less. 3.Tough but highly flexible & ductile.4.Chemically inert.

Uses: Insulation of electricity carrying wires and manufacture of squeeze bottles, toys and flexible pipes.

High density polythene(density >= 0.941 g/cm3): formed when addition polymerisation of ethene takes place in a hydrocarbon solvent in the presence of a catalyst such as triethylaluminium and titanium tetrachloride (Ziegler-Natta catalyst) at a temperature of 333-343 K and under a pressure of 6-7 atm.

Properties: 1.low degree of branching(lack of branching is

ensured by an appropriate choice of catalyst & reaction conditions).

2.stronger intermolecular forces and tensile strength,

3.Chemically inert.

Uses:for manufacturing buckets, dustbins, bottles, water pipes etc.

Environmental issue Although polyethylene can be recycled, most

of the commercial polyethylene ends up in landfills, and in the oceans such as the Great Pacific Garbage Patch. Polyethylene is not considered biodegradable, except when it is exposed to UV from sunlight. Under UV lights tertiary carbon bonds in the chain structures are the centres of attack. The UV rays activate such bonds to form free radicals, which then react further with oxygen in the atmosphere, producing carbonyl groups in the main chain.

Polystyrene is actually an aromatic polymer that is made from the monomer styrene. It is a long hydrocarbon chain that has a phenyl group attached to every carbon atom. Styrene is an aromatic monomer, commercially manufactured from petroleum. Polystyrene is a vinyl polymer, manufactured from the styrene monomer by free radical vinyl polymerization.

Polystyrene

Polystyrene is generally flexible and can come in the form of moldable solids or viscous liquids.

The force of attraction in polystyrene is mainly due to short range van der Waals attractions between chains.

Properties

The outside housing of computer, housings of most kitchen appliances, model cars and airoplanes, toys, molded parts in car are all made of polystyrene.

It is also made in the form of foam that is used for packaging and insulating.

Polystyrene is generally flexible and can come in the form of moldable solids or viscous liquids.

Uses

It is a vinyl polymer constructed of repeating vinyl groups (ethenyls) having one of their hydrogens replaced with a chloride group.

Obtained by heating a water emulsion of vinyl chloride in presence of benzyl peroxide/ hydrogen peroxide in an autoclave under high pressure.

Polyvinyl chloride

Properties:1.Colurless & odourless2.Non-inflammable & chemically inert3.Resistant to light,O2, inorganic acid &

alkalis.4.Greater stiffness & rigidity than polyethylene

but brittle.

Uses: Third most widely produced plastic Unplasticized PVC: Highly rigid but brittle,

for making sheets, tank lining, helmets ,mudguards etc.

Plasticized PVC(by adding plasticizers e.g. phthalates): Making continuous sheets of varying thickness, hoses, pipes, construction, table covers, conveyor belts etc.

Polytetrafluoroethylene (TEFLON)• It is obtained by polymerization of water-emulsion of tetrafluoro ethylene, under pressure and in the presence of benzoyl peroxide as a catalyst.

Due to presence of high electronegative fluorine in structure of TEFLON, strong interchain forces are present which make it extremely tough.

High softening point (350°c).It has high chemical resistance.It has good mechanical and electrical

properties(high-performance substitute for polyethylene)

Properties

It is used in insulating motor, transformers. It is used in making wires. Non-stick cookware coatings are made from TEFLON for eg. In frying pan. Also used for making gaskets, tank linings, pipes

and tubes for chemical industries. Used for making non lubricating bearings. one of the lowest coefficients of friction against

any solid.

Uses

Is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. Synthetic polymer of methyl methacrylate. Can be made by all types of moulding processes.

Poly(methyl methacrylate)

Properties:1.Strong & light weight2.Good impact strength ,higher than both

glass & polystyrene.3.Transmits up to 92% of light & filters UV

lights.4.coefficient of thermal expansion is relatively

high.5.Its properties can be modified to suit

requirements.

Uses: Making aquarium glasses; automobile headlights; spectator protection(e.g.- in ice hockey rinks); Aircraft windows; Helmet visors; making acrylic paints; bone cement, contact lenses etc.

AcrylonitrileButadieeneStyrene

•Monomers:-Acrylonitrile , Butadieene, Styrene•Formula :-(C8H8·C4H6·C3H3N)n

•Production :-Copolymer made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The proportions can vary from 15 to 35% acrylonitrile, 5 to 30% butadiene and 40 to 60% styrene.

•Properties :-The styrene gives the plastic a shiny, impervious surface. The butadiene, a rubbery substance, provides resilience even at low temperatures.Mechanical properties vary with temperature.

•Application :-1.Used to make light, rigid, molded products such as piping .2.Musical Instruments such as plastic clarinet.3.Golf club heads :- Used due to its good shock absorbance4.Used as a colorant in tattoo inks.

Bakelite, a phenol-formaldehyde polymer, was the first

completely synthetic plastic, first made by Leo Baekeland in 1907. Baekeland and an assistant started their research in 1904 looking for a synthetic substitute for shellac.

Bakelite was commercially introduced in 1909. Bakelite was first used to make billiard balls, but, later, was used to make molded insulation, valve parts, knobs, buttons, knife handles, many types of molded plastic containers for radios and electronic instruments, and more.

Phenol - formaldehyde polymers are the oldest synthetic polymers. These are obtained by the condensation reaction of phenol with formaldehyde in the presence of either an acid or a base catalyst. The reaction starts with the initial formation of o-and/orp-hydroxymethylphenol derivatives, which further react with phenol to form compounds having rings joined to each other through –CH2 groups. The initial product could be a linear product – Novolac used in paints.

Phenolic reins set to rigid, hard, scratch resistant, infusible, water resistant, insoluble solids, which are resistant to non-oxidizing acids, salts and many organic solvents, but are attacked by alkalis, because of the presence of free hydroxyl group in their structures, They posses excellent electrical insulating character.

Novolac on heating with formaldehyde undergoes cross linking to form an infusible solid mass called bakelite.

1.Plastic items like telephone parts,cabinets,heater handles.2.Phonograph records3.Electrical switches and berings used in propeller shafts in paper industry.4.Soft bakelite used as binding glue for laminated,wooden plants and in varnishes5.Sulphonated bakelite are used as ion exchange resins.6.For impregating fabrics,wood and paper.

Phonograph recordsvalve parts, knobs, buttons,

Melamine resin or melamine formaldehyde (also shortened to melamine) is a hard, thermosetting plastic material made from melamine and formaldehyde by polymerization at 80°C.

Melamine formaldehyde resin gives water white products,have good tensile strength, good electrical insulation, good chemical resistance, great hardness and good abrasion resistance.

The resin is formed by condensation co-polymerisation of melamine and formaldehyde.

It is a quite hard polymer and is used widely for making plastic crockery under the name Melamine. The articles made from melamine polymer do not break even dropped from considerable height. They are also used as laminates and for making decorative items. In paper industry to improve wet strength of paper. In fabric treatment as finishing agent.

Polyurethanes are made from a dialcohol and diisocyanate monomers. The isocyanate compounds contain the functional group (O=C=N-). A rearrangement reaction leads to the formation of the urethane linkage. Technically polyurethane is not a condensation polymer since no molecules are lost, but the functional group does rearrange. For example, Perlon-U (a crystalline polymer) is obtained by the reaction of 1,4-butane diol with 1,6-hexane diisocynate

1.Polyurethanes are less stable than polyamides(nylons) at elevated temperature.2.They are characterized by excellent resistance to abrasion and solvents.

Polyuraethenes are used as coatings, films, foams,adhesives and elastomers. Resilient polyurethene fibres (spandex) are used for foundation garments and swim suits.They also find use as a leather substutute(corfoam). They are used to cast to produce gaskets, and seals.

Silicone polymers do not have carbon as part of the backbone structure. The although silicon is in the same group as carbon in the periodic table, it has quite different chemistry.Many silanes are known which are analogous to the hydrocarbons with Si-Si bonds. These compounds are not very stable and hence not very useful.Silicones on the other hand have an alternating -Si-O- type structure. This basic structural unit is found in many rocks and minerals in nature including common sand.Various organic groups such as methyl or the benzene ring may be bonded to the silicon as shown in the graphic on the bottom.

Silicones are water repellent, heat stable, and very resistant to chemical attack. They find many uses in oils, greases, and rubberlike materials. Silicone oils are very desirable since they do not decompose at high temperature and do not become viscous. Other silicones are used in hydraulic fluids, electrical insulators and moisture proofing agent in fabrics.Silicones have a number of medical applications because they are chemically inert. A good deal of controversy has involved the the use of silicone in polyurethane bags as breast implants. Again they were used because they were thought to be very inert and resistant to dissolving or other reactions. Reports have cited increased cancer risk and severe immune responses from possible leakage of the silicone from the implants.

EPOXY RESIN

The first commercial attempts to prepare resins from epichlorohydrin were made in 1927 in the United States. Credit for the first synthesis of bisphenol-A-based epoxy resins is shared by Dr. Pierre Castan of Switzerland and Dr. S.O. Greenlee of the United States in 1936. Dr. Castan's work was licensed by Ciba, Ltd. of Switzerland, which went on to become one of the three major epoxy resin producers worldwide. Ciba's epoxy business was spun off and later sold in the late 1990s and is now the advanced materials business unit of Huntsman Corporation of the United States. Dr. Greenlee's work was for the firm of Devoe-Reynolds of the United States. Devoe-Reynolds, which was active in the early days of the epoxy resin industry, was sold to Shell Chemical (now Hexion, formerly Resolution Polymers and others).

THE ORIGIN OF EPOXY RESINS

Synthesis of high molecular weight epoxy resins under microwave irradiation

A new method of synthesis of high molecular weight epoxy resins is presented. All reactions were performed in a multi-mode microwave reactor “Plazmatronika” (microwave frequency - 2,45GHz, maximum of microwave power - 300W). Shortening of the reaction time for all processes performed in the microwave reactor, in comparison to conventional heating, was observed. 

Epoxy is a copolymer; that is, it is formed from two different chemicals. These are referred to as the "resin" and the "hardener". The resin consists of monomers or short chain polymers with an epoxide group at either end. Most common epoxy resins are produced from a reaction between epichlorohydrin and bisphenol-A, though the latter may be replaced by similar chemicals. The hardener consists of polyamine monomers, for example Triethylenetetramine (TETA). When these compounds are mixed together, the amine groups react with the epoxide groups to form a covalent bond. Each NH group can react with an epoxide group, so that the resulting polymer is heavily crosslinked, and is thus rigid and strong.The process of polymerization is called "curing", and can be controlled through temperature and choice of resin and hardener compounds; the process can take minutes to hours. Some formulations benefit from heating during the cure period, whereas others simply require time, and ambient temperatures.

PROPERTIES

The applications for epoxy-based materials are extensive and include coatings, adhesives and composite materials such as those using carbon fiber and fiberglass reinforcements (although polyester, vinyl ester, and other thermosetting resins are also used for glass-reinforced plastic). The chemistry of epoxies and the range of commercially available variations allows cure polymers to be produced with a very broad range of properties. In general, epoxies are known for their excellent adhesion, chemical and heat resistance, good-to-excellent mechanical properties and very good electrical insulating properties. Many properties of epoxies can be modified (for example silver-filled epoxies with good electrical conductivity are available, although epoxies are typically electrically insulating). Variations offering high thermal insulation, or thermal conductivity combined with high electrical resistance for electronics applications, are available.

APPLICATION

Electrical systems and electronics

Aerospace applications

Wind Energy applicationsEpoxy resin is used in manufacturing the rotor blades of wind turbines. The resin is infused in the core materials (balsa wood, foam) and the reinforcing media (glass, fabric). The process is called VARTM, i.e. Vacuum Assisted Resin Transfer Moulding. Due to excellent properties and good finish, epoxy is the most favoured resin for composites.

Paints and coatings Adhesives

Industrial tooling and composites

Consumer and marine applications

Nylon is used as general name for all synthetic fiber forming polyamides,i.e., having a protein like structure. These are the condensation polymers of diamines and dibasic acids A number is usually suffixed with the Nylon which refers to the number of carbon atoms present in the diamine and the dibasic acids respectively.

Nylon-6,6 is obtained by the polymerisation of adipic acid with hexamethylene diamine.

It is produced by the self condensation of caprolactum.

Beckmann Rearrangement

1.They are translucent,whitish,horny,high melting polymers .2.They posses high temperature stability and high abrasion resistance.3.They are insoluble in common organic solvents(like methylated spirit,benzene and Acetone), and soluble in phenol and formic acid.4.Their mouldings and extrusions have good physical strengths(especially high impact strength) and self lubricating properties.

1.They are light, horny, and high melting.2.They are insoluble in common solvents.3.They have good strength.4.They absorb little moisture ; and are thus ’drip-dry’ in nature.5.They are very flexible and retain original shape after use.6.They are resistant to abrasion.7.On blending with wool, the strength and abrasion resistance of the latter increases.

1.Nylon-6,6 is primarily used for fibres, which find use in making socks, ladies hoses, dresses, carpets,etc.2.Nylon-6 is mainly used for moulding purposes for gears, bearings, electrical mountings, etc. These bearings and gears work quietly without any lubrication.3.They are also used for making filaments for ropes, bristles for tooth brushes and films, tyre cords,etc.

Repeating chemical structure unit ofPolycarbonate made from bisphenol A

POLYCARBONATES

StructurePolycarbonates received their name because they are polymers containing carbonate groups (-O-(C=O)-O-). Most polycarbonates of commercial interest are derived from rigid monomers. A balance of useful features including temperature resistance, impact resistance and optical properties position polycarbonates between commodity plastics and engineering plastics

•The main polycarbonate material is producted by the reaction of bisphenol A and phosgene (COCl2). The first step involves treatment of bisphenol A with sodium hydroxide, which deprotonates the hydroxyl groups of the bisphenol A.

(HOC6H4)2CMe2 + 2 NaOH → (NaOC6H4)2CMe2 + 2 H2O

•The diphenoxide ((NaOC6H4)2CMe2) reacts with phosgene to give a chloroformate, which subsequently is attacked by another phenoxide. The net reaction from the diphenoxide is:

(NaOC6H4)2CMe2 + COCl2 → 1/n [OC(OC6H4)2CMe2]n + 2 NaCl

In this way, approximately one billion kilograms of polycarbonate is produced annually

SYNTHESIS

Uses of polycarbonates1) Domestic wares2) Electrical insulator in electronic

industries3)Other uses for polycarbonate

include greenhouse enclosures, automobile headlights, outdoor fixtures, and medical industry applications, though the list is virtually endless.

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Processing (or) moulding (or) compounding of plasticsProcessing (or) moulding (or) compounding of plastics

Compounding or mouldingCompounding or moulding is a process by which the polymer resins are is a process by which the polymer resins are mixed with some additives like fillers, plasticizers, stabilizers etc to impart mixed with some additives like fillers, plasticizers, stabilizers etc to impart some special properties to the moulded final product.some special properties to the moulded final product.

Ingredients of a plastic

Additives Examples Function/Importance

1. Resins

2. Plasticizers

Thermoplastic and thermosetting resins

Dioctylphthalate (DOP) Adipate, Oleate, Organic Phosphate

Basic binding materials and holds the constituents together. Major part of the plastics. Thermosetting resins transferred in to crosslinked plastics during moulding in presence of a catalystTo improve the elasticity and to reduce the brittleness of the plastics. Also improves the flow of polymer during the process

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Additives Examples Function/Importance

3. Fillers (or) Extenders

4. Lubricants

5. Stabilizers

6. Pigments

7. Anti-Oxidants

8. Catalyst

Mica, quartz, Limestone, Nylon

Waxes, Oils, soaps

Stearates of Pb, Ba and Cd

TiO2, ZnO (white), chromium oxide (green), carbon black, Read Lead

Phenyl, n-napthyal amine, Diphenyl-p-phenylenedimaine

H2O2 and Benzoyl peroxide

Increases the tensile and compressive strength of plastics. They reduce the shrinkage during the process of setting

To make the moulding process smooth and give the glossy finish to the final product

To increase the thermal stability of a polymer

To provide colours to the moilded articles

Protection against oxidation

Added only in the case of thermosetting resins to increase the rate of polymerisation

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Different types of Moulding technique

The moulding is different for various polymer depends on their thermal behaviour and nature of the resins.

1.1. Compression mouldingCompression moulding

2.2. Transfer mouldingTransfer moulding

3.3. Injection mouldingInjection moulding

4.4. Extension moulding and Extension moulding and

5.5. Blow mouldingBlow moulding

Used for moulding the Used for moulding the thermosetting polymersthermosetting polymers

Used for moulding the Used for moulding the thermo polymersthermo polymers

Used for moulding the Used for moulding the bottle type articles which bottle type articles which has narrow neckhas narrow neck

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PressurePressurePressure = 70 kg/cmPressure = 70 kg/cm22

Molten polymer with ingredients Molten polymer with ingredients in the cavity at 200in the cavity at 200ooCC

Top moulding part of the die Top moulding part of the die (plunger)(plunger)

Bottom moulding part of the die with cavity Bottom moulding part of the die with cavity (the shape of the cavity decides the shape (the shape of the cavity decides the shape of the final product)of the final product)

Pressed plastic Pressed plastic materialmaterial

Extraction pinExtraction pin

Guide pinsGuide pins

• The process of molding a material in a confined shape by applying pressure and usually heat.

• Almost exclusively for thermoset materials• Used to produce mainly electrical products

•A force of 2900psi is usually required for moldings up to 1inch (25 mm) thick. •An added 725psi should be provided for each 1inch (25 mm) increase.

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Plunger (top molding Plunger (top molding part)part)

Bottom molding partBottom molding part

Charger (plastic ingredients)Charger (plastic ingredients)

Molding CavityMolding Cavity

SprueSprue

Ejector pinEjector pin

HeatersHeaters

Molded Molded plasticplastic

A process of forming articles by fusing a plastic material in a chamber then forcing the whole mass into a hot mold to solidify.Used to make products such as electrical wall receptacles and circuit breakers

This is exclusively used for thermosetting plastics. The resin ingredients mixture is preheated in a preheating chamber. When the moulding mixture becomes plastic then it is forced through a orifice into the hot mould by using the plunger. After setting time it is taken out. Complicated shapes can be made.

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*

Injection partMolding partClamping

Heater bands

Hopper Hydraulic screw drive

Cavity

Barrel

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Pressing of molten polymer using die and plunger in Injection Molding

* Source: http://www.idsa-mp.org/proc/plastic/injection/injection_process.htm

Die

PlungerThe cavity in which the molten The cavity in which the molten plastic will be fed and pressedplastic will be fed and pressed

The feeding or injection of hot plastic

This method is generally used for thermoplastics.

The moulding composition is heated in a suitable chamber connected by a duct leading to the mould.

The hot softened plastic is then forced under high pressure into the relatively cool mould cavity where it is set by cooling and the moulded object is then ejected.

The temperature range used is 90 to 260oC.

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It is a process in which the molten plastic material is forced through a die It is a process in which the molten plastic material is forced through a die which produces a continuous extrudate (product) in the form of final product. which produces a continuous extrudate (product) in the form of final product. This process is used mainly for the production of films tubes, rods, hoses.This process is used mainly for the production of films tubes, rods, hoses.

It also used for the coating cables with PVC and other plastics.It also used for the coating cables with PVC and other plastics.

Molten polymer Die

Extruded pipe

Heater

Raw materials

Screw conveyer Cooling of

final product