Polymer Processing, Characterisation and

Applications

PLASTICS, ELASTOMERS AND FIBERS

Plastics• Plastics and resins or Polymers are not synonymous

though they are in use interchangeably.• Polymers or otherwise known as resins are the products

of polymerization• Pure polymers or resins cannot be processed into end

products with required properties.• Hence polymers or resins are to be admixed with several

ingredients and the resultant mix is called plastics and the process of mixing is known as compounding of plastics.

• Materials which can be deformed into desired shape under the action of heat and/or pressure are known as plastics.

Types of Plastics

Thermo Plastics• They soften on heating and

harden on cooling.

• They are made up of linear or branched polymers

• Fusible and soluble• Can be remoulded and

reused• Reclamation and recycling

of waste is possible.

Thermosetting Plastics• They harden on heating and

once hardened, it can not be softened.

• Made up of cross-linked polymers

• Infusible and insoluble• Cannot be remoulded and

reused.• Reclamation and recycling is

not possible

Important Thermo Plastics

• 1.Polyethhene• (a) LDPE – 0.91-.925 g/cm3

• Prepared by bulk polymerisation at 1000-5000 atm. and 250 oC.

• Non-Polar, Chemically inert• Tough and flexible• Low crystallinity and low softening temperature. • Uses: Films, carry bags, toys, domestic moulded

articles,

b. HDPE• Produced by using Zeigler Natta

polymerisation at 6 atm and 70 oC.• Linear in structure and hence tight packing

resulting in density 0.95-0.97 g/cm3

• High softening point (135 oC)• Excellent chemical and electrical resistance.• Higher tensile strength compared to LDPE• Uses: Pipes and tubes, carry bags where low

water permeability and gas permeability are important

2. PVC• Vinyl cholride until recently was mainly produced from

acetylene• Dry HCl and acetylene gases in equimolar proposition is

passed through multitubular reactor packed with mercuric chloride catalyst supported on activated carbon at 100 oC.

• When ethylene become abundant, it is chlorinated to dichloroethane and it is cracked into Vinyl chloride and HCl.

• Ethylene is also oxichlorinated to dichloroethane in the presence of copper chloride catalyst followed by cracking to vinyl chloride.

• PVC is mostly produced by emulsion and suspension polymerisation of vinyl chloride in water using free radical initiator.

PVC

• Due to chlorine, it is polar, resulting in strong intermolecular attraction and hence very stiff, hard and high softening point (148 oC).

• Non-inflammable and excellent chemical resistance

• Uses: Pipes, insulated wires, chemical plants, storage tanks, floor mats, helmets, doors, shoe sole.

3. Polytetrafluoroethylene or Teflon

• Tetrafluoroethylene is produced first by reacting chloroform with HF into monochlorodifluoromethane followed by its pyrolysis in the presence of Pt at 700 oC.

• CHCl3 + 2HF CHClF2 + 2HCl

• 2CHClF2 CF2=CF2 + 2HCl• Teflon is produced by polymerising the aqueous

solution of tetrafluoroethylene using free radical initiator.

Teflon• Linear polymer with crystallinity > 93% and

density 2.2 g/cm3

• Highly inert over wide range of temperature• Very low coefficient of friction• Excellent heat and electrical resistance• Uses: Gaskets, seals, films, wire insulators,

non-lubricating bearings

Thermosetting Resin Phenol-Formaldehyde Resin

Phenol-formaldehyde resin is an important example of thermosetting resin.

It has high strength, rigidity, chemical resistance, thermal stability, adhesiveness etc.

Hence used in making electrical switches, plugs, as binder in plywood manufacture, moulded products like cabinets of electronic consumer durables, varnishes, lacquers etc.

It is manufactured by (i) a single stage process involving base catalysed

addition of formaldehyde to phenol to yield phenol-formaldehyde resin called Resole

Manufacture of Phenol-Formaldehyde ResinConditions:Temperature: 160 oCCatalyst: Sodium or Ammonium HydroxidePhenol: Formaldehyde Ratio= 1:1.25 to 2.0Cross linking to Bakelite is achieved by simple pH adjustment

Manufacture of Phenol-Formaldehyde Resin

(ii) A two stage process involving an acid catalysed addition of formaldehyde to phenol to yield a linear phenol-formaldehyde resin called Novoloc.

Manufacture of Phenol-Formaldehyde ResinConditions: Temperature: 100 oC; Catalyst: Oxalic acid Phenol:Formaldehyde = 1:0.8 Crosslinking is achieved by adding cross linking agent

like hexamethylene tetramine which decomposes and form methylene bridges at the time of moulding.

Elastomers• Are long flexible chains with weak intermolecular

forces and occasional cross links.• It can be deformed to large extent (Several

hundreds times) • Once the deforming force is removed, regain their

original shape.• At molecular level they have coil like structure

resembling that of steel spring.• Upon being stretched, coil get unwounded and

straightened.• Once the deforming force is removed, they regain

the coil like structure.

Types of Elastomers• 1. Diene elastomers• Ex: a) Natural rubber(Polyisoprene),

Polybutadiene, Polychloroprene(Neoprene), Buna-S or SBR

• 2. Non-diene elastomers• Ex: Polyisobutylene, polysiloxanes,

Polyurethanes• 3. Thermoplastic elastomers• Ex: SBS Elastomer

Natural Rubber • By making incisions on the barks of Rubber trees

(Havea brasiliness), rubber latex which is an emulsion of 25-45% rubber in water along with proteins oozes out.

• Latex is diluted so as to contain 15 – 20% rubber.• Coagulation is done in tanks by adding 1 kg of

acetic acid or formic acid per 200 kg of rubber.• Soft, white coagulum is washed with water and

dried.

Natural rubber• a) Crepe rubber• Coagulum is bleached with sodium bisulphite.• Bleached rubber is passed through creping machine

from which coagulum rolls out with irregular surface of 1 mm thickness. The sheet is then dried at 50 oC in air.

• b) Smoked rubber• The bleached coagulum is rolled in to thicker sheets

having ribbed pattern which prevents them from adhering on stalking and also increases the surface area.

• The sheets are dried in smoke houses at 50 oC by burning out wood or coconut shells.

• It is amber in colour..

Vulcanization

Disadvantages of Natural rubber• Soft & sticky in summer and hard & brittle in winter• Low tensile strength and weak• Possesses tackiness• Under severe stretching, permanent deformation may occur• Poor Oxidation stability• Vulcanization is heating natural rubber at 100 – 140 oC with

sulphur resulting in cross-linking

Synthetic Diene rubber• 1.Styrene-Butadiene Rubber (SBR)Co-polymer of 10-20% styrene and the rest is butadiene obtained by free radical emulsion or co-ordination (Stereo SBR) polymerization.

• Largest synthetic elastomer consumed• Used for producing tires mainly by blending with

natural rubber

Synthetic Diene rubber• 2. Nitrile rubber• Produced by co-polymerisation of butadiene and

acrylonitrile by free radical emulsion polymerization.

• Properties:• Excellent resistance to oils, acids, but attacked by alkalis• More heat resistant and aging by sunlight than natural

rubber• Uses:• Conveyer belts, aircraft components, tank linings

Synthetic diene rubber …..• 3. Neoprene rubber• Produced by free radical polymerisation of Chloroprene in

emulsion system.

• Does not require vulcanisation. • Properties• Superior resistance to oils compared to Natural rubber, poor

compared to nitrile rubber• Fire retardant• Uses:• Cable Insulation, conveyer belts, shoe soles, reactor linings.

Non-Diene Elastomers1. Butyl or Polyisobutylene RubberProduced by co-polymerizing isobutylene with 0.5 to 2% of isoprene by cationic polymerization..

Impermeable and extremely resistant to air2. PolysiloxanesEx:Polydimethyl siloxane

Thermoplastic Elastomer

• SBS

Fibers

• Are typically semi-crystalline polymers that can be spun into long strands that have high strength to weight ratio for textile and composites applications

• Types of Fibers• 1. Natural Fibers• Ex: Plant sources:Cotton, Jute (Cellulose)

Animal Sources: Silk (Fibroin), Wool(Keratin) • 2. Synthetic fibers • Ex: Polyester, Nylon, Polyolefins, Acrylic

Processing of Plastics

• 1.Compounding of Plastics• Mixing of Polymers or resins with additives in

machineries like mills, Banbury mixers, Sigma blenders, ribbon blenders, pulverisers, Henschel mixer.

Molding constituents of Plastics(i) Resins: Main constituent binding all the ingredients.Ex: Thermo plastic resins: PE, PVC Thermosetting resins: Novolac, Resole(ii) Plasticizers: To increase the plasticity and flexibility.Ex: Vegetable oils, Phthalte esters like Diethyl Phthalate and organic phosphates like tributyl phosphate.

Molding constituents of Plastics

(iii) Fillers: To increase hardness, tensile strength, finish, workability and to reduce cost, shrinkage on setting and brittleness. Ex: Carborundum, quartz and mica to increase hardness.Barium salts to make impermeable to X-rays.Carbon black to increase abrasion resistance.(iv) Lubricants: To prevent plastic sticking to mould and impart flawless and glossy finish.Ex: Wax, oil, soaps(v) Catalysts or accelerators: Added to thermosetting resins to accelerate cross-linking.Ex: Benzoyl peroxide, Ag, Cu(vi) Stabilizers: To increase the thermal stability of resins during mouldingEx: White lead, stearates of Pb(vii) Coloring Agent Ex: Organic dyes and inorganic pigments.

2. Shaping of plastics

Shaping is done by moulding.Moulding is the process of shaping the plastic into article by the simultaneous application of heat and pressure(i) Compression Moulding(ii) Injection Moulding(iii) Extrusion Moulding(iv) Transfer Moulding(v) Thermoforming(vi) Calendaring

Compression Moulding

• Compression MouldingUsed mainly for thermosetting plastics but can

be also used for thermo plastics.Relatively low capital cost and simplest

Compression Moulding

Injection Moulding

• Injecting molten polymer into a closed, cooled mould where it solidifies to form the desired product.

• High speed moulding of thermoplastics.• 1. Injection Unit• 2.Clamp unit• Highly automated for mass production.• Complex shape can be produced

Injection Moulding

Transfer Moulding• It is mainly developed to overcome the disadvantage of

compression moulding which is slow and poor heat transmission which limits the products that can be moulded.

• Charge is melted below the curing temperature in a separate chamber and transferred into the closed and hot mould.

• As the plastic enter the mould as melt, large and intricate shapes can be filled unlike compression moulding.

• Products have high density and mechanical strength.

Transfer Moulding

Extrusion Moulding• Forcing the molten thermo plastic through the

die to get the product of uniform cross section like pipe, rod, insulated wire etc.

Extrusion Moulding

Blow Moulding

• Mainly to produce hollow articles such as containers.

• Techique was borrowed from glass industry• Plastic is made into tube called parison by

either extrusion or injection and accordingly known as extrusion blow moulding and injection blow moulding respectively.

Blow Moulding

Thermoforming

• For making trays from plastic sheet.• Vacuum or compressed air is used for forming.• For deep moulds, plug assist is used.

Thermoforming

Calendering

• For the continuous formation of sheet or film• Calender usually consists of four highly polished

rolls commonly arranged in ‘Z’, ‘I’ or inverted ‘L’ shape

• The soft or dough like plastic mass is metered between the hot rolls to give product of uniform thickness.

• Embossing effect or surface design can be produced using engraved calender roll.

Calendering

Spinning

Melt Spinning• It is used for polymers which are stable at

their melting point.Ex:• Polyethylene• Poly propylene• Nylon-6 and Nylon-6,6• PET

Melt Spinning

Solution Spinning

• Polymers which are not thermally stable at their melting point are processed by solution spinning

• Dry Spinning• Solvent is evoporated by passing hot gases.• Ex: Cellulose acetate and acrylics

Solution Spinning-Dry Spinning

Wet Spinning• Polymer Solvent Non-Solvent• Viscose rayon Carbon disulphide dil. H2SO4 • & NaOH Contg. ZnSO4

• and Na2SO4

• Polyacrylonitrile Dimethylformamide Aq. Dimethyl acetamide

• Spandex Dimethylformamide Water• (Polyurethane)

Wet Spinning

Compounding of Rubber

(1) Process aids: Plasticisers, peptizers, softeners, extenders etc.

(2) Curing agent(3) Acceleraors(4) Accelerator activators(5) Antidegradants(6) Fillers(7) Coloring agents(8) Miscellaneous (Retarders, blowing agents etc.)

Mastication and Mixing• Process of breakdown of the molecular chains of

the rubber by shearing action is known as mastication

• It makes the rubber• - Soft• - flows more readily• - to form solution of very high concentration with

low viscosity• - tacky (sticks to itself) so that articles of suitable

thickness can be made from layers of mastcated rubber.

Mastication and Mixing …..• Mastication and mixing are done using two-roll

mills or internal mixers• Two-roll open mill

Banbury type Internal Mixer

Reclaimmed rubber

• Subjecting the waste rubber to heat and chemical agents.

• Alkali digestion process

• Neutral or zinc chloride digestion process

Compounding Ingredients

• Peptizers• added at the beginning of mastication• Act chemically on the rubber and accelerate

the rate of breakdown of rubber chains and increase the efficiency of mastication

• Ex: Zinc thiobenzoate, thio-β-naphthol

• Other ingredients are added after the mastication yields rubber of desired plasticity.

Fillers

• A) Non-black fillers• Ex: China clay, Magnesium carbonate, hydrated

alumina, silicates, silica• B) Carbon blacks• Produced by thermal decomposition of NG or liquid

hydrocarbons• 90% of carbon black produced goes to rubber

industry and 80% is consumed in tyres industry• pH, Particle size, porosity and structure of carbon

blacks decide the curing rate, degree of reinforcement.

Curing agent

Sulphur is the most commonly used for curing rubber at temperatures above 140 oC for a minimum curing time of 8 hrs with sulphur dose of 8-10 phr.

Sulphur monochloride can bring curing at room temperature.

Peroxides, metal oxides, amines, amine derivatives and oximes are other curing agents for selected rubbers.

Selinium and tellurium can substitute sulphur as curing agent partially or completely.

High energy radiation can bring effective curing but not developed into a commercial process

Accelerators

• Reaction between sulphur and rubber is very slow and hence needs to be accelerated.

• Initially inorganic oxides (of Pb, Ca, Zn, Mg etc.) were used accelerators.

• Presently organic compounds are used. According to the speed of curing they are classified as;

• (i) Slow accelerators• (ii) Medium accelerators• (iii) Semi-ultra accelerators• (iv) Ultra accelerators

Accelerators …..

• Important types of accelerators

Important class of accelerators

Important class of accelerators

Advantages of accelerated Sulphur VulcanisationIncorporation of 0.2 to 2 phr of accelerator

brings down the sulphur dose from 8-10 to 0.5-3 phr and curing time from several hours (8 hr) to few minutes-an hour.

Low sulphur requirement of accelerated sulphur vulcanisation technology has eliminated bloom i.e migration of unreacted sulphur to the surface of vulcanised rubber and yielded vulcanised rubber of improved physical properties and good heat resistant and aging.

Choice of Accelerators

• Choice is dictated by nature of rubber, design of the product and processing conditions.

• With increase in curing time, initially there is a sharp increase in modulus and after reaching maximum value either the modulus remains same (Ex: SBR) or decreases, called reversion in rubbers like Natural rubber.

Choice of accelerators

• Scorching or premature vulcanisation during compounding is undesirable and this problem with ultra accelerator.

• In thick rubber products slow accelerators are preferred. As rubber is poor conductor of heat it takes more time the interiors of product to get heated by the heat flowing from the surface. Hence surface layers get overcured by the time curing begins at the interiors.

Choice of Accelerators

• For rubbers with limited unsaturation like EPDM, butyl rubber, fast accelerators are to be used at high curing temperatures.

• For butyl rubber showing reversion, duration of curing and curing temperature are to be carefully controlled.

• Ideal accelerator is the one which remains stable duting compounding, storing and processing of the mix but readily reacts at the curing temperature.

Accelerator Activators• The effect of accelerators is enhanced by the

addition of specific additives known as accelerator activators.

• They are mainly two component systems comprised of metal oxide and a long chain fatty acid. Ex: Zinc oxide and stearic acid

Additives ….• Activators must have good dispersability or solubility

in rubber.• RetardersTo minimise the hazard of scorching, retarders are added. Ex: Acids like Phthalic anhydride• AntidegradantsTo avoid degradation of rubber due to attack by oxygen and ozone, antioxidants or antiozoonants are added 1.Amine type Ex: β – Napthylamine2.Phenol type Ex: styrenated phenols.

Polymer Blends• Mixing together of two or more polymers or

copolymers to homogeneous mass having properties different from the constituents.

• Key for making polymer blends is the compatibility between polymers.

• Use of compatibilizers can bring down the phase separation in blends.

Types of Polyblends• Polymer blends are otherwise known as

polyblends(i) Mechanical polyblends(ii) Chemical polyblends(iii) Mechano-chemical polyblends(iv) Solution cast polyblends(v) Latex polyblends

Mechanical polyblends

• -made by melt blending of constituent polymers

• For amorphous polymers blending temperature must be above Tg of all the constituting polymers and in the case of semicrystalline polymers it must be well above Tm.

• Is used for polymers which donot thermally degrade.

Chemical polyblends and Mechano-chemical polyblends

• Chemical polyblend is given by chemically linking polymers either in the axial or in cross direction giving block copolymer or craft copolymer structure respectively.

• Mechanical blends also undergo cross-linking or terminal linking and been called as mechano-chemical polyblends

Solution-cast polyblends

• Polymers are dissolved in solvents and thus lower the temperature and shear force necessary to have uniform mixing

• But solvent must be completely removed after the casting.

• But after the removal of solvent, it can leave significant changes in the property of the blend

Latex Polyblends

• Most important technique commercially• Polymers are made into suspension of

microspheres of specific size with the help of stabilisers (Latex)

• When different latexes are blended, latex mixture containing different polymers is obtained.

• When the latex mixture is coagulated, intimate mixture of constituent polymers is obtained.

Properties of Polyblends• Polyblends behaviour depends on• (i) Extent of Phase separation• (ii) Nature of the phase provided by the matrix material• (iii) Character of the dispersed phase• (iv) Interaction between the constituting polymers• A polyblend is homogeneous or heterogeneous (ie phase

separated) depends on• (i) kinetics of mixing • (ii) Mixing temperature• (iii) presence of solvent and additives• (iv) Theromodynamics• ∆Gm = ∆Hm - T ∆Sm

Properties of Polyblends ….

• If ∆Gm < 0 and if

• ∂2 ∆Gm / ∂ φ22 > 0, over entire composition range

• T, p • the resultant polymer blend is homogeneous. • Different physical properties for homogeneous i.e. miscible

polyblend are related by semiempirical rule.• P= P1 φ1 + P2 φ2 + I φ1 φ2

• If I is zero, rule of additivity principle is observed. If I is +ve, blend is synergistic and if I is – ve, blend is antisynergistic.

•

Properties of Polyblends …

• If ∆Gm is positive over entire composition range at given temperature, two polymers in the poly blend will separate into pure phases of each polymer.

• For immiscible polyblend giving continuous phase (Phase 1) and dispersed phase (Phase 2)

• P/P1 = (1+ AB φ2)/(1-Bψ φ2)• Where φ2 is the concentration of the dispersed phase• Value of A varies 0 to infinity depends on the shape and

orientation of dispersed phase• Value of B depends on relative values of P1, P2 and A• Ψ is a reduced concentration which is a function of maximum

packing fraction• When A 0, dispersed phase is soft and • A infinity, dispersed phase is hard.

Practical aspects of Polymer blendingBlending polymers with low molecular weight polymeric plasticizers results in homogeneous polyblends with Undiminished rigidity low melting point (i.e energy saving during processing) higher stability no problem of plasticizers migrating to surface of finished products Ex: poly(methyl vinyl ether) to plasticize polystyrene polyethylene glycol to plasticize cellulose nitrateHomogeneous polyblends show a single refractive index which is intermediate between the two constituting polymers.

Practical aspects of Polymer blending ..

• Heterogeneous polyblends have application in high impact plastics.

• Blending of brittle plastic with small amount of rubber improves the impact resistance with diminished modulus.

• By cross linking the rubber in the blend, resultant product shows improved toughness, stiffness and impact resistance by uniformly distributing rubber in the blend and appropriate size of dispersed rubber phase.

• Heterogeneous polyblends scatters the light according to the size of dispersed phase. Larger their size more will be the scattering and behave as opaque.

Types of commercial polyblends• 1. Elastomers-Elastomer blends• Widely made because single elastomer do not

have desired properties and poor cost-performance ratio.

• Natural rubber is blended with selective synthetic rubbers to improve the properties like tackiness, resilience, wear-tear resistance, heat-build-up, low temperature flexibility.

• Ex: NR with SBR• Nitrile rubber with SBR, EPDM, polychloroprene

etc.

2.Plastomer-Plastomer blends• PVC is a flame retardant, low cost resin but

thermally unstable.• ABS (Acrylonitrile-Butadiene-Styrene terpolymer)

plastics are thermally stable but not fire retardant.• PVC-ABS polyblends are good in thermal stability,

flame retardant and good impact resistance.• ABS-polycarbonate polyblends combine high

impact strength, thermal resistance, good processing characteristics, improved environmental stress cracking resistance and cost advantage over use of polycarbonates alone

3.Elastomer-Plastomer blends• General immiscibility of polymers is turned

into advantage in making rubber-toughened plastics (Different from Thermoplastic elastomers)

• Polyolefin thermoplastics like PE, PP are blended with EPDM, NR

• By cross linking the eleastomeric component, properties can be further improved and cross linked elastomer-plastomer blends are known as Thermo-plastic vulcanizates(TPVs)

Engineering Application of Polymers• Polymers more importantly plastics are classified as• 1.Engineering and specialty polymers• 2. Commodity polymers (i.e plastics)• Engineering polymers are characterised byHigh thermal stabilityExcellent Chemical ResistanceHigh tensile strength, impact strength, flexural strength.High strength-to-weight ratioLow creep complianceEx: Polyamides (Nylon-6, Nylon-6,6)ABS resin, polycarbonate, Polysulfones,

Properties of Engineering Polymers

Polyamides• Nylon-6 and Nylon-6,6 are the most widely used

engineering polymers.• Wear and abrasion resitance• Low coefficient of friction• Good resilence• Uses: Automobile tyers and moulded parts,

packaging of oxygen sensitive foods.• Aromatic polyamides (i.e aramids) have better heat

and flammability resistance, strength and modulus higher than steel on equal weight basis.

• Uses: Substitute for steel in radial tyers, bullet resistant vests, FRP

Important Polyamides

Polycarbonate

Polysulfone

Polyphenylens sulfide

Engineering Polyesters

PBT

• PEN