Polymer processing, characterisation and applications
Published on: Mar 4, 2016
Transcripts - Polymer processing, characterisation and applications
• 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
Types of 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
• Reclamation and recycling
of waste is possible.
• They harden on heating and
once hardened, it can not be
• Made up of cross-linked
• Infusible and insoluble
• Cannot be remoulded and
• Reclamation and recycling is
Important Thermo Plastics
• (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
• 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
• Vinyl cholride until recently was mainly produced from
• 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
• 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
• 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
• Uses: Pipes, insulated wires, chemical plants,
storage tanks, floor mats, helmets, doors,
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.
• 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,
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 Resin
Temperature: 160 oC
Catalyst: Sodium or Ammonium Hydroxide
Phenol: Formaldehyde Ratio= 1:1.25 to 2.0
Cross 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 Resin
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.
• Are long flexible chains with weak intermolecular
forces and occasional cross links.
• It can be deformed to large extent (Several
• 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
• Once the deforming force is removed, they regain
the coil like structure.
Types of Elastomers
• 1. Diene elastomers
• Ex: a) Natural rubber(Polyisoprene),
Buna-S or SBR
• 2. Non-diene elastomers
• Ex: Polyisobutylene, polysiloxanes,
• 3. Thermoplastic elastomers
• Ex: SBS Elastomer
• 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
• 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
• The sheets are dried in smoke houses at 50 oC by
burning out wood or coconut shells.
• It is amber in colour..
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
Synthetic Diene rubber
• 2. Nitrile rubber
• Produced by co-polymerisation of butadiene and
acrylonitrile by free radical emulsion polymerization.
• Excellent resistance to oils, acids, but attacked by alkalis
• More heat resistant and aging by sunlight than natural
• Conveyer belts, aircraft components, tank linings
Synthetic diene rubber …..
• 3. Neoprene rubber
• Produced by free radical polymerisation of Chloroprene in
• Does not require vulcanisation.
• Superior resistance to oils compared to Natural rubber, poor
compared to nitrile rubber
• Fire retardant
• Cable Insulation, conveyer belts, shoe soles, reactor linings.
1. Butyl or Polyisobutylene Rubber
Produced by co-polymerizing isobutylene with 0.5
to 2% of isoprene by cationic polymerization..
Impermeable and extremely resistant to air
• Are typically semi-crystalline polymers that
can be spun into long strands that have high
strength to weight ratio for textile and
• 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
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
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
Ex: Benzoyl peroxide, Ag, Cu
(vi) Stabilizers: To increase the thermal stability of resins during
Ex: 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
• Compression Moulding
Used mainly for thermosetting plastics but can
be also used for thermo plastics.
Relatively low capital cost and simplest
• Injecting molten polymer into a closed, cooled
mould where it solidifies to form the desired
• High speed moulding of thermoplastics.
• 1. Injection Unit
• 2.Clamp unit
• Highly automated for mass production.
• Complex shape can be produced
• 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
• Charge is melted below the curing temperature in a
separate chamber and transferred into the closed and
• As the plastic enter the mould as melt, large and
intricate shapes can be filled unlike compression
• Products have high density and mechanical strength.
• Forcing the molten thermo plastic through the
die to get the product of uniform cross section
like pipe, rod, insulated wire etc.
• Mainly to produce hollow articles such as
• 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.
• For making trays from plastic sheet.
• Vacuum or compressed air is used for forming.
• For deep moulds, plug assist is used.
• 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
• Embossing effect or surface design can be
produced using engraved calender roll.
• It is used for polymers which are stable at
their melting point.
• Poly propylene
• Nylon-6 and Nylon-6,6
• Polymers which are not thermally stable at
their melting point are processed by solution
• Dry Spinning
• Solvent is evoporated by passing hot gases.
• Ex: Cellulose acetate and acrylics
Solution Spinning-Dry Spinning
• Polymer Solvent Non-Solvent
• Viscose rayon Carbon disulphide dil. H2SO4
• & NaOH Contg. ZnSO4
• and Na2SO4
• Polyacrylonitrile Dimethylformamide Aq.
• Spandex Dimethylformamide Water
Compounding of Rubber
(1) Process aids: Plasticisers, peptizers, softeners,
(2) Curing agent
(4) Accelerator activators
(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
• It makes the rubber
• - Soft
• - flows more readily
• - to form solution of very high concentration with
• - tacky (sticks to itself) so that articles of suitable
thickness can be made from layers of mastcated
Mastication and Mixing …..
• Mastication and mixing are done using two-roll
mills or internal mixers
• Two-roll open mill
Banbury type Internal Mixer
• Subjecting the waste rubber to heat and
• Alkali digestion process
• Neutral or zinc chloride digestion process
• 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.
• A) Non-black fillers
• Ex: China clay, Magnesium carbonate, hydrated
alumina, silicates, silica
• B) Carbon blacks
• Produced by thermal decomposition of NG or
• 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
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
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
• 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
• (i) Slow accelerators
• (ii) Medium accelerators
• (iii) Semi-ultra accelerators
• (iv) Ultra accelerators
• Important types of accelerators
Important class of accelerators
Important class of accelerators
Advantages of accelerated Sulphur Vulcanisation
Incorporation 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
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
• Ideal accelerator is the one which remains
stable duting compounding, storing and
processing of the mix but readily reacts at the
• The effect of accelerators is enhanced by the
addition of specific additives known as accelerator
• They are mainly two component systems comprised
of metal oxide and a long chain fatty acid. Ex: Zinc
oxide and stearic acid
• Activators must have good dispersability or
solubility in rubber.
To minimise the hazard of scorching, retarders are
added. Ex: Acids like Phthalic anhydride
To avoid degradation of rubber due to attack by
oxygen and ozone, antioxidants or antiozoonants
1.Amine type Ex: β – Napthylamine
2.Phenol type Ex: styrenated phenols.
• 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
(i) Mechanical polyblends
(ii) Chemical polyblends
(iii) Mechano-chemical polyblends
(iv)Solution cast polyblends
(v) Latex polyblends
• -made by melt blending of constituent
• 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
• Is used for polymers which donot thermally
Chemical polyblends and
• 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
• 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
• But after the removal of solvent, it can leave
significant changes in the property of the
• Most important technique commercially
• Polymers are made into suspension of
microspheres of specific size with the help of
• 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 / ∂ φ2
2 > 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
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 blending
Blending polymers with low molecular weight polymeric
plasticizers results in
homogeneous polyblends with Undiminished rigidity
low melting point (i.e energy saving during
no problem of plasticizers migrating to surface
of finished products
Ex: poly(methyl vinyl ether) to plasticize
polyethylene glycol to plasticize cellulose nitrate
Homogeneous polyblends show a single refractive index
which is intermediate between the two constituting
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
• 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
Types of commercial polyblends
• 1. Elastomers-Elastomer blends
• Widely made because single elastomer do not
have desired properties and poor cost-
• 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,
• PVC is a flame retardant, low cost resin but
• ABS (Acrylonitrile-Butadiene-Styrene terpolymer)
plastics are thermally stable but not fire
• 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
• General immiscibility of polymers is turned
into advantage in making rubber-toughened
plastics (Different from Thermoplastic
• 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 by
High thermal stability
Excellent Chemical Resistance
High tensile strength, impact strength, flexural strength.
High strength-to-weight ratio
Low creep compliance
Ex: Polyamides (Nylon-6, Nylon-6,6)
ABS resin, polycarbonate, Polysulfones,
Properties of Engineering Polymers
• Nylon-6 and Nylon-6,6 are the most widely used
• 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