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 otherw...
Types of Plastics
Thermo Plastics
• They soften on heating and
harden on cooling.
• They are made up of linear
or branched...
Important Thermo Plastics
• 1.Polyethhene
• (a) LDPE – 0.91-.925 g/cm3
• Prepared by bulk polymerisation at 1000-5000
atm....
b. HDPE
• Produced by using Zeigler Natta
polymerisation at 6 atm and 70 oC.
• Linear in structure and hence tight packing...
2. PVC
• Vinyl cholride until recently was mainly produced from
acetylene
• Dry HCl and acetylene gases in equimolar propo...
PVC
• Due to chlorine, it is polar, resulting in strong
intermolecular attraction and hence very stiff,
hard and high soft...
3. Polytetrafluoroethylene or Teflon
• Tetrafluoroethylene is produced first by
reacting chloroform with HF into
monochlor...
Teflon
• Linear polymer with crystallinity > 93% and
density 2.2 g/cm3
• Highly inert over wide range of temperature
• Ver...
Thermosetting Resin
Phenol-Formaldehyde Resin
Phenol-formaldehyde resin is an important example
of thermosetting resin.
...
Manufacture of Phenol-Formaldehyde Resin
Conditions:
Temperature: 160 oC
Catalyst: Sodium or Ammonium Hydroxide
Phenol: Fo...
Manufacture of Phenol-Formaldehyde Resin
(ii) A two stage process involving an acid catalysed
addition of formaldehyde to ...
Manufacture of Phenol-Formaldehyde Resin
Conditions:
 Temperature: 100 oC; Catalyst: Oxalic acid
 Phenol:Formaldehyde = ...
Elastomers
• Are long flexible chains with weak intermolecular
forces and occasional cross links.
• It can be deformed to ...
Types of Elastomers
• 1. Diene elastomers
• Ex: a) Natural rubber(Polyisoprene),
Polybutadiene, Polychloroprene(Neoprene),...
Natural Rubber
• By making incisions on the barks of Rubber trees
(Havea brasiliness), rubber latex which is an
emulsion o...
Natural rubber
• a) Crepe rubber
• Coagulum is bleached with sodium bisulphite.
• Bleached rubber is passed through crepin...
Vulcanization
Disadvantages of Natural rubber
• Soft & sticky in summer and hard & brittle in winter
• Low tensile strengt...
Synthetic Diene rubber
• 1.Styrene-Butadiene Rubber (SBR)
Co-polymer of 10-20% styrene and the rest is
butadiene obtained ...
Synthetic Diene rubber
• 2. Nitrile rubber
• Produced by co-polymerisation of butadiene and
acrylonitrile by free radical ...
Synthetic diene rubber …..
• 3. Neoprene rubber
• Produced by free radical polymerisation of Chloroprene in
emulsion syste...
Non-Diene Elastomers
1. Butyl or Polyisobutylene Rubber
Produced by co-polymerizing isobutylene with 0.5
to 2% of isoprene...
Thermoplastic Elastomer
• SBS
Fibers
• Are typically semi-crystalline polymers that
can be spun into long strands that have high
strength to weight rati...
Processing of Plastics
• 1.Compounding of Plastics
• Mixing of Polymers or resins with additives in
machineries like mills...
Molding constituents of Plastics
(iii) Fillers: To increase hardness, tensile strength, finish,
workability and to reduce ...
2. Shaping of plastics
Shaping is done by moulding.
Moulding is the process of shaping the plastic
into article by the sim...
Compression Moulding
• Compression Moulding
Used mainly for thermosetting plastics but can
be also used for thermo plasti...
Compression Moulding
Injection Moulding
• Injecting molten polymer into a closed, cooled
mould where it solidifies to form the desired
product....
Injection Moulding
Transfer Moulding
• It is mainly developed to overcome the disadvantage of
compression moulding which is slow and poor hea...
Transfer Moulding
Extrusion Moulding
• Forcing the molten thermo plastic through the
die to get the product of uniform cross section
like pi...
Extrusion Moulding
Blow Moulding
• Mainly to produce hollow articles such as
containers.
• Techique was borrowed from glass industry
• Plasti...
Blow Moulding
Thermoforming
• For making trays from plastic sheet.
• Vacuum or compressed air is used for forming.
• For deep moulds, pl...
Thermoforming
Calendering
• For the continuous formation of sheet or film
• Calender usually consists of four highly
polished rolls comm...
Calendering
Spinning
Melt Spinning
• It is used for polymers which are stable at
their melting point.
Ex:
• Polyethylene
• Poly propylene
• Nyl...
Melt Spinning
Solution Spinning
• Polymers which are not thermally stable at
their melting point are processed by solution
spinning
• Dr...
Solution Spinning-Dry Spinning
Wet Spinning
• Polymer Solvent Non-Solvent
• Viscose rayon Carbon disulphide dil. H2SO4
• & NaOH Contg. ZnSO4
• and Na2SO4...
Wet Spinning
Compounding of Rubber
(1) Process aids: Plasticisers, peptizers, softeners,
extenders etc.
(2) Curing agent
(3) Acceleraor...
Mastication and Mixing
• Process of breakdown of the molecular chains of
the rubber by shearing action is known as
mastica...
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 ...
Compounding Ingredients
• Peptizers
• added at the beginning of mastication
• Act chemically on the rubber and accelerate
...
Fillers
• A) Non-black fillers
• Ex: China clay, Magnesium carbonate, hydrated
alumina, silicates, silica
• B) Carbon blac...
Curing agent
 Sulphur is the most commonly used for curing rubber
at temperatures above 140 oC for a minimum curing
time ...
Accelerators
• Reaction between sulphur and rubber is very
slow and hence needs to be accelerated.
• Initially inorganic o...
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...
Choice of Accelerators
• Choice is dictated by nature of rubber, design of the product
and processing conditions.
• With i...
Choice of accelerators
• Scorching or premature vulcanisation during
compounding is undesirable and this problem
with ultr...
Choice of Accelerators
• For rubbers with limited unsaturation like
EPDM, butyl rubber, fast accelerators are to be
used a...
Accelerator Activators
• The effect of accelerators is enhanced by the
addition of specific additives known as accelerator...
Additives ….
• Activators must have good dispersability or
solubility in rubber.
• Retarders
To minimise the hazard of sco...
Polymer Blends
• Mixing together of two or more polymers or
copolymers to homogeneous mass having
properties different fro...
Types of Polyblends
• Polymer blends are otherwise known as
polyblends
(i) Mechanical polyblends
(ii) Chemical polyblends
...
Mechanical polyblends
• -made by melt blending of constituent
polymers
• For amorphous polymers blending
temperature must ...
Chemical polyblends and
Mechano-chemical polyblends
• Chemical polyblend is given by chemically
linking polymers either in...
Solution-cast polyblends
• Polymers are dissolved in solvents and thus
lower the temperature and shear force
necessary to ...
Latex Polyblends
• Most important technique commercially
• Polymers are made into suspension of
microspheres of specific s...
Properties of Polyblends
• Polyblends behaviour depends on
• (i) Extent of Phase separation
• (ii) Nature of the phase pro...
Properties of Polyblends ….
• If ∆Gm < 0 and if
• ∂2 ∆Gm / ∂ φ2
2 > 0, over entire composition range
• T, p
• the resultan...
Properties of Polyblends …
• If ∆Gm is positive over entire composition range at
given temperature, two polymers in the po...
Practical aspects of Polymer blending
Blending polymers with low molecular weight polymeric
plasticizers results in
 homo...
Practical aspects of Polymer blending ..
• Heterogeneous polyblends have application in
high impact plastics.
• Blending o...
Types of commercial polyblends
• 1. Elastomers-Elastomer blends
• Widely made because single elastomer do not
have desired...
2.Plastomer-Plastomer blends
• PVC is a flame retardant, low cost resin but
thermally unstable.
• ABS (Acrylonitrile-Butad...
3.Elastomer-Plastomer blends
• General immiscibility of polymers is turned
into advantage in making rubber-toughened
plast...
Engineering Application of Polymers
• Polymers more importantly plastics are classified as
• 1.Engineering and specialty p...
Properties of Engineering Polymers
Polyamides
• Nylon-6 and Nylon-6,6 are the most widely used
engineering polymers.
• Wear and abrasion resitance
• Low coef...
Important Polyamides
Polycarbonate
Polysulfone
Polyphenylens sulfide
Engineering Polyesters
PBT
• PEN
of 89

Polymer processing, characterisation and applications

chemical engineering
Published on: Mar 4, 2016
Published in: Engineering      
Source: www.slideshare.net


Transcripts - Polymer processing, characterisation and applications

  • 1. Polymer Processing, Characterisation and Applications
  • 2. PLASTICS, ELASTOMERS AND FIBERS
  • 3. 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.
  • 4. 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
  • 5. 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,
  • 6. 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
  • 7. 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.
  • 8. 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.
  • 9. 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.
  • 10. 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
  • 11. 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
  • 12. Manufacture of Phenol-Formaldehyde Resin Conditions: 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
  • 13. 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.
  • 14. Manufacture of Phenol-Formaldehyde Resin Conditions:  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.
  • 15. 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.
  • 16. 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
  • 17. 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.
  • 18. 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..
  • 19. 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
  • 20. 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
  • 21. 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
  • 22. 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.
  • 23. Non-Diene Elastomers 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 2. Polysiloxanes Ex:Polydimethyl siloxane
  • 24. Thermoplastic Elastomer • SBS
  • 25. 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
  • 26. 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.
  • 27. 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 moulding Ex: White lead, stearates of Pb (vii) Coloring Agent Ex: Organic dyes and inorganic pigments.
  • 28. 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
  • 29. Compression Moulding • Compression Moulding Used mainly for thermosetting plastics but can be also used for thermo plastics. Relatively low capital cost and simplest
  • 30. Compression Moulding
  • 31. 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
  • 32. Injection Moulding
  • 33. 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.
  • 34. Transfer Moulding
  • 35. Extrusion Moulding • Forcing the molten thermo plastic through the die to get the product of uniform cross section like pipe, rod, insulated wire etc.
  • 36. Extrusion Moulding
  • 37. 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.
  • 38. Blow Moulding
  • 39. Thermoforming • For making trays from plastic sheet. • Vacuum or compressed air is used for forming. • For deep moulds, plug assist is used.
  • 40. Thermoforming
  • 41. 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.
  • 42. Calendering
  • 43. Spinning
  • 44. 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
  • 45. Melt Spinning
  • 46. 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
  • 47. Solution Spinning-Dry Spinning
  • 48. 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)
  • 49. Wet Spinning
  • 50. 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.)
  • 51. 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.
  • 52. Mastication and Mixing ….. • Mastication and mixing are done using two-roll mills or internal mixers • Two-roll open mill
  • 53. Banbury type Internal Mixer
  • 54. Reclaimmed rubber • Subjecting the waste rubber to heat and chemical agents. • Alkali digestion process • Neutral or zinc chloride digestion process
  • 55. 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.
  • 56. 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.
  • 57. 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
  • 58. 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
  • 59. Accelerators ….. • Important types of accelerators
  • 60. Important class of accelerators
  • 61. Important class of accelerators
  • 62. 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 and aging.
  • 63. 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.
  • 64. 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.
  • 65. 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.
  • 66. 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
  • 67. Additives …. • Activators must have good dispersability or solubility in rubber. • Retarders To minimise the hazard of scorching, retarders are added. Ex: Acids like Phthalic anhydride • Antidegradants To avoid degradation of rubber due to attack by oxygen and ozone, antioxidants or antiozoonants are added 1.Amine type Ex: β – Napthylamine 2.Phenol type Ex: styrenated phenols.
  • 68. 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.
  • 69. 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
  • 70. 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.
  • 71. 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
  • 72. 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
  • 73. 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.
  • 74. 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
  • 75. 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 antisynergistic. •
  • 76. 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.
  • 77. 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 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 nitrate Homogeneous polyblends show a single refractive index which is intermediate between the two constituting polymers.
  • 78. 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.
  • 79. 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.
  • 80. 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
  • 81. 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)
  • 82. 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,
  • 83. Properties of Engineering Polymers
  • 84. 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
  • 85. Important Polyamides
  • 86. Polycarbonate
  • 87. Polysulfone
  • 88. Polyphenylens sulfide
  • 89. Engineering Polyesters PBT • PEN

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