Plastics
- 1. PLASTICS P.GANESAN ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING KAMARAJ COLLEGE OF ENGINEERING AND TECHNOLOGY VIRUDHUNAGAR
- 2. Polymers are replacing metallic components in applications such as • 1. Domestic appliances • 2. Toys • 3. Sports goods • 4. Office equipments • 5. Automobiles • 6. Aircrafts….
- 3. Some products made of polymer 1.Food containers 2.Beverage containers 3.Packaging 4.Sign boards 5.Housewares 6.Textile industries 7.Medical devices 8.Foams 9.Paints 10.Safety shields 11.Toys 12.Electrical appliances 13.Lenses 14.Gears 15.Electronic products 16.Automobile bodies & components
- 5. PLASTICS
- 6. Plastic feed stock material ❑Agricultural material … wood, cotton, soybean by-products etc. ❑Petroleum … light distillate such as benzene (C6H6) ❑Natural gas … methane (CH4)
- 7. • Feedstock materials are chemically developed into a monomer. • These monomers are linked together to form polymers by one of the following methods: 1. Addition Polymerisation 2. Co-polymerisation or Polyaddition 3. Condensation Polymerisation or Poly condensation
- 8. Addition Polymerisation • …joining several small molecules together into a chain, to form a large molecule. • …the molecules are just arranged in succession • …the product retains the same composition as the starting material • …if the starting material consists of identical molecules, the product is known as a homopolymer • … if they consist of different molecules , the product is known as co-polymer
- 9. Examples of Addition Polymerisation di mer tri mer etc.
- 10. ❑...Addition polymerisation reaction is initiated by heat, pressure & catalyst (e.g.) polystyrene (PS), n{C8H8} polypropylene (PP), n{C3H6} polyethylene (PE). n{C2H4} Teflon … C2F4 PVC … C2H3Cl
- 11. Co-polymerisation or Polyaddition • … joining together of several molecules of different starting materials, with migration of H2 atoms, but without secondary products being formed. (i.e.) it is a process of forming large chain molecules from different monomers. (i.e.) it is addition polymerisation of 2 or more different monomers. 2 different monomers ….co-polymer 3 different monomers …. tri-polymer ❑Final properties of a co-polymer depend on the ratio of monomer A to monomer B
- 12. Different co-polymer arrangements • i)Alternating copolymer … alternative arrangement of monomer A and monomer B • ii)Random copolymer … randomised arrangement of monomers A and B • iii)Block copolymer … long chain of monomer A alternating to a long chain of monomer B • iv)Graft copolymer … one main chain polymer with a side group monomer
- 14. Example for polyaddition • Polyurethane (PU) • Environmental friendly • Used for strapping tapes in packaging applications
- 15. Condensation polymerisation (polycondensation) • … different starting materials are combined to yield a single molecule, with elimination of a secondary product (usually water). • … since water is removed, we call this as condensation reaction (water condenses out) ❑ If the reaction yields only linear chains, polycondensation will give ‘THERMOPLASTICS’. ❑ If the individual molecules of the starting materials link together at several points, a 3D structure is obtained, giving rise to ‘THERMOSETS’.
- 19. Thermoplastics • When heated, becomes soft and pliable. • Can be moulded under pressure, into the required shape. • Will maintain its shape, only when it is cooled to normal temperature. • If the formed product is re-heated, again it softens and looses its shape. • At approximately 120 to 180° C, it becomes a pasty/liquid mass. • No chemical change occurs during repeated heating/cooling • Heating/cooling may be repeated indefinitely
- 20. Properties of thermoplastics • Have a linear or branched molecular structure. • Molecular structure determines their strength and thermal behaviour. • They are flexible at ordinary temperatures. • Commonly used thermoplastics: ➢ Cellulose nitrate ➢ Cellulose acetate ➢ Polyethylene ➢ Poly vinyl chloride ➢ Polystyrene ➢ acrylics
- 21. Thermosetting Plastics ➢ Cross-linked polymers. ➢ During application of heat & pressure, chemical union of molecules occurs and a stable structure is formed. ➢ Hard &very tight-meshed molecular structure. ➢ After curing, it is not possible to re-shape. ➢ Further shaping is possible only by machining.
- 22. Properties of thermosetting plastics ➢ Do not soften on re-heating. ➢ Cannot be re-worked. ➢ At high temperature, the useful properties get destroyed. (This is called ‘degradation’) ➢ Good resistance to high temperature. ➢ Good dimensional stability. ➢ Good chemical resistance. ➢ Better electrical properties than thermoplastics.
- 23. Commonly used thermosetting plastics ➢ Epoxies ➢ Polyesters ➢ Melamines ➢ Phenol-formaldehyde ➢ Urea-formaldehyde
- 24. Elastomers ➢ They also have a cross-linked structure. ➢ But they have a looser mesh. ➢ Hence they have considerable elasticity. ➢ Once cured, they also cannot be re-shaped by heating. ❑Common use of elastomer is to produce automobile tyres.
- 25. • Thermoplastics & Thermosetting plastics are commonly called as ‘Plastics’. • Elastomers are commonly called as ‘Rubber’. ❑Plastic refers to a group of materials consisting of large macro-molecules, which exhibit plastic characteristics.
- 26. Additives • To meet customer needs, plastics need additional properties, for specific applications. • So, some additives or modifiers are added (in the form of powder or pellet) to the polymers. • Such combinations are known as plastic compounds. • Polymer + Additive = Plastic compound (e.g.) • 1)Reinforcemens • 2)Fillers • 3)Colourants • 4)Flame retardants • 5)Stabilisers • 6)Antistatic agents • 7)Biocides • 8)Foaming agents
- 27. 1)Reinforcements Used to enhance the mechanical properties like i)tensile strength, ii)rigidity etc.
- 28. 2)Fillers Used to lower the cost But they reduce the mechanical properties
- 29. 3)Colourant
- 30. 4)Flame retardant They are added to slow down the rate of burning To prevent the plastic from supporting the flame
- 31. 5)Stabiliser • Helps to control or improve specific properties i)plasticiser ii)thermal stabiliser iii)Ultraviolet light stabiliser
- 32. 6)Antistatic agent To dissipate the static electricity accumulated on the surface of the plastic
- 33. 7)Biocide To avoid undesirable life formation like fungi, bacteria etc.
- 34. 8)Foaming agents To form foaming plastics used in Packaging industry, Building industry etc.
- 35. Bonding of Thermoplastics Methods of Bonding Chemical Bonding Thermal Welding
- 36. Chemical Bonding ➢ Effective method of making permanent connections ➢ Produces clean looking joints, with low weight & sufficiently strong connections. ❑ Very effective method for heat sensitive plastics, which will normally deform if heated. ❑ Does not create stresses ❑ Suited for leak-tight applications
- 37. Chemical Bonding…Limitations ➢ Adhesives & solvents are flammable ➢Preparation time is long ➢Curing time is long ➢Chemicals should not deteriorate the plastics ➢Special fixtures needed ➢Long clamping times ➢Special ovens or curing conditions may be needed ➢The chemical may be toxic: so, ventilation, solvent recovery, & worker protection are needed
- 38. Chemical Bonding Solvent Bonding Adhesive Bonding
- 39. SOLVENT BONDING • It is the process of joining the parts by treating the surfaces of the parts with a solvent ADHESIVE BONDING • Here, a third substance bonds a plastic to another plastic or metal/rubber/ceramic/ • glass/wood etc.
- 40. SOLVENTS ▪ Methylene chloride ▪ Ethylene di chloride ADHESIVES • Epoxy • Acrylic • Polyurethane • Phenolic • Rubber • Polyster • Vinyl • Cyano-acrylate
- 41. Surface contact angle • = 0 … Spreading • < 90° …Good wetting • = 90 ° … Incomplete wetting • > 180° … No wetting
- 42. POLYMER IN SPORTS FOOT BALL ❑ Net: usually made of Polypropene can also be made of Nylon ❑ Signals: made of FRP ❑ Tracksuit: made of polyurethane / polyester (known as breathable textiles) ❑ Ball: Butyl rubber bladder Inner lining (Nylon 66)
- 43. Foot ball-Design Aspects ➢ Aerodynamic ➢ Water resistant ➢ Air retentive ➢ Flight accurate ➢ Rebound ➢ Circumferance ➢ Weight
- 44. Polymer in Medical Applications • 1. Cardiovascular • 2. Mobility aids • 3. Internal artificial organs • . • . • . Many more
- 45. • 1. Polyurethane… Heart valves ✓High tensile strength ✓Abrasion resistance ✓Degradation resistance ✓Flexibility ✓Long life ✓Bio-compatibility
- 46. • 2. Silicones … Ventilation masks ✓ Very high flexibility ✓Excellent chemical resistance ✓Hard ✓High abrasion resistance ✓Waterproof
- 47. 3. Polypropylene & Polystyrene … Stethoscope ✓Tough ✓Flexible ✓Excellent electrical insulation ✓Service temperature upto 126°C ✓Good chemical resistance ✓Reasonably economical
- 48. • Polyethylene … Artificial Limbs ✓Light ✓Tough ✓High abrasion resistance ✓High melt viscosities ✓Resistance to low temperature ✓Creep resistance ✓Good impact strength ✓High durability
- 49. • Polyisoprene … Medical gloves ✓High elasticity ✓High tensile strength ✓High hardness ✓Good abrasion resistance ✓Low cost