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POLYMERS - Material Science For Engineering

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Published in: Mechanical
4,286 Views

POLYMERS

Sidhant S / Bathinda

7 years of teaching experience

Qualification: mechanical engineering

Teaches: Geography, History, Mathematics, Science, Mechanical

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  1. Polymers Organic Natural - plants & animals; wood, rubber, cotton, wool, leather, silk — Synthesized polymers — from small molecules, inexpensive & better properties — Polymers organic in origin- hydrocarbon C, H covalent bonds Methane CH4, Acetylene C2H2 Molecules in polymers are gigantic compared to hydro-carbon -C-C-C-C-C-C- Common polymers — Polyethylene (PE), poly vinyl chloride (PVC) , polystyrene (PS) Polypropylene (PP), poly tetra fluoro ethylene (PTFE), Bakelite, polycarbonate (pc), polyester (PET) Classifications Thermoplastic and thermosetting polymers Thermoplastics Softens when heated (liquify) and hardens when cooled; Reversible process can be repeated. - Polyethylene, polystyrene, poly vinyl chloride Thermosetting Become permanently hard during formation; don't get softens on heating Dimensional stability, harder, stronger as vulcanized rubber, epoxy, phenolics, polyester resin
  2. Polymers Properties Mechanical properties same as metal — Young's modulus of elasticity, strain, stress, elongation Stress strain curve for brittle, plastic and highly elastic (elastomeric) polymers Visco-elasticity Temp has effect on deformation Fracture strength low — thermosetting polymers brittle fracture failure; thermoplastics both Fatigue — under cyclic loadings Basic properties Density 0.9 — 1.36 gm/cc Tensile strength — up to 80 MPa Temp up to 150 C; max 288 C for PTFE Dielectric strength — 10 — 70 K volt/mm Impact strength — 640-854 J/m
  3. Polymers Types Polyethylene (PE) Clear, translucent, fabricated into thin film. Low cost, high density extensively used sufficient strength & toughness at room temp , good flexibility, corrosion resistance, insulating Electrical insulation, chemical tubing, house wares, packing material Poly vinyl chloride (PVC) Second largest high strength 50-62 MPa, brittle, good electrical insulation (55K), solvent resistance Building construction material, pipes, siding, window frames, gutter, PVC conduit ' Furniture, auto upholstery, rain wear, shoes, shower curtain, insulation, mats, refrig gaskets, house wares Polypropylene (PP) Good chemical & moisture resistant, heat resistant, low cost House wares, lab ware, packing, bottles, screw, closure, containers Polystyrene (PS) Clear, colorless, odorless, brittle, dimensional stability, low mold shrinkage, low cost, good insulation, adequate mechanical strength; but poor weather ability Automobile interior parts, appliances, house wares
  4. Polymers Types Poly acrylonitrile Fibre forms, high strength, resistance to moisture ' Sweaters, blankets Styrene Acrylonitrile (SAN) Rigid, & hard, gloss, clarity Automotive instruments, dash boards components & support panels, lenses, Appliances, blender, mixer bowl, jar, syringe, tumblers, mugs Acrylonitrile butadiene and styrene(ABS) Pipe & fittings, drain waste, vent pipe, automotive parts, apliances, business machine, computer housings, & covers, electrical conduit, electro magnetic interference, radio frequency shielding appliances
  5. Polymers Engineering Thermoplastics Basic properties Low density advantages, polycarbonates has outstanding impact strength, good electrical insulation, corrosion resistance, easy to shape, automated process — Polyamides (Nylons) Good toughness, low frictional properties, injection molding or extrusion methods Un-lubricated gears, bearings, antifriction parts, mechanical & automotive parts — speedometer, wind shields wiper gears, trim clips, fan blades, brakes & power steering, reservoir valve, wire insulation — Poly carbonate High strength, toughness, dimensional stability Safety shields, helmets, aircraft components, boat propeller, lenses, glaze window, solar collectors, power tools, computer components/ terminals — Acetals Long term load carrying capacity ' Replaces light metal Al, Zn , brass, lower costs Seat belts, fuel systems, mech couplings, pump impeller, gear, cam, writing pen Thermo plastic polyesters Connectors, switches, relay, TV components, high voltage components, IC boards, automotive exterior body components
  6. Polymers Thermosets Basic properties Low density, light weight advantages, rigidity, dimensional stability, resist to creep & deformation, high electrical & thermal insulation properties Can not be recycled/ reused — Phenolics ' Switch gear, connectors, relays, power assisted brake & transmission system, wiring devices Epoxy Resin Protective and decorative coating, , good adhesion, automotive primers Elastomers (Rubber) Natural rubber— latex of Hevea brasiliensis tree tropical SE Asia — Synthetic rubber— SBR styrene butadiene rubber, neoprene, nitrile rubber, silicone rubbers
  7. Polymers Polymers in bio medical Versatile bio material Cardiovascular, ophthalmic & orthopedic as implant component Coronary angioplasty, hemodialysis, dentistry implant, denture base cement, ' Low strength, low density, ease of forming, bio compatibility Bio degradable polymers, ultimate absorbed or integrate in biological system. Surgical removal not necessary Heart valve Tissue or artificial valves , connection to heart tissue by polymers Vascular graft for coronary artery bypass ; either tissues (self) or artificial grafts ; high strength, resist clogging Blood oxygenator To remove C02 and provide oxygen to blood during surgery Polymers for artificial heart & heart assisted devices Ophthalmic applications Eye correction; eye glasses, contact lenses, intera ocular implants for cataract Drug delivery system Pills & injection adverse effect on organs. Deliver at right place/ time — Suture material To close wounds & incisions — absorbable (polymers) material Orthopedic - Bone cement & joints ; to fill space b/w implant & tissues

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