Polymers

• Toughness


  • Determines ability to absorb energy and deform plastically without cracking. Designed to split dissipating energy.
• Elasticity


  • Material resistance to distortion and ability to return to its original shape. Polyurethane used in textile industry to produce fabrics that have elasticity.
• Flexibility


  • Ability of material to be bent or folded without breaking.
• Stiffness


  • Measure how rigid material is. Flexible pvc, sold by roll, used for protective coverings.
• Thermoplastics


  Vary in flexibility, thermosets rigid and stiff.
• Moldability


  • Polymer ability to be shaped into form or mould. Thermoplastics moulded in hot or molten state, usually under mechanically exerted pressure, using compressed air, hydraulics or rotation. Thermosets usually moulded in cold liquid form and cured using a catalyst.
• Cut and score


  • Depends upon hardness. Acrylic hard, easily scored and snapped, may chip and crack when machine cut. HDPE and HIPS softer, more flexible so will score less well cut more easily without chipping.
• Physical properties


  • Insulation
  • Self finishing
  • UV resistance
  • Melting points
  • Transparency and translucency
  • Resistance to chemicals and liquids
  • Ability to be combined with other polymers and additives
• Thermal insulation


  • Reduce heat transfer between objects and people. Some polymer materials formed with air trapped inside to create foams, used insulation in packaging and in construction industry.
• Electrical insulation


  • Does not allow electricity to flow freely through it. Polymers very good insulators, used in casings and shielding. Electrical light fitting, sockets made from urea formaldehyde, a thermoset heat and burn resistant.
• Melting points


  Thermoplastics soft, pliables and plastic when heat-can be shaped and moulded. Thermosetting polymers do not melt, start decomposing and char high temp.
• UV resistance


  • UV bleaches colour form polymers e.g. abs. Used in garden furniture. Effects polymer mechanical properties, degrade it + make it brittle. ASA developed alternative for ABS retains colour and greater UV resistance.
• Resistance to chemicals


  • HDPE resistant to chemicals, manufacture bleach bottles and chemically resistant piping. HDPE used in large sheets to line landfill sites, barrier between waste + soil.
• Resistance to liquids


  • Most polymers resistant to liquids. HDPE and Polyethylene Terephthalate (PET) used in plastic bottles. HDPE reusable and recyclable. PET recyclable-not reused overtime, plastic may leach chemicals into water.
• Suitability for food packaging

  • Polymer films, moulded polymer sheet used in food packaging. Hygienically protect goods, create barriers to oxygen, liquids, foreign airborne bodies and tampering. Prolong shelf life, help keep flavour and protect quality of contents.
• Problematic food packaging


  • Films and bags heat sealed to keep food inside airtight and fresh. Some bags, films, trays allow food to be cooked whilst still packaged. Many ready meals use this.
• Transparency


  How permeable a material is to light radiation. Translucent, some light passes through diffused and objects on other side will not be clear. Opaque, impermeable. Clear polymer sheets, replacement for glass in windows + signs, packaging, allow buyer to see contents.
• Self-finishing


  • No additional surface finishing is required. Surface of mould dictate surface finish. Pigment added pre-production removing surface colouring secondary.
• Additives for processing


  • Plasticisers
  • Thermal antioxidants
• Additives for performance


  • Antioxidants
  • UV light stabilisers
• Additives improve function


  • Fire retardants
  • Plasticisers
  • Antistatic additives
• Additives for biodegradability


  • Increase biodegradability
• Classification of polymers


  • Thermoplastics
  • Thermosets
• Polymer variations


  • Synthetic polymers produced from finite resources e.g coal, oil and gas
  • Natural polymers come from rubber, amber which come from trees
• Refining crude oil


  1. Fractional distillation occurs heat crude oil

  2. Each product different sized molecules with different boiling points

  3. Different polymers made from different fuels
• Cracking


  1. Convert large hydrocarbon molecules into smaller, more useful versions

  2. Large molecules don't flow very well, heat + pressure break up
• Polymerisation


  Poly (many), mono(one)
• Thermoplastics


  • Long chains of molecules, no fixed structure or pattern
  • Soft and flexible, some shape memory
• Thermoplastics cycle


  1. LDPE - Low density polyethylene, flexible, tough, translucent, opaque, excellent resistance to chemicals, used in packaging where flexibility required - squeezy bottles, snap on lids, carrier bags and toys

  2. HDPE - High density polyethylene, tough, higher strength to weight ratio than LDPE. Used for drums and bottles containing chemicals, rigid plastic toys, storage boxes, buckets, garden bins, bags for life, good chemical resistance, harder than LDPE

  3. PP-polypropylene - tough, flexible polymer with excellent fatigue resistance. Translucent, range of colours, resistant to chemicals and solvents. Food packaging, medical equipment, hinged lids, moulded furniture and rops

  4. HIPS - high impact polystyrene, rigid lightweight polymer, high impact strength, ability to retain heat without deformation, glossy appearance, food safe, yoghurt pots, cutlery, salad bowls, single use coffee cups, plastic cutlery, transparent casing

  5. ABS - acrylonitrile Butadiene Styrene, hard, tough, excellent impact strength, domestic appliance casing, rigid suitcase, safety helmets, car bumpers, good resistance to acids, alkalis, oils and grease. Easily moulded, high quality surface which can be painted

  6. PMMA- acrylic, polymethyl methacrylate, tough, lightweight material, transparent, shatter-resistance, shower trays, baths, car lamp covers, lenses in glasses, clear plastic, wide range of colours, poor resistance to chemicals
• Nylon


  • Mechanical properties, machine screws, gears, woven textiles, rope, parachutes, tents, seat belts, carpets
  • Low coefficient of friction, durable and resistant to abrasion, heat resistance
• Rigid PVC


  • Plumbing pipes, guttering and downpipes, increase fire retardancy, good chemical resistance, weather resistance, uPVC window frames and external doors
• Flexible PVC


  • Hose pipes, electrical insulation to inflatable products, clothing, upholstery alternative leather, water resistant, good chemical resistance
• Thermosetting plastics


  • Condensation polymers, two monomers form bond, small molecule of water produced
  • Cross-linked, form rigid molecular structure, when thermosets cured, using chemical catalyst cause it to harden
  • Exothermic and generates heat
• Thermosets


  • More brittle than thermoplastics, stiffer mouldings, very hard, waterproof when solid, adhesives, more difficult to mould, can't be reheated or reshaped, retain shape well at high temperatures
• Thermosetting plastics


  • UF - urea formaldehyde, hard, opaque resin, used as adhesive bind materials e.g mdf/plywood, moulded resin in electrical casings, socket and switches, good resistance to deformation, high tensile strength
  • MF - melamine formaldehyde, hard, scratch resistant, opaque polymer, surface coatings, decorative laminates, picnic ware, toilet seats, kitchen utensil handles, buttons, good resistance to heat and chemicals
  • Polyester resin - marine industry, used to produce grp boat hulls, bath tubs, chair seats, coating chopped strand matting process called laying up. Resin base must be mixed with catalyst. Polyester resin to water, heat, chemicals
  • Epoxy resin - clear resin needs to be mixed with a catalyst to cure. Hard, tough, used as adhesive to join dissimilar materials, maintains integrity at high temperatures, good chemical resistance
• Stock forms


  • Sheet
  • Film
  • Granules
  • Rod
  • Other extruded forms
  • Foam
  • Powder
• Sheet


  Solid cast or extruded sheet, fluted sheet, laminated sheet. Flat form/may be cut or moulded.
• Film


  Packaging films, membranes, carrier bags, photographic film.
• Granules


  Thermoplastics produced in granule form which makes the process easy when moulding. E.g. PVC and rubber granules used for sports, playground surface, filling soft toys.
• Rod


  Extrusion is method by polymer granules e.g nylon, PP are melted and formed into continuous profile. Used in manufacturing of precision plastic parts such as bearing, gears, seals.