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Polymers

Polymers. A level Product Design Unit 2. Plasticity is a material property & not a material “the ability to be shaped or formed” Plastic Materials Bone Horn Clay Concrete A polymer is a certain type of material There are natural & synthethic polymers

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Polymers

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  1. Polymers A level Product Design Unit 2

  2. Plasticity is a material property & not a material • “the ability to be shaped or formed” • Plastic Materials • Bone • Horn • Clay • Concrete • A polymer is a certain type of material • There are natural & synthethic polymers • We are only interested in synthetic polymers Whats the difference between a plastic & a polymer ?

  3. an individual chemical molecule is called a monomer • When many monomers are linked together to form a chain, a polymer molecule is formed • A plastic consists of many large polymer molecules What is a Polymer ?

  4. A chemical reaction forms the polymer molecule (makes the chain) • polymerisation • Normally, chains are randomly arranged and form a 3d pattern • Imagine a piece of string scrunched up into a ball What is a polymer ?

  5. Long chain polymers Crosslinked polymers Thermoplastics Thermosetting Plastics Elastomers Semi-crystalline amorphous Synthetic Polymer Categories

  6. Very strong • Strong bonds between chains (crosslinks) and intra-chain • Level of crosslinking determines Tg • Thermosetting plastics (eg Araldite) are highly linked • Chemical reaction forms the links • One way process – cannot be reversed • Will not soften with heat - very high Tg • Araldite is a tradename for a resin based polymer • The resin is mixed with an activator to start curing • Materials like rubbers are lightly crosslinked • Tg is below freezingie. Is in a rubbery state at all temperatures above 0 • Below Tg, material is hard & brittle (useless) Crosslinked Polymers

  7. Strong covalent bonds • Bonds between individual chain elements • Weak bonds between chains • These bonds can be easily broken with heat • Breaking all bonds causes return to original shape • Recyclable by re-heating • Energy cost ! • Contamination is a big issue Thermoplastics

  8. Amorphous thermoplastics • Chains are randomly entangled • Generally transparent • Eg. PolyCarbonate (CDs) • Glass transition temperature (Tg) is a key property • Semi-crystaline thermoplastics • Cooling causes molecules to fold in a regular structure and form a crystal • Crystal is dense and so plastic is opaque • Eg. Polyethylene (gas and water pipes) • Have a definate meting point (Tm) Thermoplastics

  9. The more crystalline a material is: • The stronger it gets • It has more resistance to solvents • Solvents need to dissolve into a material • Amorphous plastics have greater free space • Higher density • Higher modulus (stiffness) • Higher melting point (Tm) • The lower its transparency • Reduced impact resistance (brittle) • Reduced ductility • Ability to be deformed without cracking Semi-Crystalline Thermoplastics

  10. Tg (glass to rubber) Tm (melting point) Stiffness (modulus) Temperature Amorphous thermoplastic Semi-crystalline thermoplastic Effect of temperature on thermoplastics

  11. 15% of plastic production • Polyurethane • Carpet underlay • bed foam • Urea formaldehyde (UF) • Mains plugs/sockets/light switches • Phenol Formaldehyde (PF) • Tradename: Bakelite • Epoxy Resin • Tradename: Araldite • Used as coatings & adhesives or to form compositeseg. Carbon fibre • Can cause health problems • Melamine formaldhyde • Work top laminates • Office furniture Thermosetting Plastics

  12. Oil (carbon) • 4% of crude oil is used for plastics • Sustainable sources (biopolymers) • Wheat & corn • Carrot • Recycling • Difficult: all recycled items must be of the same polymer • Mixed plastics can be used for low level products such as road surfacing, wood replacement Sources of Polymers

  13. PolyPropylene (PP) • Tupperware (lunch boxes) • Poly Vinyl Chloride (PVC) • Window frames • PolyStyrene (PS) • Packaging • Yoghurt pots / vending machine cups Carbon Based Polymers

  14. Acrylic • Paint • Point of sale displays • Baths • Car lights • HDPE (High Density PE) • Bottles (biggest application) • milk bottles (largest bottle sector) • LDPE (low Density PE) • Supermarket carrier bags • Packaging film (eg. cling film) • Washing up liquid bottles • PET (PE Terephthalate) • fizzy drinks bottles • Carbonation makes HDPE unsuitable • Space blankets • ABS (Acrylonitrile Butadiene Styrene) • Car batteries • Calculators / mobile phones • Safety helmets Carbon Based Polymers

  15. Amorphous • Good resistance against medium temperatures (< 1000C) • Hard • tough • antistatic. • good resistance against chemicals. • Poor resistance to UV-light • Can be painted • Min temp: -250C • Max Temp: 800C • Glass Temp: 1100C Material Properties: ABS

  16. Very light • AKA: Polyester • Can stand high tensile stress • Often used for magnetic tape • hard, stiff, strong • dimensionally stable • absorbs very little water • good chemical resistance except to alkalis • Medium resistance to UV • most commonly recycled plastic • drinks bottles are made from PET • Semi-crystaline • Must be rapid cooled to make it amorphous & transparent • Can degrade & become discoloured during heat treatment • Adds an unwanted flavour to food (can be compensated for at addition cost) • Min Temp: -500C • Max Temp: 1700C • Glass transition temperature: 82oC. • Melting point: 250oC. Material Properties: PET

  17. Excellent for any food related products • Not microwaveable • Machines extremely well (cut, bond, drill etc.) • Good chemical resistance • Good impact resistance • light weight • Poor UV tolerance • very low moisture absorption • high tensile strength • Not a good candidate for gluing. • Primarily used for blow moulding • Colours fade over time • Min Temp: -1000C • Max temp: 1100C • Melting point: 1300C • Glass temp: -95 • Applications • Milk bottles • trays and tanks • pipe fittings, wear plates, hinges • cutting boards. Material Properties: HDPE

  18. Amorphous (transparent) • Is typically coloured to make opaque • Good UV resistance • Excellent chemical resistance • glue able and weld able • easily machine able & heat bends nicely • Stiff • Tough • hard • Tg can be reduced down to -400c by adding plasticizer • Makes PVC suitable for hose pipes etc • Max Temp: 600C • Min Temp: -250C • Glass temp (Tg): 830C Material Properties: PVC PVC Applications (2000)

  19. Lower density & chemical resistance than HDPE • More transparent than HDPE • Less expensive than HDPE • Colours fade over time • Poor UV tolerance • Very soft & pliable • Max temp 700c • Min temp -50oc • Melting point 1200c • Glass temp: -1100C Material Properties: LDPE

  20. Poor UV resistance • Translucent (semi-crystaline) • Rigid • Very light • Excellent chemical resistance • food storage applications • Medical applications (syringes) • Carpets • Microwaveable • Max temp 1350C • Min temp 00C • Melting point: 1700C • Glass temp: -180C Material Properties: PP

  21. Amorphous • Flammable • Excellent thermal insulation • Used in fridge linings • Solid: • Light, Hard, Stiff, Brittle • Expanded: • Light, Bouyant, Crumbles • Min temp: -400C • Max temp: 600c • Glass transition point: 1000C Material Properties: PS

  22. amporphous • Trade names: perspex & plexiglass • Weather resistant (Can withstand sunlight for long durations) • Difficult to recycle • Can be done but is very expensive (not cost effective) • Stiff (Flexible compared to glass) • Less breakable than glass • Scratches easily • brittle • Resistant to most chemicals and industrial fumes • Can be cut by various methods • Corrosion resistant • Good electrical insulator • Min Temp: 50C • Max temp: 410C • Glass temperature : 1100C Material Properties: Acrylic

  23. Some acrylic Products

  24. Safety • Many chemical plastisizers contain oestrogen • Gender bending chemical • Some plastics (eg. PET) degrade & emit cancerous material over time • Life Cycle • Carbon based plastics take thousands of years to degrade • Biodegradeable plastics are being researched now • Sustainability • What would land used to grow organic polymers normally be used for ? • Are organic polymers at the expense of food grade crop ? • Today: a 500ML water bottle takes 3 fl/oz of crude oil to produce (+ energy to manufacture) • Energy for manufacture • All polymers (apart from elastomers) require heat to make them plastic • All plastics must be sorted and washed before being recycled • Where does this energy come from ? • Plastic is itself a fuel and can be incinerated • Toxic fumes are a consequence • Plastic can also be manufactured into a synthetic oil Issues

  25. Sources of rubbish (2006) • Plastic mining of landfill sites may become a future industry • The price of plastic is linked to the price of oil Issues

  26. http://www.dynalabcorp.com/files/Use and Care of Plastics.pdf Useful Web Sites

  27. Guess the plastic ….

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  31. HDPE ABS PVC Acrylic Answers!

  32. Exam Question...

  33. Exam Question...

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