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National 4/5 Sub-topic 3B – Materials and Plastics Summary Plastics and Synthetic Fibres Synthetic fibres are man-made fibres e.g. polyester, polyamide and terylene. Some synthetic fibres are PLASTICS. Plastic Property y Use Polyamide (Nylon) tough, fairly hard, resists wear, good resistance to chemicals and machines lkkkkkrhggdf Bearings, gear wheels, casings for power tools, hinges for small cupboards, curtain rail fittings and clothing Polypropylene Light, hard but scratches easily, tough, good resistance to chemicals Medical equipment, laboratory equipment, 'plastic' seats, string, rope, kitchen equipment Polystyrene Light, hard, stiff, transparent, brittle, with good water resistance Toys, especially model kits, packaging, 'plastic' boxes and containers polythene Tough, good resistance to chemicals, flexible, fairly soft, good electrical insulator Packaging, especially bottles, toys, packaging film and bags 1 When Plastics Burn Plastics can burn to release toxic fumes and use up a lot of oxygen in the process. Plastic Elements present Toxic fumes Poly(ethene) Carbon and hydrogen Carbon monoxide Carbon, hydrogen and Hydrogen chloride chlorine (acidic) Carbon, hydrogen and Hydrogen cyanide nitrogen (toxic) Carbon and hydrogen Dense, black smoke P.V.C. Polyurethane foam Polystyrene Biodegradable Plastics • Plastic packaging does not rot away and so causes major litter problems. • Many plastics are non-biodegradable, meaning they will not rot away naturally. • Plastics are now being introduced that are biodegradable e.g. Biopol (biodegradable polymer). • Paper, originally used for packaging, did rot away under the action of microbes, and is described as biodegradable. • BIODEGRADABLE means that the material will decay naturally. 2 New Plastics Technology Kevlar - (discovered in 1960’s) Bullet-proof vests are made from tightly woven fibres and are much more flexible and comfortable than hard body armour. Kevlar is used Kevlar as a protective material because it is: Flexible and light Heat resistant Five times stronger than steel Smart Materials Smart materials are plastic and metal items designed to instantly change their properties when triggered by a stimulus. Common properties that can be significantly altered in smart materials include: Size and shape State (solid, liquid, gas) Viscosity Conductivity Different smart materials can respond to different stimuli, such as temperature, pressure, magnetism and voltage/current. Ceramics Properties Uses of ceramics - Extremely hard - Resistant to corrosion - Heat resistant - Low ductility - Low toughness - Low density • - used in cars, Spark plugs boat engines, lawnmowers, etc. are all made out of ceramic. • Different forms of ceramics can make excellent insulators, semiconductors, superconductors and magnets. 3 Monomers and Polymers • Plastics are long chain molecules called polymers. • A polymer is a very big molecule made from many small molecules called monomers. • The process in which the monomers join to make a polymer is called polymerisation. • The name of the polymer can be worked out from the name of the monomer. • The term “poly” is put in front of the name of the monomer to name the polymer. • E.g. ethene is polymerised to make polyethene. Plastics can be made by either:1. Addition Polymerisation 2. Condensation Polymerisation 4 Addition Polymerisation Polyethene is an example of an addition polymer. It is made from the monomer ethene. Polyethene forms when a chemical is added which breaks the double bond between the two carbon atoms of ethene to make a very reactive unit. Reactive units join together, end to end and a big molecule or polymer is made. All plastics made by addition polymerisation form when the monomer units join together to give one product, by a series of reactions in which the double bond breaks. When drawing a monomer it has to be in an “H” shape with the double bond in the middle. i.e. H H I I C=C I This would be an ethene monomer I H H 5 A propene monomer would be drawn like this H H H H H I I I I I C = C C I I I I H H C CH3 H C = C Making polypropene :- H H H H H H C = C C = C C = C C C C CH3 CH3 H H H H H H C C C C C C C CH3 C CH3 C CH3 6 CH3 Repeating Unit Part of Polymer 7 Condensation Polymers Condensation polymers are any kind of polymers formed through a condensation reaction— where molecules join together--losing small molecules of water. Polyester is an example of a condensation polymer that contains lots of ester links. ESTER LINK It can be made by reacting – alcohols with two -OH groups, one at either end of the molecules and acids with two –COOH groups, one at either end of the molecule. HO OH Diol HO O O C C OH Diacid • The acid group loses an –OH and the alcohol loses an –H to form water and a new bond8forms between the monomer units. Forming a Condensation Polymer Polyesters are a type of condensation polymer HO OH HO O O C C OH HO OH HO O O C C OH • The polyester molecules can continue to grow in both directions. • The acid and alcohol group join together. • The acid group loses an –OH and the alcohol loses an –H to form water and a new bond forms between the monomer units. O O O O C C O O O O C C O • These OCO groups are called ester links or ester groups. • These groups identify this chain as a polyester. 9 O O O C C 10