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Nonmetallic MaterialsMaterials that do not have the properties of, or do not contain, metaland that are able to combine with hydrogen to form stablecompounds, acids, acidic oxides, and anions.Polymers has a repeating structure, usually based on a carbonbackbone. The repeating structure results in large chainlikemolecules. In each polymer molecule, the atoms are bound togetherby covalent bonds.
Types of polymers• Linear polymers polyethylene, polyvinyl chhloride, polystyrene, nylon, teflon2. Branched polymers elastomers or polymeric rubbers3. Crosslinked polymers thermosetting polymers4. Network polymers epoxies
Polymers are useful because they are:3. lightweight4. corrosion resistant5. easy to process at low temperatures6. inexpensiveThe mechanical properties of polymers:10. low strength11. high toughnessThe distinct properties of polymers is they are poor conductors of electricity and heat, which makes them good insulators.
Physical properties of polymers2. Composed of very large molecules3. Low stiffness/elasticity4. Low tensile and compressive strengths5. Deformation is sensitive to temperature6. Crystalline structure7. Low thermal and electrical conductivity – good conductor8. Creep at room temperature9. Low temperature makes plastics brittle10. Plastic deformation
Thermoplastics2. Soften when heated and harden when cooled3. Varying degree of ductility4. Can be recycled5. Can not withstand high temperatureThermosets2. Become permanently hard after the initial heating- cooling cycle3. Brittle4. Can not be recycled5. Can withstand high temperature
EXAMPLE THERMOPLASTICS1. Acrylic (Known also as PERSPEX) is the most common plasticused. It is purchased usually in the form of sheets and comes in a rangeof colours. It can be translucent (e.g. smoked), transparent or opaque. Itis resistant to most acids and weather conditions.2. Polyethylene or Polythene (PE) can be moulded into almost anyform due to its excellent moulding qualities. Used for the productionof bottles, bowls, toys, tube etc... It is available in large sheets. Thereare two types: High density which is rigid and hard, and low densitywhich is tough and flexible. Machine parts are generally made fromhigh density polystyrene whilst bottles are made from the low densitypolystyrene.
3. Polyvinyl Chloride also known as PVC. It is a tough material whichcan be purchased as a hard material or alternatively a flexible form. Itcan be welded or bonded with an adhesive. It has a range of usesincluding water pipes, raincoats, long play records, coating onelectrical wires and many more.4. Polypropylene (PP) is used for carpet fibers, ropes, liquid containers(cup, buckets, tanks), pipes, etc5. Polystyrene (PS) is used for pakaging foams, egg cartoons, lightpanels, electrical appliance components, etc
EXAMPLE THERMOSETTING PLASTICS1. Many adhesives (glues) are thermosetting plastics. A good exampleis ‘Araldite’ which is an epoxy resin that hardens when a secondchemical is added (a catalyst). It will bond most materials includingwoods and metals as well as some plastics.2. Polyurethane. This forms the basis of many paints and varnishesbecause it is very tough and has water resistant qualities.3. Melamine Formaldehyde is used in the production of plasticlaminates because of its smooth surface and hygienic qualities. It isalso used in electrical plugs and sockets because it can be cast and it isan excellent insulator.4. Polyester resins. If resins are combined with a material such as fibreglass the result is a very tough material that can resist impact. Thistype of material is known as a glass reinforced plastic (GRP) and isused in car body repairs, sailing boats, corrugated sheet because of itslightness, toughness and resistance to water.
MORE USEFUL PLASTICSStyrofoam is a light-weight dense foam. It is easy to shape with saws,files and abrasive paper and is ideal as a model making material.Expanded Polystyrene is an efficient insulator used in cavity walls andas decorative tiles and covering on ceilings. It can also be used forbasic model making.Nylon is used in engineering to make gears and bearings. It’s oilynature means that friction is reduced between moving parts madefrom nylon.