- POLYMERS such as rubbers and plastics are organic structures.
- They can be natural, modified or synthetic.
- Synthetic polymers are produced from coal, gas and oil.
- Most plastics have good chemical and electrical resistance.
- They are light in weight, durable and have good strength to weight ratios.
PLASTICS ARE DIVIDED INTO TWO GROUPS
THERMOPLASTICS (page 20&21 of AQA text book is a table of plastics)
- ONCE CURED, THEY CAN NOT BE SOFTENED. HAVE A HARDER SURFACE THAN THERMOPLASTICS SO ONLY A FEW ARE USED FOR CONSTRUCTION PURPOSES IN SCHOOLS.
- Made up of molecules that are heavily cross-linked.
- This results in a rigid molecular structure.
- Although they soften the first time when heated, they then become permanantly stiff and CAN NOT BE RESHAPED.
- CAN BE SOFTENED BY HEATING AND HARDENED BY COOLING.
- Each time a thermoplastic is reheated it will return to its original flat state.
- Unless it has been damadged by over heating or over stretching.
- They are made up of lines of long chain molecules.
- Have very few cross linkages.
- This allows them to soften when heated so they can bend in different shapes and become stiff again when cooled.
- This process can be repeated many times.
ACRYLIC: (also known as perspex). Most common plastic in school workshops. Used for vacuum forming. Residstant to most acids and weather conditions.
POLYTHENE: Can be moulded into almost any form. Used for making bottles, bowls, toys etc. Available in large sheets. HIGH DENSITY- rigid and hard, used for machine parts . LOW DENSITY - tough and flexible, used for bottles.
POLYVINIL CHLORIDE: Better known as PVC. Tough material, can be purchased as a hard or flexible material. Can be welded or bonded with a glue. Used for water pipes, rain coats etc.
POLYTHENE: The most common plastic in everyday life. Used for plastic bottles, shopping bags, shampoo bottles and childrens toys.
POLYCARBONATE: Machines well and can be solvent bonded or welded. Tough and resistant to damadge, ideal for mobile phones. Used as an insulator, comes in a range of colours.
More useful plastics
STYROFOAM: Lightweight dense foam. Easy to cut and shape with saws and files. Is ideal for model making.
EXPANDED POLYSTYRENE: Efficent insulator used in cavity walls and decorative tiles. Can also be used for model making.
NYLON : Used in engineering to make gears & bearings. It's oily nature means thst friction between two moving nylon parts is reduced.
What forms are plastics available in?