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This lesson covers thermoplastics — polymers that can be repeatedly heated and reshaped. Thermoplastics are a major topic in AQA GCSE Design and Technology (8552), Section 3.1.6, and are among the most versatile materials available to designers.
Thermoplastics are polymers with long-chain molecules held together by weak intermolecular forces. When heated above their softening point, the chains can slide past each other, allowing the material to be reshaped. When cooled, it solidifies again. This process can be repeated multiple times.
| Property | Detail |
|---|---|
| Appearance | Clear, transparent (transmits 92% of visible light — better than glass) |
| Hardness | Hard surface; scratches can be polished out |
| Strength | Stiff but can shatter on impact (brittle) |
| Weight | Half the weight of glass |
| Colours | Available in a wide range of transparent, translucent and opaque colours |
| Machinability | Easily cut, drilled, laser-cut, polished and line-bent |
| Weathering | Excellent UV resistance; does not yellow over time |
Uses: Shop signs, display cases, aircraft windows, fish tanks, shower screens, car rear lights, point-of-sale displays, picture frames, school D&T projects.
AQA Exam Tip: Acrylic is the most commonly used thermoplastic in school workshops. Know that it can be line-bent using a strip heater, laser-cut for precise shapes and polished to restore a clear finish.
| Property | Detail |
|---|---|
| Flexibility | Excellent — can be bent repeatedly without breaking (living hinge) |
| Chemical resistance | Excellent — resists acids, alkalis and solvents |
| Weight | Very lightweight (lowest density of common plastics) |
| Food safety | Food-safe; widely used in food packaging |
| Fatigue resistance | Outstanding — the "living hinge" property |
| Melting point | Relatively high for a thermoplastic (~160 °C) |
Uses: Food containers (takeaway boxes, yoghurt pots), bottle caps, living hinges (flip-top lids), medical equipment (syringes — sterilisable), rope, carpet fibres, car bumpers, plastic chairs.
A living hinge is an extremely thin section of polypropylene that can be bent back and forth thousands of times without breaking. Tic Tac boxes and shampoo bottle flip-tops use living hinges.
| Property | Detail |
|---|---|
| Strength | High stiffness and strength for a plastic |
| Chemical resistance | Excellent — resists most chemicals |
| Impact resistance | Good |
| Weight | Lightweight |
| Recyclability | Widely recycled (recycling code 2) |
| Food safety | Food-safe and approved for drinking water |
Uses: Milk bottles, detergent bottles, plastic bags (supermarket carriers), water pipes, plastic crates, chopping boards, playground equipment, recycling bins.
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