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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.
graph TD
TP["Thermoplastics<br/>can be remelted & reshaped"]
TP --> AC["Acrylic / PMMA<br/>clear, hard, brittle<br/>signs, baths, displays"]
TP --> PP["Polypropylene / PP<br/>tough, fatigue resistant<br/>chair shells, food containers"]
TP --> HD["HDPE<br/>tough, chemical resistant<br/>bottles, pipes, chopping boards"]
TP --> PET["PET<br/>clear, tough, food-safe<br/>drinks bottles, fibre"]
TP --> AB["ABS<br/>tough, impact resistant<br/>casings, LEGO, helmets"]
TP --> NY["Nylon / PA<br/>strong, low friction<br/>gears, bearings, ropes"]
TP -.processed by.-> PR1[Injection moulding]
TP -.processed by.-> PR2[Vacuum forming]
TP -.processed by.-> PR3[Blow moulding]
TP -.processed by.-> PR4[Extrusion]
TP -.processed by.-> PR5[Line bending]
| 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.
| Property | Detail |
|---|---|
| Clarity | Transparent and glossy |
| Strength | Good tensile strength; tough |
| Gas barrier | Excellent — keeps carbonation in fizzy drinks |
| Weight | Lightweight |
| Recyclability | The most recycled plastic in the world (recycling code 1) |
| Food safety | Food-safe |
Uses: Drinks bottles (water, fizzy drinks), food packaging (salad containers, fruit punnets), polyester fabric (clothing), electrical insulation, carrier trays.
| Property | Detail |
|---|---|
| Impact resistance | Excellent — tough and resilient |
| Surface finish | Smooth, glossy surface; can be painted and plated (chrome effect) |
| Stiffness | Good rigidity |
| Machinability | Machines well; good for injection moulding |
| 3D printing | One of the most common FDM filament materials |
| Chemical resistance | Moderate |
| Temperature resistance | Good — higher than many thermoplastics |
Uses: LEGO bricks, car dashboards and interior trim, motorcycle helmets, computer keyboard keys, 3D printing filament, power tool housings, luggage, musical instrument cases.
AQA Exam Tip: ABS is the material used for LEGO bricks — this is a very commonly referenced example. ABS provides the excellent impact resistance and precise dimensional accuracy that LEGO requires.
| Property | Detail |
|---|---|
| Strength | Very strong, especially in tension |
| Wear resistance | Excellent — self-lubricating surface |
| Weight | Lightweight |
| Flexibility | Good — can be made into fibres or solid shapes |
| Chemical resistance | Good |
| Moisture absorption | Absorbs water, which can reduce dimensional stability |
| Friction | Low coefficient of friction — ideal for moving parts |
| Melting point | Relatively high (~220 °C) |
Uses: Gear wheels (nylon gears are quieter than metal gears), bearings, bushings, cable ties, combs, clothing (stockings, sportswear), fishing line, toothbrush bristles, hinges, zip fasteners, 3D printing (SLS).
| Thermoplastic | Key Property | Primary Use | Recycling Code |
|---|---|---|---|
| Acrylic (PMMA) | Transparent, hard, UV-resistant | Signs, displays, aircraft windows | 7 (Other) |
| Polypropylene (PP) | Living hinge, chemical-resistant | Food containers, bottle caps | 5 |
| HDPE | Strong, chemical-resistant | Milk bottles, pipes, crates | 2 |
| PET | Clear, excellent gas barrier | Drinks bottles, food packaging | 1 |
| ABS | Tough, glossy, impact-resistant | LEGO, car parts, 3D printing | 7 (Other) |
| Nylon (PA) | Strong, self-lubricating, wear-resistant | Gears, bearings, clothing | 7 (Other) |
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