Thermoforming and Thermosetting Polymers
Some plastics melt and remould again and again; others set hard for good. Sort thermoforming from thermosetting polymers, meet acrylic, HIPS, polyester resin and urea formaldehyde, and pick the right one for each job.
Justify the choices, the way you are assessed
Free interactive practice on the decisions the assessment actually asks you to justify.
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Two families of plastic
Polymers, or plastics, come in two great families. Some can be melted and remoulded again and again; others set hard once and keep their shape for good. Knowing which is which, thermoforming or thermosetting, is the key to almost every polymer question in Design and Technology.
The language of polymers
Four ideas run through this module:
Thermoforming or thermosetting?
The two families behave very differently when they are heated.
Can it be remoulded?
What happens if you strongly heat a thermosetting polymer that has already set?
- It stays solid and does not remould; it may char or burn
- It softens and can be moulded into a new shape
- It turns back into a liquid resin to reuse
- It becomes a thermoforming polymer
Match the polymer to its use
- Acrylic
- High impact polystyrene
- Polyester resin
- Urea formaldehyde
- Clear signs and light units, where you need a rigid see-through material
- Vacuum-formed packaging and yoghurt pots
- Boat hulls and panels, set hard with glass fibre
- Electrical fittings and plug sockets
Which are thermoforming?
Select the TWO thermoforming polymers.
- Acrylic
- High impact polystyrene
- Polyester resin
- Urea formaldehyde
What polymers are good at
Many polymers share three useful properties. They are good insulators of heat, good insulators of electricity, and can be tough, resisting knocks without breaking. These properties are why urea formaldehyde, a thermosetting polymer, is chosen for electrical fittings: it will not conduct electricity and will not soften near warm wiring.
Polymers in words
A polymer that can be reheated and _____ many times is thermoforming, while a _____ polymer sets permanently. Acrylic is a common _____ polymer, and polyester _____ is a thermosetting one. Both kinds are good _____ of heat and electricity.
Vacuum forming
Vacuum forming shapes a thermoforming polymer like HIPS. Put the steps into the right order.
- Place a mould on the bed of the vacuum former
- Clamp a sheet of HIPS above the mould
- Heat the sheet until it is soft and floppy
- Raise the mould up into the softened sheet
- Turn on the vacuum to suck the sheet onto the mould
Which polymer reshapes?
Tap the TWO statements that are TRUE about polymers.
- Thermoforming polymers can be reheated and reshaped many times.
- Thermosetting polymers can be melted down and remoulded.
- Urea formaldehyde is a good insulator of electricity.
- All polymers conduct electricity well.
- Acrylic sets permanently and can never be reshaped.
Why urea formaldehyde?
Why is urea formaldehyde a good choice for an electrical plug socket?
- It is a good electrical insulator and will not soften with heat
- It conducts electricity to complete the circuit
- It can be melted and remoulded on site
- It is the cheapest metal available
Choose the polymer
A designer must pick the right polymer for three products. Help them choose.
- A clear, rigid cover for a shop sign that must let light through. Which polymer?
- A yoghurt pot to be vacuum formed in large numbers. Which polymer?
- The casing for an electrical switch that must resist heat and not conduct. Which polymer?
Explain the difference
Explain the difference between thermoforming and thermosetting polymers. Write in full sentences and use named examples.
- Explain what a thermoforming polymer is and give a named example
- Explain what a thermosetting polymer is and give a named example
- Explain what happens to each type when it is heated
- Explain one product each type suits and why