Polymers

Question 1

How are the properties of polymers determined?

Answer 1

They are determined by how their long molecules are arranged and bond to each other

Question 2

Give examples of polymers in nature

Answer 2

silk, wool, cellulose, chitin, keratin, proteins and natural rubber (sap from the rubber tree

Question 3

Name the 7 manufacturing methods for thermoplastics

Answer 3

Injection moulding, extrusion, blow moulding, rotational moulding, thermoforming/vacuum forming, calendaring, 3D printing

Question 4

Name the 4 manufacturing methods for thermosets

Answer 4

Compression moulding, transfer moulding, lamination, pultrusion

Question 5

What are the main properties of thermoplastics?

Answer 5

They are recyclable
Low melting temperature
Easy moulded
Can be melted and reshaped
low tensile strength 
soft, flexible
suffer from creep

Question 6

List examples and full names of the 7 most common thermoplastics

Answer 6

1. Polyethylene (PE)
2. Polypropylene (PP)
3. Polystyrene (PS)
4. Acrylic (PMMA)
5. Nylon (polyamides)
6. PVC (poly vinyl chloride)
7. ABS (acrylonitrile butadiene styrene)

Question 7

What are the main properties and features of thermosetting plastics?

Answer 7

Non-recyclable
stiffer, rigid
higher melting temp
higher tensile strength
Can only be moulded once
Cannot be melted and reshaped 
Good insulator of electricity and heat

Question 8

List examples and full names of the 5 most common thermosetting plastics

Answer 8

1. Phenol-Formaldehyde (PF) (Bakelite)
2. Urea Formaldehyde (UF)
3. Melamine formaldehyde
4. Polyurethanes
5. Epoxy resins

Question 9

What are the main properties and features of elastomers?

Answer 9

elastic, rubber-like
Return to original shape when stretched
Soft and flexible 
Can seal against gas and liquid 
low tensile strength 
can be thermoset or thermoplastic

Question 10

List examples and full names of the 4 most common elastomers under 2 separate titles (thermoplastics and thermosets)

Answer 10

Thermoset elastomers:

1. Vulcanized natural rubber
2. Polybutadiene (synthetic rubber)
3. Neoprene, silicone rubbers

Thermoplastic elastomers:
4. EVA, Spandex (lycra)

Question 11

Explain the structure of thermoplastics in terms of appearance, bonding and effects of heating

Answer 11

• Linear or branched chains
• Weak secondary bonds between polymer chains (Van der Waals)
• These weak bonds can be broken by heat, so the plastic becomes soft as the polymer chains slip over each other.
• When cooled, the weak forces hold the chains together again

Question 12

Explain the structure of thermosets in terms of appearance, bonding and effects of heating

Answer 12

• cross-linked chains
• Strong primary bonds between the chains and cross-links
• This lattice of strong chemical bonds makes thermosets stiffer, stronger, and more resistant to heat
• These long chemical bonds cannot be broken by heat, so the thermosets do not soften and reshape (they just burn).

Question 13

Explain the structure of elastomers in terms of appearance, bonding and effects of heating

Answer 13

• Coiled chains
• Can stretch out and return
• Thermoplastic elastomers (TPEs) can be heat-softened and re-shaped
• Thermoset elastomers have cross-links between the polymer chains so they are stiffer, stronger, and can’t be heated & reshaped

Question 14

What can some polymers have that makes them return to their original shape when heated?

Answer 14

They can have shape memory

Question 15

What is shape memory?

Answer 15

Some polymers return to their original shape when heated