Elastomers and Thermosets

Question 1

what is an elastomer?

Answer 1

an amorphous polymer with a Tg less than Troom, and can reversibly extend up to 700-900%

Question 2

what is vulcanising?

Answer 2

reacting Rubber with sulphur to form sulphide crosslinks between polymer chains, this is a type of curing

Question 3

what is curing?

Answer 3

Hardening/toughening a polymer by adding crosslinks between polymer chains

Question 4

what happens to rubber over time?

Answer 4

rubber degrades and loses flexibility and elasticity

Question 5

what are thermoplastic elastomers (TPE)?

Answer 5

Block copolymers formed by 3 or more blocks where the polymers are not miscible and some form hard segments due to high crystallinity of high Tg and some form soft segments which are amorphous having low Tg

Question 6

What 2 types of hard segments can you get in a TPE?

Answer 6

A hard crystalline segment or an amorphous segment with a very high Tg so is hard at Troom

Question 7

give 2 examples of TGE?

Answer 7

Lycra and SBS

Question 8

applications of elastomer:

Answer 8

tissue engineering, eg providing walls to the heart

Question 9

how do you make a thermoset?

Answer 9

1) mix monomers
2) allow the mixture to cure creating crosslilnks
3) when fully cured we have a thermoset

Question 10

how can curing be stopped?

Answer 10

lower the temperature

Question 11

what is Gelation?

Answer 11

as curing occurs more crosslinks form which increases viscosity, when the maximal number of crosslinks have formed and all the chains are linked the mixture has a gel like consistency known as the gel point

Question 12

what is Vitrification?

Answer 12

If the temp required to cure the thermoset is equal to Tg, then the material will become glassy

Question 13

how do we avoid vitrification?

Answer 13

cure at a higher temperature, above the material Tg

Question 14

difference between shelf life and pot life:

Answer 14

shelf life indicates how long the thermoset can be stored, whereas pot life is the time taken for the mixed system to double in viscosity

Question 15

advantages of thermosets:

Answer 15

• starting material are low viscous so easy to handle
• youngs modulus and tensile/flexural strength is high
• high temp resistance
• low pressure required when moulding as they are viscous liquids

Question 16

Disadvantages of thermosets:

Answer 16

• contains some reactive toxic and volatile components
• Poor impact strength and low elongation at break
• difficult to recycle as they cannot be remelted

Question 17

what is thermal recycling:

Answer 17

• using heat to break down composites to reuse them

Question 18

what is mechanical recycling?

Answer 18

• shredding materials down into a powder to reuse

Question 19

applications of thermosets:

Answer 19

• biomedical scaffolding
• epoxy resin adhesive
• formaldehyde laminates and electrical fittings

Question 20

what is a biobased polymer with an example:

Answer 20

A polymer in which the monomer is derived from a renewable source
- Nylon 11, derived from caster oil

Question 21

what is a biodegradable polymer with an example:

Answer 21

A polymer which will decompose in aerobic or anaerobic conditions by microorganisms due to the weaker C-O bond in the back bone
- PLA or PCL

Question 22

what is a Biocompatible polymer with an example:

Answer 22

A polymer that can be used to replace living tissue p-PVC