Polymers

Question 1

Thermoplastics

Answer 1

Many long linear chains to form the structure, with no cross-links. Able to be melted and dissolved, as the lack of cross-links means the movement of chains isn’t restricted. Fabrication involves melting, shaping and cooling.

Question 2

Thermosets

Answer 2

A 3-D network of chains and cross-links. They cannot be melted or re-shaped as the cross-links resist chain motion at high temperatures, also cannot be dissolved. Fabrication involves a chemical reaction.

Question 3

Amorphous Polymers

Answer 3

Those with a random molecular structure and no long range order. They have a glassy behaviour, being both hard and brittle.
They all have a Tg, a point at which the properties change.

Question 4

Semi-crystalline thermoplastic

Answer 4

A two-phase material with both crystalline and amorphous regions. the crystalline regions hold the material together when it is above the Tg. Tie chain molecules in the amorphous material connect the adjacent lamellae. There is now a melting point, which is a characteristic of the crystalline regions.

Question 5

Two regions of behaviour

Answer 5

The hard region, below Tg of the amorphous stage

The ductile region, between Tg and Tm.