Polymers

Question 1

What is a polymer?

Answer 1

Extremely long chains, can be linear or branched

Question 2

Describe linear chains

Answer 2

Just have primary and secondary bonds

Question 3

Describe cross linked chains

Answer 3

Covalent bonds inside and in between the chain, makes the structure more rigid

Question 4

Describe semicrystalline

Answer 4

Chain of polymers folded in an orderly pattern

Question 5

Describe amorphous

Answer 5

Chain of polymers that are folded randomly

Question 6

What mechanical property does high amorphous provide?

Answer 6

High toughness

Question 7

What mechanical property does crystallinity provide?

Answer 7

High tensile strength

Question 8

What are tie molecules?

Answer 8

They start in the crystalline region, pass through amorphous region and rejoin the next crystalline region, (they hold the structure together)

Question 9

What is Tg?

Answer 9

Glass transition temp, characteristic of amorphous materials

Question 10

What is Tm?

Answer 10

Melting temp, characteristic of crystalline materials

Question 11

What happens below and above Tg?

Answer 11

Below polymer is brittle, above polymer is ductile

Question 12

What do plasticisers do?

Answer 12

Change the Tg and therefore change the mechanical properties at different temps

Question 13

What are thermoplastics?

Answer 13

A material that can be moulded and shaped when heated (can be recycled)

Question 14

What are thermosets?

Answer 14

Once formed, does not become mouldable or or soften when reheated

Question 15

What are elastomers?

Answer 15

Any material that can be stretched multiple times its original length without breaking

Question 16

Describe the structure of thermoplastics

Answer 16

Can be amorphous or semi-crystalline, between linear chains are Van der Waals or linear bonds

Question 17

Describe the structure of thermosets

Answer 17

Mainly amorphous, covalent bonds between lightly cross-linked chains

Question 18

Describe the structure of elastomers

Answer 18

Mainly amorphous, covalent and Van der Waals bonds between fully cross-linked chains

Question 19

Describe the process of extrusion

Answer 19

Hopper feeds pellets into a turning screw which passes them through a heater, the molten plastic is then forced through a die to form extrudate

Question 20

Describe the process of injection moulding

Answer 20

Hopper feed pellets into turning screw which passes through a heater, the molten plastic is then injected into the molten mould

Question 21

Describe the process of blow moulding

Answer 21

Same as extrusion, molten plastic then forms a parison which gets expanded into the shape of the mould

Question 22

Describe the process of film blowing

Answer 22

Same as extrusion, molten plastic forms air bubble which is then rolled into sheets

Question 23

Describe the process of melt spinning

Answer 23

Same as extrusion, molten plastic falls die forming thin fibres