Polymers Flashcards

1
Q

What is a polymer?

A

Extremely long chains, can be linear or branched

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2
Q

Describe linear chains

A

Just have primary and secondary bonds

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3
Q

Describe cross linked chains

A

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

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4
Q

Describe semicrystalline

A

Chain of polymers folded in an orderly pattern

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5
Q

Describe amorphous

A

Chain of polymers that are folded randomly

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6
Q

What mechanical property does high amorphous provide?

A

High toughness

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7
Q

What mechanical property does crystallinity provide?

A

High tensile strength

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8
Q

What are tie molecules?

A

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

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9
Q

What is Tg?

A

Glass transition temp, characteristic of amorphous materials

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10
Q

What is Tm?

A

Melting temp, characteristic of crystalline materials

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11
Q

What happens below and above Tg?

A

Below polymer is brittle, above polymer is ductile

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12
Q

What do plasticisers do?

A

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

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13
Q

What are thermoplastics?

A

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

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14
Q

What are thermosets?

A

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

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15
Q

What are elastomers?

A

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

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16
Q

Describe the structure of thermoplastics

A

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

17
Q

Describe the structure of thermosets

A

Mainly amorphous, covalent bonds between lightly cross-linked chains

18
Q

Describe the structure of elastomers

A

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

19
Q

Describe the process of extrusion

A

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

20
Q

Describe the process of injection moulding

A

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

21
Q

Describe the process of blow moulding

A

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

22
Q

Describe the process of film blowing

A

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

23
Q

Describe the process of melt spinning

A

Same as extrusion, molten plastic falls die forming thin fibres