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Material Science Y1 > Plastics and properties > Flashcards

Plastics and properties Flashcards

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1
Q

What are the different types of polyethylene?

A

1) Low Density PE - LDPE
2) Linear Low Density PE - LLDPE
3) High Density PE - HDPE
4) Ultra High Molecular Weight PE - UHMWPE

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2
Q

Structure of polyethylene?

A

simple chains of (CH2) monomers

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3
Q

Linear Low Density PE is a copolymer of what?

A

ethylene and small amounts of 1-hexene/1-octene/1-butene

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4
Q

Advantages of PE (5)

A

1) Good Processability
2) Biocompatible
3) Flexible
4) Many purposes
5) Low Oxygen Permeability

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5
Q

Disadvantages of PE (6)

A

1) High Thermal Expansion
2) Poor weathering Resistance
3) Subject to stress cracking (more ordered PEs)
4) Inert
5) Flammable
6) Low strength/Stiff

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6
Q

why is low O2 permeability an advantage?

A

for food packaging to keep foods like meat fresh for longer

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7
Q

Applications of PE:

A
  • Mostly Packaging
  • Piping
  • Bottles
  • Bags
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8
Q

What is UHMWPE and what can it be used for?

A
  • This is extremely linear and very strong (fewer branches) PE
  • This is spun into fibres for protective armour, and long lasting prosthetics
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9
Q

Why can polypropylene have 3 different structures?

A

The methyl group can be arranged to form Isotactic/Syndiotactic and Atactic PP

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10
Q

Which type of PP is in highest demand?

A
  • iPP because its regularity it forms a highly crystalline structure which forms plastics
  • sPP and aPP are more amorphous so have fewer uses, apart from adhesives
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11
Q

what catalyst is used to make PP?

A

Ziegler-Natta Catalysts

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12
Q

what shape does iPP, aPP and sPP make?

A
  • All fold into helices
  • iPP and aPP fold into amorphous chains
  • sPP folds into crystalline structures like zigzag planar
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13
Q

Structural properties of PP:

A
  • more susceptible to oxidation than PE

- can resist attack of polar substances eg, soap, alcohol

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14
Q

additional properties of iPP:

A
  • good mechanical properties eg stiffness
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15
Q

additional properties of sPP:

A
  • has better impact strength and clarity
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16
Q

Thermal properties of PP:

A
  • can withstand high temps for continuous periods
  • Tg is 0 degrees, so rubbery at room temp
  • Elastic Modulus declines with temperature
17
Q

melting points of iPP and sPP:

A 
iPP = 160-170 degrees C
sPP = 130 degrees C
18
Q

How can we lower Tg of PP?

A

Add specific monomers which reduce crystallinity and Tg

19
Q

Why is PP a good living hinge?

A
  • they can be folded millions of times before failure
20
Q

what is a living hinge?

A

1 piece material hinges that allow opening and closing, eg plastic wallets

21
Q

what is the structure of polystyrene?

A
  • chain of styrene monomers

- each monomer has a benzene group

22
Q

what is the most common type of polystyrene out of the 3? and why?

A
  • Atactic polystyrene is the most common

- made by free radical polymerisation which is random

23
Q

how can you synthesise syndiotactic and isotactic PS?

A

Using a metallocene catalyst but these have fewer uses

24
Q

properties of PS?

A
  • Tg ~ 100 degrees
  • low density
  • resistant to dilute acids and alcohols but not ketones
  • poor weathering resistance
  • easily recyclable and cheap
25
Q

what are the 3 different plastics that are modified polystyrene?

A
  • HIPS (High impact PS)
  • SAN (Styrene acrylonitrile)
  • ABS (Styrene with acrylonitrile and PB)
26
Q

How is HIPS made?

A

1) Mixing chains of PB with PS
2) Combining PB and PS to become a copolymer
3) Grafting PB onto PS chains like branches

27
Q

what does PB (Polybutadiene) add in terms of properties when added with PS?

A

Increases impact resistance hence HIPS

28
Q

How is SAN made?

A

copolymerisation of styrene with acrylonitrile

29
Q

what does adding acrylonitrile to PS do?

A

improves strength and chemical resistance

30
Q

what is ABS?

A

The copolymer of Styrene and acrylonitrile blended or grafted with PB

31
Q

properties of ABS:

A

Strong and chemically resistant due to Acrylonitrile
Tough and impact resistant due to PB
also heat resistant and glossy

32
Q

which modification of PS is the most brittle and which is the toughest?

A

most brittle - SAN

most tough - HIPS

33
Q

PS applications

A
  • packaging, electrical goods

- disposables which are sterilised with gamma

34
Q

applications of expanded PS:

A

insulation in houses and packaging protection

35
Q

applications of SAN:

A

optical fibres, battery cases, kitchen wear

36
Q

applications of ABS

A

car bumpers, lego, plumbing

Material Science Y1 (4 decks)

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