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Plastics Flashcards

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1
Q

First synthetic plastic? What was it made from?

A

Bakelite (1907)

phenol + formaldehyde -> cross-linked resin

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2
Q

Define ‘plastics’

A

synthetic polymers + additives

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3
Q

What is a polymer?

A

large molecule made of repeating units (monomer)

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4
Q

What is a monomer?

A

molecule that combines with others (same or different) w/ covalent bonds -> forms polymer

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5
Q

Current synthetic polymers are made from _____. What elements are they made of?

A

petrochemicals

C, H, O (sometimes Cl, F, N, Si, P, S)

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6
Q

2 sources of petrochemicals?

A

raw natural gas

crude oil

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7
Q

How are the materials for plastic synthesis obtained from raw natural gas?

A

gas -> processing (release methane) -> produce ethane, propane, butane
STEAM CRACKER -> ethylene, propylene, benzene, butadiene, byproducts

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8
Q

How are the materials for plastic synthesis obtained from crude oil?

A

oil -> refinery -> Naphtha, gas oil -> STEAM CRACKER -> ethylene, propylene, benzene, butadiene, byproducts

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9
Q

What does the Steam Cracker do?

A

uses catalyst to process raw hydrocarbon materials -> monomers with doub bond

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10
Q

What is “BTX?”

A

Benzene, toluene, xylenes (produced from crude oil -> refining)

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11
Q

What is BTX used for?

A

processed into monomers for polystyrenes, nylons, polyesters

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12
Q

The chemical process that joins monomers is called ______. What rxn can be used? (2)

A

polymerization

addition
condensation

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13
Q

2 types of polymers (based on monomer content)?

A

Homopolymer (1 monomer type)

Copolymer (2+ monomers types)

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14
Q

3 descriptive characteristics of polymers (and monomers)

A

molecular weight
chemical composition
molecular structure

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15
Q

How does molecular weight/size affect melting point?

A

longer chain length (larger size) -> increased melting point

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16
Q

Why does polyethylene have a higher melt point than wax?

A

much longer chain length (molecule size) - 70 vs 1500

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17
Q

The higher the molecular weight, the greater the ________ (5)

A 
melt point
tensile strength
hardness
stiffness
barrier properties
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18
Q

True/False: increased molecular weight of a polymer will increase solubility

A

false: will decrease solubility

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19
Q

What monomers is polyethylene made of? what properties does it have?

A

ethylene

poor O2 barrier, good moisture barrier

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20
Q

What monomers is polyvinyl alcohol made of? What properties does it have?

A

vinyl alcohol

good O2 barrier, poor moisture barrier (O2 soluble)

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21
Q

Copolymer made from PE and PVA:

What is the advantage?

A

ethylene-vinyl alcohol

excellent O2 barrier, reduced water solubility (properties from each type)

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22
Q

Why is PVA a poor moisture barrier?

A

water soluble (OH groups)

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23
Q

What is the proportion of PE vs PVA in ethylene vinyl alcohol? why is this important?

A

27-48% PE (52-73% PVA)

properties will be shifted towards the polymer with higher %

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24
Q

what is polarity?

A

how electrons are shared:
equal sharing = no dipole moment = nonpolar
unequal sharing = dipole (‘charged’) = polar

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25
Q

polar molecules are attracted to ____ and not attracted to _____

A

polar molecules

nonpolar molecules

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26
Q

water is (polar/nonpolar). CO2 is (polar/nonpolar)

A

polar

nonpolar

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27
Q

What is ‘like dissolves like?’

A

molecules with same polarity -> soluble

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28
Q

What is a complete barrier? what materials qualify?

A

prevents substances from passing through (moisture, gas)

glass, metal

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29
Q

Are plastics complete barriers?

A

No; selective permeability

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30
Q

Why are most plastics generally better as moisture barriers than gas barriers?

A

water = polar molecule (repelled by nonpolar plastic)

O2 and CO2 = nonpolar, small -> pass through easier

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31
Q

What are the nonpolar plastics? (4)

A

PE, PP, PS, PTFE

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32
Q

What are the polar plastics? (3)

A

Polyester, Polyamide, PVC

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33
Q

Why is molecular shape important?

A

determines packing of molecules (amorphous or crystalline)

affects clarity, melt point, barrier properties, stiffness…

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34
Q

Regular shapes can be packed into ___ structures. Irregular shapes become _____ structures.

A

crystalline

amorphous

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35
Q

True/False: melted polymers can be amorphous or crystalline

A

False; all are amorphous when melted

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36
Q

How does the cooling process affect structure formation?

A

rapid cooling -> amorphous

slow cooling -> crystalline

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37
Q

Compare clarity in amorphous vs crystalline:

A

amorphous: clear
crystalline: hazy (unless very small crystals)

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38
Q

T/F: crystalline structures are stiffer then amorphous structures

A

true

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39
Q

Which is a better barrier, crystalline or amorphous structures?

A

crystalline

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40
Q

T/F: amorphous structures have a higher melt point than crystalline

A

False; lower melt point

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41
Q

____ _____ will align molecules, making amorphous structures more crystalline (organized)

A

molecular orientation

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42
Q

Types of molecular orientation: (2)

A

Uniaxial (1 direction)

Biaxial (2 directions)

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43
Q

What are ‘memory’ plastics? How are they made?

A

Shrinkable plastics (when heated)

heat to soften -> stretch -> cool quickly (will retain ‘memory’)

When reheated to same temperature, will shrink

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44
Q

What happens if a plastic is heat stretched, and cooled slowly?

A

becomes heat stable (will not shrink with re-heating)

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45
Q

Most plastics used for food are _____

A

thermoplastics

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46
Q

What are the properties of thermoplastics?

A

soften when heated (no set melt point)
solidify when cooled
can be re-melted
viscoelastic

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47
Q

Examples of thermoplastics (4)

A

polyethylene
polypropylene
polystyrene
polyvinyl chloride

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48
Q

What is a thermoset plastic and its properties?

A

plastic that cannot be melted/re-formed once it is set (polymer chains are crosslinked into 1 giant molecule)

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49
Q

Examples of thermoset polymers: (3)

A

urethane
bakelite
melmac

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50
Q

Can Urethane be used to make shrink-wrap?

A

No; it is a thermoset plastic (cannot be melted/re-formed)

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51
Q

Polyethylene was heat-stretched and cooled quickly. What will happen when it is reheated to the same temperature?

A

shrinkage

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52
Q

What are some plastic additive types? (8)

A 
plasticizer
stabilizer
flame retardant
antistatics
slip agents
foaming agents
pigments
fillers
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53
Q

What is the purpose of plasticizers?

A

increase flexibility & plasticity

reduce flow temperature & hardness

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54
Q

How are plasticizers incorporated into the polymer?

A

expose polymer to plasticizer -> diffuses into polymer network

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55
Q

examples of plasticizers: (5)

A 
phthalate (P4)
di-n-octylphthalate (P5)
tri-n-butyl citrate (P1)
dioctyl adipate (P3)
dioctyl sebacate (P2)
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56
Q

What are stabilizers for?

A

protect from degradation from UV, heat, oxygen

57
Q

examples of plastic stabilizers: (5)

A 
Carbon black, 
TiO, 
hydroxybenzophenone, 
organometallic compounds, 
antioxidants
58
Q

examples of flame retardants: (2)

A

PBDE (poly brominated diphenyl ethers)

Al(OH)3

59
Q

What compounds are used as antistatics?

A

long chain aliphatic amines

60
Q

What is a pelletizer used for?

A

making materials (plastic powder/pellets) for further processing

recycling

61
Q

What is the process of plastic pelleting?

A 
raw materials (resins, hardeners, pigment, flow additive) -> premix
extruder -> cooling belt -> cutter -> grinder (reduce to powder) -> sieve (remove coarse powder)

powder -> packaging manufacture

62
Q

What is plastics extrusion?

A

raw plastic melted -> forced through extruder -> single continuous form

63
Q

Types of extruders:

A 
single screw
twin screw (conical, parallel)
64
Q

main zones of an extruder screw:

A
  1. solids conveying (feeds resin into extruder)
  2. melting (most material is melted, channel gets smaller)
  3. metering (melts last particles, mixes for even temp/composition)
65
Q

What melts the plastic in an extruder? What gives it the shape?

A

heated barrel, intense pressure/friction from screw

forced through die at end

66
Q

The different rotation and alignment patterns for twin screws:

A

intermeshing, non-intermeshing

co-rotating, counter-rotating

67
Q

Plastic can be extruded into what forms?

A

tubing, pipes, sheets, films, specific shapes (structural parts)

68
Q

The resin (raw material) is added to the extruder through the _____

A

feed hopper

69
Q

The product exiting the extruder is called the _____

A

extrudate

70
Q

types of molds connected to extruders?

A

blown mold
injection mold
compression mold (hot press)

71
Q

how does a blown mold work?

A

split mold with parison inside
mold closed -> air blown in -> expands plastic (press against mold)
mold opened -> bottle

72
Q

How does a injection mold work?

A

inject liquid plastic into closed mold

open mold to eject (automatic ejector pins)

73
Q

What is compression molding for plastics?

A

place plastic material (charge) in mold

Use hot press (heat + pressure) -> compress into desired shape

open press to remove

74
Q

What is blown film extrusion?

A

extrude molten plastic through die -> inflate with air -> thin film bubble -> collapse to make film

75
Q

What are the parts of a blown film extrusion process?

A
  1. extruder (molten plastic pumped out)
  2. air forced through tubing die
  3. tenter frame (stabilizes inflated tube)
  4. Collapser (tube -> film)
  5. Chill rollers (annealing/cool slowly under tension)
  6. wind-up roll
76
Q

Why is anealing under tension important in blown film extrusion?

A

reduces residual stresses

prevents shrinkage

77
Q

What is the orientation formed in the blown film structure?

A

bi-axial:
machine direction + transverse direction
(formed during blowing)

78
Q

What is the ‘double bubble’ process?

A

Similar to normal blown film process, but after the first inflation the bubble/tube is preheated and re-inflated (secondary bubble)
-> collapsed, annealed, collected

79
Q

What are the advantages of the double bubble process?

A
  1. cooling extrudate limits crystallization/spherulite growth -> better optical properties
  2. reheating/stretching while maintaining orientation -> better tensile properties
  3. further biaxial orientation
  4. rapid air cooling will freeze orientation formed in stretching
  5. annealing under tension reduces residual stress, prevent shrinkage
80
Q

printing is a ____ treatment

A

surface

81
Q

What affects printability?

A

polarity

additives

82
Q

Printing is improved by: (3)

A

electric discharge (corona)
flame treatment
plasma treatment

83
Q

The density range of plastics:

A

0.9-1.4g/mL

84
Q

List the common 6 plastics from least to greatest density

A 
PP (0.89-0.91)
LDPE (0.91-0.93)
HDPE (0.94-0.97)
PS (1.04-1.08)
PVC (1.35)
PET (1.35-1.4)
85
Q

important properties of plastic to consider for packaging: (7)

A 
density
breakage/sharp edges
sealability
flexibility
strength/durability
permeability (gas, odor, light)
printability
86
Q

The 7 plastic identification codes:

A
  1. PETE
  2. HDPE
  3. V
  4. LDPE
  5. PP
  6. PS
  7. Other
87
Q

What is PETE? How is it produced?

A

polyethylene terephthalate

acid (terephthalic acid) + alcohol (ethylene glycol) => condensation rxn

88
Q

Which plastic has the highest tensile strength?

A

polyethylene terephthalate

89
Q

T/F: PET is a good moisture barrier, but a poor gas barrier

A

false: good moisture barrier AND good gas barrier

90
Q

Disadvantages of PET:

A 
No heat sealability
lack printability (chemical inertness)
91
Q

Advantages of PET:

A 
Stable (low/high temp, humidity)
clarity
chemical resistance
tear resistance
good barrier properties
high tensile strength
92
Q

____ printing can be done for poor-printability materials

A

flexographic

93
Q

How can PET be improved? (2)

A

2 way stretching (bi-orientation)

high-temp crystallization

94
Q

What does 2 way stretching achieve for PET?

A

Improves tensile strength, flexibility, tear strength

95
Q

What does high temp crystallization achieve in PET?

A

improve thermal stability + barrier properties

96
Q

Types of PET:

A

Amorphous (APET)
Crystalline (CPET)
Shrinkable (30%)

97
Q

____ PET is better in heat applications

A

crystalline

98
Q

Applications of PET in food packaging:

A

films, oven trays/pouches, heat shrink film, bottles, thermoformed containers

99
Q

PE is made of ____ monomers. What is the difference between HDPE and LDPE production?

A

Ethylene
HDPE: low pressure + catalyst => linear
LDPE: high pressure + catalyst => Long branched chain

100
Q

How does branching affect properties in PE?

A

increase clarity, elongation

decrease crystallinity, moisture/grease barrier, density, tensile strength, melt point

101
Q

structure/strength properties of HDPE:

A

crystalline, low branching

high stiffness/tensile strength, low impact/tear strength, translucent

102
Q

Barrier properties of HDPE:

A

POOR oxygen barrier, good moisture barrier

103
Q

T/F: HDPE is not stable at low temp

A

False; retains properties at low temp (good for freezer use)

104
Q

Applications of HDPE:

A

Grocery bags, box liners, laminates, containers, tubs, crates/cases, pails/drums

105
Q

T/F: LDPE softens at a lower temp than HDPE

A

True (softens at very low temp)

106
Q

a plastic with a low melt point is good for ______

A

heat sealability

107
Q

advantages of LDPE:

A

heat sealable
non reactive
clarity
elongation (shrink wrap)

108
Q

disadvantages of LDPE:

A

High tear strength
low stiffness
very poor O2 barrier, fair moisture barrier

109
Q

Applications of LDPE:

A

Stretch wrap, heat seal film/coating, bags, liners, shrink film, squeeze bottles, caps/closures

110
Q

What is plastic #3? How is it made?

A

PVC (polyvinyl chloride)
polymerize vinyl chloride monomers (ethylene Cl -> ethylene dichloride -> heat -> vinyl chloride + HCl -> vinyl chloride -> polyvinyl chloride)

111
Q

Advantages of PVC:

A 
excellent clarity
good thermoforming properties
heat-shrinkability 
cling, tear resistance
sealability
chemical resistance
high moisture barrier
moderate gas perm (breathable)
high tensile strength
elongation
printable
112
Q

Applications of PVC:

A

cling film, shrink film, blister packs, portion control packs, chilled packaging, clear/strong bottles and jars

113
Q

What is plastic #5? What is the monomer unit?

A

polypropylene

made from propylene monomers

114
Q

What has a higher softening point, PE or PP?

A

PP

115
Q

advantages of PP over PE:

A

higher softening point (can hot-fill)
better clarity
better barrier (O2, moisture)
better grease resistance

116
Q

describe the structural strength of PP:

A

high tensile strength
low density
resists scratching/cracking
brittle at low temp

117
Q

How can low temperature affect PP?

A

brittleness

118
Q

Is PP printable?

A

yes, after treatment with corona discharge

119
Q

applications of PP:

A

pouches/bags, clear wraps, clear labels, shrink packages, laminates, dairy tubs (no freezer), hot-fill bottles

120
Q

What is plastic #6?

A

polystyrene (styrene monomers)

121
Q

styrene monomers are linked to produce PS through _______

A

free radical vinyl polymerization

122
Q

advantages of PS:

A

Low cost
hard & stiff
crystal clear (transmit all light)

123
Q

disadvantages of PS:

A

Brittle
poor resistance to solvents (reactive, acid damage)
poor barrier (moisture/gas)

124
Q

Of the common plastics, which is the most clear?

A

Polystyrene

125
Q

What are some modified PS types? what qualities do they have?

A

HIPS (high impact PS): with rubber -> better impact strength
EPS (expanded PS): foamed with hexene/N2 -> better insulation
OPS (oriented): orientation increases strength (but not WVTR)

126
Q

How is styrofoam made?

A

expanded PS: foam with hexene and N2 initiator -> better insulation (but doesn’t improve gas barrier properties)

127
Q

PS applications:

A

Labels, window panels for bag/boxes, soak pads (meat), boxes, jars, liners, tray/tub/protective packaging, cups

128
Q

What plastics are classified under #7? (6)

A 
polyamide (nylon)
polyvinylidene chloride
ionomers
polyvinyl alcohol
ethylene-vinyl acetate
ethylene vinyl alcohol
129
Q

What is nylon made from?

A

(acid + amide)
adipic acid + hexamethylene diamide => nylon 6, 6

or from caprolactam => nylon 6

130
Q

good nylon properties:

A 
good barrier (gas, oil)
clear
chemical/grease resistant
tough & stiff
temp resistant (high and low)
131
Q

disadvantage of nylon:

A

poor moisture barrier

132
Q

Applications of nylon:

A

films for process meats/cheese, strapping, boil-in-bag, seafood film, multilayer bottles, laminates (with EVA, PVDC, LDPE)

133
Q

What #7 polymer is very difficult to make? How is it usually made?

A

PVDC (polyvinylidene chloride)

made of vinylidene Cl units; made as a copolymer with PVC

134
Q

properties of PVDC:

A

excellent moisture/gas barrier,
high cling
clarity
strong

135
Q

What is PVDC usually used for?

A

thin layers to coat other films (improve them)

136
Q

What are ionomers?

A

made from ethylene methacrylic acid copolymer (EMAA)

Some H on carboxyl groups replaced by Na or Zn (charged ionic areas)

137
Q

ionomer polymers are used when?

A

when a strong seal is needed (greasy, crumbly products)

in laminates, skin packaging

138
Q

properties of ionomers:

A 
strong (puncture/impact resistant)
excellent adhesive
excellent clarity
excellent moisture barrier
oil resistant
139
Q

PVA is made from:

A

polyvinyl acetate -> NaOH, methanol -> PVA

Food Packaging (11 decks)

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