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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
polar molecules are attracted to ____ and not attracted to _____
polar molecules | nonpolar molecules
26
water is (polar/nonpolar). CO2 is (polar/nonpolar)
polar | nonpolar
27
What is 'like dissolves like?'
molecules with same polarity -> soluble
28
What is a complete barrier? what materials qualify?
prevents substances from passing through (moisture, gas) glass, metal
29
Are plastics complete barriers?
No; selective permeability
30
Why are most plastics generally better as moisture barriers than gas barriers?
water = polar molecule (repelled by nonpolar plastic) | O2 and CO2 = nonpolar, small -> pass through easier
31
What are the nonpolar plastics? (4)
PE, PP, PS, PTFE
32
What are the polar plastics? (3)
Polyester, Polyamide, PVC
33
Why is molecular shape important?
determines packing of molecules (amorphous or crystalline) | affects clarity, melt point, barrier properties, stiffness...
34
Regular shapes can be packed into ___ structures. Irregular shapes become _____ structures.
crystalline | amorphous
35
True/False: melted polymers can be amorphous or crystalline
False; all are amorphous when melted
36
How does the cooling process affect structure formation?
rapid cooling -> amorphous | slow cooling -> crystalline
37
Compare clarity in amorphous vs crystalline:
amorphous: clear crystalline: hazy (unless very small crystals)
38
T/F: crystalline structures are stiffer then amorphous structures
true
39
Which is a better barrier, crystalline or amorphous structures?
crystalline
40
T/F: amorphous structures have a higher melt point than crystalline
False; lower melt point
41
____ _____ will align molecules, making amorphous structures more crystalline (organized)
molecular orientation
42
Types of molecular orientation: (2)
Uniaxial (1 direction) | Biaxial (2 directions)
43
What are 'memory' plastics? How are they made?
Shrinkable plastics (when heated) heat to soften -> stretch -> cool quickly (will retain 'memory') When reheated to same temperature, will shrink
44
What happens if a plastic is heat stretched, and cooled slowly?
becomes heat stable (will not shrink with re-heating)
45
Most plastics used for food are _____
thermoplastics
46
What are the properties of thermoplastics?
soften when heated (no set melt point) solidify when cooled can be re-melted viscoelastic
47
Examples of thermoplastics (4)
polyethylene polypropylene polystyrene polyvinyl chloride
48
What is a thermoset plastic and its properties?
plastic that cannot be melted/re-formed once it is set (polymer chains are crosslinked into 1 giant molecule)
49
Examples of thermoset polymers: (3)
urethane bakelite melmac
50
Can Urethane be used to make shrink-wrap?
No; it is a thermoset plastic (cannot be melted/re-formed)
51
Polyethylene was heat-stretched and cooled quickly. What will happen when it is reheated to the same temperature?
shrinkage
52
What are some plastic additive types? (8)
``` plasticizer stabilizer flame retardant antistatics slip agents foaming agents pigments fillers ```
53
What is the purpose of plasticizers?
increase flexibility & plasticity | reduce flow temperature & hardness
54
How are plasticizers incorporated into the polymer?
expose polymer to plasticizer -> diffuses into polymer network
55
examples of plasticizers: (5)
``` phthalate (P4) di-n-octylphthalate (P5) tri-n-butyl citrate (P1) dioctyl adipate (P3) dioctyl sebacate (P2) ```
56
What are stabilizers for?
protect from degradation from UV, heat, oxygen
57
examples of plastic stabilizers: (5)
``` Carbon black, TiO, hydroxybenzophenone, organometallic compounds, antioxidants ```
58
examples of flame retardants: (2)
PBDE (poly brominated diphenyl ethers) | Al(OH)3
59
What compounds are used as antistatics?
long chain aliphatic amines
60
What is a pelletizer used for?
making materials (plastic powder/pellets) for further processing recycling
61
What is the process of plastic pelleting?
``` raw materials (resins, hardeners, pigment, flow additive) -> premix extruder -> cooling belt -> cutter -> grinder (reduce to powder) -> sieve (remove coarse powder) ``` powder -> packaging manufacture
62
What is plastics extrusion?
raw plastic melted -> forced through extruder -> single continuous form
63
Types of extruders:
``` single screw twin screw (conical, parallel) ```
64
main zones of an extruder screw:
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
What melts the plastic in an extruder? What gives it the shape?
heated barrel, intense pressure/friction from screw forced through die at end
66
The different rotation and alignment patterns for twin screws:
intermeshing, non-intermeshing | co-rotating, counter-rotating
67
Plastic can be extruded into what forms?
tubing, pipes, sheets, films, specific shapes (structural parts)
68
The resin (raw material) is added to the extruder through the _____
feed hopper
69
The product exiting the extruder is called the _____
extrudate
70
types of molds connected to extruders?
blown mold injection mold compression mold (hot press)
71
how does a blown mold work?
split mold with parison inside mold closed -> air blown in -> expands plastic (press against mold) mold opened -> bottle
72
How does a injection mold work?
inject liquid plastic into closed mold | open mold to eject (automatic ejector pins)
73
What is compression molding for plastics?
place plastic material (charge) in mold Use hot press (heat + pressure) -> compress into desired shape open press to remove
74
What is blown film extrusion?
extrude molten plastic through die -> inflate with air -> thin film bubble -> collapse to make film
75
What are the parts of a blown film extrusion process?
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
Why is anealing under tension important in blown film extrusion?
reduces residual stresses | prevents shrinkage
77
What is the orientation formed in the blown film structure?
bi-axial: machine direction + transverse direction (formed during blowing)
78
What is the 'double bubble' process?
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
What are the advantages of the double bubble process?
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
printing is a ____ treatment
surface
81
What affects printability?
polarity | additives
82
Printing is improved by: (3)
electric discharge (corona) flame treatment plasma treatment
83
The density range of plastics:
0.9-1.4g/mL
84
List the common 6 plastics from least to greatest density
``` 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
important properties of plastic to consider for packaging: (7)
``` density breakage/sharp edges sealability flexibility strength/durability permeability (gas, odor, light) printability ```
86
The 7 plastic identification codes:
1. PETE 2. HDPE 3. V 4. LDPE 5. PP 6. PS 7. Other
87
What is PETE? How is it produced?
polyethylene terephthalate | acid (terephthalic acid) + alcohol (ethylene glycol) => condensation rxn
88
Which plastic has the highest tensile strength?
polyethylene terephthalate
89
T/F: PET is a good moisture barrier, but a poor gas barrier
false: good moisture barrier AND good gas barrier
90
Disadvantages of PET:
``` No heat sealability lack printability (chemical inertness) ```
91
Advantages of PET:
``` Stable (low/high temp, humidity) clarity chemical resistance tear resistance good barrier properties high tensile strength ```
92
____ printing can be done for poor-printability materials
flexographic
93
How can PET be improved? (2)
2 way stretching (bi-orientation) | high-temp crystallization
94
What does 2 way stretching achieve for PET?
Improves tensile strength, flexibility, tear strength
95
What does high temp crystallization achieve in PET?
improve thermal stability + barrier properties
96
Types of PET:
Amorphous (APET) Crystalline (CPET) Shrinkable (30%)
97
____ PET is better in heat applications
crystalline
98
Applications of PET in food packaging:
films, oven trays/pouches, heat shrink film, bottles, thermoformed containers
99
PE is made of ____ monomers. What is the difference between HDPE and LDPE production?
Ethylene HDPE: low pressure + catalyst => linear LDPE: high pressure + catalyst => Long branched chain
100
How does branching affect properties in PE?
increase clarity, elongation decrease crystallinity, moisture/grease barrier, density, tensile strength, melt point
101
structure/strength properties of HDPE:
crystalline, low branching high stiffness/tensile strength, low impact/tear strength, translucent
102
Barrier properties of HDPE:
POOR oxygen barrier, good moisture barrier
103
T/F: HDPE is not stable at low temp
False; retains properties at low temp (good for freezer use)
104
Applications of HDPE:
Grocery bags, box liners, laminates, containers, tubs, crates/cases, pails/drums
105
T/F: LDPE softens at a lower temp than HDPE
True (softens at very low temp)
106
a plastic with a low melt point is good for ______
heat sealability
107
advantages of LDPE:
heat sealable non reactive clarity elongation (shrink wrap)
108
disadvantages of LDPE:
High tear strength low stiffness very poor O2 barrier, fair moisture barrier
109
Applications of LDPE:
Stretch wrap, heat seal film/coating, bags, liners, shrink film, squeeze bottles, caps/closures
110
What is plastic #3? How is it made?
PVC (polyvinyl chloride) polymerize vinyl chloride monomers (ethylene Cl -> ethylene dichloride -> heat -> vinyl chloride + HCl -> vinyl chloride -> polyvinyl chloride)
111
Advantages of PVC:
``` 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
Applications of PVC:
cling film, shrink film, blister packs, portion control packs, chilled packaging, clear/strong bottles and jars
113
What is plastic #5? What is the monomer unit?
polypropylene | made from propylene monomers
114
What has a higher softening point, PE or PP?
PP
115
advantages of PP over PE:
higher softening point (can hot-fill) better clarity better barrier (O2, moisture) better grease resistance
116
describe the structural strength of PP:
high tensile strength low density resists scratching/cracking brittle at low temp
117
How can low temperature affect PP?
brittleness
118
Is PP printable?
yes, after treatment with corona discharge
119
applications of PP:
pouches/bags, clear wraps, clear labels, shrink packages, laminates, dairy tubs (no freezer), hot-fill bottles
120
What is plastic #6?
polystyrene (styrene monomers)
121
styrene monomers are linked to produce PS through _______
free radical vinyl polymerization
122
advantages of PS:
Low cost hard & stiff crystal clear (transmit all light)
123
disadvantages of PS:
Brittle poor resistance to solvents (reactive, acid damage) poor barrier (moisture/gas)
124
Of the common plastics, which is the most clear?
Polystyrene
125
What are some modified PS types? what qualities do they have?
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
How is styrofoam made?
expanded PS: foam with hexene and N2 initiator -> better insulation (but doesn't improve gas barrier properties)
127
PS applications:
Labels, window panels for bag/boxes, soak pads (meat), boxes, jars, liners, tray/tub/protective packaging, cups
128
What plastics are classified under #7? (6)
``` polyamide (nylon) polyvinylidene chloride ionomers polyvinyl alcohol ethylene-vinyl acetate ethylene vinyl alcohol ```
129
What is nylon made from?
(acid + amide) adipic acid + hexamethylene diamide => nylon 6, 6 or from caprolactam => nylon 6
130
good nylon properties:
``` good barrier (gas, oil) clear chemical/grease resistant tough & stiff temp resistant (high and low) ```
131
disadvantage of nylon:
poor moisture barrier
132
Applications of nylon:
films for process meats/cheese, strapping, boil-in-bag, seafood film, multilayer bottles, laminates (with EVA, PVDC, LDPE)
133
What #7 polymer is very difficult to make? How is it usually made?
PVDC (polyvinylidene chloride) | made of vinylidene Cl units; made as a copolymer with PVC
134
properties of PVDC:
excellent moisture/gas barrier, high cling clarity strong
135
What is PVDC usually used for?
thin layers to coat other films (improve them)
136
What are ionomers?
made from ethylene methacrylic acid copolymer (EMAA) | Some H on carboxyl groups replaced by Na or Zn (charged ionic areas)
137
ionomer polymers are used when?
when a strong seal is needed (greasy, crumbly products) | in laminates, skin packaging
138
properties of ionomers:
``` strong (puncture/impact resistant) excellent adhesive excellent clarity excellent moisture barrier oil resistant ```
139
PVA is made from:
polyvinyl acetate -> NaOH, methanol -> PVA

Food Packaging (11 decks)

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