General Concepts
Chapter 2
Professor Joe Greene
CSU, CHICO
1
MFGT 144
Chapter 2 Objectives
• Objectives
–
–
–
–
–
–
–
–
–
Monomers and Polymerization
Homopolymers
Amorphous State
Crystallinity
Cross-linking and Molecular Networks
Copolymers
Polyalloys
Fillers, Reinforcements
Additives
2
Bonding
• Covalent bonding (most important for plastics)
– Occurs when two nonmetal atoms are in close proximity.
– Both atoms have a tendency to accept electrons, which results in
shared outer electron shells of the two atoms.
– Number of shared electrons is usually to satisfy the octet rule.
– Resulting structure is substantially different that the individual
atoms, e.g., C and H4 make CH4, a new and distinct molecule.
– Atoms is covalent bonds are not ions since the electrons are shared
rather than transferred as in ionic or metallic bonds.
e- eH
H H
eeeeH
H
e- C eee- H
eH
ee- C eee-
3
H
Bonding
• Secondary bonding: weaker than ionic, metallic, covalent
– Hydrogen bonding
• Occurs between the positive end of a bond and the negative end of another
bond.
• Example, water the positive end is the H and the negative end is O.
– van der Waals
• Occurs due to the attraction of all molecules have for each other, e.g.
gravitational. Forces are weak since masses are small
– induced dipole
• Occurs when one end of a polar bond approaches a non-polar portion of
another molecule.
4
Naming Organic Compounds
• Basis for naming organic compounds
– Indicate the family of organic compounds to which a molecule
belongs (importance to polymers)
• Dependent upon functional group, e.g. alcohol group, methanol or methyl
alcohol.
• Dependent upon the number of carbon atoms in the repeating molecule.
Number
– 1C
– 2C
– 3C
– 4C
– 5C
Counting Carbons
Meth
Eth
Pro
But
Pent
Counting functional groups
mono
Di
Tri
Tetra
Penta
• Example,
– CH4 has one carbon and no functional groups (alkane), thus is meth ‘ane.
– C2H2 has 2 carbons and has a double bond (alkene), thus is eth ‘ene.
5
Monomers and Polymerization
• Polymers are formed from a
– monomer, which is a small (low MW) molecules with
inherent capability of forming
• chemical bonds with the same or other monomers in such a
manner that long chains (polymer chains or macromolecules)
are formed
• Typical polymer chains involves hundreds or thousands of
Polyethylene polymer (powder or solid)
monomeric molecules
Ethylene Monomer (gas)
H H
H H
H H
H H Polymerization
C C
C C
C C
C C
Heat,
…...
pressure,
H H …...
H H
H H
catalyst
H H
6
Definition of Plastics
• Plastics come from the Greek plastikos, which
means to form or mold.
– Plastics are solids that flow (as liquid, molden, or soften
state) when heat is applied to material.
• Polymers are organic materials that come from
repeating molecules or macromolecules
– Polymer materials are made up of “many” (poly)
repeating “units”(mers).
– Polymers are mostly based in carbon, oxygen, and
hydrogen. Some have Si, F, Cl, S
– Polymers are considered a bowl of spaghetti or a bag of
7
worms in constant motion.
Polymerization Mechanisms
• Chain Growth (Addition) Polymerization
– Polymerization begins at one location on the monomer
by an initiator
– Instantaneously, the polymer chain forms with no byproducts
• Step-wise (Condensation) Polymerization
– Monomers combine to form blocks 2 units long
– 2 unit blocks form 4, which intern form 8 and son on
until the process is terminated.
– Results in by-products (CO2, H2O, Acetic acid, HCl
etc.)
8
Condensation Polymerization Example
• Polyamides
– Condensation Polymerization
• Nylon 6/6 because both the acid and amine contain
6 carbon atoms
NH2(CH2)6NH2 + COOH(CH2)4COOH
Hexamethylene diamene
Adipic acid
n[NH2(CH2)6NH2 ·CO(CH2)4COOH] (heat)
Nylon salt
[NH(CH2)4NH · CO(CH2)4CO]n + nH2O
Nylon 6,6 polymer chain
9
Polymerization Methods
• 4 Methods to produce polymers
– Some polymers have been produced by all four methods
• PE, PP and PVC are can be produced by several of these
methods
• The choice of method depends upon the final polymer form, the
intrinsic polymer arrangement (isotactic, atactic, etc), and the
yield and throughput of the polymer desired.
–
–
–
–
Bulk Polymerization
Solution Polymerization
Suspension Polymerization
Emulsion Polymerization
10
Formation of Polymers
• Polymers from Addition reaction
– LDPE
HDPE
PP
H H
H H
H H
C C
C C
C C
H H
n
– PVC
H H
H CH3
n
PS
H H
H H
C C
C C
H Cl
n
n
H
n
11
Other Addition Polymers
• Polyetheretherketone (PEEK)
– Wholly aromatic structure
– Highly crystalline
– High temperature resistance
O
O
O
O
C
n
12
Other Addition Polymers
• Polyphenylene
• Polyphenylene oxide
O
O
O
• Poly(phenylene sulfide)
S
• Polymonochloroparaxylyene
S
Cl
S
Cl
CH2
CH2
13
Other Addition Polymers
• Vinyl- Large group of addition
polymers with the formula:
– Radicals (X,Y) may be attached to this
repeating vinyl group as side groups to
form several related polymers.
• Polyvinyls
– Polyvinyl chloride
– Polyvinyl dichloride
(polyvinylidene chloride)
– Polyvinyl Acetate (PVAc)
H
H
C
C
H
X
or
H
Y
C
C
H
X
H
H
H
Cl
C
C
C
C
H
Cl
H
Cl
H
H
C
C
14
H
OCOCH3
Formation of Polymers
• Condensation Polymerization
– Step-growth polymerization proceeds by several steps which result
in by-products.
• Step-wise (Condensation) Polymerization
– Monomers combine to form blocks 2 units long
– 2 unit blocks form 4, which intern form 8 and son on until the
process is terminated.
– Results in by-products (CO2, H2O, Acetic acid, HCl etc.)
15
Common Polymer Synthesis
• Polyamides
– Condensation Polymerization
• Nylon 6/6 because both the acid and amine contain
6 carbon atoms
NH2(CH2)6NH2 + COOH(CH2)4COOH
Hexamethylene diamene
Adipic acid
n[NH2(CH2)6NH2 ·CO(CH2)4COOH] (heat)
Nylon salt
[NH(CH2)4NH · CO(CH2)4CO]n + nH2O
Nylon 6,6 polymer chain
16
Nylon Family
• The repeating -CONH- (amide) link is
present in a series of linear, thermoplastic
Nylons
– Nylon 6- Polycaprolactam:
• [NH(CH2)5CO]x
– Nylon 6,6- Polyhexamethyleneadipamide:
• [NH(CH2)6NHCO (CH2)4CO]x
– Nylon 12- Poly(12-aminododecanoic acid)
• [NH(CH2)11CO]x
17
Polycarbonate
• Polycarbonates are linear, amorphous polyesters
because they contain esters of carbonic acid and an
aromatic bisphenol (C6H5OH)
• Polymerized with condensation reaction
OH
2
+ CH3
O
C CH2
Phenol + Acetone
CH2
OH
OH +
C
CH2
Bisphenol-A + water
H2O
18
Polycarbonate
CH2
C
CH2
OH
OH
+ nCOCl2
O
CH2
O
C
CH2
Bisphenol-A
+ Phosgene
O
+
C
NaCl
n
Polycarbonate + salt
19
Condensation Polymerization
• Polyhydroxyethers (Phenoxy)- Reaction of Bisphenol A and
epichlorohydrin. Similar to polycarbonate. Sold as thermoplastic
epoxide resins.
H H H
CH2
O
C
CH2
O
C C C
H OH H
20
n
Other Condensation Polymers
• Thermoplastic Polyesters
– Saturated polyesters (Dacron).
• Linear polymers with high MW and no
crosslinking.
• Polyethylene Terephthalate (PET). Controlled
crystallinity.
• Polybutylene Terephthalate (PBT).
R
O
O C R
O
O C
– Aromatic polyesters (Mylar)
R
O
O
C
C
R
21
Other Condensation Polymers
• Polysulfones- Repeating unit is benzene rings joined by
sulfone groups (SO2), an isopropylidene group (CH3CH3C), and
an ether linkage (O).
CH3
C
O
SO2
O
CH3
n
22
Characteristics of
Addition and Condensation
• Table 2.4
23
Polymerization by other than
Addition or Condensation
• Ring opening
– Epoxy is created via ring opening to generate active
species and initiate polymerization.
– Epoxy plus amine produces epoxy polymerization
– Nylon 6 is formed when caprolactam ring is opened.
– Acetal polymer is made by the opening of the trioxane
ring.
24
Polymer Length
• Polymer notation represents the repeating group
• Example, -[A]-DP where A is the repeating monomer and DP
represents the number of repeating units.
• Molecular Weight
– Way to measure the average chain length of the polymer
– Defined as sum of the atomic weights of each of the
atoms in the molecule.
• Example,
– Water (H2O) is 2 H (1g) and one O (16g) = 2*(1) + 1*(16)= 18g/mole
– Methane CH4 is 1 C (12g) and 4 H (1g)= 1*(12) + 4 *(1) = 16g/mole
– Polyethylene -(C2H4)-1000 = 2 C (12g) + 4H (1g) = 28g/mole * 1000 =
28,000 g/mole =MW
– Polystyrene -(C2H3)(C6H5) 1000 = 8C (12g) +8H(1g) = 104 g/mole
*1000 Then MW = 104,000 = DP x M1 = 1000 * 104 = 104,00025
Molecular Weight
• Average Molecular Weight
– Polymers are made up of many molecular weights or a
distribution of chain lengths.
– The polymer is comprised of a bag of worms of the same repeating unit,
ethylene (C2H4) with different lengths; some longer than others.
» Polyethylene -(C2H4)-1000 has some chains (worms) with 1001
repeating ethylene units, some with 1010 ethylene units, some with
999 repeating units, and some with 990 repeating units.
» The average number of repeating units or chain length is 1000
repeating ethylene units for a MW of 28*1000 or 28,000 g/mole .
Material DP
M1 g/mole MW
PE
10,000
28 300,000
UHMWPE 200,000
28 5,000,000
PS
3,000
104 300,000
PVC
1,500
100,000
PA
120
15,000
PC
200
40,000
PET
100
20,000
POM
1,000
40,000
26
Molecular Weight
• Average Molecular Weight
– Distribution of values is useful statistical way to
characterize polymers.
• For example,
– Value could be the heights of students in a room.
– Distribution is determined by counting the number of students in the
class of each height.
– The distribution can be visualized by plotting the number of students on
the x-axis and the various heights on the y-axis.
Frequency
Histogram of Heights of Students
25
20
15
10
5
0
Series1
60
70
Height, inches
80
27
Molecular Weight
• Molecular Weight Distribution
– Count the number of molecules of each molecular weight
– The molecular weights are counted in values or groups that have
similar lengths, e.g., between 100,000 and 110,000
• For example,
– Group the heights of students between 65 and 70 inches in one group,
70 to 75 inches in another group, 75 and 80 inches in another group.
• The groups are on the x-axis and the frequency on the y-axis.
• The counting cells are rectangles with the width the spread of
the cells and the height is the frequency or number of molecules
• Figure 3.1
• A curve is drawn representing the overall shape of the plot by
connecting the tops of each of the cells at their midpoints.
28
• The curve is called the Molecular Weight Distribution (MWD)
Molecular Weight
• Average Molecular Weight
– Determined by summing the weights of all of the chains
and then dividing by the total number of chains.
– Average molecular weight is an important method of
characterizing polymers.
– 3 ways to represent Average molecular weight
• Number average molecular weight
• Weight average molecular weight
• Z-average molecular weight
29
Gel Permeation Chromatography
• GPC Used to measure Molecular Weights
– form of size-exclusion chromatography
– smallest molecules pass through bead pores, resulting in
a relatively long flow path
– largest molecules flow around beads, resulting in a
relatively short flow path
– chromatogram obtained shows intensity vs. elution
volume
– correct pore sizes and solvent critical
30
Gel Permeation Chromatography
31
Number Average Molecular Weight, Mn
• M   N i M i  N1 M 1  N 2 M 2  N 3 M 3  ...
n
N
i
N1  N 2  N 3  ...
• where Mi is the molecular weight of that species (on the x-axis)
• where Ni is the number of molecules of a particular molecular
species I (on the y-axis).
– Number Average Molecular Weight gives the same weight to all
polymer lengths, long and short.
• Example, What is the molecular weight of a polymer sample in which the
polymers molecules are divided into 5 categories.
– Group Frequency
 N i M i  N1 M 1  N 2 M 2  N 3 M 3  ...
M

n
– 50,000
1
N1  N 2  N 3  ...
 Ni
– 100,000 4
1(50 K )  4(100 K )  5(200 K )  3(500 K )  1(700 K )
Mn 
– 200,000 5
(1  4  5  3  1)
M n  260,000
– 500,000 3
32
– 700,000 1
Molecular Weight
• Number Average Molecular Weight. Figure 3.2
– The data yields a nonsymmetrical curve (common)
– The curve is skewed with a tail towards the high MW
– The Mn is determined experimentally by analyzing the
number of end groups (which permit the determination of
the number of chains)
– The number of repeating units, n, can be found by the
ratio of the Mn and the molecualr weight of the repeating
unit, M1, for example for polyethylene, M1 = 28 g/mole
– The number of repeating units, n, is often called the
Mn
degree of polymerization, DP.
DP 
– DP relates the amount of
M1
33
monomer that has been converted to polymer.
Weight Average Molecular Weight, Mw
2
N
M
 i i
N1 M 12  N 2 M 22  N 3 M 32  ...
Mw 

 N i M i N1 M 1  N 2 M 2  N 3 M 3  ...
• Weight Average Molecular Weight, Mw
– Favors large molecules versus small ones
– Useful for understanding polymer properties that relate to
the weight of the polymer, e.g., penetration through a
membrane or light scattering.
– Example,
• Same data as before would give a higher value for the
Molecular Weight. Or, Mw = 420,000 g/mole
34
Z- Average Molecular Weight
Mz 
3
N
M
 i i
2
N
M
 i i
N 1 M 13  N 2 M 23  N 3 M 33  ...

N 1 M 12  N 2 M 22  N 3 M 32  ...
– Emphasizes large molecules even more than Mw
– Useful for some calculations involving mechanical properties.
– Method uses a centrifuge to separate the polymer
• Example Calculations
– Mn and Mw and Polydispersity = Mw/Mn
Ni
1,000
2,000
4,000
7,000
14,000
Mi
1,000
4,000
10,000
4,000
19,000
Mn=
Mw=
NiMi
1.00E+06
8.00E+06
4.00E+07
2.80E+07
7.70E+07
NiMi2
1.00E+09
3.20E+10
4.00E+11
1.12E+11
5.45E+11
5.50E+03
7.08E+03
Poly Disp PS =
1.29E+00
narrow if < 5 broad if >5
35
Molecular Weight Distribution
• Molecular Weight Distribution represents the
frequency of the polymer lengths
• The frequency can be Narrow or Broad, Fig 2.3
• Narrow distribution represents polymers of about
the same length.
• Broad distribution represents polymers with varying
lengths
• MW distribution is controlled by the conditions
during polymerization
• MW distributions can be symmetrical or skewed.
36
Physical and Mechanical Property
Implications of MW and MWD
• Higher MW increases
• Tensile Strength, impact toughness, creep resistance, and
melting temperature.
– Due to entanglement, which is wrapping of polymer
chains around each other.
– Higher MW implies higher entanglement which yields
higher mechanical properties.
– Entanglement results in similar forces as secondary or
hydrogen bonding, which require lower energy to break
than crosslinks.
37
Physical and Mechanical Property Implications
of MW and MWD
• Higher MW increases tensile strength
• Resistance to an applied load pulling in opposite directions
• Tension forces cause the polymers to align and reduce the
number of entanglements. If the polymer has many
entanglements, the force would be greater.
• Broader MW Distribution decreases tensile strength
• Broad MW distribution represents polymer with many shorter
molecules which are not as entangled and slide easily.
• Higher MW increases impact strength
• Impact toughness or impact strength are increased with longer
polymer chains because the energy is transmitted down chain.
• Broader MW Distribution decreases impact strength
38
• Shorter chains do not transmit as much energy during impact
Thermal Property Implications of MW & MWD
• Higher MW increases Melting Point
• Melting point is a measure of the amount of energy necessary to
have molecules slide freely past one another.
• If the polymer has many entanglements, the energy required
would be greater.
• Low molecular weights reduce melting point and increase ease
of processing.
• Broader MW Distribution decreases Melting Point
• Broad MW distribution represents polymer with many shorter
molecules which are not as entangled and melt sooner.
• Broad MW distribution yields an easier processed polymer
* Decomposition
39
Melt Index
• Melt index test measure the
ease of flow for material
• Procedure
– Heat cylinder to desired temperature (melt
temp)
– Add plastic pellets to cylinder and pack
with rod
– Add test weight or mass to end of rod
(5kg)
– Wait for plastic extrudate to flow at
constant rate
– Start stop watch (10 minute duration)
– Record amount of resin flowing on pan
during time limit
– Repeat as necessary at different
temperatures and weights
40
Melt Index and Viscosity
• Melt index is similar to viscosity
• Viscosity is a measure of the materials resistance to flow.
– Viscosity is measured at several temperatures and shear rates
– Melt index is measured at one temperature and one weight.
• High melt index = high flow = low viscosity
• Low melt index = slow flow = high viscosity
• Example, (flow in 10 minutes)
Polymer Temp Mass
– HDPE 190C
10kg
– Nylon 235C
1.0kg
– PS
200C
5.0Kg
41
Melt Index and Molecular Weight
• Melt index is related closely with average molecular weight
• High melt index = high flow = small chain lengths = low Mn
• Low melt index = slow flow = long chain lengths = high Mn
• Table 3.1 Melt Index and Average Molecular Weight
Mn
Melt Index* (g/10min)
• 100,000
10.00
• 150,000
0.30
• 250,000
0.05
* Note: PS at T= 200C
and mass= 5.0Kg
42
States of Thermoplastic Polymers
• Amorphous- Molecular structure is incapable of forming
regular order (crystallizing) with molecules or portions of
molecules regularly stacked in crystal-like fashion.
• A - morphous (with-out shape)
• Molecular arrangement is randomly twisted, kinked, and
coiled
43
Amorphous Materials
•
•
•
•
•
•
•
•
•
PVC
Amorphous
PS
Amorphous
Acrylics
Amorphous
ABS
Amorphous
Polycarbonate Amorphous
Phenoxy
Amorphous
PPO
Amorphous
SAN
Amorphous
Polyacrylates Amorphous
44
States of Thermoplastic Polymers
• Crystalline- Molecular structure forms regular order
(crystals) with molecules or portions of molecules regularly
stacked in crystal-like fashion.
• Very high crystallinity is rarely achieved in bulk polymers
• Most crystalline polymers are semi-crystalline because
regions are crystalline and regions are amorphous
• Molecular arrangement is arranged in a ordered state
45
Crystalline Materials
•
•
•
•
•
•
•
•
•
•
•
LDPE
HDPE
PP
PET
PBT
Polyamides
PMO
PEEK
PPS
PTFE
LCP (Kevlar)
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
Crystalline
46
Factors Affecting Crystallinity
• Crystallization is time-dependent process
– Several factors affect the speed at which it takes place
(kinetics), but also the resulting morphology which can
occur as course or fine grains. (Fig 2.10)
– Density increases with increased crystallinity
Course
– Factors
•
•
•
•
Fine
Density
Semi-cryst
Amorphous
Crystalline
Cooling Rate from mold temperatures
Crystallinity
Barrel temperatures
Injection Pressures
Drawing rate and fiber spinning: Manufacturing of
thermoplastic fibers causes Crystallinity
• Application of tensile stress for crystallization of rubber
47
Form of Polymers
• Thermoplastic Material: A material that is
solid, that possesses significant elasticity
at room temperature and turns into a
viscous liquid-like material at some
higher temperature. The process is
reversible
Melt
Temp
• Polymer Form as a function of
temperature
– Glassy: Solid-like form, rigid, and
hard
– Rubbery: Soft solid form, flexible, and
elastic
– Melt: Liquid-like form, fluid, elastic
Tm
Rubbery
Tg
Glassy
Polymer
Form 48
Glass Transition Temperature, Tg
• Glass Transition Temperature, Tg: The temperature
by which:
– Below the temperature the material is in an immobile
(rigid) configuration
– Above the temperature the material is in a mobile
(flexible) configuration
• Transition is called “Glass Transition” because the
properties below it are similar to ordinary glass.
• Transition range is not one temperature but a range
over a relatively narrow range (10 degrees). Tg is
not precisely measured, but is a very important 49
characteristic.
Glass Transition Temperature, Tg
• Glass Transition Temperature, Tg: Defined as
– the temperature wherein a significant the loss of modulus
(or stiffness) occurs
– the temperature at which significant loss of volume
occurs
Modulus
(Pa)
or
(psi)
Vol.
Tg
-50C 50C 100C 150C 200C 250C
Temperature
Tg
Tg
-50C 50C 100C 150C 200C 250C
Temperature
50
Crystalline Polymers Tg
• Tg: Affected by Crystallinity level
– High Crystallinity Level = high Tg
– Low Crystallinity Level = low Tg
Modulus
(Pa)
or
(psi)
High Crystallinity
Medium Crystallinity
Low Crystallinity
Tg
-50C
50C
100C
150C
200C
250C
Temperature
51
Liquid Crystalline Plastics (LCPs)
• The molecules of LCPs are rod-like structures
organized in large parallel domains, not only in the
solid state but also in the melt state. Fig 2.12
Mechanical Properties
Density, g/cc
Tensile Strength,
psi
Tensile Modulus,
psi
Tensile
Elongation, %
Impact Strength
PEEK
1.30-1.32
LCP Polyester
1.35 - 1.40
Nylon 6,6
1.13-1.15
10,000 – 15,000
16,000 – 27,000
14,000
500K
1,400K - 2,800K
230K – 550K
30% - 150%
1.3%-4.5%
15%-80%
0.6 – 2.2
2.4 - 10
0.55 – 1.0
R120
R124
R120
40 - 47
25-30
80
320 F
356F -671F
180F
ft-lb/in
Hardness
CLTE
10-6 mm/mm/C
HDT
264 psi
52
Cross-Linking and Molecular Networks
• The polymer chain grows in length to build
molecular weight
– The polymer chains intertwine to exhibit stiffness.
• Some polymers have exchange of electrons across
polymer chains which is called crosslinking.
– Thermoset polymers are crosslinked
– The polymers are stiffer because of the cross-linking
between chains.
– The chains are 3 dimensional and interconnected
– Fig 2.13
53
Interpenetrating Polymer Networks (IPN)
• Formed with blends and alloys or two
macromolecules of two distinct types are mixed
– A dispersion occurs at the molecular level causing large
separate phases or domains.
• The different domains are crosslinked resulting in a 3D
interpenetrating (interwoven, intertwined, interlocked) network
• Fig 2.17
– Materials are usually elastomers
• Silicone with
– thermopalstics (PA, PET, PBT, PP, PMO, etc.)
– elastomers (TPE) or thermosets (PU)
• Urethanes with
– acrylics, epoxy, polyester, PS
54
Homopolymers
• Table 3-2 Plastics Involving Single Substitutions
X Position
Material Name
Abbreviation
H
Cl
Methyl group
Benzene ring
CN
OOCCH3
OH
COOCH3
F
Polyethylene
Polyvinyl chloride
Polypropylene
Polystyrene
Polyacrylonitrile
Polyvinyl acetate
Polyvinyl alcohol
Polymethyl acrylate
Polyvinyl fluoride
PE
PVC
PP
PS
PAN
PvaC
PVA
PMA
PVF
Note:
Methyl Group is:
|
H–C–H
|
H
Benzene ring is:
55
Homopolymers
• Plastics Involving Two Substitutions
H
Y
C
C
H
X
n
X Position
Y Position
Material Name
Abbreviation
F
Cl
CH3 (Methyl group)
COOCH3
F
Cl
CH3
CH3
Polyvinylidene fluoride
Polyvinyl dichloride
Polyisobutylene
Polymethyl methacrylate
PVDF
PVDC
PB
PMMA
56
Homopolymers
• Plastics Involving Three+ Substitutions (use Table 3.2)
Z
Y
C
C
W X
n
e.g. PTFE
polytetrafluoroethylene
(Teflon)
F
F
C
C
F
F
n
57
Copolymers
• Plastics Involving Two mers in chain (use Table 3-2)
H H
H H
C
C
C
H X1
n
e.g. SAN
styrene
acronitrile
C
H X2
m
H H
H H
C C
C C
H
H C:::N
n
m
58
Copolymers
• Structure of two mers can be
–
–
–
–
Alternating- ABABABABABABAB
Random copolymer- AABBABBBAABABBBAB
Block copolymer- AABBBAABBBAABBBAABBB
Graft copolymer- AAAAAAAAAAAAAAAA
B
B
B
B
B
B
B
B
B
59
Terpolymers
• Plastics Involving Three mers in chain (use Table 3-2)
H H
H H
H H
C
C
C
C
H X1
e.g. ABS
acronitrile
butadiene
styrene
n
C
H X2
C
H X3
m
k
H H
H
H
H H
C C
C
C
C C
H C:::N
CH2 CH2
n
H
m
k
60
Terpolymers
• Structure of three mers can be
–
–
–
–
Alternating- ABCABCABCABCABCABCABC
Random copolymer- AABCBABCBBCAABCABCB
Block copolymer- AABBCAABBCAABBCAABBC
Graft copolymerC
C
C
C
C
C
C
C
AAAAAAAAAAAAAAAA
B
B
B
B
B
B
B
B
B
61
Polyalloys
• Polyalloys are also called blends of plastics
– Combine characteristics of one plastic with another one
– Limited number of polymers can be mixed and are
miscible
• PS and PP are impossible to mix and form a blend
– They form coarse aggregates with little or no adhesion between them
• PC and ABS mix well and are well dispersed and soluble
– Examples,
• PC/ABS: Dow Pulse plastic for the Saturn Door panel
• PPO/PBT: GE GTX plastic for the Saturn and Camero fender
62
Mechanical Properties of Acrylic, PC,
PC/ABS
Mechanical Properties
Density, g/cc
Tensile Strength,
psi
Tensile Modulus,
psi
Tensile
Elongation, %
Impact Strength
Acrylic
1.16- 1.19
PC
1.2
ABS
1.16-1.21
PC/ABS
1.07 - 1.15
5,000 - 9,000
9,500
3,300 - 8,000
5,800 - 9,300
200K – 500K
350 K
320K-400K
350K -450K
20 - 70%
110%
1.5%-25%
50%-60%
0.65 -2.5
16
1.4-12
6.4 - 11
M38-M68
M70
R100-120
R95 -R120
48 - 80
68
65- 95
67
165-209F
270
190F - 225F
225F
ft-lb/in
Hardness
CLTE
10-6 mm/mm/C
HDT 264 psi
63
Additives
• Antioxidants- Oxidation of the polymer
breaks down long chain molecules
– More severe at elevated temperatures
– Primary antioxidants: terminates reactions
(phenolic, amine)
– Secondary antioxidants: neutralizes reactive
materials (phosphite, thioesters)
– Susceptible Materials: PP and PE oxidize
readily
• Antistatic– agents attract moisture, causing the surface to
be more reactive, dissipates charges
64
Additives
• Colorants
– Dyes: [Brilliant Colors]
• Organic colorants that are soluble in plastics and
color material by forming chemical linkages.
• Best for transparent product.
• Some have poor thermal and light stability
• May migrate to other plastic areas causing unwanted
coloring
– Organic pigments: [Brilliant Colors]
• Not soluble in common solvents or resin.
• Must be mixed thoroughly. (Though difficult)
• Can form clumps causing spots or specs
65
Additives
– Inorganic pigments [less Brilliant Colors]
• Most are based on metals
• Heavy metals cause environmental conserns
– Lead*, Mercury*, Gold, Tungsten, Barium, Cesium
– ,Iodine, Tin, Cadmium*, Silver, Bromine, Chromium*
• Use of metals is restricted due to potential to leach
out of landfills and into ground water
• Alternative- Heavy Metal Free (HMF) colorants
• Other OK inorganic colorants
–
–
–
–
carbon (black), iron oxide (red), and cobalt oxide (blue)
lead sulfate (white), cadmium sulfide (yellow)
Easily dispersed
Resist light and heat more effectively
66
Additives
– Special-effects pigments
• Colored glass powder for exterior uses
• Metal flakes of Al, Brass, Cu, Gold
• Metallic powders for Auto lighting
• Luminescence
– Fluorescence- sulfides of zinc, Ca, Mg
– Phosphorescence- Ca sulfide or strontium sulfide
67
Additives
• Coupling agents- Promotors of surface adhesion
between dissimilar materials, e.g., glass and
polymers. Silane and titanate
• Curing agents- chemicals that cause crosslinking.
– Inhibitors used to establish shelf life
– Catalyst (hardeners) start reactions. Organic peroxides
used to cross-link thermoplastics (PVC, PS, LDPE, EVA,
and HDPE) as well as thermosets (polyester, PU), e.g.,
Benzoyl peroxides and MEK.
– Promoters or accelerators speed reactions up, e.g., cobalt
naphthanate.
68
Additives
• Flame retardants
– Based on combinations of bromine, Cl,
antimony, boron, and phosphorous
– Many emit afire-extinguishing gas when heated
– Others swell or foam to form a insulating
barrier against heat and flame.
– Alumina trihydrate (ATH) emits water
69
Additives
• Foaming/Blowing agents
– Used to make polymers with a cellular structure
– Physical foaming agents: decompose at specified
temperatures and release gasses.
– Chemical foaming agents release gasses due to a
chemical reaction
– Chlorinated fluorocarbons (CFC) were efficient
foaming agents for polyurethanes.
– Hydrochlorofluorocarbone (HCFC) relaced CFC with 2
to 10% ozone deletion rate
– For thermoplastics, chemical blowing agent,
azodicarbonamide produces cellular HDPE, PP, ABS,
PS, PVC, and EVA.
70
Additives
• Heat Stabilizers
– Retard thermal decomposition for PVC
– Based on lead and cadmium in past. 28% Ca
pollution came from plastics
– New developments based on barium-zinc, Cazinc, Mg-Zinc, etc..
• Impact Modifiers
– Elastomers added to polymers
– PVC is toughened with ABS, CPE, EVA, etc.
71
Additives
• Lubricants
– Needed for making plastics.
• Reduce friction between resin and equipment
• Emulsify other ingredients with lubricant
• Mold release for the mold
– Causes surface blemishes and poor bonding
– Common materials
• waxes (montan, carnauba, paraffin, and stearic acid)
• metallic soaps (stearates of lead, cadmium, barium,
calcium, zinc) Table 7-1
72
Additives
• Plasticizers
– Chemical agent added to increase flexibility,
reduce melt temperature, and lower viscosity
– Neutralize Van der Waals’ forces
– Results in leaching for
• Food contamination
• Reduced impact and reduced flexibility, PVC hoses
• Over 500 different plasticizers available
– Examples: Dioctyl phtalate (DOP), di-2ethylhexyl phthalate (carcinogenic in animals)
73
Additives
• Preservatives
– Protects plastic (PVC and elastomers) against
attacks by insects, rodents, and microorganisms
– Examples
• Antimicrobials, mildewicides, fungicides, and
rodenticides
• Processing Aids
–
–
–
–
Antiblocking agents (waxes) prevents sticking
Emulsifiers lowers surface tension.
Detergents and wetting agents (viscosity)
Solvents for molding, painting, or cleaning
74
Additives
• UV Stabilizers
– Plastics susceptible to UV degredation are
• Polyolefins, polystyrene, PVC, ABS, polyesters, and
polyurethanes,
– Polymer absorbs light energy and causes crazing, cracking,
chalking, color changes, or loss of mechanical properties
– UV stabilizers can be
• Carbon black, 2-hydroxy-benzophenones, 2-hydroxy-phenylbenzotrizoles
• Most developments involve hindered amine light stabilizers
(HALS)
• HALS often contain reactive groups, which chemically bond
onto the backbone of polymer molecules. This reduces 75
migration and volatility.
Reinforcements
• Lamina
– unidirectional fibers, cloth, mat, woven cloth, or sheets
– bi-directional mat, cloth, or woven roving (0/90, +/-45)
– random mat or cloth
• Glass fiber
–
–
–
–
Most common reinforcement
Manufactured in glass plant
Highest volume application in roof shingles
Most common type is E glass (good electrical properties
and high strength)
76
– C glass for chemical resistane, S glass for high strength
Reinforcements
• Glass fiber
– From glass manufacturer the glas is put in rovings or
dofts (similar to yarn packaging or a rope)
– Each roving is comprises of bundles of continuous glass.
– Glass rovings are then
•
•
•
•
cut in chopped glass
hammered for milled glass
woven in mat products
chopped for mat products
– Glass rovings need sizing and coupling agents added for
specific plastic materials
77
Reinforcements
• Polymer fiber
– Synthetic polymer fibers for PE, PA, PAN, PVA, and
cellulose acetate
– Kevlar aramid is an aromatic polyamide polymer fiber
• nearly twice the stiffness and about half the density of glass
• non-conductive, non-affected by radio waves
• used for ballistic protection, ropes, helmets, etc.
• Inorganic fibers
– short crystalline fibers from crystal whisker fibers (Alo,
beryllium oxide, MgO, etc..
– Very costly and slow manufacturing process
78
– tensile strength > 40 GPa
Reinforcements
• Carbon fiber
– Exceed glass in strength and modulus
– Lower density than glass
– Can be used with existing composite manufacturing
except for NEMA 12 electrical standards
– Cost is $10 to $20 per pound for roving. (Large tows may
be $5 to $8 per pound)
– Fiber can be woven or chopped into mat products
– Currently used in many aerospace applications
– Manufactured by 2 methods.
• Mineral fibers- mica, wollastonite
79
• Particle Class
Fillers
• Calcium carbonate: powdery filler that is inexpensive and nonreinforcing. Particle size is about 1 micron. Carbon black: color
• Talc: hydrated magnesium silicate used in platelet-shaped form
of high aspect ratio to give reinforcing properties. Low abrasive
• Kaolin: alumina silicates, clay (1 to 10 microns); Felsparanhydraous alkali-aluminum silicate (20 to 50 microns) is good
for trasparency. Baryte- barium sulfate: high density filler for
sound deadening.
• Silica: irregular sphere-like is inexpensive and reinforcing.
Quite abrasive. Solid glass sphere (beads)- microspheres (5 to
1000 microns) used to add stiffness and strength and light.
• Aids in
• reducing shrinkage, CLTE, costs, strength
• increase stiffness and viscosity (thixotropic)
80