1

General ConceptsChapter 2

Professor Joe Greene

CSU, CHICO

MFGT 144

2

Chapter 2 Objectives

• Objectives– Monomers and Polymerization– Homopolymers– Amorphous State– Crystallinity– Cross-linking and Molecular Networks– Copolymers– Polyalloys– Fillers, Reinforcements– Additives

3

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.

H e-

H e-

H e-

H e-

e-

C

e-

e- e-C e-

e- e-

e-H

e-

H

H

H

e- e-

e-

4

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.

5

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 Counting Carbons Counting functional groups

– 1 C Meth mono

– 2 C Eth Di

– 3 C Pro Tri

– 4 C But Tetra

– 5 C Pent 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.

6

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 monomeric molecules

C C

H H

H H

…...

Polymerization

Ethylene Monomer (gas)

C C

H H

H H

C C

H H

H H

C C

H H

H H

…...

Polyethylene polymer (powder or solid)

Heat, pressure,catalyst

7

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 worms in constant

motion.

8

Polymerization Mechanisms• Chain Growth (Addition) Polymerization

– Polymerization begins at one location on the monomer by an initiator

– Instantaneously, the polymer chain forms with no 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.)

9

Condensation Polymerization Example• Polyamides

– Condensation Polymerization• Nylon 6/6 because both the acid and amine contain 6

carbon atoms

NH2(CH2)6NH2 + COOH(CH2)4COOHHexamethylene 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

10

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

11

Formation of Polymers• Polymers from Addition reaction

– LDPE HDPE PP

– PVC PS

C C

H H

H H

n

C C

H H

H H

n

C C

H CH3

H H

n

C C

H Cl

H H

n

C C

H

H H

n

12

Other Addition Polymers

• Polyetheretherketone (PEEK)– Wholly aromatic structure– Highly crystalline– High temperature resistance

O O O C

O

n

13

Other Addition Polymers• Polyphenylene

• Polyphenylene oxide

• Poly(phenylene sulfide)

• PolymonochloroparaxylyeneS S S

O OO

CH2 CH2

Cl Cl

14

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)

C C

H X

H Y

orC C

H X

H H

CC

H Cl

H H

C C

H Cl

H Cl

C C

H OCOCH3

H H

15

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.)

16

Common Polymer Synthesis• Polyamides

– Condensation Polymerization• Nylon 6/6 because both the acid and amine contain 6

carbon atoms

NH2(CH2)6NH2 + COOH(CH2)4COOHHexamethylene 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

17

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

18

Polycarbonate• Polycarbonates are linear, amorphous polyesters

because they contain esters of carbonic acid and an aromatic bisphenol (C6H5OH)

• Polymerized with condensation reaction

Phenol + Acetone Bisphenol-A + water

2

OH

+H2O+

C CH2CH3

OC

CH2

CH2

OHOH

19

Polycarbonate

Bisphenol-A + Phosgene Polycarbonate + salt

NaCl+

C

CH2

CH2

OHOH + nCOCl2

O C

CH2

CH2

C

O

O

n

20

Condensation Polymerization• Polyhydroxyethers (Phenoxy)- Reaction of Bisphenol A

and epichlorohydrin. Similar to polycarbonate. Sold as thermoplastic epoxide resins.

n

O C

CH2

CH2

C

OH

O

H

H

C C

H H

H

21

Other Condensation Polymers• Thermoplastic Polyesters

– Saturated polyesters (Dacron). • Linear polymers with high MW and no crosslinking.• Polyethylene Terephthalate (PET). Controlled crystallinity.• Polybutylene Terephthalate (PBT).

– Aromatic polyesters (Mylar)

O C

O

R O C

O

R

C

O

C

O

R R

22

Other Condensation Polymers

• Polysulfones- Repeating unit is benzene rings joined by sulfone groups (SO2), an isopropylidene group (CH3CH3C), and an ether linkage (O).

n

C

CH3

CH3

OO SO2

23

Characteristics of Addition and Condensation

• Table 2.4

24

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.

25

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 = 104,000

26

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 MWPE 10,000 28 300,000UHMWPE 200,000 28 5,000,000PS 3,000 104 300,000PVC 1,500 100,000PA 120 15,000PC 200 40,000PET 100 20,000POM 1,000 40,000

27

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.

Histogram of Heights of Students

05

10152025

60 70 80

Height, inches

Fre

qu

en

cy

Series1

28

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.

• The curve is called the Molecular Weight Distribution (MWD)

29

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

30

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

31

Gel Permeation Chromatography

32

Number Average Molecular Weight, Mn•

• 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

– 50,000 1

– 100,000 4

– 200,000 5

– 500,000 3

– 700,000 1

...

...

321

332211

NNN

MNMNMN

N

MNM

i

iin

000,260

)13541(

)700(1)500(3)200(5)100(4)50(1

...

...

321

332211

n

n

i

iin

M

KKKKKM

NNN

MNMNMN

N

MNM

33

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 degree of polymerization, DP.

– DP relates the amount of

monomer that has been converted to polymer.

1M

MDP n

34

Weight Average Molecular Weight, Mw

• 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

...

...

332211

233

222

211

2

MNMNMN

MNMNMN

MN

MNM

ii

iiw

35

Z- Average Molecular Weight

– 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

...

...233

222

211

333

322

311

2

3

MNMNMN

MNMNMN

MN

MNM

ii

iiz

Ni Mi NiMi NiMi21,000 1,000 1.00E+06 1.00E+092,000 4,000 8.00E+06 3.20E+104,000 10,000 4.00E+07 4.00E+117,000 4,000 2.80E+07 1.12E+11

14,000 19,000 7.70E+07 5.45E+11

Mn= 5.50E+03Mw= 7.08E+03

Poly Disp PS = 1.29E+00narrow if < 5 broad if >5

36

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.

37

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.

38

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• Shorter chains do not transmit as much energy during impact

39

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

Mec

hani

cal

Pro

pert

ies

MW

Mel

ting

Poi

nt

MW

* Decomposition

40

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

41

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

42

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

43

• 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

States of Thermoplastic Polymers

44

Amorphous Materials• PVC Amorphous

• PS Amorphous

• Acrylics Amorphous

• ABS Amorphous

• Polycarbonate Amorphous

• Phenoxy Amorphous

• PPO Amorphous

• SAN Amorphous

• Polyacrylates Amorphous

45

• 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

States of Thermoplastic Polymers

46

Crystalline Materials• LDPE Crystalline• HDPE Crystalline • PP Crystalline • PET Crystalline • PBT Crystalline• Polyamides Crystalline• PMO Crystalline• PEEK Crystalline• PPS Crystalline • PTFE Crystalline• LCP (Kevlar) Crystalline

47

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

– Factors• Cooling Rate from mold temperatures• Barrel temperatures• Injection Pressures• Drawing rate and fiber spinning: Manufacturing of thermoplastic

fibers causes Crystallinity• Application of tensile stress for crystallization of rubber

Course Fine Density

CrystallinityCrystallineAmorphous

Semi-cryst

48

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

• 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

Temp

Glassy

Rubbery

Melt

PolymerForm

Increa

sing T

emp

Tm

Tg

49

Glass Transition Temperature, Tg• Glass Transition Temperature, Tg: The temperature by

which:– Below the temperature the material is in an immobileimmobile (rigid)

configuration– Above the temperature the material is in a mobilemobile (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 characteristic.

• Tg applies to all polymers (amorphous, crystalline, rubbers, thermosets, fibers, etc.)

50

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)

Temperature-50C 50C 100C 150C 200C 250C

Tg

Vol.

Temperature-50C 50C 100C 150C 200C 250C

Amorphous

Cry

stal

line

TgTg

51

Crystalline Polymers Tg• Tg: Affected by Crystallinity level

– High Crystallinity Level = high Tg– Low Crystallinity Level = low Tg

Modulus (Pa) or (psi)

Temperature-50C 50C 100C 150C 200C 250C

Tg

High Crystallinity

Medium Crystallinity

Low Crystallinity

52

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 PropertiesPEEK LCP Polyester Nylon 6,6

Density, g/cc 1.30-1.32 1.35 - 1.40 1.13-1.15

Tensile Strength,psi

10,000 – 15,000 16,000 – 27,000 14,000

Tensile Modulus,psi

500K 1,400K - 2,800K 230K – 550K

TensileElongation, %

30% - 150% 1.3%-4.5% 15%-80%

Impact Strengthft-lb/in

0.6 – 2.2 2.4 - 10 0.55 – 1.0

Hardness R120 R124 R120

CLTE10-6 mm/mm/C

40 - 47 25-30 80

HDT 264 psi 320 F 356F -671F 180F

53

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

54

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

55

Homopolymers• Table 3-2 Plastics Involving Single Substitutions

X Position Material Name AbbreviationH Polyethylene PECl Polyvinyl chloride PVCMethyl group Polypropylene PPBenzene ring Polystyrene PSCN Polyacrylonitrile PANOOCCH3 Polyvinyl acetate PvaCOH Polyvinyl alcohol PVACOOCH3 Polymethyl acrylate PMAF Polyvinyl fluoride PVF

Note:Methyl Group is:

|H – C – H | H

Benzene ring is:

56

Homopolymers• Plastics Involving Two Substitutions

C C

H X

H Y

n

X Position Y Position Material Name AbbreviationF F Polyvinylidene fluoride PVDFCl Cl Polyvinyl dichloride PVDCCH3 (Methyl group) CH3 Polyisobutylene PBCOOCH3 CH3 Polymethyl methacrylate PMMA

57

Homopolymers• Plastics Involving Three+ Substitutions (use Table 3.2)

C C

W X

Z Y

n

C C

F F

F F

n

e.g. PTFEpolytetrafluoroethylene(Teflon)

58

Copolymers• Plastics Involving Two mers in chain (use Table 3-2)

C C

H X1

H H

n

C C

H X2

H H

m

e.g. SAN styrene acronitrile

C C

H

H H

n

C C

H C:::N

H H

m

59

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

60

Terpolymers• Plastics Involving Three mers in chain (use Table 3-2)

C C

H X3

H H

k

e.g. ABS acronitrilebutadiene styrene

C C

H

H H

km

C C

H X1

H H

n

C C

H X2

H H

m

C C

H C:::N

H H

n

C C

CH2 CH2

H H

61

Terpolymers• Structure of three mers can be

– Alternating- ABCABCABCABCABCABCABC– Random copolymer- AABCBABCBBCAABCABCB– Block copolymer- AABBCAABBCAABBCAABBC– Graft copolymer- C C C C

C C C C

AAAAAAAAAAAAAAAA B B B

B B B

B B B

62

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

63

Mechanical Properties of Acrylic, PC, PC/ABS

Mechanical PropertiesAcrylic PC ABS PC/ABS

Density, g/cc 1.16- 1.19 1.2 1.16-1.21 1.07 - 1.15

Tensile Strength,psi

5,000 - 9,000 9,500 3,300 - 8,000 5,800 - 9,300

Tensile Modulus,psi

200K – 500K 350 K 320K-400K 350K -450K

TensileElongation, %

20 - 70% 110% 1.5%-25% 50%-60%

Impact Strengthft-lb/in

0.65 -2.5 16 1.4-12 6.4 - 11

Hardness M38-M68 M70 R100-120 R95 -R120

CLTE10-6 mm/mm/C

48 - 80 68 65- 95 67

HDT 264 psi 165-209F 270 190F - 225F 225F

64

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

65

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

66

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

67

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

68

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.

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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

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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.

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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, Ca-zinc,

Mg-Zinc, etc..

• Impact Modifiers– Elastomers added to polymers– PVC is toughened with ABS, CPE, EVA, etc.

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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

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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-2-ethylhexyl phthalate (carcinogenic in animals)

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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

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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-phenyl-benzotrizoles

• Most developments involve hindered amine light stabilizers (HALS)

• HALS often contain reactive groups, which chemically bond onto the backbone of polymer molecules. This reduces migration and volatility.

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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)– C glass for chemical resistane, S glass for high strength

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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

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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– tensile strength > 40 GPa

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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

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Fillers• Particle Class• Calcium carbonate: powdery filler that is inexpensive and non-

reinforcing. 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); Felspar- anhydraous

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)