1. 1 General Concepts Chapter 2 Professor Joe Greene CSU, CHICO MFGT 144

2. 2 Chapter 2 Objectives Objectives –Monomers and Polymerization –Homopolymers –Amorphous State –Crystallinity –Cross-linking and Molecular Networks –Copolymers –Polyalloys –Fillers, Reinforcements –Additives

3. 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 H 4 make CH 4, 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 H H C C H H H H

4. 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. 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. NumberCounting Carbons Counting functional groups –1 C Meth mono –2 C EthDi –3 C ProTri –4 C ButTetra –5 C PentPenta Example, –CH 4 has one carbon and no functional groups (alkane), thus is meth ‘ane. –C 2 H 2 has 2 carbons and has a double bond (alkene), thus is eth ‘ene.

6. 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 CC HH HH …... Polymerization Ethylene Monomer (gas) CC HH HH CC HH HH CC HH HH …... Polyethylene polymer (powder or solid) Heat, pressure, catalyst

7. 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. 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 (CO 2, H 2 O, Acetic acid, HCl etc.)

9. 9 Condensation Polymerization Example Polyamides –Condensation Polymerization Nylon 6/6 because both the acid and amine contain 6 carbon atoms NH 2 (CH 2 ) 6 NH 2 + COOH(CH 2 ) 4 COOH Hexamethylene diamene Adipic acid n[NH 2 (CH 2 ) 6 NH 2 ·CO(CH 2 ) 4 COOH] (heat) Nylon salt [NH(CH 2 ) 4 NH · CO(CH 2 ) 4 CO] n + nH 2 O Nylon 6,6 polymer chain

10. 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. 11 Formation of Polymers Polymers from Addition reaction –LDPEHDPE PP –PVCPS CC HH HH n CC HH HH n CC HCH 3 HH n CC HCl HH n CC H HH n

12. 12 Other Addition Polymers Polyetheretherketone (PEEK) –Wholly aromatic structure –Highly crystalline –High temperature resistance O O O C O n

13. 13 Other Addition Polymers Polyphenylene Polyphenylene oxide Poly(phenylene sulfide) Polymonochloroparaxylyene SSS OOO CH 2 Cl

14. 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 HY or C C H X HH C C H Cl HH CC H H C C H OCOCH 3 HH

15. 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 (CO 2, H 2 O, Acetic acid, HCl etc.)

16. 16 Common Polymer Synthesis Polyamides –Condensation Polymerization Nylon 6/6 because both the acid and amine contain 6 carbon atoms NH 2 (CH 2 ) 6 NH 2 + COOH(CH 2 ) 4 COOH Hexamethylene diamene Adipic acid n[NH 2 (CH 2 ) 6 NH 2 ·CO(CH 2 ) 4 COOH] (heat) Nylon salt [NH(CH 2 ) 4 NH · CO(CH 2 ) 4 CO] n + nH 2 O Nylon 6,6 polymer chain

17. 17 Nylon Family The repeating -CONH- (amide) link is present in a series of linear, thermoplastic Nylons –Nylon 6- Polycaprolactam: [NH(CH 2 ) 5 CO] x –Nylon 6,6- Polyhexamethyleneadipamide: [NH(CH 2 ) 6 NHCO (CH 2 ) 4 CO] x –Nylon 12- Poly(12-aminododecanoic acid) [NH(CH 2 ) 11 CO] x

18. 18 Polycarbonate Polycarbonates are linear, amorphous polyesters because they contain esters of carbonic acid and an aromatic bisphenol (C 6 H 5 OH) Polymerized with condensation reaction Phenol + Acetone Bisphenol-A + water 2 OH + H2OH2O+ C CH 2 CH 3 O C CH 2 OH

19. 19 Polycarbonate Bisphenol-A + Phosgene Polycarbonate + salt NaCl+ C CH 2 OH + nCOCl 2 O C CH 2 C O O n

20. 20 Condensation Polymerization Polyhydroxyethers (Phenoxy)- Reaction of Bisphenol A and epichlorohydrin. Similar to polycarbonate. Sold as thermoplastic epoxide resins. n O C CH 2 C OH O H H CC HH H

21. 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 RC O C O R R

22. 22 Other Condensation Polymers Polysulfones- Repeating unit is benzene rings joined by sulfone groups (SO 2 ), an isopropylidene group (CH 3 CH 3 C), and an ether linkage (O). n C CH 3 O O SO 2

23. 23 Characteristics of Addition and Condensation Table 2.4

24. 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. 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 (H 2 O) is 2 H (1g) and one O (16g) = 2*(1) + 1*(16)= 18g/mole –Methane CH 4 is 1 C (12g) and 4 H (1g)= 1*(12) + 4 *(1) = 16g/mole –Polyethylene -(C 2 H 4 )- 1000 = 2 C (12g) + 4H (1g) = 28g/mole * 1000 = 28,000 g/mole =MW –Polystyrene -(C 2 H 3 )(C 6 H 5 ) 1000 = 8C (12g) +8H(1g) = 104 g/mole *1000 Then MW = 104,000 = DP x M1 = 1000 * 104 = 104,000

26. 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 (C 2 H 4 ) with different lengths; some longer than others. »Polyethylene -(C 2 H 4 )- 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.

27. 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.

28. 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. 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. 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. 31 Gel Permeation Chromatography

32. 32 Number Average Molecular Weight, M n 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 –50,0001 –100,0004 –200,0005 –500,0003 –700,0001

33. 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, M 1, for example for polyethylene, M 1 = 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.

34. 34 Weight Average Molecular Weight, M w –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, M w = 420,000 g/mole

35. 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

36. 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. 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. 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. 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 Mechanical Properties MW Melting Point MW * Decomposition

40. 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. 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 –HDPE190C 10kg –Nylon235C 1.0kg –PS200C 5.0Kg

42. 42 Melt Index and Molecular Weight Melt index is related closely with average molecular weight High melt index = high flow = small chain lengths = low M n Low melt index = slow flow = long chain lengths = high M n Table 3.1 Melt Index and Average Molecular Weight MnMelt Index* (g/10min) 100,00010.00 150,000 0.30 250,000 0.05 * Note: PS at T= 200Cand mass= 5.0Kg

43. 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. 44 Amorphous Materials PVCAmorphous PSAmorphous AcrylicsAmorphous ABSAmorphous Polycarbonate Amorphous PhenoxyAmorphous PPOAmorphous SANAmorphous PolyacrylatesAmorphous

45. 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. 46 Crystalline Materials LDPECrystalline HDPECrystalline PPCrystalline PETCrystalline PBTCrystalline PolyamidesCrystalline PMOCrystalline PEEKCrystalline PPSCrystalline PTFECrystalline LCP (Kevlar)Crystalline

47. 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 Crystallinity CrystallineAmorphous Semi-cryst

48. 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 Polymer Form Increasing Temp Tm Tg

49. 49 Glass Transition Temperature, T g Glass Transition Temperature, Tg: The temperature by which: immobile –Below the temperature the material is in an immobile (rigid) configuration mobile –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). T g is not precisely measured, but is a very important characteristic. T g applies to all polymers (amorphous, crystalline, rubbers, thermosets, fibers, etc.)

50. 50 Glass Transition Temperature, T g 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 -50C50C100C150C200C250C Tg Vol. Temperature -50C50C100C150C200C250C Amorphous Crystalline Tg

51. 51 Crystalline Polymers T g Tg: Affected by Crystallinity level –High Crystallinity Level = high Tg –Low Crystallinity Level = low Tg Modulus (Pa) or (psi) Temperature -50C50C100C150C200C250C Tg High Crystallinity Medium Crystallinity Low Crystallinity

52. 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

53. 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. 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. 55 Homopolymers Table 3-2 Plastics Involving Single Substitutions

56. 56 Homopolymers Plastics Involving Two Substitutions CC HX HY n

57. 57 Homopolymers Plastics Involving Three+ Substitutions (use Table 3.2) CC WX ZY n CC FF FF n e.g. PTFE polytetrafluoroethylene (Teflon)

58. 58 Copolymers Plastics Involving Two mers in chain (use Table 3-2) CC HX1 HH n CC HX2 HH m e.g. SAN styrene acronitrile CC H HH n C C H C:::N HH m

59. 59 Copolymers Structure of two mers can be –Alternating- ABABABABABABAB –Random copolymer- AABBABBBAABABBBAB –Block copolymer- AABBBAABBBAABBBAABBB –Graft copolymer- AAAAAAAAAAAAAAAA BBB

60. 60 Terpolymers Plastics Involving Three mers in chain (use Table 3-2) CC HX3 HH k e.g. ABS acronitrile butadiene styrene CC H HH k m CC HX1 HH n CC HX2 HH m C C H C:::N HH n C C CH 2 HH

61. 61 Terpolymers Structure of three mers can be –Alternating- ABCABCABCABCABCABCABC –Random copolymer- AABCBABCBBCAABCABCB –Block copolymer- AABBCAABBCAABBCAABBC –Graft copolymer- CCCC CCCC AAAAAAAAAAAAAAAA BBB

62. 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. 63 Mechanical Properties of Acrylic, PC, PC/ABS

64. 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. 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. 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. 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. 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.

69. 69 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

70. 70 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.

71. 71 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.

72. 72 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

73. 73 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)

74. 74 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

75. 75 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.

76. 76 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

77. 77 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

78. 78 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

79. 79 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

80. 80 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)