Handbook of Plastics Technologies Part 9 ppsx

PLASTICS ADDITIVES 5.7 ers (iron particularly), or from corrosion of process equipment, or as adjacent surfaces on final products (insulation on copper wire), they may aggravate the attack of atmospheric oxygen and the resulting degradation of the polymer. One way to remove the metal from the system is to tie it up in an inactive complex, in which form it is no longer able to catalyze the oxidation reaction. These complexing agents are usually organo nitrogen compounds or polyols. They are not used alone but are added as synergists to a system that already contains primary antioxidants. 5.1.1.4 Acid Scavengers. Oxidation of polymers produces organic acids. Chlorine and bromine, from catalyst residues and flame-retardants, produce stronger acids. These can cause hydrolysis of polymers and corrosion of process equipment. Therefore, it is fairly common practice to add acid scavengers to neutralize them. These are mildly alkaline sub- stances such as calcium and zinc stearates, hydrotalcite, hydrocalumite, and zinc oxide. 5.1.1.5 Use in Commercial Plastics. LDPE is usually stabilized by 0.005 to 0.05 percent BHT. DLTDP and nonylphenyl phosphite may be added as well. For wire and cable insulation, metal deactivator is also needed. LLDPE and HDPE use higher-molecular-weight phenols and higher concentrations. Cross-linked polyethylene, containing carbon black, permits use of thiodiphenols and diaryl amines, since their discoloration is masked by the carbon black. For wire and cable, hydrazides and triazines are common metal deactivators to protect against copper catalysis of oxidation. Polypropylene contains less-stable tertiary hydrogens and processes at higher temperatures, so it requires higher concentrations (0.25 to 1.0 percent) of higher-molecular-weight phenols and more vigorous use of aliphatic sulfides and aromatic phosphites. Poly-1- butene is similar. ABS contains 10 to 30 percent of butadiene rubber, whose C=C bonds are very sensitive to oxidation, producing embrittlement and discoloration. Triaryl phosphites are used as primary antioxidants, in concentrations up to 2.5 percent, producing excellent stabilization. “Crystal” polystyrene is resistant to oxidation, but most “polystyrene” is actually impact styrene containing 2 to 10 percent of butadiene rubber. Like ABS, it requires similar stabilization, but lower concentrations are sufficient. Acetal resins are sensitive to oxidation and are generally stabilized by high-molecular- weight phenols. Polyesters and polyurethanes are commonly stabilized by phosphites. Polyamides are stabilized by phosphites and also (surprisingly) by copper and manganese salts, presumably through complex formation with the amide groups themselves. 5.1.1.6 Market Analysis See Table 5.6 for an analysis of worldwide consumption of antioxidants. 5.1.2 Antiozonants The C=C in most rubber molecules, and in many high-impact plastics, is very sensitive to traces of natural and man-made ozone in the atmosphere. Ozone adds to the double bonds, forming ozonides that break down into various oxidized species, causing severe embrittlement. This requires vigorous protection to give products with useful lifetimes. Two types of additives are used: physical and chemical. 5.1.2.1 Physical Antiozonants. Saturated waxes are added during rubber compounding. Being immiscible, they migrate to the surface (bloom), forming a barrier coating that Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES 5.8 CHAPTER 5 keeps ozone from reaching the rubber. Paraffin waxes bloom rapidly but are too brittle. Microcrystalline waxes bloom more slowly but are less brittle. Mixture of the two types gives broader protection. These are adequate for static performance but are too brittle for dynamic stretching and flexing. A saturated rubber can be coated on the surface to provide a barrier against ozone. Eth- ylene/propylene, plasticized PVC, and polyurethane are typical coatings. However, these involve problems of adhesion, elasticity, and cost, so they are not commonly used. 5.1.2.2 Chemical Antiozonants. These are mostly secondary alkyl aryl amines R-NH- Ar and related compounds. They give excellent protection. Most of them discolor badly, but several are recommended for nonstaining applications. Most compounders use a combination of physical and chemical antiozonants and achieve excellent protection in this way. For more severe ozone-resistance problems, there are, of course, a number of specialty elastomers that are saturated and therefore completely ozone-resistant: ethylene/propylene rubber, chlorinated and chlorosulfonated polyethylene, ethylene/vinyl acetate, ethylene/acrylic esters, butyl rubber, SEBS, plasticized PVC, butyl acrylate copolymers, polyepichlorohydrin and copolymers, polyetherester block copolymer, polyurethane, and silicone. 5.1.3 PVC Heat Stabilizers PVC is very heat sensitive. When it is heated during processing, or even during use, it loses HCl, which is toxic and corrosive; forms C=C bonds which cause discoloration; and cross-links, causing clogging of process equipment and embrittlement of products (Fig. 5.2). The problem is caused by an occasional unstable Cl atom that is destabilized by being adjacent to a branch point, a C=C group, a C=O group, or an oxygen atom. It requires strong and precise stabilization for practical use. There are three major classes of heat stabilizers for PVC, as described below. 5.1.3.1 Lead Compounds. These were the earliest in commercial practice. “Normal” lead salts included sulfate, silicate, carbonate, phosphite, stearate, maleate, and phthalate. “Basic” lead salts combined these with lead oxide, giving greater stability. They were low- cost, efficient, and gave excellent electrical resistance. Disadvantages were opacity, sulfur- staining, and toxicity. Due to worries about toxicity, their use has been restricted to electrical wire and cable insulation. TABLE 5.6 World Consumption of Antioxidants Type Percent BHT 14 Higher phenols 42 Phosphites 31 Sulfides 9 Other 4 Thousand metric tons 207 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES PLASTICS ADDITIVES 5.9 5.1.3.2 Ba/Ca Soap + Cd/Zn Soap + Epoxidized Fatty Ester + Organic Phosphite. This synergistic combination has always been unnecessarily secretive, sold under vague names such as “mixed metal,” “synergistic,” and so on. It is universally used for plasticized PVC, because it is soluble, economical, and effective. The metal soap may be phenate, octoate, neodecanoate, naphthenate, benzoate, laurate, myristate, palmitate, or stearate. The Group IIB metal soap (Cd or Zn) is the primary stabilizer. It replaces an unstable Cl atom by a stable ester group, Polymer-Cl + M(O 2 CR) 2 → Polymer-O 2 CR + MCl 2 Cd is more reliable, but worries about toxicity have practically eliminated its use. Zn is more powerful but tricky, so compounders have had to learn how to handle it very care- fully. The Group IIA metal soap (Ba or Ca) is a reservoir to regenerate the essential Group IIB metal soap: Ba(O 2 CR) 2 + ZnCl 2 → BaCl 2 + Zn(O 2 CR) 2 Ba works best, but there is some worry about toxicity. Ca is less effective but completely nontoxic, so it is used when there is worry about toxicity. The epoxidized fatty ester may be epoxidized soybean oil for compatibility and non- toxicity, or epoxidized tall oil esters for low cost and low-temperature flexibility. It is generally believed to function by neutralizing HCl. It may also replace unstable Cl on the polymer or complex ZnCl 2 to keep it from degrading the PVC. The organic phosphite is generally believed to function by complexing ZnCl 2 to keep it from degrading the PVC. The synergistic effect is clearly seen by comparing the individual ingredients with the total system (Table 5.7). Typical concentrations are about 2 percent metal soap, 5 percent epoxidized fatty ester, and 1 percent organic phosphite. 5.1.3.3 Organotin Salts. The most powerful and expensive stabilizers for PVC are organotin compounds, most generally of the type R 2 SnX 2 . The R group is most often butyl, but FIGURE 5.2 Thermal degradation of PVC. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES 5.10 CHAPTER 5 sometimes is octyl for food packaging or methyl for higher efficiency. The most powerful X group is –SCH 2 CO 2 C 8 H 17 , which is called isooctyl thioglycollate or isooctyl mercap- toacetate. For greater lubricity or UV stability, the X group may be maleate or laurate (Table 5.8). The relative amounts of R and X are sometimes varied for subtle reasons. In rigid PVC, where high melting point and high viscosity cause the most serious instability problems, organotin is always used. Concentrations range from 2 to 3 percent down to one tenth as much, depending on the equipment and process. 5.1.3.4 Miscellaneous Stabilizers. A variety of other stabilizers are vaguely mentioned in the literature, mainly by vendors. Polyols and organo-nitrogen compounds may be added to complex iron impurities in fillers and keep them from catalyzing degradation of PVC. Other additives are more secretive and their benefits less clear. Bisphenol is added to wire and cable insulation to stabilize the plasticizer rather than the PVC. UV stabilizers may be added for outdoor use, and biostabilizers are important to protect the plasticizer. 5.1.3.5 Other Organohalogens. Thermal instability is also a problem in other polymers such as chlorinated polyethylene, chlorinated PVC, polyvinylidene chloride, chlorinated rubber, and chlorinated and brominated flame-retardants. PVC heat stabilizers may help here, too, but require careful adjustment for optimum performance in each system. TABLE 5.7 Synergistic Stabilization of PVC: Gardner Color After Aging in 150°C Oven Aging time, minutes 0 50 200 1 percent barium laurate 1 13 14 1 percent cadmium laurate 1 3 3 1 percent zinc laurate 1 18 18 5 percent epoxidized soybean oil 2 10 13 1 percent alkyl diaryl phosphite 1 17 18 All five together 1 1 2 TABLE 5.8 Organotin Stabilization of PVC: Gardner Color After Aging in 175°C Oven Aging time, minutes 30 60 Unstabilized 13 15 3% dibutyl tin dilaurate 2 5 3% dibutyl tin maleate 2 3 3% dioctyl tin bis-octylthioacetate 1 2 3% dibutyl tin bis-octylthioacetate 1 2 3% dimethyl tin bis-octylthioacetate 1 1 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES PLASTICS ADDITIVES 5.11 5.1.3.6 Market Volume. The total market for PVC heat stabilizers may be about 100 million pounds in the United States and 1 billion pounds worldwide, half for organotin and half for metal soap-epoxidized fatty ester-organic phosphite systems. 5.1.4 Ultraviolet Light Stabilizers Five percent of the sunlight that penetrates the ozone layer and reaches the Earth is high- energy short-wavelength ultraviolet (UV) radiation, 290 to 400 nm. When polymers are used out of doors, absorption of this UV energy raises the electrons of primary covalent bonds from their low, stable energy level up to higher unstable energy levels that lead to degradation (Tables 5.9 and 5.1). Polymer structures that can absorb UV include benzene rings, C=C, C=O, OH, ROOH (Table 5.10), and especially conjugated groups of such structures. Even polymers that do not contain such groups may still degrade, and the blame is then placed on impurities or complex-formation. UV degradation can lead to cleavage to lower molecular weight or cross-linking to higher molecular weight, unsatura- tion, photooxidation, and photohydrolysis, all of which result in weathering deterioration. There are a number of ways to protect plastic products for use outdoors, as described below. TABLE 5.9 UV Wavelengths and Energy Levels UV wavelength, nm Energy level, kcal 259 111 272 105 290 100 300 95 320 90 340 84 350 81 400 71 TABLE 5.10 UV Absorption by Functional Groups in Polymers Benzene rings <350 nm C=C <250 nm C=O <360 nm O-H <320 nm ROOH <300 nm Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES 5.12 CHAPTER 5 5.1.4.1 UV Reflectors. If a UV-resistant material will reflect UV light away from the polymer, this can increase its lifetime tremendously. A metallized surface can give such protection, and, if it is made extremely thin, it may be able to combine UV stability and visible transparency. Pigmented fluoropolymer and acrylic coatings can be applied to the polymer, either by coextrusion of capstock or by post-coating, and provide such stability. More simply, dispersion of TiO 2 and especially aluminum flake in the polymer can reflect away most of the UV before it reaches more than a few surface molecules of the polymer, and this technique has been very popular. 5.1.4.2 UV Absorbers. Certain classes of additives absorb UV so efficiently that there is very little UV left to attack the polymer. They also have the little-understood ability to dispose of the excess energy harmlessly. o-hydroxy benzophenones, and especially o-hydrox- yphenyl benzotriazoles, are quite successful, even in concentrations below 1 percent (Fig. 5.3, Tables 5.11 through 5.13). Salicylic esters are less effective at lower cost. Car- bon black is the most effective additive for stabilizing against UV degradation (Table 5.14), but, of course, it limits color to opaque black; also, it may generate so much heat that it can cause thermal degradation. Zinc oxide is the most efficient inorganic UV FIGURE 5.3 Ultraviolet light stabilizers. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES PLASTICS ADDITIVES 5.13 absorber and is useful especially when combined with organic synergists, typically in HDPE and polypropylene. 5.1.4.3 Quenchers. When a polymer absorbs UV energy, it may be able to dispose of it harmlessly by intermolecular transfer to certain additives that can then carry the energy away and dispose of it harmlessly. These additives are referred to as energy quenchers. Or- TABLE 5.11 Polypropylene UV Stabilization: Laboratory-Accelerated UV to 50 Percent Loss of Tensile Strength Stabilizer Hours None 350 0.50 percent UV absorbers 800–2000 0.25 percent HALS 4000 0.50 percent HALS 6800 TABLE 5.12 ABS UV Stabilization: Retention of 20 kg/m 2 Impact Strength After Lab-Accelerated UV Aging Stabilizer Hours None 225 1 percent UV absorber 500 1 percent HALS 1225 0.5 percent UVA + 0.5 percent HALS 2000 TABLE 5.13 Polycarbonate UV Stabilization: Laboratory-Accelerated UV Aging to Yellowness Index +5 Unstabilized 700 hr 0.25 percent UV absorbers 2800 hr TABLE 5.14 ABS Stabilization by Carbon Black Impact Strength Retained After Five Years Outdoor Weathering Natural color 40% Black 82% Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES 5.14 CHAPTER 5 gano-nickel compounds are often useful as quenchers. Carbon black probably functions partly as a quencher. 5.1.4.4 Hindered-Amine Light Stabilizers (HALS). Most UV degradation is actually photooxidation—UV-accelerated free-radical attack by atmospheric oxygen. The most re- cent and most popular way of stabilizing polymers against it is by addition of hindered amines to interfere with the free-radical chain reaction. R 2 NH + O 2 → R 2 NO . This nitroxide radical reacts with a degrading polymer radical R´ . R 2 NO . + . R´ → R 2 NOR´ This reacts with another degrading polymer radical R´´ . R 2 NOR´ + . R´´ → R 2 NO . + R´R´´ This produces stable polymer R´R´´ and regenerates the nitroxide radical to continue its work (Tables 5.11 and 5.12). Since UV absorbers and HALS operate by different mechanisms, combined use of the two types of stabilizers offers beneficial synergism (Table 5.12). 5.1.4.5 Market Volume. Table 5.15 provides market volume information for some leading stabilizers. 5.1.4.6 Prodegradants. When plastics accumulate in solid waste, it might be desirable to accelerate their UV degradation. This has been accomplished semicommercially by in- corporating enough C=O groups to absorb UV energy and initiate photodegradation processes. It has also been demonstrated experimentally by adding transition metal compounds such as ferrous laurate to catalyze photooxidation of the polymer (Table 5.16). TABLE 5.15 Leading UV Stabilizers HALS 46 percent Benzotriazoles 27 percent Benzophenones 20 percent Others 7 percent Total 24,800 tons Use in polymers Polypropylene 45 percent Polyethylene 29 percent PVC 9 percent Engineering plastics 7 percent Styrenics 5 percent Others 5 percent Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES PLASTICS ADDITIVES 5.15 These techniques do not destroy the polymer, but they embrittle it enough to crumble, and oxidize it enough to promote biodegradation later (Table 5.17). 5.1.5 Biostabilizers Microorganisms such as bacteria, actinomycetes, and fungus can attack plastics, producing discoloration and degradation of mechanical and electrical properties. They thrive pri- marily at 20 to 30°C and high humidity, whenever they can find a source of food. Natural polymers such as cellulose and protein are a good source of food. Animal fats and vegeta- ble oils are a good source of food; when they are used in paints, alkyds, and urethanes, these polymers are biodegradable. Synthetic polymers that contain aliphatic hydroxyl and ester groups may be a good source of food; these include polycaprolactone, polyester urethanes, and the new purposely biodegradable polylactic acid, polyhydoxybutyrate, and polyhydroxyvalerate. Fairly sensitive polymers include polyvinyl acetate, polyvinyl alco- hol, and ethylene/vinyl acetate. Most other polymers are not inherently biodegradable. However, monomeric additives are often an excellent source of food and primary focus of biological attack: ester plasticizers, epoxy ester stabilizers, and natural esters used in polyurethanes and fatty ester lubricants are the most common problems. (Starch fillers have actually been used to incorporate biodegradability in plastics.) A variety of chemicals can be used to stabilize plastics against biological attack. TABLE 5.16 Accelerated UV Embrittlement of Polypropylene Time to embrittlement Ferrous laurate, % Unstabilized, hr Heat-stabilized, hr 0 118 384 0.01 0 167 0.1 0 167 1.0 0 95 2.0 0 47 TABLE 5.17 Fungus Growth * on Molded Plastics: Effect of UV Degradation *.Trace = barely noticeable, slight = 10–30% of surface, moderate = 30–60% of surface, heavy = 60–90% of surface. UV degradation before fungus test None 4 months High-density polyethylene Trace Heavy Polystyrene Trace Trace 90 percent PS + 10 percent styrene/vinyl ether copolymer Trace Slight 50 percent PS + 50 percent styrene/vinyl ether copolymer Trace Moderate Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES 5.16 CHAPTER 5 Testing usually begins by placing plastics samples in Petri dishes, injecting microorganisms, and observing whether they grow. Further testing may include humidity, soil burial, and other natural exposures. A major problem is that species of microorganisms vary from one geographic region to another, so it is hard to design reliable broad-spectrum laboratory tests and to recommend successful additives from one region to another. The greatest problem is differential toxicity. Any chemical that is toxic to microorganisms will probably be toxic to macroorganisms such as ourselves. Thus, it is necessary to distinguish those additives that offer maximum toxicity toward microorganisms along with minimum toxicity toward macroorganisms, and to define the critical balance for different plastic products. 5.1.5.1 10,10´-oxy-bis(phenoxarsine) (OBPA). This (Fig. 5.4-I) is the leading commercial antimicrobial. It is very efficient, so it can be used at very low concentration (0.04 percent) and can be synergized by bis(trichloromethyl) sulfone. 5.1.5.2 2-n-octyl-4-isothiazoline-3-one. This (Fig. 5.4–II) is a newer antimicrobial that is nontoxic to humans and is used at 3 percent in vinyls and paints. 5.1.5.3 Trichloromethyl Thio Phthalimide. This (Fig. 5.4–III) is harmless to humans and is useful at 0.25 to 0.50 percent to control actinomycetes, which cause pink staining of plasticized vinyls. 5.1.5.4 Diphenyl Antimony 2-Ethylhexoate. This (Fig. 5.4–IV) is approved for use in vinyl shower curtains, wallpaper, upholstery, and rug underlay. 5.1.5.5 Copper Quinolinolate. This (Fig. 5.4–V) is relatively harmless to humans. Used at 0.5 percent, it controls mildew. Because of its deep yellow-green color, it is used mainly for military purposes. FIGURE 5.4 Biostabilizers. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES [...]... sharp edges of filler particles and the sharp ends of fibers that protrude from the surface of the polymer matrix FIGURE 5.5 Unbreakable plastics Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies All rights reserved Any use is subject to the Terms of Use as given at the website PLASTICS ADDITIVES 5. 19 PLASTICS ADDITIVES... Concentrations of Foaming Agents Used in Processing Process Soft plastisol % 2–4 Extrusion of structural foam Injection molding of structural foam 0.3–0.5 Elimination of sink marks in injection molding 5.6.4 0.2–1.0 0.05–0.1 Combinations of Foaming Agents Processors have always had some interest in using combinations of foaming agents, such as combinations of volatile hydrocarbons or combinations of fluorocarbons... silica, silicates) 5.5.5 Major Use in Polymers 5.5.5.1 Market Distribution A breakdown of lubricant market distribution is provided in Table 5. 29 TABLE 5. 29 Use of Lubricants in Plastics Lubricant % Polyvinyl chloride 44 Styrenics 12 Polyolefins 7 Other thermoplastics 4 Thermosets Total lubricants/total plastics 33 0. 19 5.5.5.2 Polyvinyl Chloride Average lubricant concentration 0.6 percent Paraffin and... Terms of Use as given at the website PLASTICS ADDITIVES PLASTICS ADDITIVES 5.35 5.5 LUBRICANTS AND PROCESSING AIDS The term lubricants is used by a variety of specialists to cover a range of chemicals that are added to plastics to improve a variety of performance characteristics in processing or in final properties When they are used to improve processing, the field may expand to include other types of. .. inventor of plasticized PVC lived healthily to the age of 101 5.4.4 Permanence Plasticizer failure can shorten the useful life of the plastic product Failure can be either loss of plasticizer (it is “fugitive”) or degradation of the plasticizer (“aging”) 5.4.4.1 Fugitivity Plasticizer may escape for a number of reasons Volatility is gradual evaporation at higher temperatures, such as fogging of auto... cost of commodity plastics, but they may actually reduce the cost of some high-end engineering thermoplastics 5.2.2 Extender Fillers Simple inorganic particles are generally added to plastics to increase modulus, friction, and opacity, and to reduce raw material cost 5.2.2.1 Glass Microspheres Glass microspheres range in size from 5000 down to 4 µm and may be solid or hollow down to one tenth of solid... reserved Any use is subject to the Terms of Use as given at the website PLASTICS ADDITIVES PLASTICS ADDITIVES 5.25 5.2.5.2 Thermal Conductivity Thermal conductivity can be increased to shorten molding cycles and to avoid overheating of electrical equipment Silver, copper, and aluminum have conductivities 1000 times that of unfilled plastics; loading them into plastics can increase conductivity considerably,... injection molding, 0.5 percent of 3-µm metal oxide, metal salt, pigment, or other minerals, and ionomer are mentioned For thermoformed food trays, 1 to 3 percent of lowMW polyolefin 5.5.6 .9. 4 Nylon Mentioned most often is 0.1 percent of silica Others mentioned include Na benzoate, minerals, MoS2, FeS, TiO2, talc, Na phenyl phosphinate, and higherMP polymers 5.5.7 Effects of Lubricants on Other Final Properties... percent of the market 5.6.3.3.3 AZDN [Azo-Di(Carbonamide)] or ABFA [Azo-bis(Formamide)] Catalysts permit use at lower temperatures; coarse particle size permits use at higher temperatures It is widely used in commodity thermoplastics and even some engineering thermoplastics; about 90 percent of the market 5.6.3.3.4 TSSC: p-Toluene Sulfonyl Semicarbazide Somewhat better for engineering thermoplastics... toward lower and lower temperatures, in proportion to the amount of plasticizer added This lowers the stiffening temperature of flexible plastics It also lowers the softening temperature of rigid plastics, which limits maximum use temperature but improves melt processability When epoxidized fatty esters are used to synergize thermal stabilization of PVC (Sec 5.1.3.2), these are liquids which therefore also . 0 95 2.0 0 47 TABLE 5.17 Fungus Growth * on Molded Plastics: Effect of UV Degradation *.Trace = barely noticeable, slight = 10–30% of surface, moderate = 30–60% of surface, heavy = 60 90 % of. the cost of commodity plastics, but they may actually reduce the cost of some high-end engineering thermoplastics. 5.2.2 Extender Fillers Simple inorganic particles are generally added to plastics. rights reserved. Any use is subject to the Terms of Use as given at the website. PLASTICS ADDITIVES PLASTICS ADDITIVES 5. 19 5.2.1.8 Coefficient of Thermal Expansion (CTE). CTE is inverse to the

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