10.6 |
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SECTION 10 |
|
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injection molding. Common liquid foaming agents are short-chain aliphatic hydrocarbons in the C |
5 |
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to C 7 |
range and their chlorinated or fluorinated analogs. |
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The chemical foaming agent used varies with the temperature employed during processing. At |
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|
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relatively low temperatures (15 to |
200 |
C), the foaming agent is often |
4,4 |
-oxybis- |
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(benzenesulfonylhydrazide) or p -toluenesulfonylhydrazide. In the midrange (160 to |
232 |
C), either |
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sodium hydrogen carbonate or 1,1 |
azobisformamide is used. For the high range (200 to |
285 |
C), |
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there are |
p -toluenesulfonyl semicarbazide, 5-phenyltetrazole and analogs, and trihydrazinotriazine. |
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10.2.7 Inhibitors
Inhibitors slow or stop polymerization by reacting with the initiator or the growing polymer chain. The free radical formed from an inhibitor must be sufficiently unreactive that it does not function
as a chain-transfer agent and begin another growing chain. Benzoquinone is a typical free-radical chain inhibitor. The resonance-stabilized free radical usually dimerizes or disproportionates to produce inert products and end the chain process.
10.2.8 Lubricants
Materials such as fatty acids are added to reduce the surface tension and improve the handling qualities of plastic films.
TABLE 10.1 Plastic Families
Acetals
Acrylics
Poly(methyl methacrylate) (PMMA) Poly(acrylonitrile)
Alkyds
Alloys
Acrylic-poly(vinyl chloride) alloy Acrylonitrile-butadiene-styrene-poly(vinyl chlo-
ride) alloy (ABS-PVC) Acrylonitrile-butadiene-styrene-polycarbonate al-
loy (ABS-PC) Allyls
Allyl-diglycol-carbonate polymer Diallyl phthalate (DAP) polymer
Cellulosics
Cellulose acetate resin Cellulose-acetate-propionate resin Cellulose-acetate-butyrate resin Cellulose nitrate resin
Ethyl cellulose resin Rayon
Chlorinated polyether Epoxy
Fluorocarbons Poly(tetrafluoroethylene) (PTFE)
Poly(chlorotrifluoroethylene) (PCTFE) Perfluoroalkoxy (PFA) resin
Fluorinated ethylene-propylene (FEP) resin
Fluorocarbons ( continued ) Poly(vinylidene fluoride) (PVDF) Ethylene-chlorotrifluoroethylene copolymer Ethylene-tetrafluoroethylene copolymer Poly(vinyl fluoride) (PVF)
Melamine formaldehyde Melamine phenolic Nitrile resins Phenolics
Polyamides Nylon 6 Nylon 6/6 Nylon 6/9 Nylon 6/12 Nylon 11 Nylon 12 Aromatic nylons
Poly(amide-imide) Poly(aryl ether) Polycarbonate (PC) Polyesters
Poly(butylene terephthalate) (PBT) [also called polytetramethylene terephthalate (PTMT)]
Poly(ethylene terephthalate) (PET) Unsaturated polyesters (SMC, BMC)
Butadiene-maleic acid copolymer (BMC) Styrene-maleic acid copolymer (SMC)
Polyimide