Cellular vinyls, production

Poly(vinylchloride). Cellular poly(vinyl chloride) can be produced from several expandable formulations as well as by decompression techniques. Rigid or flexible products can be made depending on the amount and type of plasticizer used (43). 

A variety of cellular plastics exists for use as thermal iasulation as basic materials and products, or as thermal iasulation systems ia combination with other materials (see Foamed plastics). Polystyrenes, polyisocyanurates (which include polyurethanes), and phenoHcs are most commonly available for general use, however, there is increasing use of other types including polyethylenes, polyimides, melamines, and poly(vinyl chlorides) for specific appHcations. 

A substantial part of the market for the ethylene-vinyl acetate copolymer is for hot melt adhesives. In injection moulding the material has largely been used in place of plasticised PVC or vulcanised rubber. Amongst applications are turntable mats, base pads for small items of office equipment and power tools, buttons, car door protector strips and for other parts where a soft product of good appearance is required. Cellular cross-linked EVA is used in shoe parts. 

In the massive form poly(vinyl chloride) is a colourless rigid material with limited heat stability and with a tendency to adhere to metallic surfaces when heated. For these, and other, reasons it is necessary to compound the polymer with other ingredients to make useful plastics materials. By such means it is possible to produce a wide range of products, including rigid piping and soft elastic cellular materials. 

The moisture resistance, low cost, and low-density closed-cell structure of many cellular polymers resulted in their acceptance for buoyancy in boats, floating docks, and buoys. Because each cell is a separate flotation unit, these materials cannot be destroyed by a single puncture. Foamed-in-place polyurethane between thin skins of high tensile strength is used in pleasure craft [98]. Other cellular polymers that have been used where buoyancy is needed are produced from polystyrene, polyethylene, poly(vinyl chloride), and certain types of rubber. Foams made from styrene-acrylonitrile copolymers are resistant to petroleum products [99,100]. 

Flexible plastic foams may be found in the form of very soft cushioning materials used in upholstery, clothing interlayers, automobile seats, vibration absorbers, etc. The most common flexible foam resins are polyurethanes, foamed vinyls, cellular polyethylene, cross-linked polyethylene, and silicone foam. Semirigid foams are used for floatation devices, marine bumpers, special electrical insulation on television cables, packaging, and a host of other applications. Rigid foams are used in the production of airplane parts, boats, electronic encapsulation, and many furniture applications where wood was formerly used. 

Pre-treatment of rats with phenobarbitone, which is known to increase the P450 content of microsomal enzymes, increased the mutagenic response to vinyl chloride monomer in vitro (Bartsch etal. 1975). In an aqueous solution at pH 7.4 and 37 °C the epoxy compound had a half-Ufe of 1.6 min, and its rate of hydrolysis followed a first order kinetic. Chloroethylene oxide, but not 2-chloroacetaldehyde, showed a strong alkylating activity as determined by its reaction with 4-(p-nitrobenzyl)pyridine (Malaveille etal. 1975). 2-Chloroacetaldehyde is a chemically reactive and toxic compound (Lawrence et al. 1972), and is covalently bound to cellular nucleophiles. It reacts at pH 3.5-4.5 and 37 °C with adenosine or cytidine to give fluorescent products, which have been characterised as 3- 3-D-ribofuranosyl-imidazo-(2,l-i)pur-ine or 5,5-dihydro-5-dihydro-5-oxo-5- 3-D-ribofu-... 

The combination of structural strength and flotation has stimulated the design of pleasure boats using a foamed-in-place polyurethane between thin skins of high tensile strength (242). Other cellular poljmiers that have been used in considerable quantities for buoyancy applications are those produced from polyethylene, polystyrene, poly(vinyl chloride), and certain types of rubber. The susceptibility of polystyrene foams to attack by certain petroleum products that are likely to come in contact with boats led to the development of foams from copolymers of styrene and acrylonitrile that are resistant to these materials (243,244). 

A variety of hydroxy-terminated unsaturated polyesters have been evaluated as intermediates in polyurethane foams.These intermediates include the ethoxylated or propoxylated derivatives of lignin-, sorbitol-pentaerythritol-MA condensation products. " MA has also been blended with poly(vinyl chloride) and diisocyanates to obtain cellular PVC materials. "- " ... 

Recommended for products adhesives, blood bags, cellular rubber goods, film sheeting, gaskets, general purpose film, industrial hose and tubing, low viscosity plastisols, packaging, sealants, PVC film, vinyl foam ... 

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