Polyethylene degradation of chlorinated

Pyrolysis products of chlorinated polyethylene contain molecules similar to those found in polyethylene pyrolysates and, in addition, compounds similar to that obtained from vinyl chloride (significant amount of HCI). Chlorosulfonated polyethylene typically contains only about 1.5% sulfur, but sulfur-containing compounds such as SO2 can be detected among its pyrolysis products. The distribution of chlorine atoms in chlorinated polyethylene has been investigated using Py-GC [55, 56]. The polymer was considered equivalent with a terpoiymer poly[ethylene-co-(vinyl chloride)-co-(1,2-dichloroethylene)]. The level of specific degradation products such as aromatic molecules (benzene + toluene + styrene + naphthalene), chlorobenzene, and dichlorobenzenes correlates well with the carbon/chlorine ratio in the polymer. 

Heat stabilizers protect polymers from the chemical degrading effects of heat or uv irradiation. These additives include a wide variety of chemical substances, ranging from purely organic chemicals to metallic soaps to complex organometaUic compounds. By far the most common polymer requiring the use of heat stabilizers is poly(vinyl chloride) (PVC). However, copolymers of PVC, chlorinated poly(vinyl chloride) (CPVC), poly(vinyhdene chloride) (PVDC), and chlorinated polyethylene (CPE), also benefit from this technology. Without the use of heat stabilizers, PVC could not be the widely used polymer that it is, with worldwide production of nearly 16 million metric tons in 1991 alone (see Vinyl polymers). 

ACS polymers, developed primarily in Japan, are grafts of acrylonitrile and styrene onto elastomeric chlorinated polyethylene. Although the polymer has good weathering properties it is somewhat susceptible to thermal degradation during processing and to date these polymers have been of limited interest. 

Most properties of polypropylene are similar to polyethylene but polypropylene has higher softening point and at 140°C polypropylene still retains its shape. Polypropylene is more susceptible to oxidation by air at higher temperature. Cross-linking, chlorination and other reactions lead to degradation of Polymer chain and are not very useful commercially. 

In this case, there are too few macroradicals available for reaction because of insufficient polymer degradation. In the disk-type extruder, a higher-stress gradient is achievable, more macroradicals are generated, and intensive cross-linking between polyethylene or highly chlorinated polyethylene and maleic anhydride or methyl methacrylate can be obtained (Heinicke 1984, Zhao et al. 2002, 2003). 

In all cases, authors showed that such copolymers are stable only if intramolecular peroxides resulting from ozonization have been preliminary thermally decomposed before the above reactions. Their presence in the polymer backbones leads, in a very short time, to dehydrochlorination reactions and degradation of polymers. These works have been extended to other polymers, such as chlorinated polyethylene, vinyl chloride-vinyl acetate copolymers [127]. 

A chemical destruction method that has been used for the treatment of PCBs in contaminated dielectric liquids or soil is based on the reaction of a polyethylene glycol/potassium hydroxide mixture with PCBs (De Filippis et al. 1997). This method can be used successfully for the destruction of higher chlorinated PCBs with an efficiency of >99%, but was found to be unsuitable for the treatment of di- and trichlorobiphenyls due to low destruction efficiencies (Sabata et al. 1993). Irradiation of PCBs in isooctane and transformer oil by y-radiation resulted in degradation of PCBs to less chlorinated PCBs and PCB-solvent adducts (Arbon et al. 1996). Supercritical fluid technology has shown promise as a method for extraction of PCBs from soils, coupled with supercritical water oxidation of the extracted PCBs (Tavlarides 1993,1998a). Hofelt and Shea (1997) demonstrated the use of semipermeable membrane devices to accumulate PCBs from New Bedford Harbor, Massachusetts water. Another method showing... 

At the same time, we confirmed that ZnCl2 catalyses the dehydrochlorination of polychloroprene at temperatures below 200°C, but the reaction is very slow, and also accelerates on the evolution of hydrogen chloride by thermal degradation. The effect of ZnO has been observed in other chlorine - containing polymers including polyvinylidene chloride, chlorinated polyethylene and polyepichlorohydrin. The phenomenon thus seems unlikely to be a function of polymer structure. 

A copolymer of methyl methacrylate and vinyl chloride containing labelled chlorine ( "Cl) has been examined using thermovolatilization analysis and radiochemical assay. The yields of methyl chloride and hydrogen chloride agree with predictions made from sequence distribution calculations. The thermal degradation of a number of chlorine-containing polymers, poly(vinyl chloride), chlorinated polyethylene, chlorosulphonated polyethylene, polychloroprene, poly-epichlorhydrin, and co- and ter-polymers of epichlorhydrin has been compared and structural effects elucidated. ... 

When a molded material contacts a strongly oxidizing medium, such as nitric acid, sulfuric acid, chlorine, bromine, and ozone, oxidative attack has to be expected. Table 5.68 shows the influence of chlorine on polyethylene resistance. Polymers with double bonds or with tertiary bound hydrogen atoms, such as polypropylene, are particularly prone to oxidation. Degradation due to oxidizing substances causes significant changes in mechanical, electrical, and optical properties. 

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