Polyethylene peroxide-cured

Vinyl Free radical cure systems crosslinked polyethylene, peroxide cured elastomers, polyesters. Polyethylene. Polypropylene. 

FIGURE 5.15 Failure envelope of various mixes A, natural rubber-polyethylene (NR-PE) vul-canizate (peroxide cured) , NR-PE vulcanizate (sulfur cured) , NR-PE vulcanizate with CPE as compati-bilizer V, EPDM-PE vulcanizate o, EPDM-PP vulcanizate (sulfur cured) NR-ENR-PE -PE. (Erom Roy Choudhury, N. and Bhowmick, A.K., J. Mat. Sci., 25, 161, 1990. With permission from Chapman HaU.)... 

Polyethylene can also be blended with a number of other mbbers. When ozonolysed natural mhher is blended with polyethylene and cured, it was found that sulphur dynamic vulcanization was better than peroxide curing, with a higher crosslink density resulting in a change in the LDPE crystallization behaviour [62]. 

The methods by which antioxidants function were outlined in Section 9.2. Subsequent sections however amply demonstrated that the behaviour of an antioxidant in an accelerated-sulphur cured diene rubber vulcanizate can be very different from its behaviour in a simple hydrocarbon like petrol or polyethylene or even a peroxide-cured natural rubber. Antioxidant combinations which in some circumstances behave synergistically may in other cases be antagonistic to each other. As was demonstrated in Fig. 9.1 an increase in the antioxidant loading may decrease the degree of pro-... 

Chlorinated polyethylene (CM) is produced by the chlorination of high density polyethylene either in solvent solution or aqueous suspension. The substituent chlorine on the saturated olefin backbone enhances heat and oil resistance. The chlorine also provides flame resistance. The polymer is thermoplastic when processed on conventional elastomer equipment, and compounds can be molded, calendered or extruded. Chlorinated polyethylene is most often steam cured using a peroxide curing system. The major end use is wire and cable applications, particularly flexible cords for up to 600 volts. Other major uses are in automotive hose, sheet goods and as an impact modifier in plastics. 

W.H. Davis, Jr., R.L. Laakso, Jr., L.B. Hutchinson, and S.L. Watson, Peroxide-Cured Chlorinated Polyethylene Compounds Having Enhanced Resistance to Ozone-Induced Cracking, American Chemical Society Ruhher Division, May 29-June 1,1990, PaperNo. 8. 

Another use is of minor proportions of polyfunctional aHyl esters, eg, diaHyl maleate, ttiaHyl cyanurate, and ttiaHyl isocyanurate, for cross-linking or curing preformed vinyl-type polymers such as polyethylene and vinyl chlotide copolymers. These reactions ate examples of graft copolymerization in which specific added peroxides or high energy radiation achieve optimum cross-linking (see Copolymers). 

Po[yamine disulphides do not inhibit peroxide vulcanization of polyethylene, are stable in air up to 300-350°C, exhibit good compatibility and show no sweating out from the polyethylene mass. Table 8 gives the comparison between the efficiency of polyamine disulphides as thermostabilizers of cured polyethylene. 

Additional curing is often achieved with sulfur, peroxide, or maleimide formulations. Chloro-sulfonated polyethylene has improved resistance to oil, ozone, and heat compared to many other elastomers. Applications include harrier membranes and liners, surface coatings on fabrics, automobile air-conditioner hose, electrical cable insulation, and spark-plug boots [Andrews and Dawson, 1986],... 

EP-4 developed by ERDL is a very flexible polyester based on polyethylene glycol with molecular weight-200 (PEG-200), isophthalic acid (IPA) and maleic anhydride (MAn). Before its use, it is blended with styrene monomer (1 1) and cured at room temperature using cobalt naphthenate (as an accelerator) and methyl ethyl ketone (MEK) peroxide (as a catalyst). This meets the requirements of the main inhibitor and is used for inhibition of DB and CMDB propellants after the application of a barrier coat (generally a rigid polyester such as PR-3). However, it is observed during manufacture of EP-4 that there is a lot of batch-to-batch variation in properties in spite of the strict quality control measures adopted during its manufacture. 

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