Radiation Cross-Link Promoters

Experiments on cross-linking by irradiahon have revealed that in many cases the cross-link densities equivalent to those obtained by conventional methods of cross-linking require relatively high radiation doses. Therefore, a great deal of experimental work has been done on the use of additives, which promote cross-linking by irradiation. Such compounds are called radiation cross-link promoters or prorads. 

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The tensile strength of NR compounds in the presence of cross-link promoters such as dichlorobenzene is increased as compared to the sulfur-accelerator and peroxide-curing systems. The retention of the maximum tensile strength at elevated temperamres is greater for radiation cured than for chemically vulcanized NR [326,327]. Also reported are a higher abrasion resistance [328] and a lower flex life in the case of radiation-cured system. Effect of phenoxy ethyl acrylate (PEA)... 

Thermal degradation studies of EB-cured terpolymeric fluorocarbon rubber [430] by nonisothermal thermogravimetry in the absence and presence of cross-link promoter TMPTA reveal that thermal stability is improved on radiation and more so in the presence of TMPTA. Initial decomposition temperature, maximum decomposition temperature and the decomposition... 

There are essentially two types of promoters of radiation cross-linking or prorads.32 One group, indirect cross-link promoters, do not enter directly into the cross-linking reaction, but merely enhance the formation of reactive species such as free radicals,... 

The promotion of cross-linking of polypropylene51 and ethylene-propylene copolymers52 has been confirmed. However, other bases such as amines, were not found effective — in some cases in fact, they acted as retarders of radiation cross-linking.53... 

Irradiation is an efficient method to modify the structure of a polymer. Various phenomena could be promoted by irradiation like cross-linking, grafting, chain scissioning, and oxidation. The net effect of irradiation depends mainly on the chemical structure of the polymer, on the radiation dose, on the presence of some additives (radicals scavengers or cross-linking promoters) and on some other conditions (like atmosphere). 

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