Natural Rubber NR and Synthetic Polyisoprene

Natural rubber and guttapercha consist essentially of polyisoprene in a s-1,4 and trans-1,4 isomers, respectively. Commercially produced synthetic polyisoprenes have more or less identical structures but reduced chain regularity, although 

A very important process occurring during irradiation is the formation of free radicals that leads to other changes, such as cross-linking, polymerization reactions, and grafting. 

About 98% of gas formed during radiolysis of natural rubber and polyiso-prene is hydrogen, the rest consists of methane and higher-molecular-weight hydrocarbons. The yield of hydrogen is directly proportional to dose up to 200 Mrad (2,000 kGy). Moreover, it is independent of dose rate and the type of radiation (gamma, electron beam).i  

Cross-linking of natural rubber and synthetic polyisoprene has been studied by several investigators using electron beam and gamma radiation. The general conclusion is that the yield of chemical cross-links, G(X), is constant with dose and independent of dose rate and the type of radiation used. Effects of temperature are reported in Bohm and Tveekrem.  

Clearly, large doses are required for a full cure. The dose levels for attaining a maximum tensile strength are within 20 to 50 Mrad (200 to 500 kGy). 

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