Effects of chemical blowing agents on swelling properties of expanded elastomers

Two commercial chemical blowing agents, azodicarbonamide (ADC) and oxybisen zenesulphonylhydrazide (OBSH), were used alone and in blends for expanded n atural rubber vulcanisates. The expanded rubber vulcanisates were character ised with respect to the apparent foam density, degree of crosslinking, ten sile properties and swelling behaviour. For a given blowing agent, the appa rent foam density and crosslink density were found to change with blowing a gent content. The swelling behaviour greatly changed with OBSH content, but was unaffected by ADC content. The OBSH blowing agent seemed to generate m ore voids in the vulcanisates as compared to the ADC blowing agent and thus increased swelling. The swelling ratio of the NR vulcanisates having blend ed blowing agents tended to be more influenced by OBSH than ADC blowing age nts.