Effects of Chemical Blowing Agents on Swelling Properties of Expanded Elastomers

Two commercial chemical blowing agents, azodicarbonamide (ADC) and oxybisenzenesulphonylhydrazide (OBSH), were used alone and in blends for expanded natural rubber vulcanisates. The expanded rubber vulcanisates were characterised with respect to the apparent foam density, degree of crosslinking, tensile properties and swelling behaviour. For a given blowing agent, the apparent foam density and crosslink density were found to change with blowing agent content. The swelling behaviour greatly changed with OBSH content, but was unaffected by ADC content. The OBSH blowing agent seemed to generate more voids in the vulcanisates as compared to the ADC blowing agent and thus increased swelling. The swelling ratio of the NR vulcanisates having blended blowing agents tended to be more influenced by OBSH than ADC blowing agents.