Study on foaming kinetics and preparation of EPDM foams

Abstract

The ethylene–propylene–diene terpolymer (EPDM) foam article was prepared by mixing a compound in a two roll mill, extruding the compound through a cold feed extruder and finally vulcanising the extrudate in a circulating hot air oven. The blowing kinetics of EPDM compounds was studied using a moving die rheometer, and the effect of blowing agent content and process temperature on the cell structures was investigated. The results show that kinetic parameters determined from the autocatalystic model equation have good agreement with the experimental results. The calculated activation energy of azodicarbonamide (AC) decomposition is higher than that of rubber cure, which indicates the rate of blowing agent AC decomposition accelerates more quickly than that of rubber vulcanisation with increasing temperature. The density of foam article decreases with increasing blowing agent content or elevated temperature. The foams have a closed cell structure and the larger cells inlay among the smaller cells, which shows cell materials with structural multihierarchy. This shows the rubber vulcanisation and blowing agent decomposition could match only using extremely slow accelerator diphenylguanidine (DPG), which is dissimilar to the conventional EPDM sponge requiring very quick scorch.