Effect of rubber composition on foaming and properties of EVA/NR/PP thermoplastic vulcanisates (TPVs)

Thermoplastic vulcanisate (tpv) foams made of ethylene vinyl acetate (eva),natural rubber (nr) and polypropylene (pp) were prepared via dynamic vulcanisation and subsequently foamed using a single screw extrusion process. eva and nr were blended at different compositions by keeping proportion of the rubber part (eva/nr blend) to pp at 60/40%wt. azodicarbonamide was used as a chemical blowing agent. scanning electron microscopic study was performed to evaluate the foaming behaviour of tpvs and morphology of unfoamed tpvs. blending eva alone with pp resulted in low cell density and large cell diameter. however,the cell density increased and cell diameter decreased significantly upon partial replacement of eva with nr. the bulk density of eva/nr/pp foams was found to be independent of blend composition. tensile strength and elongation at break were improved with increased nr content,but these two properties were reduced after heat ageing. thermogravimetric analysis indicated that thermal stability of the tpv foams was not affected as more eva in the component rubber was replaced with nr. the present study suggested that the production of light weight and good thermal resistant eva/nr/pp tpv foams with improved cell structure and strength was obtained with the partial replacement of eva by 12%wt nr.