Observation of morphology in EPDM/nylon copolymer thermoplastic vulcanizates by atomic force microscopy

A thermoplastic vulcanizate (TPV) of an ethylene propylene diene terpolymer (EPDM) and nylon copolymer (PA) was prepared. Maleic anhydride‐grafted EPDM (EPDM‐ g ‐MAH) and MAH‐grafted EPR (EPR‐ g ‐MAH) were used as compatibilizers and sulfur was used as a curative. The phase morphology of EPDM/PA TPVs was investigated by atomic force microscopy (AFM). AFM images showed that, although there was a compatibilization reaction between EPDM‐ g ‐MAH and PA, phase inversion always existed for EPDM/EPDM‐ g ‐MAH/PA TPVs and the rubber phase could be finely dispersed in the PA matrix with an increasing compatibilizer content. For TPVs using EPR‐ g ‐MAH as a compatibilizer, three phases existed because of noncrosslinkability of EPR by sulfur. Crosslinked EPDM particles dispersed in a comatrix of PA and EPR‐ g ‐MAH could be observed by increasing the content of EPR‐ g ‐MAH to 26 wt %. For an EPR‐ g ‐MAH content of 26 wt %, the uncrosslinked EPR‐ g ‐MAH existing in the interface between crosslinked EPDM and PA tended to coalesce and thus resulted in a morphology of large rubber regions composed of small crosslinked particles. When the dosage of EPR‐ g ‐MAH was 52 wt %, the phase morphology of the blends changed to being one of PA and crosslinked EPDM particles dispersed in the MAH‐ g ‐EPR matrix.