CB filled EOC/EPDM blends as a shape-memory material: Manufacturing, morphology and properties

Abstract

According to theoretical prediction using the Z-model proposed by us a predominant localization of carbon black (CB) in the ethylene propylene diene rubber (EPDM) phase of ethylene octene copolymer (EOC)/EPDM blends was found for a thermodynamic equilibrium state, in case that rheological effects do not play a significant role. In this paper, a special mixing procedure based on the well-known dynamic vulcanization techniques was developed to localize CB in the EOC matrix in order to obtain a low electrical resistivity. Effect of size of the EPDM domains on the electrical resistivity was characterized and it was found that exceeding a critical EPDM domain size of about 30 μm the electrical resistivity decreases exponentially. An inhomogeneous CB distribution formed in the EOC matrix at EPDM domain sizes above 30 μm is the reason for the strong decay of resistivity. The effect of CB network formation during cross-linking process on the resistivity was also characterized by means of the online measured electrical resistance. The electrical resistivity changes strongly after peroxidic cross-linking process, while it remains nearly unchanged after cross-linking with high energy electrons. The Joule heating shape-memory recovery of CB filled EOC/EPDM blends cross-linked by peroxide and by high energy electrons was comparatively characterized and discussed.