Foamability of Thermoplastic Vulcanizates Blown with Various Physical Blowing Agents

Abstract

Thermoplastic vulcanizate (TPV) is a special class of thermoplastic elastomers (TPEs) made of a rubber/plastic polymer mixture in which the rubber phase is highly vulcanized. It is prepared by melt mixing a thermoplastic with an elastomer and by in situ crosslinking of the rubber phase. Currently, TPV is replacing EPDM rubber dramatically because of the impressive advantages for automotive sealing applications. Some of the advantages of TPV compared to that of EPDM rubber are good gloss, recyclability, improved colorability, shorter cycle time, and design flexibility. The development of TPV foaming technology is to fulfill the requirement of achieving lower cost, lighter weight, and better fuel economy. Foaming of TPV has not been investigated extensively. The complete dissolution of the blowing agent in the molten polymer is the most critical step in TPV foaming processing, and this strongly depends on the solubility of the blowing agent, the saturation pressure, the degree of mixing, and residence time. In our study, we attempted to understand the foaming behavior of commercial TPVs in general, with various blowing agents. The effect of blowing agent type and concentration on the expansion behavior, the cell-number density, and the foam structure under the different processing conditions are examined. These experimental results will be used to determine optimized TPV formulations to ensure good foamability, while retaining the properties of TPV.