The Study On Stretching Orientation And Strain-Induced Crystallization Of EPDM

Stretching orientation and strain-induced crystallization (SIC) of rubber are widely recongnized to play key roles in the self-reinforcement of natural rubber and some synthetic rubbers. Therefore, studying this phenomenon and behavior has substantial significance for understanding the mechanism of the rubber reinforcing. In this work, we investigate the impact of ethylene content and crosslink density on stretching orientation and SIC of EPDM by combined Infrared Dichroism, Synchrotron WAXD and Sonic Method, and then establish EPDM's structure-property relationship. Main contents and conclusions are as follows.(1) Infrared Dichroism and Synchrotron Radiation WAXD are used to investigate the impact of ethylene content on stretching orientation and strain-induced crystallization of EPDM. It is found that ethylene segment and propylene segment in EPDM70(eth ylene content-70%) are markedly higher than that of EPDM59(ethylene content-59%) and EPDM52(ethylene content-52%). It is also revealed that only EPDM70has strain-induced crystallization phenomenon, and the crystal take place approximately at strain1. The crystal is highly oriented when it occur (orientation function up to92%). Both Synchrotron WAXD and FTIR demonstrate that this crystal belong to hexagonal PE. Besides, for EPDM70, both the orientation degree and crystallinity increase firstly and then decrease with crosslink density increase.(2) Sonic method is for the first time used to study orientation of EPDM, finding that the average orientation degree obtained by Sonic Method is almost agreement with that obtained by Infrared Dichroism da. In addition, Sonic method also suggests some phenomenon which can not be detected by Synchrotron WAXD, SAXS and FTIR, that is, apart from less-orientated amorphous phase, some highly-orientated local-ordered domains should be formed in EPDM52induced by strain, though SIC does not occur.