Effect of chlorinated polyethylene on dynamic mechanical and thermal properties of SAN/EPDM blends in dependence of mixing conditions

The effect of chlorinated polyethylene (CPE) on the compatibilization and thermal properties of styrene-acrylonitrile copolymers (SAN)/Ethylele-Propylene-Diene-polyMethylene rubber (EPDM) blends (80/20) was investigated. Two different mixing procedures were employed, that is, single- and two-step blending. In the single-step process, EPDM was melt blended with CPE and SAN simultaneously, which led to a droplet morphology. In the two-step process, first, a masterbatch of EPDM and CPE in SAN was prepared, and then mixed with further amounts of SAN and CPE in order to reach the same fixed blend ratio of 80/20 for SAN/EPDM. The morphology changed from EPDM droplets for the one-step mixing to co-continuous for the two-step blending process. This morphological change was reflected in a change of the complex modulus. The characteristics of thermogravimetric analysis (TGA) curves (T1%, T5%, T30%, and T50%) were examined, as indicators for improved thermal stability of the blends. The intermolecular interaction characterized by the Kwei equation showed higher values for the blends prepared by the two-step mixing procedure. The dynamic mechanical analysis supported the occurrence of chain scission in the SAN phase at the beginning of aging and cross-linking of SAN at higher temperatures and longer times as a result of cyclization of CN groups in SAN.