Studies on compatibilization of natural rubber and ethylene propylene diene rubber and effect on their vulcanizate properties

Abstract

The compatibility between natural rubber (NR) and Ethylene Propylene Diene Rubber (EPDM) was investigated in order to improve ozone resistance and mechanical properties of NR/EPDM blends by utilization of liquid rubbers and homogenizing agents. The first part of this work deals with finding the optimum vulcanizing system by varying types and amount of various accelerators. Proper cure characteristics and tensile properties of the rubber vulcanizates were used to determine the most suitable accelerators. 70/30 and 80/20 parts by weight were used in the study. The results indicated that BBS (N-t-Butylbenzothiazole-2sulfenamide) was the most appropriate accelerator for this study. In the second part, the composition optimization of NR/EPDM was investigated for further study. The ozone resistance property of the blend vulcanizates was used as a criteria to find the most suitable composition of rubber blends for further study investigation of the effect of compatibilizer. The results showed that composition of NR/EPDM at 70/30 and 80/20 by weight should be chosen. The reasons are that 70/30 NR/EPDM 70/30 can resist to ozone cracking longer than 5 days while 80/20 NR/EPDM failed within 24 hours under the same condition. In the third part, the ozone resistance and the mechanical properties of blend vulcanizates were measured. Homogenizing agents (Struktol 40 MS, Rhenosin 145), liquid EPDM, natural rubbers (LEPDM, LNR) and their combination were added to the blends and their effects on vulcanizates properties were investigated. LNR was prepared by chemical treatment of NR. LNR and LEPDM were partially crosslinked by sulfur vulcanization before mixing with NR and EPDM. The results showed that LEPDM could improve ozone resistance and some physical properties of the blends. Utilization of the combination of LNR and LEPDM, as partially crosslinked and uncrosslinked mixture 3 phr gave slight improvement of tensile properties but no improvement in ozone resistance has been observed of 70/30 NR/EPDM rubber blend except the plasticizing effect. Slight improvement of physical properties of the blends were also observed by addition of Struktol 40 MS. The energy of mixing of rubber blends were also studied since the change of mixing torque with time revealed the miscibility of the blends.