Studies On Preparation And Properties Of NR/EPDM Compounds

Natural rubber (NR) vulcanisates have good elasticity and strength properties but poor resistance to heat and ozone. Ethylene-propylene-terpolymer rubber (EPDM) vulcanisates on the other hand have excellent heat ageing and ozone resistance. It has been a practice that NR is blended with EPDM in order to obtain the best characteristics of each component or for cost consideration. However, this practice often results in poor physical properties. This has partially been explained by migration of curatives from the EPDM to the NR phase resulting in the EPDM being undercured and the NR overcured.In order to improve co-curability, NR/modified EPDM blends had been developed in this paper, with blending NR with series of modified EPDM compounds. The approach used to modified EPDM, termed as ’dynamic pretreated", was to increase the cure rate of EPDM by modifying the EPDM phase to make it more reactive using commercially available sulphur donors or accelerant. The process to material preparation was, firstly to prepare NR and EPDM masterbatches mix separately on a two-roll mill. The next step was to pretreat EPDM masterbatches mix with DTDM, si69 in a Brabender mixer at the stated temperature and time. The last step was to blend NR and modified EPDM masterbatches mix (according to the ratio required) in the two-roll mill. And then, NR/p-EPDM and NR/si69-EPDM blends are carried out.The rheological properties and physical testing of the blends were investigated compared with conventional NR/EPDM blends. The result had shown that the ’dynamic pretreated’procedure for EPDM mastermatch mix could make it reactive, improve its curability. The bound rubber content of the modified EPDM mastermatch mix had increased distinctly. It also made scorch time TS1 and cure time TC90 of NR/modified EPDM blends shortened, and made physical properties improved on a large degree. Especially to NR-50/modified EPDM-50 blends, the tensile strength had even increased more than 70% relative to conventional NR/EPDM blends. The blend morphology as revealed by SEM studies had accounted for significant improvement in physical properties. It was very effective by’dynamic pretreated’ EPDM mix to restrict the curative migration, to give improved co-crosslinking, morphology and good interaction with NR. The cure-rate mismatch problem could thus be solved by’dynamic pretreated’EPDM before blended with NR.