Study On Covulcanized Properties Of NR/EPDM Blends

Natural rubber (NR) vulcanizates have good elasticity and strength properties,wheres they show poor aging resistance. Blending with ethylene propylene dienerubber (EPDM) has been found to improve aging resistance and the bloom ofanti-aging agent to the rubber surface which has bad effect on aging resistance of NRis restrained. However, NR-EPDM blends usually display inferior mechanicalproperties mainly at a composition required for adequate aging resistance, that is, at anhigher concentration. This is because the low degree of unsaturation of EPDM and itscure incompatibility. On the basis of vulcanization system of NR-EPDM blendsstudied in this work, the covulcanized properties of NR-EPDM blends cured bydifferent vulcanization system as pivot were studied. A few new ideas for theimproving of covulcanization of NR-EPDM blends was offered.The covulcanized properties of NR-EPDM blends cured by organic peroxide werestudied in the fourth chapter, included feasilble study for improving the mechanicalproperties of NR-EPDM blend vulcanizates and study on covulcanized properties ofNR-EPDM blends cured by dicumyl peroxide (DCP) in combination with secondaryvulcanizing agent. The results showed that the tensile strength of NR-EPDM blendvulcanizates was improved significantly after that the EPDM blends were pretreated.Differential scanning calorimeter (DSC) analysis indicated that the pretreatmentEPDM resulted in a marked increased of covulcanization of NR-EPDM blends, inaddition, the blend vulcanizates morphology, as revealed from the scanning electronmicrographs (SEM), corroborated the physical date obtained so far.It was difficult of improving tensile strength of NR-EPDM blends cured by sulfur,because the difference in olefin concentration of EPDM and NR resulted in acure-rate-incompatible blend. Silane coupler Si69 was used in rubber industry as bothcoupling agent and vulcaning agent. The properties of blends of NR and in-situ EPDMgum blends by Si69 were studied in the fifth chapter. The results showed that theactive reaction between coupling agent and carbon black resulted in an increase on thebound rubber content, in addition, the covulcanization of NR-EPDM blends wereimproved by the active reaction between coupling agent and EPDM, and these resulted in a substantial increase of the tensile strength. Dynamic mechanical studies ofvulcanizates and Morphological studies of the tensile-fractured surfaces of theNR/EPDM (1:1) blend vulcanizates by scaning electron microscopy corroborate theimprovement of covulcanization of NR-EPDM blends.