Abstract
Hydrogenated nitrile rubber (HNBR) could be blended with natural rubber (NR) to improve its oil and aging resistance without affecting drastically the dynamic properties. The polarity difference between the polymers is reduced by incorporation of small quantities of dichlorocarbene modified NR (DCNR) which is formed during the alkaline hydrolysis of chloroform in presence of NR. The enhancement in technical properties in presence of DCNR is due to its dipole interaction with the –CN group of the acrylonitrile segments in HNBR as revealed from a shift in the characteristic IR absorption peak. Thus modified form of NR enables the formation of a more uniformly mixed blend of NR and HNBR resulting in more cross links as revealed from an increase in rheometric torque. In blends, the NR matrix cross links to a same extent as pure NR, while the level of crosslinking of HNBR matrix is lower than that obtained for the pure HNBR. However in the presence of DCNR there is the formation of interfacial crosslinks as evaluated from selective solvent swelling. During aging at a comparatively lower temperature the NR matrix of the blend undergoes crosslinking reactions while at high temperatures it undergoes scission reactions. The scission reactions taking place in the NR matrix are reduced in presence of DCNR as observed from the application of two-network theory for samples subjected to high temperature stress relaxation. A reduction in chain scission reactions at high temperature results in better aging characteristics of the modified blends.
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