Effect of African walnut shell (Tetracarpidium conophorum) on the physico-mechanical properties of modified and unmodified natural rubber

Natural rubber (NR) in its natural state is soft and weakly linked together. It is relatively easy to pull apart, which accounts for its stretchy and elastic nature. Walnut shell (WS), being a biodegradable agricultural waste, was chosen in anticipation of reinforcing the blends thereby helping to improve the strength and mechanical properties of the NR. Two different samples of NR were prepared through chemical modification via depolymerization and epoxidation. Depolymerized Natural Rubber (DNR) was produced by depolymerization of natural rubber latex using nitrobenzene and Epoxidized Natural Rubber (ENR) was produced by reaction with performic acid. Walnut shells were de-shelled, washed, dried, milled, sieved and were characterized by determining the moisture content, Ash content, volatile matter, pH measurement and Loss on Ignition. The NR, DNR and ENR composites filled with WS at three ratios of 100/0, 50/50 and 0/100 were prepared and labeled as mixes A to C. The physico-mechanical properties of the different vulcanizates were studied. It was observed that the tensile strength of the modified natural rubber was higher than that of the unmodified natural rubber. The values for the elongation break point and the hardness also increased with the addition of the WS into the modified NR composites with values higher than that of the unmodified NR. However, it was observed that there was a reduction in the compression set from the unmodified NR to the modified NR, which is due to modification which increased the stiffness of the composite.