Physico-mechanical Effects of Surface-modified Sorgum Stalk Powder on Reinforced Rubber

Abstract

Stalk of sorghum was crushed into fine particle size and given three surface treatments: with groundnut oil, alkali, and 3-chloro-2-hydroxyl propyl trimethylammonium chloride. It was presumed that the oil treatment will preclude any negative surface potential that cellulose is known to acquire in aqueous environment. The alkali treatment was to remove the natural surface admixtures but to preserve the negative surface potential, and the tertiary ammonium salt was to confer positive potential to it. The four samples including the untreated fiber were used to produce fiber-reinforced natural rubber composite at varying filler loadings. The pycnometric specific density measurement indicated the following decreasing trend: cationized filler, untreated, causticized, and finally the oil treated. In each case, the density increased with filler volume. The tensile strength of the composites also varied such that both the cationized and alkali-treated fillers recorded higher values than the untreated filler, the oil-treated filler was the least. However, the oil-treated filler did best with the elongation at break for filler loading higher than 40 phr; for loadings lower than 40 phr, the alkali-treated filler did better. The cationized filler recorded low values but was better than the untreated filler. The impact tests demonstrated critical loading effect for all the different samples; the trend showed increase from 10 to 40 phr and then declined, the untreated and the oil-treated did better than the causticized and cationized which recorded the least value. The hardness index did not show much difference between the untreated, causticized, and cationized fillers both of which did better than the oil treated. This work has shown some general improvements arising from cationization of cellulosic filler as reinforcing material for natural rubber.