Natural rubber samples were filled with agricultural waste products (cocoa pod husks and rubber-seed shell) at 50 phr, mixed on a two-roll mill, and cured using the semiefficient vulcanization system. The physicomechanical properties, tensile strength, modulus at 100% elongation, elongation at break, hardness, abrasion resistance, flex fatigue and compression set, of the agricultural waste products-filled natural rubber compounds were determined and compared with the values obtained for vulcanisates filled with commercial carbon black (HAF N330). The effect of blending the raw and carbonized agricultural waste products with the commercial grade N330 carbon black on the physicomechanical properties of the natural compounds was studied. It was found that the raw agricultural waste products were ineffective compared with N330 carbon black as reinforcing filler for natural rubber compound mixes and could be classified as semireinforcing fillers. Blends containing up to 40 wt % of the raw agricultural waste products and more than 60 wt % of the carbonized waste products gave natural rubber compounds with comparable physciomechanical properties with compound obtained with N330 carbon black.
Cocoa pod powdered (CP) and Carbonized Cocoa pod powdered (CCP) sieved through 150 m mesh were characterized in terms of loss on ignition, surface area, moisture content, and oil absorption and used as filler in compounding natural rubber and vulcanized using efficient vulcanization system. The processing and curing characteristics of the compound mixes were determined on a Monsanto Rheometer. Physical-mechanical properties of the vulcanizates were measured as a function of filler loading. It was found that vulcanizates with 40 -50% filler loading showed maximum tensile strength of 8.4 MPa for CP, and 9.5 MPa for CCP. Hardness showed increased with increased filler loading for all the compounds. The reinforcing ability of the cocoa pod husk is not much inferior when compared to Carbon Black, N330.
Samples of rubber seed shells were carbonized at varying temperatures (100, 200, 300, 400, 500, 600, 700 and 800 °C) for three hours each and sieved through a 150 µm screen. The portion of the rubber seed shell carbon that passed through the screen was characterized in terms of loss on ignition, surface area, moisture content, pH, bulk density, and metal content and used in compounding natural rubber. The characterization shows that the pH, conductivity, loss on ignition and the surface area increases with the increases of the heating temperature, unlike the bulk density which decreases. The compound mixes were cured using the efficient vulcanization system. Cure characteristics of compounds and physico-mechanical properties of the vulcanisates were measured as a function of filler loading along with that of N330 carbon-black filled natural rubbers. The results showed that the cure times, scorch times and the torque gradually increased, with increasing the filler content for rubber seed shell carbon-filled natural rubber, with the filler obtained at carbonizing temperature of 600 °C tending to show optimum cure indices. The physicomechanical properties of the vulcanisates increase with filler loading. The reinforcing potential of the carbonized rubber seed shell carbon was found to increase markedly for the filler obtained at the temperature range of 500-600 °C and then decreases with further increase in temperature.
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