Experimental and Modeling Study on the Curing Properties of Natural Rubber Composites Filled with Varying Proportions of Carbon Black, Modified Bentonite and Raw Bentonite

Abstract

The aim of this study was to investigate the effect of replacing carbon black (CB) with inexpensive and environmentally friendly fillers – bentonite (BNT) and modified bentonite (M-BNT), on the curing properties of natural rubber (NR) composites. A control sample (unfilled NR) and thirteen NR composites filled with varied proportions of CB (x1), M-BNT (x2), and BNT (x3) based on a third degree – simplex lattice mixture design of experiment (DOE) were prepared in this study. Rheometric results showed that 33% substitution of CB with M-BNT provides the highest elastic torque values. Mixture of 10phr CB and 5phr M-BNT (CB/M-BNT/BNT 10/5/0) produces synergistic effect on curing. The presence of CB increases vulcanization rate due to its high basicity and low oxygen content while M-BNT serves as vulcanizing accelerator due to the present amine groups. Coefficients of reduced hierarchical models showed that the main factors contributed mainly on the curing parameters: β1 for the torque values, β2 for the scorch and curing time, and β3 for CRI. High values of coefficient of determination (r2) were computed particularly for MH (98.20%), ΔS (99.13%), ts2(95.68%), tc90(95.70%) and CRI (95.97%) establishing best fit between the model and experimental values.