Cure Characteristics and Mechanical Properties of Rubber Compound Reinforced with Activated Carbon from Coconut Husks as Alternative to Carbon Black

Abstract

Selection of raw materials for rubber products is an important aspect of rubber engineering. One of the components often investigated is the filler material, wherein among the considerations include reinforcing capability, cost, and environmental impact. In this study, a greener alternative to carbon black (CB) was explored using activated carbon (AC) from coconut husk. Results showed that AC has lower fixed carbon content (33.64 wt%C) than CB (96.92 wt%C) due to the retained volatile organic components. AC also has a larger particle size distribution (< 150μm) in terms of 80% passing than CB (which is 28-36 nm for technically specified particle size of commercial N330). However, AC exhibits larger BET surface area (423.66 m2/g) due to natural porosity of activated carbon materials as compared to CB (58.109 m2/g). Moreover, AC was found to be basic while CB has a neutral pH. Consequently, the tensile strength and complex modulus G* of the AC-compound (4.3 MPa and 75.36 kPa, respectively) are inferior to CB-compound (20.3 MPa and 87.41 kPa, respectively). This is thought to be mainly due to the larger particle size and porous structure of the activated carbon. Yet, the % elongation and hardness values are comparable. Processability may also be a concern in using activated carbon as a filler due to higher Mooney viscosity (45.8 M). Nonetheless, the scorch time and cure index of the two compounds were found to be comparable. Hence, the potential of complete replacement of carbon black with activated carbon is viable for rubber products with low tensile strength requirements, such as protective matting.