Characterization and utilization of cacao shell powder as a biofiller in natural rubber composite

Abstract

The cacao shell, a by-product of the chocolate industry, is considered a waste and is normally discarded. This work aims to study the feasibility of using cacao shell powder (CSP) as a biofiller in rubber applications. The CSP was initially prepared, characterized, and incorporated into natural rubber (NR) at different loadings. Its reinforcement was compared with calcium carbonate (CaCO3) and carbon black (CB). The results showed that CSP had a relatively large average particle size (∼152 μm) and, thus, a very small specific surface area (4.5 m2/g). It mostly consisted of organic substances like cellulose, hemicellulose, lignin, proteins, etc. When incorporated into NR, both scorch time and optimal cure time decreased due to the existence of nitrogen-containing compounds, whereas hardness and modulus increased gradually with increasing CSP loading due to the dilution effect. At a given loading, CSP showed shorter scorch and cure times with greater hardness and modulus than CaCO3, indicating its greater cure activation ability and higher reinforcement magnitude. However, its reinforcement was far lower than that of carbon black. The maximum tensile strength was found at 30 phr of CSP loading, with a value of approximately 19.2 MPa, which was about 3% higher than that of CaCO3 but approximately 19% lower than CB. The findings suggest that, like other inert fillers, CSP can be employed for cost-reduction purposes in many applications where exceptionally high strengths are not essential, such as rubber bands, rubber flooring, rubber mats for livestock, etc.

Keywords

• Cacao shell
• Rubber
• Waste
• Biofiller
• Reinforcement
• Mechanical properties