Characterization of the coir fiber from different coconut varieties to enhance the performance of coir fiber-reinforced natural rubber composites

The manufacture of composite materials reinforced with bristle fiber that possess distinct properties is highly attractive for novel applications. The quality variations in coir fiber-reinforced rubber composites (CFRC) are mainly affected by several factors, including the type of rubber matrix used, the interfacial adhesion between the coir fiber and the rubber matrix, the fiber length, and fiber loading. The objectives of this study were to assess and characterise coir fibers extracted from diverse Sri Lankan coconut varieties to identify high-quality coir fiber suitable for the fabrication of high-performance coir fiber-reinforced rubber composites, and the optimal range of coir fiber length and loading was investigated to maximize the mechanical properties of the composites. In this research, the extracted bristle fiber from different coconut varieties was examined for distinct properties and chemical composition. The varying lengths, specifically ranging from 0 to 0.5 mm and 0.5-1.0 mm of fiber from selected coconut varieties, were used for making CFRC. Different loadings of the selected range of coir fiber were used for partial replacement of carbon black in CFRC. Results showed that the Kamandala and Tall x Tall varieties had significantly high tensile strengths, with the Tall x Tall variety selected due to its superior mechanical properties and high abundance. The replacement of carbon black filler in natural rubber composites with 10 phr of coir fiber obtained from the Tall x Tall variety, with a length range of 0 to 0.5 mm, possessing coir-to-carbon black weight ratios of 10/40 phr, demonstrated superior properties in terms of tensile strength, tear strength, and elongation compared to composites containing 10 phr of coir fiber with a length range of 0.5-1 mm and other coir fiber to carbon black ratios. These findings provide insightful information for the development of composite materials and promote the sustainable and responsible utilization of coconut resources.