Effects of oil palm trunk biochar as filler on physical and mechanical properties of deproteinised and epoxidised natural rubber latex foam

Oil palm trunk biochar (OPTB) serves as a flame-retardant additive aimed at enhancing the thermal stability of natural rubber (NR) latex foam. This study explores whether OPTB affects the physical and mechanical properties of specialty NR (SpNR) latex foam, specifically deproteinised NR (DPNR) latex foam and epoxidised NR (ENR) latex foam. The results indicate that the addition of OPTB up to 8 phr insignificantly increases the density of DPNR and ENR latex foams, but significantly at 16 phr and 24 phr (p < 0.05). Shore F hardness also shows a significant increase with OPTB loading (p < 0.05), while volume shrinkage decreases with higher OPTB loading (p < 0.05), thereby enhancing foam dimensional stability. The study also found that the addition of OPTB reduced the elasticity of both DPNR and ENR latex foams, resulting in higher hysteresis loss ratios as OPTB loading increased from 8 to 16 phr and 24 phr. The highest observed hysteresis loss ratio was 0.32 in DPNR latex foam loaded with 24 phr of OPTB. Additionally, OPTB loading up to 24 phr in DPNR latex foam decreased its rebound resilience from 66 to 55% and increased its vibration-damping ratio from 0.14 to 0.24. This implies that the addition of OPTB to SpNR latex foam alters its physical and mechanical properties, making it ideal for applications requiring good vibration damping and impact absorption, such as seat cushions and headliners for vehicles.