Effect of Oil Palm Frond-Based Biochar on Natural Rubber Latex Foam Composites Physical Properties, Flammability and Thermal Stability

Natural rubber (NR) latex foam is a favorable rubber foam due to the unique properties and characteristics of NR. NR latex foam, however, has poor thermal stability and flammability. The favorable properties are attributed to the cis-1,4 isoprene repeating units, while the allylic carbon of 1,4 isoprene leads to poor thermal stability and flammability. A flame retardant such as oil palm frond-based biochar (OPFB) is a potential, sustainable solution. This study focuses on the effect of OPFB on low-ammonia NR latex foam composites. Within the OPFB loadings studied (0-30 phr), the density increased while the volume shrinkage decreased with OPFB loading, due to a higher solid-to-air-phase ratio. A high cross-link density of the foam, even without OPFB, is hypothesized to have led to no significant effect on hardness. The flammability, tested according to the UL 94 horizontal burning foamed material test, showed that OPFB reduced flammability. However, even at 30 phr, the foam composites were still not able to meet the UL 94 requirements of < 40 mm/min. Thermogravimetric analysis showed better thermal stability with OPFB loadings. Thus, it can be concluded that OPFB is a potential sustainable filler in the applications of NR latex foams which require thermal stability.