Nut shell and grain husk waste biochar as carbon black replacements in styrene-butadiene rubber composites and improvements through steam activation

Biochar has been used in research as a full or partial replacement of carbon black in rubber composites to varying degrees of success. Choosing the right feedstocks and developing effective treatment methods of biochar can improve its properties and lead to more effective reinforcement filler. This study creates and characterizes biochar from two different low-ash nut shell feedstocks (hazelnut and walnut) and two high-silica grain husk feedstocks (oat and rice). These biochars are subjected to slurry-based steam activation and used to create and characterize vulcanized rubber composite formulations and compared to a traditional carbon black filled rubber composite. The results demonstrate that the nut shell biochars provide high reinforcement properties that meet or exceed those of carbon black and that slurry-based activation of biochar improves mechanical properties in the filled composite. The study presents correlations of low ash content in potential feedstocks with improved reinforcement performance.