Assessment and enhancement of starch-based biochar as a sustainable filler in styrene-butadiene rubber composites via steam and CO2 activation treatments

Biochar synthesized from corn starch with three different amylose/amylopectin ratios were characterized and their reinforcing performance in styrene-butadiene rubber (SBR) rubber was compared to carbon black N772. Biochar samples were produced via slow pyrolysis. Additionally, 3 different activated biochar samples were created, notably (1) activation under CO2, (2) activation with steam and N2 (Steam), and (3) steam activation via pyrolysis of a biochar-water slurry (SteamT2). The properties of the fillers were examined, and all biochar samples were blended with SBR to form composites, which were tested to evaluate their cure profiles and tensile properties. The results indicate that the amylose and amylopectin ratios of the feedstock had little effect on the reinforcing performance of the composites, but composites with biochar from high amylose corn starch had longer scorch periods during curing. Physical activation treatments, however, had a significant impact on the physicochemical properties of the biochar, specifically on the porosity, carbon, oxygen, and ash content. In terms of performance in SBR, composites with biochar pyrolyzed under normal N2 conditions and biochar activated with Steam had the most consistent tensile performance with the least brittle characteristics. Conversely, composites made with biochar activated with SteamT2 were exceptionally brittle, with limited reinforcement capabilities, despite having a comparatively higher carbon content. Thus, though physical activation can increase the carbon concentration of biochar, this does not necessarily correlate to improvements in its mechanical performance in SBR. As such, other optimization techniques may be more useful to tailor biochar for application in the rubber filler industry.