Birchwood biochar as partial carbon black replacement in styrene–butadiene rubber composites

Birchwood feedstock was used to make slow pyrolysis biochar that contained 89% carbon and <2% ash. This biochar was blended with carbon black (CB) as filler for styrene–butadiene rubber (SBR). Composites made from blended fillers of 25/75 biochar/CB were equivalent to or superior to their 100% CB analogs in terms of tensile strength and toughness at all filler concentrations. Composites made with 50/50 biochar/CB were equivalent to or superior to CB composites in tensile strength, elongation, and toughness properties at total filler concentrations up to 30%. These results demonstrate the potential to use renewable birchwood biochar to replace up to half the CB in certain SBR composites.