Reducing Biochar Particle Size with Nanosilica and Its Effect on Rubber Composite Reinforcement

Since biochar is a renewable source of carbon, it has been examined as a substitute for carbon black as rubber composite filler. Although biochar can approach carbon black in terms of carbon and ash content, substituting carbon black with biochar typically degrades the mechanical properties of rubber composites because of the much larger particle size of biochar. Biochar is produced from biomass and must be size reduced by “top-down” methods such as milling. Thus, biochar frequently has populations of particles greater than 10 µm in diameter, which greatly reduce reinforcement properties by introducing localized stresses in the rubber composite. In this work we explore using nanosilica as a co-milling material with biochar as a means to reduce its particle size and consequently improve its ability to replace carbon black as rubber composite filler. Biochar co-milled with 1 wt% nanosilica was able to replace 40% of the carbon black filler in a styrene–butadiene rubber composite with virtually no loss in tensile strength. Also, elongation and toughness properties of the optimal biochar substituted composites were improved by over 31 and 24%, respectively.