Carbon black (CB) has been the dominant filler in the tire industry for decades. The demand for this petroleum byproduct is ever increasing, although petroleum markets can be volatile due to geopolitical issues. Finding sustainable, renewable substitutes for CB reduces the dependence on petroleum. Biochar is a renewable source of carbon that was studied as a potential CB replacement filler in styrene–butadiene rubber (SBR) composites, but little has been done in terms of natural rubber (NR). In this work, biochar made from fast-growing Paulownia elongata
was co-milled with small amounts of silica in order to reduce the larger particle size typical with biochar respective to CB. The resulting silica-milled Paulownia
biochar (PB) was then used to replace CB in natural rubber (NR) composites. By using this method to make natural rubber composites with 30% total filler, half of the CB was fully replaced with silica-milled biochar with very little loss (<6%) of tensile strength, and equal or better elongation and toughness compared to the 100% CB-filled control composite.
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