Abstract
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.
Highlights
Natural rubber (NR) is an organic, elastic substance obtained from the sap of trees, and it is the precursor to modern synthetic rubber products
Biochar created from Paulownia elongata hardwood feedstock that was co-milled with silica in order to reduce the particle size was substituted for carbon black (CB) in composites using natural rubber (NR) as the rubber matrix
Biochar made from P. elongata showed promise for athletic turf application [26] and other broader-based horticultural applications [11]
Summary
Natural rubber (NR) is an organic, elastic substance obtained from the sap of trees, and it is the precursor to modern synthetic rubber products. Paulownia is a robust tree that can grow well in hardiness zones 6–11 [9], which means it could grow over virtually the entire southeastern United States from the Carolinas to Texas It is currently used as a filler for wood–plastic composites [10], and biochar made from it was studied as a horticultural amendment to soil [11]. Milled biochars would have a certain population of particles with diameters of 10–100 μm This is problematic in rubber composite samples because even a small amount of these larger biochar particles will cause localized stresses to develop and significantly weaken the composite in terms of tensile strength via fracture, tearing, or other types of defects. Biochar created from Paulownia elongata hardwood feedstock that was co-milled with silica in order to reduce the particle size was substituted for CB in composites using NR as the rubber matrix. The tensile strength, elongation, and toughness of these composites were compared with a 100% CB-filled control composite to determine to what extent CB could be replaced with Paulownia biochar (PB) while still retaining the same desirable tensile properties as the control
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