Co-milled silica and coppiced wood biochars improve elongation and toughness in styrene-butadiene elastomeric composites while replacing carbon black

Authors: Peterson, Steven - Steve; JOSHEE, NIRMAL - Fort Valley State University

Submitted to: Journal of Elastomers and Plastics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2017
Publication Date: 1/21/2018
Citation: Peterson, S.C., Joshee, N. 2018. Co-milled silica and coppiced wood biochars improve elongation and toughness in styrene-butadiene elastomeric composites while replacing carbon black. Journal of Elastomers and Plastics. 50(8):667-676. 10.1177/0095244317753653.
DOI: https://doi.org/10.1177/0095244317753653

Interpretive Summary: In this research, 30% of the carbon black in a rubber composite common in the tire industry was replaced with biochar, and the resulting composite was just as strong with improved elasticity. Carbon black is a petroleum byproduct and it benefits the United States to reduce dependence on petroleum. Biochar is a potentially high-carbon charcoal that is made from renewable biomass. In this work, two tree species were studied as biochar feedstocks; Paulownia and poplar. Both of these trees have wide geographical footprints in the United States and are very fast growing, so they can produce a large amount of wood per unit area. Additionally, the wood from them can be cut and regrown for decades (aka short rotation coppicing), so a finite area can continually produce feedstock over time. Past research has shown biochar to be inferior to carbon black as rubber composite filler because of its larger particle size, which causes weak spots in the rubber composite and reduces its strength. In this work, a new method of mixing silica powder with the biochar was successfully used in order to reduce the particle size of the biochar. Biochars from both of these trees mixed with a small amount of silica were able to replace 30% of the carbon black in rubber composites with virtually no loss in strength as well as improved elongation properties. Since the current carbon black market is over 1 million tons per year in the tire industry, this represents a huge potential reduction in carbon black usage and a good foundation for making the tire industry "greener".

Technical Abstract: Carbon black (CB) is a petroleum by-product with a million ton market in the US tire industry. Finding renewable substitutes for CB reduces dependence on oil and alleviates global warming. Biochar is a renewable source of carbon that has been studied previously as a replacement for CB in styrene-butadiene rubber (SBR) composites. However, biochar typically has lower carbon content, higher ash content, and larger particle size, which are all significant detractors to making biochar a viable drop-replacement for CB. In this study, high carbon and low ash biochars made from fast-growing Paulownia elongata and Populus tremuloides were co-milled with small amounts of silica in order to reduce the particle size, and the biochar/silica blends were then used to partially replace CB in SBR composites. Using this method both Paulownia and poplar biochars were able to replace 30% of the CB filler and improve elongation and toughness with virtually no loss of tensile strength, compared to the 100% CB-filled control composite.