Silica-milled Paulownia biochar as partial replacement of carbon black filler in natural rubber

Authors: Peterson, Steven - Steve

Submitted to: Journal of Composites Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2019
Publication Date: 12/13/2019
Citation: Peterson, S.C. 2019. Silica-milled Paulownia biochar as partial replacement of carbon black filler in natural rubber. Journal of Composites Science. 3(4):107. https://doi.org/10.3390/jcs3040107.
DOI: https://doi.org/10.3390/jcs3040107

Interpretive Summary: In this research, fully half of the carbon black in a natural rubber composite was replaced with biochar, with very minimal loss in strength and improved elasticity. Carbon black is made from the petroleum industry, and it is in the best interest of the U.S. to find renewable replacements for petroleum products for both geopolitical and ecological reasons. Biochar is a high-carbon-containing charcoal that is made from renewable biomass; in this case, fast-growing Paulownia trees. This tree has a wide geographical footprint in the U.S. and can produce a large amount of wood per unit area. Additionally, the wood from these trees can be cut and regrown for decades (aka short rotation coppicing), so a finite area can continually produce feedstock over time. Silica-milling is a technique developed in our lab to help reduce the particle size of biochar and allow a higher replacement rate; this technique helped enable 50% replacement of carbon black with Paulownia biochar. Since the current carbon black market is over one 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" for applications using natural rubber.

Technical 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.