Replacement of carbon black with coppiced biochar in guayule rubber composites improves tensile properties

Authors: Peterson, Steven - Steve; McMahan, Colleen

Submitted to: Journal of Composites Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2023
Publication Date: 12/2/2023
Citation: Peterson, S.C., Mcmahan, C.M. 2023. Replacement of carbon black with coppiced biochar in guayule rubber composites improves tensile properties. Journal of Composites Science. 7(12):499. https://doi.org/10.3390/jcs7120499.
DOI: https://doi.org/10.3390/jcs7120499

Interpretive Summary: In this research, we discovered that sustainable biochar blended with carbon black improves the strength, elongation, and toughness of guayule rubber composites. Natural rubber is a critical natural resource for the US, as it is vital for national security, transportation, and the medical industry, among other things. However, nearly all our natural rubber is sourced from southeast Asia from the Hevea natural rubber tree. Guayule rubber can be grown domestically. Biochar is also a sustainable, domestic resource. This work shows that rubber composites made from guayule can have improved strength, elongation, and toughness, while reducing our dependence on foreign natural rubber and petroleum (the source of carbon black).

Technical Abstract: Natural rubber, commonly sourced from Hevea brasiliensis trees in southeast Asia, is a critically important resource for transportation, national security, and medical products, among other uses. The guayule shrub is a domestic alternative source of natural rubber that is emerging with advantages over Hevea since it is hypoallergenic and well-suited for many medical and consumer applications. Biochar is a sustainable form of carbon made from biomass that is a potential replacement for petroleum-sourced carbon black, the most common filler for rubber composites. The coppiced-wood species hybrid poplar (Populus x canadensis) and Paulownia elongata are both rapidly growing hardwoods that have shown promise as feedstocks for biochar that can replace carbon black in common rubber composites such as Hevea natural rubber, styrene-butadiene, and polybutadiene. In this work, poplar and paulownia biochars were used to partially replace carbon black as filler in guayule rubber composites. Guayule composites with up to 60% of the carbon black replaced with poplar or paulownia biochar had superior tensile strength, elongation, and toughness compared to the 100% carbon black filled control. These composites would be excellent candidates for rubber applications such as gloves, belts, hoses, and seals, while reducing dependence on fossil fuels and Hevea natural rubber.