Lauric acid treatments to oxidized and control biochars and their effects on rubber composite tensile properties

Authors: Peterson, Steven - Steve; Thomas, Andrew - Aj

Submitted to: C - Journal of Carbon Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2022
Publication Date: 10/29/2022
Citation: Peterson, S.C., Thomas, A.J. 2022. Lauric acid treatments to oxidized and control biochars and their effects on rubber composite tensile properties. C - Journal of Carbon Research. 8(4). Article 58. https://doi.org/10.3390/c8040058.
DOI: https://doi.org/10.3390/c8040058

Interpretive Summary: When renewable materials, such as trees, are heated to high temperature in a little to no oxygen environment, ‘biochar’ is produced. This biochar approaches 100% carbon and will be similar in appearance to charcoal. Biochar is a renewable source of carbon that can replace carbon black (a petroleum product, which is nearly 100% carbon) as filler in rubber composite materials, such as tires. This is significant as up to 40% of the weight of a tire can be carbon black. However, since biochar is not as pure in terms of carbon content as carbon black, it needs to be modified and improved to be an acceptable substitute. One way to improve biochar is to change its surface so that it mixes more effectively with rubber when making the final product. Surface modifications can be carried out by modifying the process (time, temperature etc.) or adding materials to coat the biochar. ARS researchers in Peoria, Illinois developed a two-stage method to change the surface of biochar particles: 1) gas treatment at 300°C, and 2) coating the biochar particles with a vegetable oil-based acid. This two-stage method is easy to incorporate into current rubber manufacturing practices. It was found that gas treatment of the biochar improves the stiffness of the final rubber composites, and that acid coating of biochar improves the strength of the rubber composite by 19% and its toughness by 48%.

Technical Abstract: Biochar is a renewable source of carbon that can partially replace carbon black as filler in rubber composites. Since the carbon content of biochar is less pure than carbon black, improvements and modifications must be made to biochar to make it a viable co-filler. In this work, two methods to change the surface chemistry of biochar were employed: 1) gas-treatment at 300°C with either air or carbon dioxide, and 2) coating with lauric acid. Both methods are amenable to the current rubber processing industry. After biochar was treated with these methods, they were used as co-filler in rubber composite samples. Gas treatment with either air or carbon dioxide was found to increase stiffness in the final composites. Although lauric acid coating of biochar by itself did not have a significant effect on tensile properties, biochar that was first treated with carbon dioxide and then coated with lauric acid showed a 19% increase in tensile strength and a 48% increase in toughness. Gas treatment and lauric acid coating of biochar provide relatively simple processing techniques to improve the stiffness and tensile strength of biochar as rubber composite filler.