Turning biomass into better rubber: Biochar emerges as a sustainable alternative to carbon black
image: Role and potential of biochar as a sustainable alternative reinforcing filler to carbon black in rubber composites
Credit: Laleen Karunanayake, Thusitha Etampawala, Dilusha Jayanidu de Silva, Jagath Bandara, Anushka Upamali Rajapaksha & Meththika Vithanage
A new review highlights how biochar, a carbon-rich material made from agricultural and organic waste, could help transform the rubber industry by reducing reliance on fossil-derived carbon black while maintaining strong material performance.
Carbon black has long been the dominant reinforcing filler in rubber products such as tires, seals, and industrial components. Its unique structure enhances strength, durability, and resistance to wear. However, producing carbon black is energy-intensive and environmentally damaging, releasing large amounts of carbon dioxide and hazardous byproducts. According to the study, about 2.4 tons of CO2 can be emitted for every ton of carbon black produced.
In response to growing environmental concerns, researchers are exploring biochar as a more sustainable alternative. Biochar is produced by heating biomass such as rice husks, wood waste, or agricultural residues under low oxygen conditions. This process converts organic material into a stable, carbon-rich solid with a porous structure and high surface area.
“Biochar offers a promising pathway to replace or reduce the use of fossil-based fillers in rubber, while also contributing to waste valorization and carbon management,” the authors explain.
The review synthesizes current research on how biochar performs when incorporated into different types of rubber, including natural rubber, styrene-butadiene rubber, and nitrile rubber. Results show that while biochar alone does not yet fully match the reinforcing performance of carbon black, it can significantly improve mechanical properties such as tensile strength, elasticity, and toughness under certain conditions.
One key finding is that blending biochar with carbon black often produces the best results. Partial replacement strategies can maintain high performance while lowering environmental impact. In some cases, replacing 30 to 50 percent of carbon black with biochar achieved comparable strength and even improved flexibility and toughness.
The effectiveness of biochar depends strongly on how it is produced. Feedstock type, pyrolysis temperature, and post-treatment methods all influence its structure, surface chemistry, and particle size. These factors determine how well biochar interacts with rubber polymers at the molecular level.
For example, biochar with higher surface area and optimized functional groups can better bond with rubber, improving stress transfer and durability. Mechanical treatments such as ball milling can reduce particle size and enhance dispersion, while chemical modifications can tailor surface properties to improve compatibility with the rubber matrix.
Despite its promise, challenges remain. Biochar typically has lower surface uniformity and carbon purity than carbon black, which can limit its reinforcing efficiency. Variability in raw materials also leads to inconsistent performance. The authors emphasize that further research is needed to standardize production methods and optimize biochar properties for industrial applications.
Still, the potential benefits are substantial. Biochar is derived from renewable resources, can utilize agricultural waste streams, and may contribute to carbon sequestration. Its use in rubber composites aligns with broader efforts to develop circular, low-carbon materials.
“Our findings suggest that biochar is not just a substitute, but a versatile material that can be engineered for specific performance needs,” the researchers note. “With continued innovation, it could play a key role in building a more sustainable materials economy.”
As industries seek greener alternatives without sacrificing performance, biochar-based rubber composites may offer a compelling solution that bridges environmental responsibility and engineering demands.
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Journal Reference: Karunanayake, L., Etampawala, T., de Silva, D.J. et al. Role and potential of biochar as a sustainable alternative reinforcing filler to carbon black in rubber composites. Biochar 7, 60 (2025).
https://doi.org/10.1007/s42773-025-00429-3
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.