Rubber is essential to modern life, appearing in everything from high-performance vehicle tires to critical medical devices and industrial conveyor belts. To make these products durable and strong, manufacturers add “reinforcing fillers,” traditionally relying on carbon black. However, carbon black is derived from non-renewable petroleum and its production is environmentally taxing, releasing approximately 2.4 tons of carbon dioxide for every single ton produced. In a review published in the journal Biochar, authors Laleen Karunanayake, Thusitha Etampawala, Dilusha Jayanidu de Silva, Jagath Bandara, Anushka Upamali Rajapaksha, and Meththika Vithanage explored the potential of biochar as a sustainable, low-cost substitute for this traditional filler.

Biochar, unlike carbon black, which has a very high purity and ultra-fine particle size, biochar features a more variable structure depending on its “feedstock” and production temperature. The researchers noted that while biochar particles are generally larger and more porous than carbon black, they can be engineered to mimic desirable industrial properties. This engineering involves fine-tuning the pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More process or using physical modifications like ball-milling to reduce particle size, which helps prevent stress fractures in the final rubber product.

The review highlights that while rubber made entirely with biochar fillers often falls short of high-performance carbon black standards, “hybrid” composites show excellent potential. For example, replacing 30% to 50% of carbon black with fine-tuned biochar can result in rubber that maintains its tensile strength while actually improving its toughness and ability to stretch. These biochar-rubber blends also tend to be lighter and produce less heat during use, which can improve the flexibility and lifespan of certain products.

Ultimately, the transition toward biochar-reinforced rubber represents a major opportunity for “green” manufacturing. Because biochar is carbon-neutral and derived from waste materials, it helps the rubber industry move away from fossil fuel dependency. While challenges remain in ensuring the consistency of biochar across large quantities, the partial replacement of carbon black with tailormade biochar offers a practical pathway to reducing the environmental impact of tires and other rubber goods without sacrificing essential mechanical performance.

Source: Karunanayake, L., Etampawala, T., de Silva, D. J., Bandara, J., Rajapaksha, A. U., & Vithanage, M. (2025). Role and potential of biochar as a sustainable alternative reinforcing filler to carbon black in rubber composites. Biochar, 7(60).