In a recent paper published in the journal RSC Sustainability, researchers Apurv Gaidhani, Guoshan Min, Lauren Tribe, and Paul Charpentier explore how a common waste product from the timber industry can transform one of the most widely used building materials. Polystyrene foam is a staple in the construction industry due to its low cost and effectiveness at trapping heat. However, because it is derived from petroleum and is difficult to recycle, it carries a significant environmental footprint. This study introduces a more sustainable version by blending wood-derived biochar into the plastic matrix before it is foamed using supercritical carbon dioxide.

The researchers found that adding small amounts of biochar, specifically at a concentration of 2.5 weight percent, significantly alters the internal structure of the foam. In the manufacturing process, the biochar particles act as tiny seeds around which gas bubbles form. This results in a much denser network of smaller, more uniform bubbles compared to standard polystyrene. Specifically, the foam with 2.5 weight percent biochar reached a cell density of approximately 330 million cells per cubic centimeter, with an average bubble size of only 86 micrometers. This refined structure is the primary reason for the material’s improved ability to block heat.

The results of these structural changes are quantitatively impressive. The thermal conductivity of the foam dropped from 36 to 32 milliwatts per meter-kelvin when the optimal amount of biochar was added. This represents an 11% improvement in insulation efficiency. Furthermore, the mechanical integrity of the material saw a dramatic boost. The specific compressive strength of the 2.5 weight percent biochar foam reached 3.9 megapascals per gram per cubic centimeter, which is roughly 100% higher than the strength of pristine polystyrene foam. This means the material can support significantly more weight without becoming heavier itself.

Sustainability was a core focus of the research team, as they benchmarked the new composite against traditional insulation. By using biochar, which is a carbon-rich residue from burning wood waste in low-oxygen environments, the study provides a way to sequester carbon within a long-lasting building product. This approach not only diverts waste from landfills but also displaces some of the fossil-fuel-based plastic required for production. Using supercritical carbon dioxide as the blowing agent further enhances the green credentials of the process, as it serves as a non-toxic alternative to traditional chemical foaming agents.

Beyond just laboratory performance, the study utilized a pilot-scale extrusion line to prove that these findings are relevant to industrial manufacturing. This indicates that the transition from standard polystyrene to this biochar-enhanced version is technically feasible for large-scale production. By improving both the strength and the insulation value of the foam, the researchers have created a material that could lead to more energy-efficient buildings and a reduction in global greenhouse gas emissions. This work directly supports global goals for sustainable cities and responsible consumption by turning a waste product into a high-performance construction material.

Source: Gaidhani, A., Min, G., Tribe, L., & Charpentier, P. (2026). Supercritical CO₂-foamed polystyrene composites containing wood-derived biochar for sustainable thermal insulation. RSC Sustainability.