Food waste becomes membrane with 96.1% higher heat transfer, lasts 1,000 cycles

A new membrane made partly from food waste could help buildings store heat, move it more efficiently and manage moisture at the same time. Researchers combined food-waste-derived biochar, graphene and a phase-change material into a paper membrane designed for thermal management and energy recovery ventilation. The material addresses a common problem with phase-change materials, which absorb heat when they melt and release it when they solidify. While useful for storing thermal energy, many such materials have low thermal conductivity and can leak when they become liquid. The researchers produced biochar by carbonizing mixed food waste at 752°F and then activating it with potassium hydroxide at temperatures between 1,112°F and 1,472°F. They added graphene and impregnated the resulting porous structure with docosane, a phase-change material used to store and release heat. The version activated at 1,292°F performed particularly well. It developed a surface area of 323.1 square meters per gram, with mesopores making up 82.8 percent of its pore structure. The pores provided space for the phase-change material while helping hold it in place. Waste carbon stores heat Graphene further improved the composite’s thermal performance. The graphene-engineered systems increased latent heat storage by as much as 72 percent compared with composites made using pristine engineered biochar. The optimized FK7G/C22 composite reached a phase-change enthalpy of 93.1 J/g at 116.1°F. It also retained up to 90.2 percent of its enthalpy after 1,000 heating and cooling cycles, indicating that the material could withstand repeated thermal storage and release. The researchers then integrated the composite into a commercial paper membrane. The resulting material was designed to work with ventilation systems, where it could exchange heat while also allowing water vapor to pass through. “By engineering waste derived biochar and integrating it with graphene and a phase change material, we were able to combine thermal energy storage, heat transfer, structural stability, and moisture management within a single membrane system,” said corresponding author Professor Sumin Kim of Yonsei University. The membrane showed a heat-storage rate 96.1 percent higher than the reference pristine paper membrane while retaining 80.2 percent of the bulk composite’s latent heat. That means the paper-based system could store a significant portion of the heat-storage capacity of the material while improving heat transfer. One membrane, multiple jobs Moisture handling was another key part of the design. The membrane recorded an equivalent air-layer thickness of 0.71, below the critical threshold of 1.0, indicating high water-vapor permeability. The researchers said it also met relevant ISO 12572 and ASTM performance criteria. The combination could be useful in energy recovery ventilation, where incoming and outgoing air streams exchange heat and moisture. Instead of relying only on conventional membrane heat transfer, the phase-change layer can temporarily store thermal energy and release it as conditions change. The approach also gives food waste another potential use. Rather than treating the waste solely as something to dispose of, the researchers converted its carbon content into a porous material that serves as the structural framework for thermal energy storage. The team says the material could eventually be used in energy recovery ventilation, building facades, thermal comfort systems and other building applications. However, larger-scale deployment will require further work on production energy requirements, manufacturing costs and techno-economic performance.The findings were published in the journal Biochar.Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.