Cellulose microfibers from rice straw: Low-temperature alkali-mediated extraction and functionalization for thermal insulation and electromagnetic shielding

Highly efficient and cost-effective extraction of cellulose biomass from straws is of high significance for the development of eco-friendly materials in the field of sustainable biorefineries, however, the current approaches generally suffer from high solvent toxicity, energy consumption, and environmental pollution. Here, we demonstrate a low-temperature alkali-treating method to prepare cellulose microfibers from rice straw. The underneath mechanism, i.e., entropy-driven separation mediated by cellulose swelling and polymorphic transformation, is disclosed. Notably, the cellulose microfibers are explored to develop thermal insulation materials, which exhibit low relative density (19.7 mg/cm3) and extremely low thermal conductivity (0.037 W·m−1·K−1), surpassing untreated straw powders and even cotton materials. Furthermore, the microfibers can be further constructed into electromagnetic shielding films with a high shielding efficiency of up to 28 dB, blocking over 99 % of electromagnetic waves. These findings pave a foundation for high value-utilization of straw biomass to create high-performance functional green materials.