Green facile fabrication of flame-retardant straw cellulose nanofiber laminate with enhanced mechanical strength

Natural biomass resources are highly valued for their high biodegradability, high sustainability, and easy modification. However, their large-scale application is limited by their flammability. Numerous flame-retardant modification methods have been developed. However, they are limited by low performance and poor mechanical properties. In this study, a novel method was proposed for preparing flame-retardant cellulose nanofiber laminates, focusing on raw material selection, modification method, and laminated structure. The silica in natural straw was retained, and the fibers were swollen using the green and environmentally friendly deep eutectic solvent, resulting in the partial dissolution of cellulose. This process reduced the energy consumption of mechanical treatment during the preparation of straw cellulose nanofibers. Sulfonic acid groups were grafted onto the straw cellulose to impart flame-retardant properties to the material. By leveraging the laminated structure to block heat transfer between layers, the material achieved excellent flame-retardant performance and mechanical properties. The flame-retardant straw cellulose nanofiber laminate achieved an LOI of 61.9 %. The results of thermogravimetric analysis showed that the residual carbon content can reach 37.6 %, which is 40.3 % higher than that of the CNFL. This study presents a novel approach to developing flame-retardant biomass boards.