Ultra-flexible flame-retardant wood composites with resistance to extreme temperatures and mildew

Low-cost wood materials exhibit excellent physical properties owing to their smart porous structure design. These materials have advantages over nonrenewable or hard-to-degrade plastics, polymers, and metals in some specific fields. Here, we report ultra-flexible wood composites prepared through coupling delignification and in situ polymerization. The polyacrylamide (PAM)-lignocellulosic and PAM-water bonds are broken and re-formed during the folding process. The PAM chains of the hydrogel unfold and slide, resulting in full dispersion of the stress in the wood composites. Hydrated calcium ions (Ca2+(H2O)1–6), derived from polyacrylamide-based hydrogel, can further allow the wood composites to lock in the liquid water. Therefore, the wood composites exhibit good flexibility at −40°C and 50°C. Their ultra-flexibility can withstand evaluation in extreme environments, such as 1,000 folds with a 180° bending angle or vacuum dehydration for 24 h. Good flexibility provides great application potential for the wood composite materials.