Cellulose-based composite thermal-insulating foams toward eco-friendly, flexible and flame-retardant

Cellulose nanofibrils (CNFs) have been developed as building blocks for highly porous foams which are superior in thermal insulation. Unfortunately, the flammability and poor mechanical performance of CNF foams limited their practical applications. In this strategy, biopolymer sodium alginate, together with nontoxic boric acid and borate, were explored to play the roles of flame retardants for methyltrimethoxysilane cross-linked CNF foams. Their co-effects on preventing CNF foams from being ignited were revealed. The composite foams were self-extinguish and showed a considerably increased limited oxygen index (up to 39.5%). Additionally, the foams were flexible with good resilience and bendability. The eco-friendly foams with low thermal conductivity (0.028 W m^-1 K^-1 at 25 °C), flexibility, and non-ignitability can meet the satisfactory in energy-conservation, wide applicability, and use safety.