Synthesis of bio-based phosphorus-nitrogen hybrid cellulose nanocrystal flame retardant for improving of fire safety of epoxy resin

Bio-based materials as flame retardants meet the requirements of green strategy and sustainable development. Here nitrogen and phosphorus-modified bio-based cellulose nanocrystal composite (NPCNCs) were designed and added to epoxy resin (EP) to determine fire safety and mechanical properties. NPCNCs were successfully synthesized using ice bath polymerization and exhibited a fibrous appearance with rough surface. When corresponding into EP, NPCNCs endowed EP composite with excellent flame retardancy. For EP/6NPCNCs, the LOI value was 27.6% which was higher than that of pure EP (23.5%). Compared with pure EP, the total heat release, peak heat release rate, total smoke production and peak smoke production rate values of EP/6NPCNCs decreased by 27.27%, 43.34%, 70.21% and 66.67%. This was attributed to catalysis-dehydration and carbonization, carbon support of cellulose nanocrystals and gas phase dilution. In addition, the flame retardant EP composite mechanical properties were basically maintained compared with the pure EP. This article will provide a new way for the design bio-based P and N-modified flame retardants.