Fabrication of novel halogen-free flame retardant containing functionalized chitosan from fisheries waste through the sol-gel technology and its fire safety performance in polyurethane resin

Chitosan (CS) derived from fisheries waste, such as shrimp and crab shells, was used to fabricate a bio-based, ecofriendly flame retardant. By reacting the –NH₂ groups of CS and the NH₂ groups of melamine polyphosphate (MPP) with the NCO groups of polymethylene polyphenyl polyisocyanate (PMPI), a novel intumescent flame retardant, CS-PMPI-MPP, was synthesized. Isophorone diisocyanate (IPDI) was reacted with polyol and aminopropyltriethoxysilane (APTS) to form a polyurethane containing silicon (Si-PU), into which the flame retardant was incorporated to produce a high-polymer composite through the sol-gel technology. The structure, thermal properties, flame retardancy, mechanical properties, toxicity, and char formation of the composites were analyzed. Fourier transform infrared spectroscopy, thermogravimetric analysis, limiting oxygen index, cone calorimeter, UL-94, thermogravimetric analysis with infrared spectroscopy, universal testing machine, scanning electron microscopy, X-ray photoelectron spectroscopy, raman spectroscopy, and smoke density test analyses were performed. The thermogravimetric test results indicated an increase in char yield from 0.5 wt% in pristine polyurethane to 25.9 wt% upon the addition of CS-PMPI-MPP, signifying an enhancement in the thermal stability of pristine polyurethane. According to limiting oxygen index and UL-94 data, the incorporation of CS-PMPI-MPP improved the limiting oxygen index and UL-94 ratings from 18.2 % (Fail) to 26.5 % (V-1), demonstrating the exceptional flame-retardant property of CS-PMPI-MPP within the pristine polyurethane formulation.