A P-N-B Flame Retardant Synergistically Improving Fire Safety and Mechanical Properties of Ramie Fabric/Epoxy Composites

Ramie fiber-reinforced epoxy composites have high mechanical strength and outstanding corrosion resistance, and are widely used in many fields. However, ramie fiber and epoxy resin are inherently flammable, and there is an increasing focus on the flame-retardant improvement of Ramie fiber-reinforced epoxy (EP/RF) composites. In this study, an eco-friendly and higher efficient P-N-B flame retardant (denoted as DBC) was synthesized and subsequently applied to ramie fabric to impart flame retardancy of EP/RF composites. When the weight gain on ramie fabric was about 10 wt%, the limiting oxygen index of EP/RF-DBC is 32.6%, and EP/RF-DBC has been upgraded from UL-94 No rating to UL-94 V-0 rating. Compared with EP/RF, the peak heat release rate and total heat release of EP/RF-DBC reduced by 31.9% and 32.0%, respectively, indicating that the introduction of DBC reduces the fire hazard of EP/RF. The presence of DBC promotes the dehydration of EP/RF into residual chars, which act as a barrier to block the exchange of heat and gas, releasing more noncombustible gases and diluting the concentration of combustible gases. In terms of mechanical properties, due to the low acidity of DBC and the presence of many amino groups in chitosan oligosaccharide, the adhesion between RF and EP is improved. The flexural strength and modulus of EP/RF-DBC are increased by 15.3% and 32.1%, respectively, compared with EP/RF.