Preparation of boron-containing chitosan derivative and its application as intumescent flame retardant for epoxy resin

A new boron-containing chitosan-based compound HBS was synthesized and used in combination with ammonium polyphosphate (APP) as an efficient flame retardant with good compatibility for epoxy resin. The modified EP composites were investigated by thermogravimetric analysis (TGA), UL-94 V (vertical burning), limited oxygen index (LOI) and cone calorimetry (CC) test. The sample labeled S3 with the total addition of HBS and APP was 10%, simultaneously the weight ratio of HBS and APP was 1:3, which passed the UL-94 V-0 rating. LOI value of sample S3 was 30.5%, which was higher than that of EP (S0, 22.6%) and EP modified with 10% APP (S5, 26.1%). CC tests results showed that PHRR (peak heat release rate), THR (total heat release), PSPR (peak smoke production rate) and TSP (total smoke production) values of sample S3 were 515.9 kW/m(2), 50.6 MJ/m(2), 0.14 m(2)/s and 10.9 m(2), respectively, which were 51.5, 33.5, 74.5 and 84.7% lower than those of unmodified EP, respectively. What's more, flame retardancy parameters such as fire index growth rate (FIGRA), maximum average rate of heat emission (MARHE) and average effective heat of combustion (av-EHC) also decreased. The char residue of sample S3 was 61.3%, which was 506.9% higher than that of EP. The introduction of HBS and APP was beneficial to form a sufficient, dense, homogeneous and high strength char layer on the EPs surface during combustion. Due to the effective protective layer, the transfer and diffusion of heat can be effectively inhibited, the production of combustible gases can be restricted, and the emission of smoke can be inhibited, thus reducing the release of heat and smoke.