Synergistic effect of chitosan derivative and DOPO for simultaneous improvement of flame retardancy and mechanical property of epoxy resin

Abstract In this work, the effects of a chitosan-based derivative (CSA), DOPO and CSA-DOPO additives on the flammable properties of EP composites were systematically studied, where CSA was synthesized by a facile condensation between chitosan (CS) and 9-anthralaldehyde and. DOPO was 9, 10-dihydro-9-oxa-10- phosphaphenanthreene-10-oxide. The mass ratio of CS and 9-anthralaldehyde in CSA was determined by elemental analysis and theoretical calculation, which matched well with each other. Under the 8% addition in EP, EP/2.66%/5.34%DOPO sample was the only one, which passed the UL-94 rating and exhibited the highest LOI value of 36.4%. Compared with EP, the cone calorimeter test (CC) showed that the total smoke emission value and the peak heat release rate of the CSA and DOPO modified EP decreased 36.0% and 61.9%, respectively, and the residual char amount increased by 151%. The possible flame retardant mechanism of CSA/DOPO towards EP was proposed according to the results of the real time FTIR spectra at different pyrolysis temperatures, cone calorimeter and Py-GC/MS analysis for EP and EP/2.66%CSA/5.34%DOPO samples, and Raman spectra and XPS for their char residues. Moreover, the incorporation of CSA/DOPO effectively improved the mechanical properties, especially, the flexural strength was increased by 52.3%. It was proposed that CSA/DOPO plays roles in both vapor and condensed phases, and the synergistic effect of CSA and DOPO significantly improve the flame retardancy and mechanical strength of EP.