Function of chitosan in a DOPO-based flame retardant modified epoxy resin

A bio-based flame retardant (PDE) was synthesized through a facile one-pot reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with protocatechualdehyde and ethanol. PDE was fully characterized by fourier transform infrared spectroscopy (FTIR), 1 H NMR, 31 P NMR and ESI-MS. Epoxy resin (EP) with 9 wt% PDE (EP/9%PDE) passed UL94 V-0 rating and possessed the limited oxygen index (LOI) value of 33.2%, the curved EP thermosets kept transparent. When chitosan (CS) was used to replace one-third of PDE in EP/9% PDE, the modified EP also passed UL94 V-0 rating with the LOI value of 32.3%, the curved thermosets kept transparent and owned better absorption effect toward ultraviolet light. Cone calorimeter test and TG-FTIR analysis were performed on the EP samples, the chars after burning were characterized by scanning electron microscope (SEM), energy-dispersive X-Ray spectroscopy (EDX), Raman spectrum and FTIR. The results showed that the synergistic effect of PDE-CS on flame retardant was ascribed to the protective effect of denser char layer, the release of some phosphorus containing free radicals and the dilution effect of released nonflammable gases such as H 2 O and CO 2 .