Novel halogen-free flame retardant thermoset from a hybrid hexakis (methoxymethyl) melamine/phosphorus-containing epoxy resin cured with phenol formaldehyde novolac

This paper describes the curing behaviours, thermal properties and flame-resistance of a novel halogen-free epoxy hybrid thermoset, prepared by the curing reaction of hexakis (methoxymethyl) melamine (HMMM), a phosphorouscontaining epoxy resin (EPN-D) with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) group and phenol formaldehyde novolac (n-PF). The resultant thermosets showed high glass-transition temperatures (Tg, 123–147°C) as determined by thermal mechanical analysis (TMA), excellent thermal stability with high 5 wt% decomposition temperatures (Td,5% ≥ 308°C) and high char yields (Yc ≥ 39.4 wt%) from the thermogravimetric analysis (TGA). All the cured EPND/ HMMM/n-PF hybrid resins achieved the UL 94 V-0 grade with high limited oxygen indices (LOI > 45.7). It is found that phosphorous and nitrogen elements in the cured EPN-D/HMMM/n-PF hybrid resins had a positive synergistic effect on the improvement of the flame retardancy.