An improved intumescent flame-retardant epoxy resin with hydroxylated melamine as both charring and blowing agent

Generally, pentaerythritol (PER) and melamine are, respectively, used as charring agent and blowing agent to combine with ammonium polyphosphate (APP) to establish an intumescent flame retardant (IFR). As for IFR system, the intumescent volume and compactness of char residues are the keys to enhance the flame retardancy of polymers. In this work, hydroxylated melamine (MOH) was synthesized and used as both charring agent and blowing agent to replace pentaerythritol and melamine simultaneously, and it was combined with APP to develop an excellent intumescent flame retardant for epoxy resin. This APP/MOH intumescent flame retardant at the mass ratio of 3:1 significantly improved the LOI value of epoxy resin to 32.5% and reached UL 94 V-0 by 15 mass% loading contents. However, both APP and APP/PER system failed to pass UL-94 vertical burning test and lower LOI was obtained. Additionally, the peak of heat release rate and peak of smoke production rate of APP/MOH based epoxy resin were reduced by 68.3% and 39.0%, respectively, compared with those of neat epoxy resin. After analysis of the pyrolysis products from the gaseous and condensed phases, it was found that APP/MOH system produced higher intumescent volume and better compactness of char, which is a good barrier to hinder the transfer of fuels and heats.