Effects of intumescent flame retardant system consisting of tris (2-hydroxyethyl) isocyanurate and ammonium polyphosphate on the flame retardant properties of high-density polyethylene composites

An intumescent flame retardant (IFR) system composed of tris (2-hydroxyethyl) isocyanurate (THEIC) and ammonium polyphosphate (APP) was used to prepare high density polyethylene (HDPE) composites, and their thermal and flammability properties were studied. The limiting oxygen index of the HDPE composite containing 30 wt% of IFR with an APP: THEIC weight ratio of 3:1 (HD31) reaches 31.5%. The cone calorimeter analysis shows that the peak and average heat release rate of HD31 are reduced by 69.5% and 58.1% respectively; while the average mass loss rate is reduced by 77.2%. The thermogravimetric analysis suggests that the IFR/HDPE composites have good char forming ability. The structural analysis of the char residue shows that the intumescent char is composed of a polyaromatic structure containing nitrogen in five or six-membered ring linked to phospho-carbonaceous structure via the POC linkage, and some phosphorous degradation products containing POP structure.