Synthesis of a novel polyhydroxy triazine-based charring agent and its effects on improving the flame retardancy of polypropylene with ammonium polyphosphate and zinc borate

A novel polyhydroxy triazine-based charring agent, N-tris(hydroxymethyl)-amino triazine-piperazine copolymer (TTPC), was synthesized from piperazine, cyanuric chloride and tris(hydroxymethyl) aminomethane. The chemical structure of TTPC was characterized by Fourier transform infrared spectroscopy and C-13 solid-state nuclear magnetic resonance. TTPC, ammonium polyphosphate (APP) and zinc borate (ZB) were then introduced into polypropylene (PP) by melt compounding to improve the fire performance of the composites. The test results showed that the presence of 21% APP-TTPC-ZB with mass ratio of 16:4:1 could significantly reduce the peak heat release rate from 1547 to 230 kW/m(2), increase the limiting oxygen index value from 18.0 to 29.6% and upgrade the UL-94 rating from no rating to V-0, accompanied by the elimination of melt dripping. The thermal stability and charring behaviors of the composite samples were investigated by thermogravimetric analysis. The results showed that TTPC was a highly efficient charring agent, and ZB could act as synergist in the intumescent system. Based on the comprehensive study of fire performance, char morphology and mechanical properties, it can be concluded that TTPC is a superior charring agent, especially compared with the generally used pentaerythritol. (C) 2020 Elsevier Ltd. All rights reserved.