Flame Retardancy Comparison of Type I and Type II Ammonium Polyphosphate Respective in Combination with 1,3,5-Tris(2-hydroxyethyl)cyanurate in Polypropylene

Abstract

In this work, synergic flame retardancy of type I (APP-I) and type II (APP-II) ammonium polyphosphate respective with 1,3,5-tris(2-hydroxyethyl) isocyanurate (THEIC) in polypropylene was studied and compared by limiting oxygen index measurement, the vertical burning test and the cone calorimeter test and the mechanism was also discussed by thermogravimetric and residure char analysis. The experimental results indicated that when the weight ratio of ammonium polyphosphate (APP)/1,3,5-tris(2-hydroxyethyl) isocyanurate (THEIC) was 2.5/1 and the loading of the flame retardant combinations was 30 wt % based on the total weight of the composites, the LOI of the flame-retarded polypropylene composite with APP-II/THEIC (referred as FR2) could be up to more than 30, the demanding V-0 classification of the burning test according to the UL 94 standard could be achieved, while the LOI of the composite with APP-I/THEIC (referred as FR1) was lower than 28 and any classification could not be reached. However, there is only little difference between the both in the changes of the heat release rate, mass loss rate and total heat release with combustion time. FR2 could promoted markedly the carbonization of polypropylene, but FR1 could not over 370 ºC, which resulted in the higher char-forming yields and bettter flame retardancy of the former than the latter.