Effect of triphenylphosphate flame retardant on properties of polybenzoxazines

Abstract

To enhance flame retardancy of polybenzoxazines, non-halogenated phosphorus compound has been evaluated for its potential flame retardant. In this research, the resulting flame retardanted polybenzoxazines were prepared by mixing phosphorus flame retardant with three types of arylamine-based benzoxazine resins. Their fire resistance, thermal, and mechanical properties were investigated. The weight ratios of benzoxazine resins/TPP were varied to different phosphorus content. DSC results indicated that, in the presence of TPP, the onse and maximum temperature of the exothermic peak due to the ring opening polymerization of benzoxazine resins shifted to lower temperature. From TGA results, The degradation temperatures at 5% weight loss of polybenzoxazines were reduced. All polybenzoxazines possessed relatively high char yield, which increased as the TPP content increased. This implied that their flame retardancy could be enhanced. The flame-retardancy of these thermosets was evaluated by limiting oxygen index (LOI) and and UL-94 vertical tests. Upon adding 10 wt% of TPP, LOI increased from 23.5, 23, 22 to 26, 25, 24, for BA-a, BA-mt, and BA35x, respectively. Furthermore, the flammability was found to be in an order of BA-a <BA-mt <BA-35x. The maximum flame retardancy of V-0 class specimens were obtained when adding TPP at 2 wt% for BA-mt and 5 wt% for BA-a and BA-35x. That is TPP contributes to the enhancement of flame retardancy of polybenzoxazines even at a relatively low amount of the TPP. Additionally, it was found that flexural strength and flexural modulus of those polybenzoxazines decreased with an addition of TPP. Finally, the reduction of Tg of BA-a, BA-mt, and BA-35x with increasing of TPP were also observed possibly from the plasticizing effect of the TPP additive.