Effects of types and amount of phenolic resins on curing condition, thermal properties and ignition behavior of benzoxazine/phenolic polymer alloys

Abstract

Polymer alloys between benzoxazine and phenolic resins were prepared by mixing these two components followed by heating until the alloys were completely cured. From DSC studies, it was found that the suitable curing condition for benzoxazine/novolac phenolic alloys was 150 ?C/1 hour and 180 ?C/1 hour when the amount of novolac resin was lower than 50% by weight and the suitable curing condition was 150 ?C/1 hour and 180 ?C/2 hours when the amount of novolac resin was higher than 50% by weight. On the other hand, the suitable curing condition for benzoxazine/resole phenolic alloys was 100 ?C/2 hours and 180 ?C/1.5 hours when the amount of resole resin was lower than 50% by weight and the suitable curing condition was 100 ?C/2 hours and 180 ?C/2 hours when the amount of resole resin was higher than 50% by weight. Both phenolic resins improved thermal stability and increased flame retardation of benzoxazine resin. It can be seen that as the amounts of both phenolic resins in the alloys increased, thermal decomposition temperatures and LOI values increased while burning rates decreased. However, it is clearly seen that at the same blending ratio, benzoxazine/resole alloys gave higher char yield than benzoxazine/novolac alloys. This indicates that the former has better flame retardation than the latter.