Preparation of Pentaerythritol Aryl Phosphonates and Their Mechanisms in Flame Retardant Epoxy Resins
In order to improve the flame retardant performance of epoxy resin(EP),the flame retardant pentaerythritol aryl phosphonate(PBPP)was successfully prepared by nucleophilic substitution reaction using the traditional char-forming agents pentaerythritol(PER)and phenylphosphonyl dichloride(PPDC)as raw materials.PBPP was introduced into the EP matrix to prepared flame retardant EP composites.The tests show that the EP/PBPP6 composites successfully obtain UL-94 V-0 rating with the limiting oxygen index(LOI)of 32.5%when the mass fraction of PBPP is 6%,and the melting droplets of EP/PBPP are significantly suppressed.Thermogravimetric analysis show that the addition of PBPP promotes the early degradation and charring of the EP matrix and results in the formation of a dense and hard char layer on the surface of EP/PBPP composites,which effectively acts as barrier in condensed phase.Thus,the PHRR and THR of EP/PBPP composites are reduced by 66.9%and 50.4%compared to pure EP.In addition,the phosphorus-containing radicals generated during the decomposition of PBPP effectively exert the inhibiting effect in gas phase,resulting in a significant reduction in the av-EHC of EP/PBPP composites and endowing the EP composites with excellent fire safety properties.