| Epoxy resin(EP)is a typical thermosetting polymer that is widely used in many applications.However,EP is extremely flammable,so many applications where flame retardancy is required are greatly limited.The addition of flame retardants is the easiest way of modify EP,but it often affects the properties of EP,so it is necessary to develop suitable flame retardants for EP.In this paper,three low phosphorus content flame retardants were synthesized,which blended with EP to prepare flame retardant multifunctional EP composites.The EP composites were characterized for their flame retardancy,mechanical properties and other functionalities,and the related mechanisms were studied.The main experimental results are as follows.(1)A low phosphorus content flame retardant,DOPO-SGA,was synthesized from syringaldehyde,3,5-diamino-1,2,4-triazole and DOPO.DOPO-SGA was then introduced into epoxy by blending to improve flame retardancy and mechanical properties.The presence of 3% DOPO-SGA increased the LOI to 33.2%,upgraded the UL-94 rating to V-0,and reduced the release of smoke and heat of epoxy.The tensile and impact strength were also enhanced after the introduction of DOPO-SGA.The addition of5% DOPO-SGA increased the tensile strength and impact strength by 47%and 42%,respectively,compared with that of the control EP sample.(2)A flame retardant DPPVA was synthesized through a Schiff-base reaction of vanillin,3,5-diamino-1,2,4-triazole,and diphenylphosphinyl chloride,which was used to improve the thermal stability,flame retardancy,and antibacterial activity of the cured epoxy resin.The EP/4% DPPVA sample looked yellow,but it was still transparent,and it passed the V-0rating with a LOI of 34.5%.The presence of 4% DPPVA in EP decreased the peak heat release rate(p HRR),total heat release(THR),and total smoke production(TSP)by 32.5%,25.2%,and 29.3%,respectively.Compared with that of the control EP,the char residue was increased to14.9% from 9.6%.The EP/4%DPPVA sample exhibited effective repellence to E.coli and S.aureus.(3)The phosphorus and boron containing flame retardant was synthesized by dehydration and substitution reaction between boric acid,pentaerythritol and phenyl dichlorophosphate.Added to EP in various mass ratios to improve the flame retardancy,mechanical properties and dielectric properties of EP.Only 2% POSB was required to pass the V-0 rating and EP/5%POSB in cone calorimeter tests was resulted in an expanded carbon layer of 3 cm.Moderate additions of POSB improved the tensile and flexural strength of EP composites.Although EP/POSB was turned to be green,it was still transparent and the dielectric constant and dielectric loss were gradually decreased with increasing additions. |
