Preparation Of All-in-one Intumescent P/N/Si-containing Flame Retardant And Its Application To Epoxy Resin

Epoxy(EP)resin-based composites have a variety of excellent properties,including excellent adhesion,heat resistance and mechanical properties,so they are widely used in construction materials,adhesives,coatings,electronic packaging,laminates and composites.However,conventional EP and its compounds are usually highly flammable and can pose a significant safety hazard.An economical and efficient solution is to introduce flame retardants into EP.For safety and environmental reasons,intumescent flame retardants(IFR)are considered one of the most promising types of flame retardants.Traditional IFR formulations include multiple components that assume the roles of acid source,charring agent and blowing agent,separately.However,though multicomponent IFR systems import flame retardant properties to polymers,they also bring a series of problems,such as incompatibility problems between multicomponent additives and polymer matrix,and deterioration of mechanical properties of composite materials.In order to solve these problems,the concept of synthesizing an all-in-one IFR with three functions has been proposed.In the past,integrated flame retardants usually combined acid source,charring agent and blowing agent by encapsulation or microencapsulation.However,the most ideal way is to combine the "three functions" in one molecular structure by chemical bonding,so as to produce a true all-in-one IFR molecule.In this study,a silyl compound,3-aminopropyltriethoxysilane(APTES),was bonded with commercial ammonium polyphosphate(APP)acting as both an acid source and a blowing agent,through a cation exchange reaction.Different products of APTES-APP were prepared using different degrees of polymerization of APP and then they were applied to the EP matrix to improve the flame retardancy of the composites.First,a lower degree of polymerization of APP 1.0(n=200)was reacted with APTES,and the high temperature thermal stability of the resulting product APTES-APP1.0 was greatly improved compared with that of APP.However,at an addition level of 10 wt%,APTES-APP1.0 was not capable of flame-retarding EP alone,but was more suitable as a charring agent.Working with APP of high polymerization degree,it had synergistic flame retardant effect and could improve the flame retardant performance of APP.The flame retardant EP with the same 10 wt%addition and APP2.0(n>1000):APTES-APP1.0=4:1 was capable of passing the vertical burning test(UL-94,1.6 mm)with the highest rating of V-0,and in the cone calorimetric test(CCT),the peak heat release rate(PHRR)and peak smoke production rate(PSPR)decreased by 53.2%and 29.5%,respectively,and the residual char rate was also increased to 13%.However,the percentage of NH4+ ions substituted by APTES for APP was too high,so that the product APTES-APP1.0 had a large amount of-Si-OH.It makes the APTES-APP1.0 particles easy to agglomerate the dispersion in the EP matrix becomes poor,which seriously reduces the mechanical properties of the EP composites.Second,a highly polymerized APP2.0(n>1000)was used to react with APTES.By varying the experimental conditions,the product APTES-APP2.0 was obtained,which partially retains the NH4+ ionic structure of the raw material APP2.0 and produces a new structure containing organosilicon.APTES-APP2.0 has both gas-phase and condensed-phase flame retardant effects and is an all-in-one intumescent P/N/Si-containing flame retardant.When APTES-APP2.0 is added to EP alone,an addition of 8 wt%imports the flame retardant EP an limiting oxygen index(LOI)of 26.0 vol%and the highest rating of V-0 in the vertical burning test(UL-94,1.6 mm).In CCT,the PHRR,total heat release rate(THR),PSPR and total smoke production rate(TSP)of this flame retardant EP were reduced by 68.1%,34.0%,44.2%and 31.3%,respectively,compared to those of EP.The ignition time(TTI)and the time to reach PHRR(tPHRR)of this flame retardant EP were delayed by 9 s and 25 s,respectively,and the fire growth rate index(FIGRA)was reduced by 63.2%compared with EP.The flame retardant mechanism of APTES-APP2.0 was completely investigated by scanning electron microscopy(SEM),thermogravimetry-infrared coupling test(TG-IR)and X-ray photoelectron spectroscopy(XPS).The study concluded that the flame retardant structure of APTES-APP2.0 containing P,N,and Si heteroatoms,while releasing non-flammable gases during combustion,also contributed to the formation of a dense and strong cross-linked carbon layer of flame retardant EP,which effectively protected the plastic substrate.Tensile tests showed that the tensile strength of EP/APTES-APP2.0 was 5.8%higher than that of EP/APP with the same 8 wt%addition of flame retardant EP,which was attributed to the improved compatibility of the EP matrix with APTES-APP2.0 by-Si-OH.