Four-arm-polysiloxane/Oxaphosphine Compound Flame Retardant And Application On Epoxy Resin

This research had successfully synthesized four-armed polysiloxane flame retardant(FRSi)with adamantane and dichloromethylphenylsilane.Synergistic effect was expected between 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide(DOPO)and FRSi.DOPO was introduced as a reactive flame retardant while FRSi was utilized as an additive flame retardant.The combustion performance,thermal degradation,dispersity and mechanical properties of EP incorporated with FRSi/DOPO had been researched.Temperature of initial decomposition of FRSi is 134.4°C.Char yield of FRSi at 800°C was 31.8% under nitrogen and 18.5% under air,showing excellent char formation ability.When the total addition amount of DOPO and FRSi was controlled at 15%,the limited oxygen index(LOI)reached a highest value 26.9% and UL 94 V-0 class was achieved when the mole ratio of P and Si atom was 3:1.Various samples were designed and P:Si ratio was controlled at 3:1.When the addition amount of FRSi/DOPO reached 20%,the LOI of EP composites showed an LOI of 28.8% and UL 94 V-0 rating.When the addition amount kept rising,the LOI of EP got further improvement and was still classified as V-0 class.Thermogravimetric test has carried out on EP/FRSi/DOPO composites.It was obvious that EP/FRSi/DOPO composites produced abundant char residue not only in air but in nitrogen,which enhanced its flame retardancy.Different from flame retardants which promotes the char forming by accelerating the thermal degradation,FRSi/DOPO flame retardant enhances the thermal stability of epoxy resin,for the reason that the initial decomposition temperature increased when the addition amount raised.This compound flame retardant improved the tensile strength of EP.With only 20% of FRSi/DOPO added,the tensile strength was enhanced from 15.7MPa to 46.9MPa.The pronounced enhancement widens the application of EP and makes it possible to meet higher demands.EDX showed that element Si and P dispersed quite well in both EP composites,indicating that the compatibility of EP and the compound flame retardant was excellent.SEM showed a chapped,cracked and porous surface on residue char of pure EP.Flammable gas and oxygen can easily exchange and mix through this char,providing combustion with more heat.On the other hand,EP/FRSi/DOPO formed thick,dense and smooth char after combustion.This sort of char is more effective in blocking the transfer of heat,flammable gas and oxygen,thus plays a significant role in condensed phase.