Flame Retardancy Of Epoxy Resin With Metal-Organic Framework Hybrid And Hexaphenoxycyclotriphosphazene

Epoxy resin(EP)is widely used in various industries due to its advantages of easy processing,excellent mechanical and electrical insulation properties,excellent corrosion resistance and chemical resistance.However,EP is easy to burn,which may bring great hidden danger to people’s life and property safety.Therefore,it is of great significance to improve the flame retardancy of EP for broadening its application field.Phosphazenes are a kind of organic phosphorus flame retardants with halogen free,low toxicity and good compatibility with polymers.Hexaphenoxycyclotriphosphazene(HPCP)has become a common flame retardant for EP due to its good flame retardancy and high thermal stability.In order to improve the flame retardant efficiency of HPCP and reduce its negative effects on other properties of EP,two metal-organic framework hybrids were prepared,and the compounded effects of their compound pairing with HPCP on the comprehensive performance(mainly flame retardant performance)of EP were studied.Firstly,a zinc-based metal-organic framework(IRMOF-3)was synthesized via precipitation method,and then the metal-organic framework hybrid(I-P)was prepared by combining IRMOF-3 with diphenylphosphonyl chloride.I-P and HPCP were compounded to study the flame retardant modification of EP.The results showed that when 3wt%I-P and 6wt%HPCP were added,EP passed the UL-94 V-0 grade and the LOI was 32.0%.However,the release of heat and smoke during combustion increased in the Cone test.The introduction of the I-P transferred the intumescent and loose carbonecous layer formed in EP flame retarded by pure HPCP to the dense and constrictive layer,resulted in reduced complexity of the heat and smoke channel,which lead to the char barrier effect weakened.It is found that I-P can inhibit the chain reaction in the gas phase and promoted the formation of a denser carbon layer in the condensed phase,resulting in the self-extinguishing of EP at the beginning of combustion.Dynamic thermo-mechanical test(DMA)showed that the glass transition temperature(Tg)of EP decreased and thermo-mechanical properties deteriorated after adding I-P.Tensile and flexural tests showed that the addition of I-P can maintain the flexural strength of EP composites,but the tensile strength deteriorates.Secondly,metal-organic framework hybrid(H-U)of halloysite nanotubes(HNTs)supported zirconium-based metal-organic framework(UiO66-NH2)was prepared via hydrothermal method.And the the HPCP/H-U flame retardant system was prepared by adding H-U and HPCP into EP.The results showed that after adding 3wt%H-U and 6wt%HPCP,the LOI of EP reached 35.2%and passed the UL-94 V-0 grade.However,in the Cone test,the introduction of H-U resulted in increasing heat release and smoke release.Flame retardant mechanism study showed that HPCP and H-U acted as the synergistic flame retardant in both gas phase and condensed phase:In the gas phase,the N and P generated by the decomposition of HPCP and H-U play a flame retardant role.In condensed phase,the compound of HPCP and H-U formed denser and higher oxidation degree of char residue,preventing flame combustion to the underlying materials.DMA study found that the introduction of H-U can maintain the Tg and improve the storage modulus(E’)of EP composites.At the same time,the tensile and flexuaral tests showed that H-U can alleviate the negative effects of HPCP on EP mechanical properties.