Modification Of Epoxy Resin With Halloysite Nanotubes Grafted By Siloxane Benzoxazine

Halloysite is a nano-tube mineral with a unique structure,which has received extensive attention in the field of polymer modification in recent years.In HNTs/polymer composites,the surface modification of HNTs is the key point that determines the final performance of the material.This study hopes to prepare a composite by copolymerizing siloxane-based benzoxazine surface grafted HNTs with an epoxy resin to achieve the purpose of improving the heat resistance and mechanical properties of the epoxy resin and expanding its application range.Bisphenol A type benzoxazine monomer(B-aptes)and cardanol type benzoxazine monomer(C-aptes)are prepared by two-step method using bisphenol A and cardanol as phenol sources,respectively.The two products were characterized by infrared spectroscopy(FTIR)and nuclear magnetic resonance hydrogen spectroscopy(~1H NMR),confirming that the two benzoxazine monomers have been successfully synthesizedIn order to improve the interfacial compatibility between HNTs and epoxy matrix and the dispersion of HNTs in epoxy matrix,two benzoxazine monomers were grafted onto the surface of HNTs as silane coupling agents,the mass ratio of benzoxazine to HNTs was 3:1.TG analysis was performed on HNTs grafted with two siloxane-based benzoxazines(B-HNTs,C-HNTs).B-HNTs and C-HNTs were blended with bisphenol A epoxy resin(DGEBA)in a certain proportion,and the mixture was cured according to the heating process to prepare two kinds of halloysite/epoxy composite with mass ratio of 0%,1%,2%,3%,4%HNTs(B-HNTs/DGEBA,C-HNTs/DGEBA).The two types of composite materials were tested and characterized by DSC,TG,DMA,SEM,mechanical property tests.The optimal curing temperature of the composite material was determined by DSC and it was found that the addition of HNTs can reduce the curing temperature and curing enthalpy of epoxy resin.The residual rate of two types of composites at 800°C was studied,and the results showed that the residual rate of both materials increased with the increase of HNTs content.When the content of HNTs is 4%,the residual rates of B-HNTs/DGEBA and C-HNTs/DGEBA are 25.4%and 22.8%respectively,which are 129%and 105%higher than those of pure epoxy resins.Flexural and impact performance test results show that the introduction of silicone-based benzoxazine grafted HNTs can strengthen the mechanical properties of epoxy resin.When the content of HNTs is 3%,the flexural strength of B-HNTs/DGEBA and C-HNTs/DGEBA are 100.3 and 105.2 MPa,respectively,which are15%and 20%higher than pure epoxy.Similarly,when the content of HNTs is 3%,the impact strength of the two systems is 29.0 and 30.7 k J/m~2,respectively,which is 21%and 28%higher than that of pure epoxy resin.DMA test results show that the storage modulus of both composite systems is improved compared to pure epoxy resin.DMA test results show that the storage modulus of the two composite system is higher than that of pure epoxy resin.When the content of HNTs is 4%,the storage moduli of B-HNTs/DGEBA and C-HNTs/DGEBA are 2258 MPa and 2243 MPa,which are 13.6%and 12.9%higher than pure epoxy resin.Similarly,when the HNTs content is 4%,the glass transition temperatures of B-HNTs/DGEBA and C-HNTs/DGEBA are 111.5°C and 109.4°C,which are increased by 6°C and 4°C,respectively.From the above analysis results,it can be concluded that silicone-based benzoxazine grafted HNTs can significantly improve the heat resistance and mechanical properties of epoxy resins,and the heat resistance of B-HNTs/DGEBA systems is higher than that of C-HNTs/DGEBA systems;but the mechanical properties of the C-HNTs/DGEBA systems are stronger than the B-HNTs/DGEBA systems.