Preparation And Properties Of Benzoxazine/Halloysite Nanotubes Nanocomposites

This work aims to modify the benzoxazine resin by using siloxane benzoxazine-modified halloysite nanotubes to overcome its shortcomings in thermal stability and mechanical properties.Two kinds of siloxane benzoxazine monomers were synthesized by using KH-550,paraformaldehyde,phenol and bisphenol A as raw materials,respectively,namely phenol/KH-550 benzoxazine monomer(p-BZ)and bisphenol A/KH-550benzoxazine monomer(b-BZ).The reaction products were characterized by infrared spectroscopy(FTIR)and were confirmed to be the target products.In order to improve the compatibility of HNTs with the organic matrix and have a good dispersion in the system,the grafted reactions were carried out on the surface of the purified HNTs by p-BZ and b-BZ,respectively.The dispersions of HNTs in p-BZ/HNTs and b-BZ/HNTs were investigated.The results show that the dispersion ratio of HNTs in both of them can reach 20 wt%.p-HNTs and b-HNTs were used as modifiers with HNTs content of 20 wt%,and hexamethylenediamine-type benzoxazine(Ba-h)was used as the matrix to be blended,followed by 1:0,9:1,7:1,6:1,4:1,7:3,3:2 mass ratio,and each proportion of the blend was solidified according to a certain curing procedure.Thus a series of standard splines containing HNTs mass ratios of 0%,2%,2.5%,3%,4%,6%,and 8%were prepared.The nanocomposites were tested and characterized by DSC,TG,DMA,SEM and mechanical performance tests.The results showed that the curing temperature of P(Ba-h)/p-HNTs and P(Ba-h)/b-HNTs was significantly lower than that of pure P(Ba-h)resin.When the amount of HNTs was 8%,the residual ratios of P(Ba-h)/p-HNTs and P(Ba-h)/b-HNTs composites can reach 44%and 43%,respectively,which are about 28%and 27%higher than that of P(Ba-h),respectively.When the amount of HNTs was 6%,the tensile strength of the two composite systems increased by 87%and 65%on the basis of P(Ba-h),respectively.When the amount of HNTs was 2.5%,the impact strengths of the two systems increased by 52%and 125%on the basis of P(Ba-h),respectively.When the addition amount was 3%,The flexural strength of the P(Ba-h)/p-HNTs composite can reach 43 MPa,while the flexural strength of the P(Ba-h)/b-HNTs composite system reaches a maximum of 53MPa when the amount of HNTs was 2.5%,which increased by 47%and 81%respectively.The storage modulu of P(Ba-h)/p-HNTs composite was increased by 35%compared with PBa-h when the addition amount was 4%,and its T_g was also increased by 14°C when the addition ratio was 8%.The storage modulu of P(Ba-h)/b-HNTs composite was 38%higher than that of PBa-h,and its T_g was also increased by 17°C on the basis of pure benzoxazine.According to the results,the HNTs modified by the siloxane benzoxazine can significantly improve the thermal stability and mechanical properties of the benzoxazine resin.However,the system of P(Ba-h)/b-HNTs has a more significant improvement than P(Ba-h)/p-HNTs.In general,b-HNTs have the more obvious modification effect on polybenzoxazine-based composites.