Study On The Modification Of Benzoxazine Resin Matrix

Benzoxazine is well known as a new class of thermosetting resin with high thermal stability,flame retardant and near zero curing shrinkage.These characteristics can beattributed to the stabilization of the Mannich bridges by the very stable intra molecular hydrogen bonding between the phenolic OH and the nitrogen atom of the Mannich bridge.Therefore,benzoxazine resin has a broad application prospects in the aerospace field.However,the higher curing temperature and brittleness of the resin limited the industrial application.In this paper,the catalyst modification and molecular design modification are used to reduce the curing temperature and improve the viscosity characteristics for developing hot melt benzoxazine resin matrix.The toughening modification of benzoxazine resin matrix is carried out by structural design and blending with other resin,and the heat resistance,mechanical properties and flame retardance are studied.Specific work is divided into the following sections:(1)Diphenylmethane diamine type benzoxazine(M-BOZ)was catalytic modified with organic acid,anhydride,epoxy resin,phenolic compound and catalyst F respectively.Differential scanning calorimetry(DSC)characterization temperature was used to characterize the reactivity of the modified M-BOZ resin matrix.The results show that both the organic acid and the acid anhydride could improve the reactivity of the M-BOZ resin effectively.But the organic acid will cause poor storage period of M-BOZ and there are small molecules released when acid anhydride is blended with the M-BOZ.Both of above two methods are not suitable for the preparation of hot melt prepreg resin matrix.Epoxy resin modification will affect theflame retardance ofthe M-BOZ resin,but it can effectively improve the glass transition temperature.Nonylphenol and catalyst F not only improve the viscosity-temperature characteristics of M-BOZ resin,but also raise the reactivity of M-BOZ resin and reduce the curing temperature to 160?.(2)A high activity and high heat resistance benzoxazine resin(BA35-BOZ)is synthesized from 3,5-dimethylaniline,bisphenol A and formaldehyde as raw materials.DSC result shows that the curing temperature of BA35-BOZ is 24? lower than that of M-BOZ,mainly due to the electron-withdrawing effect of two methyl groups on the benzene ring,which makes the aminomethyl ions formed by ring opening of oxazine ring more stable.The result of dynamic mechanical thermal analysis(DMA)shows that the glass transition temperature(Tg)of BA35-BOZ is 41? higher than that of M-BOZ,mainly due to the Mannich bridge structure of bisphenol-type structure more stable,so that the thermal performance.(3)Two kinds of methods are taken for tougheningmodification of M-BOZ resin matrix by.First,two benzoxazine resins(D230-BOZ and TTD-BOZ)containing ether bond are synthesized.The two resins are blended with M-BOZ resin,and the thermal properties,mechanical properties and flame retardant properties were studied.It was found that the thermal properties and flame retardant of the modified resin matrix are decrease and the tensile strength isincrease.Second,the mechanical properties and flame retardant of the modified resin matrix are studied by blending liquid rubber(CTBN)and polyimide(PEI)with M-BOZ resin matrix.It was found that the tensile strength and impact strength of the resin matrix areincrease and the flame retardantisdecrease after modification of CTBN.The tensile properties,impact properties and flame retardantare improved after modification of PEI.(4)Benzoxazine resin matrix for hot melt prepreg is prepared,which has a high reactivity at 160°C,and Tg of 170°C,an carbon ratio of 41% at 800°C,and maintain a good flame retardant properties.The preparation process of benzoxazine / glass fiber prepreg and the mechanical properties of composite materials are studied.The tensile strength of the composites is 731.1MPa,the flexural strength is 856.2MPa,the shear strength is 73.9MPa,and the mechanical properties are closed to that of the epoxy resin prepreg.Oxygen index of 42 ~ 45.