Study On Polysulfone Toughened Modifide Epoxy Resin And Its Interlayer Toughenend Liquid Formed Carbon Fiber Composites

Carbon fiber composites have been widely used in aerospace applications due to their high specific strength,elastic modulus and excellent thermal stability.Unfortunately,there are obvious defects between the layers of carbon fiber composites,that lead to the decrease of compressive strength and easy delamination damage.Researchers have found through extensive research that the cause of problems is mainly related to the brittleness of the matrix epoxy resin.Therefore,how to improve the brittleness of epoxy resin and thus develop the interlaminar toughness of carbon fiber composites has always been an important topic in the research of composites,and plays an important role in the wide application of composites,especially in the aviation industry.In this paper,polysulfone was selected as toughening agent to modify epoxy resin.Firstly,the PSF/EP resin blend system was prepared by the method of heating and melting.The solubility and curing reaction kinetics of PSF/EP blends were studied.The results show that polysulfone and epoxy resin have good compatibility.The addition of polysulfone to epoxy resin can promote the curing process of epoxy resin,but does not affect the curing mechanism.Based on the above study,PSF/EP blends were prepared.The effects of different PSF contents on the properties of PSF/EP blends were systematically studied.The experimental results show that the addition of PSF significantly improves the bending strength,fracture toughness and impact strength of PSF/EP,increasing by 18.5%,89%and 65.3%respectively,but the tensile property of PSF/EP decreases somewhat.During the curing of the epoxy resin,phase separation occurs based on reaction-induced phase separation mechanism and polysulfone precipitates from the system to form polysulfone phase.With the increase of polysulfone content,the microstructure of PSF/EP blends is in turn of island structure,bicontinuous structure and partial inversion.The addition of polysulfone increases the thermal stability of the epoxy resin.The above research shows that polysulfone can improve the toughness of epoxy resin,but the addition of polysulfone causes the tensile properties of epoxy resin to decrease obviously.In order to solve the problem that the mechanical properties of epoxy resin decrease,a method of adding a small amount of graphene oxide to a PSF/EP blend system has been used.In this paper,the original graphene was oxidized firstly,and then the effects of different graphene contents on the structure and properties of PSF/EP resin were studied.The results showed that the dispersibility of graphene was significantly improved after oxidation modification.Graphene oxide increased the curing reaction rate of epoxy resin,but did not change the curing mechanism.When the content of graphene oxide is0.5wt%,the mechanical properties of composites were optimized,and the tensile strength,bending strength,fracture toughness and impact strength were 83.65MPa,121.38 MPa,6.17 MPa m^1/2 and 59.7J/m respectively,which are increased by 37.0%,12.7%,27.4%and 56.2%,respectively.The addition of graphene oxide can further improve the toughness of the composites,which is mainly caused by crack deflection and separation/delamination of graphene oxide sheets.With the increase of graphene oxide content,the glass transition temperature?T_g?of the composite material gradually decreases.The study of PSF/epoxy resin system,is feasible to use polysulfone to toughen epoxy resin matrix and further improve the interlaminar toughness of composite materials.However,the molecular weight of the polysulfone itself is relatively large,resulting in an increase in the viscosity of PSF/EP system,which conflicts with the low viscosity of resin required by VARI molding process and is difficult to pour resin.Therefore,it is very difficult to use PSF/EP blend directly as perfusion resin to prepare carbon fiber composites by VARI molding.In this paper,the polysulfone nanofiber membranes were prepared by electrospinning method,and then carbon fiber composites toughened between polysulfone nanofiber membranes were prepared.Without increasing the viscosity of the resin system,polysulfone is introduced by uniformly laying polysulfone nanofiber membranes between the layers to achieve the toughening effect.The results show that polysulfone nanofiber membrane and epoxy resin have good solubility,and reaction-induced phase separation occurs during the curing of epoxy resin,thus forming polysulfone toughening phase.The toughness of the composite matrix determines the resistance of the composite layer to delamination,so the interlayer toughness of the composite material is measured by the type I interlayer toughness.It is found that when the content of polysulfone nanofiber membrane between carbon fiber composite layers is less than 15g/m²,the toughening effect of polysulfone nanofiber membrane on carbon fiber composite layers is not obvious.When the content of polysulfone nanofiber membrane is 15,20 g/m²,the G?C_-Prop of the composite material is increased by 27.5%and 37.3%respectively compared with that of the non-toughened composite material.Among them,the G?C_-Prop of the sample with 20 g/m² polysulfone nanofiber membrane reached the maximum 613.84 J/m²,which was 37.3%higher than that of the composite without toughening.Therefore,through the toughening modification of epoxy resin,the proposed method of interlayer toughening of composite materials can significantly improve the interlaminar toughness of carbon fiber composites without increasing the viscosity of the liquid during liquid forming.Molding in the industrialized large-scale application of carbon fiber composites provides an effective technical route.