Study On The Structures And Properties Of Polyethersulfone/Phenolphthalein-based Polyetherketone Toughened Epoxy Resin And Its Liquid-formed Carbon Fiber Composites

Carbon Fiber Reinforced Polymer(CFRP)is widely used in the aerospace industry due to its high specific strength,high specific modulus,and strong designability.Thermosetting epoxy resin(Epoxy Resin,EP)has good mechanical and thermal properties,and is currently the matrix resin often used in CFRP.However,EP is cured to form a highly cross-linked network structure,which makes it brittle and has poor impact fracture resistance.As a result,the interlayer performance of CFRP after molding is poor,and delamination damage is easy to occur.Therefore,how to improve the interlayer toughness of CFRP is of great significance to the application of composite materials.Polyethersulfone(PESU)and phenolphthalein-based polyetherketone(PEK-C)are selected as thermoplastic blend resins to toughen and modify one-component epoxy resin(3770EP)in this thesis,and PESU/PEK-C/3770EP is prepared by hot melt method.When the mass ratio of PESU and PEK-C is 1:1,the effect of adding different content of PESU/PEK-C blended thermoplastic resin on the structure and properties of 3770EP was studied.The results show that the addition of a small amount of PESU/PEK-C blended resin can reduce the curing reaction activation energy of 3770EP,and promote the curing reaction;the addition of PESU/PEK-C improves the fracture toughness,impact strength,and flexural strength of 3770EP.When the content is 15phr,the increase effect is the best,and the properties are increased by 25.0%,16.0%,and 37.4%;however,the introduction of PESU/PEK-C makes the tensile strength of 3770EP drop to a certain extent;In the late stage of epoxy resin curing,PESU/PEK-C undergoes reaction-induced phase separation,and the nucleation growth process forms a sea-island phase structure in the epoxy.The toughening of oxygen resin is due to mechanisms such as crack-nail anchoring,cavitation effect and particle yield.;At the same time,the study found that the addition of PESU/PEK-C did not adversely affect its thermal properties.On this basis,this thesis selects 15 phr PESU/PEK-C to study the effect of blended thermoplastic resins with different ratios of PESU/PEK-C on the structure and performance of3770EP.The research results show that different ratios of PESU/PEK-C blend resins have different modification effects on 3770EP:when the ratio of PESU:PEK-C is 1:5,the fracture toughness,impact strength,tensile strength and bending strength of the epoxy resin system are the best,increasing by 54.6%,43.1%,20.3%and 37.6%.Moreover,this thesis have found that PESU has poor solubility in 3770EP and will cause phase separation in the curing reaction.When PESU accounts for a high proportion of the phase separation mechanism is spinodal phase separation,forming a bicontinuous or reverse phase state;When the proportion of PEK-C is greater than or equal to PESU,the phase separation mechanism of PESU changes to nucleation phase separation,which mainly presents the island-sea phase structure.PEK-C has good compatibility in 3770EP and play the main toughening effect.Finally,this thesis selected PESU:PEK-C=1:5,and adopted wet film forming method to prepare PESU/PEK-C porous films with different areal densities,which are used for interlayer toughening and vacuum-introduction liquid molding(VARI)to prepare CFRP,And studied the effect of PESU/PEK-C porous film on the structure and performance of CFRP.The results show that the interpositon of the PESU/PEK-C porous film significantly improves the type I interlaminar fracture toughness(G_IC)and type II interlaminar fracture toughness(G_IIC)of CFRP;When the areal density is 32gsm,the G_IC of CFRP increased by 53.8%and the G_IIC increased by 194.2%.The SEM study of the interlayer microstructure of the composite material found that PESU and PEK-C thermoplastic blend resins formed the particles by the phase separation of the resin can effectively cooperate to block the cracks or cause the cracks to deflect.In addition,the microspheres between the composite layers can also play a good anchoring role to the resin matrix,which is greatly improved the interlayer performance of the CFRP.