Competitive Reaction Between Sizing And Carbon Fiber With Resin And Its Influence On Interfacial Properties Of Composite

Carbon fiber reinforced resin composites are widely used in transportation,sporting,aerospace,energy because of their outstanding performance,such as light weight,high strength,high modulus.However,pristine carbon fiber has low surface energy and lacks active functional group,resulting in a weak interfacial bonding between fiber and resin.In addition,carbon fiber is a brittle material,fluffing and filament breakage appear during mechanical manufacturing process,which will reduce strength of carbon fiber.Hence,during the manufacture process,carbon fiber will be coated with a layer of sizing agent.On the one hand,it can protect carbon fiber and improve its processing capacity.On the other hand,it can enhance oxygen-containing functional groups of fiber,and further improve the interfacial strength of composite.Although sizing agent has made some progress in surface modification of carbon fiber,the principle and regular of sizing agent during interface formation,especially the competitive reaction mechanism between sizing agent and fiber with resin is not clear.Hence,in the dissertation,carbon fiber was treated through typical temperature of resin during curing process.The degree of chemical reaction between sizing agent and carbon fiber and its influence on the chemical reaction between sizng agent and resin were studied.The competitive synergistic mechanism of chemical reaction between sizing agent and carbon fiber with resin was revealed,and the effect of competitive reaction mechanism on the interfacial properties of composites was further studied.The main contents and results of this dissertation were as follows:(1)Referring to curing process of epoxy resin,carbon fiber was treated through typical temperature.In addition,the mixtures of sizing agent and resin were treated according to the curing temperature of resin.The results showed that the degree of chemical reaction between sizing agent and fiber increased with the increase of treated temperature,while high degree of chemical reaction between sizing agent and carbon fiber would limit diffusion from sizing agent to epoxy resin and reduce the chemical reaction between sizing agent and resin.(2)Based on the first part,monofilament composites and composite laminates were prepared using epoxy resin and bismaleimide resin as the matrix resin,respectively.For epoxy resin system,compared with untreated fiber,after carbon fiber was treated at 150?,interfacial shear strength(IFSS)and interlaminar shear strength(ILSS)of composites increased by 57.4%and 7.0%,respectively.When the treated temperature was 200?,IFSS and ILSS decreased.For bismaleimide resin,compared with untreated fiber,after carbon fiber was treated at 150?,IFSS and ILSS of composites increased by 12.8%and 6.1%,respectively.When the treated temperature was 200?,IFSS and ILSS showed a decreasing trend,indicating the high degree of chemical reaction between fiber and sizing agent,which reduced chemical interaction between sizing agent and resin,and was not conducive to improving the interfacial properties of composites.In addition,for bismaleimide resin,self-polymerization of bismaleimide monomer and ring opening reaction of imide at the higher curing temperature could reduce the chemical reaction between sizing agent and resin,and had little effect for bismaleimide resin during the competitive reaction between sizing agent and fiber with resin.(3)Effect of curing agent content on the reavtivity of sizing agent was studied by adding different content of curing agent(15%,30%,60%of stoichiometric ratio of epoxy sizing agent)to sizing agent and treating at 150?.The result showed when the content of curing agent is 15%,30%and 60%,the reaction degree of sizing agent is 4%,37%and 47%,respectively.The growth rate of reaction degree from 15%stoichiometric curing agent to 30%stoichiometric curing agent was significantly higher than that from 30%stoichiometric curing agent to 60%stoichiometric curing agent.After treating through 150?,too much curing agent in sizing agent would not obviously increase reaction degree of sizing agent.Furthermore,carbon fiber was treated by sizing.When curing agent content was 15%,IFSS value of composite was 122.4 MPa,which was 26.7%higher than that of sized fiber without curing agent.This was attributed to the presence of sizing agent,which improved the polar component of fiber and increased the wettability between fiber and resin.Meanwhile,a gradient interphase in cross-linking density was formed between fiber and resin,which improved the interfacial adhesion property of composite.Moreover,after 150? pretreatment on sized fibers with curing agent,IFSS of composite was 116.4 MPa when curing agent content was 30%,which was 11.9%higher than that of untreated system.This was attributed to the appearance of layered structure on fiber surface after temperature treatment,which was beneficial to improve fiber surface roughness.Furthermore,the interface between fiber/sizing agent and sizing agent/resin formed appropriate chemical bond,which was conducive to improve interfacial adhesion strength between fiber and resin.