| With the development of science and technology,many fields such as life and military industry have put forward higher requirements for the performance of materials.Carbon fiber with high specific strength,specific modulus and temperature resistance has become a hot topic of current research and has a very wide range of applications in the field of composite materials.Sizing is a very important process in carbon fiber production.At present,sizing agent is usually solvent type sizing agent,causing great pollution to the environment.Waterborne epoxy resin sizing agent has good stability and heat resistance.After sizing treatment,the wettability and interfacial bonding strength between carbon fiber and resin are enhanced,and the surface defects are obviously improved.The preparation process is simple and low cost,which generates practical application value.In this paper,waterborne epoxy resin sizing agent was prepared by using epoxy resin,diethanolamine and glacial acetic acid as raw materials.The optimal synthesis process of waterborne epoxy resin was explored by orthogonal experiment.The optimal reaction time was 2 h,the optimal reaction temperature was 80 °C,and the optimal neutralization degree was 120 %.It was obtained that the addition amount of diethanolamine had the greatest influence on waterborne epoxy resin.Through analyzing the particle size,distribution of emulsion,infrared spectrum,thermogravimetric analysis and stability of sizing agent emulsion,the optimum dosage of diethanolamine determined by the molar ratio of diethanolamine to epoxy resin was 1.2:1.In this way,the emulsion was stable with narrow diameter distribution.The functional groups were successfully introduced into the chains of the epoxy resin and the decomposing temperature was increased by 50 °C.By analyzing the surface morphology,surface element content,sizing rate,processing performance and various mechanical properties of carbon fiber,when the sizing agent concentration is 1%,the performance of carbon fiber after sizing is the best.In this way,the surface defects of carbon fiber are obviously improved,and the filament strength was increased by 10.8%,interfacial shear strength was increased by 23.7%,transverse tensile strength was increased by 22.5%.Based on the above research,the waterborne epoxy resin was further modified by adding the allyloxy polyethylene glycol(APEG)with flexible molecular chains.Four formulations with mass ratios of epoxy resin to APEG(10:1,7.5:1,5:1,3:1)were designed,and the influence of the amount of APEG on the performance of sizing agent was explored.As the results of that,both the high temperature stability and mechanical stability were improved when the addition of the APEG.Sizing agent emulsion kept stable when stored in room temperature for 30 days and the emulsion turned from little blue to white when incubated in 60 °C for 30 days without demulsification.The diameter of the emulsion was 30?60 nm with narrow distribution.From the analysis of FTIR and XPS,the functional groups from the sizing agent were introduced into the surface of the carbon fiber.From TGA test,the decomposing temperature of the modified sizing agent was 290 °C.By analyzing the performance of sizing agent and the sizing treated carbon fiber,it was determined that when the mass ratio of self-made waterborne epoxy resin to APEG was 7.5:1,the interfacial shear strength of the carbon fiber after sizing was increased by 11.6 %,which is slightly lower than that of the sizing agent without APEG.Filament strength and transverse tensile strength was increased by 18.3% and37.0%.The stiffness of carbon fiber was obviously reduced,which had good weaving performance and great application value. |
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