Preparation Of Bio-based Polyurethane And Its Application In Sizing Agent Of Carbon Fiber

Carbon fiber reinforced thermoplastic resin matrix composites(CFRTP),as a research hotspot of carbon fiber composites in recent years,have the advantages of low price,recyclable,easy processing and good toughness.However,due to the smooth surface and inertia of carbon fiber,there is a problem of poor bond with resin.At present,epoxy sizing agent is generally used to treat carbon fiber in industrial production,which is not well combined with thermoplastic resin and can not effectively enhance the interface properties of composites,and even the use of epoxy sizing agent in the actual production process can reduce the mechanical properties of thermoplastic resin composites.For the short of carbon fiber sizing agent matching with thermoplastic matrix,two polyurethane molecules with different structure were designed for waterborne sizing agent preparing based on similarity compatibility principle,which effective strengthen the carbon fiber/polyamide 6 composites.This paper is mainly as follows:(1)A novel autocatalytic bio-based waterborne polyurethane(WPU)was designed and used to prepare sizing agent for carbon fiber(CF).A carboxyl modified long chain diol(CMLCD)with autocatalytic ability was synthesized,which could be used as both reactant and catalyst to promote the reaction between hydroxyl group and isocyanate group,avoiding the use of highly toxic catalyst to prepare WPU.The negative effects of catalysts which are difficult to remove during WPU synthesis are avoided.At the same time,the biological raw material tartaric acid was used as chain extender to prepare WPU.Compared with CF composites without sizing,the tensile strength,bending strength and impact strength of CF composites with 1.0wt%concentration waterborne polyurethane sizing agent reached 132.1 MPa,208.3 MPa and 7.65 k J/m~2,respectively.Increases of 14.3%,24.4%and 119.6%,respectively.This study provided a potential way for industrial production and application of green WPU sizing agent.(2)At present,the domestic commercial WPU is generally 2,2-dihydroxymethylpropionate(DMPA)carboxylic acid waterborne polyurethane as chain extender.However,the carboxylic acid with low ionic strength is difficult to make waterborne coatings with high solid content.Therefore,the solid content of such products is generally low,generally in 20%?35%.However,many literatures have shown that negative/non-ionic groups have synergistic effects,in which the anionic groups produce electric bilayer and generate electrostatic repulsion,while the non-ionic hydrophilic groups reduce the interfacial tension and make the dispersion performance good.These actions together make the emulsion stable and can improve the solid content of the emulsion.In this experiment,tartaric acid was used as raw material to replace the commonly used petroleum based raw material DMPA to introduce carboxylic acid group,while polyethylene glycol was used to introduce polyoxyethylene ether as non-ionic hydrophilic chain segment,which formed a synergistic effect with carboxylic acid group and improved the solid content of the grouting agent.The negative/non-ionic compound WPU sizing agent with high solid content was prepared.The solid content of the sizing agent reached 46%,which was obvious higher than ordinary products.Compared with CF composites without sizing,treating by optimal sizing concentration of 1.0wt%,the interlaminar shear strength and flexural strength of CF composites with 1.0wt%concentration of waterborne polyurethane sizing agent reached 60.16 MPa and 491.36 MPa,which were increased by 53.8%and 38.15%,respectively.