Synthesis Of Aqueous Poly(Amide-imide) Sizing And Performance Of CFRTP

Recently,Carbon Fiber Reinforced Thermoplastic Polymers(CFRTP)have been increasingly used in aviation,aerospace,and automotive for their advantages of good impact strength,fast and diverse molding methods,and recyclability.However,traditional epoxy sizings fail to meet the molding temperatures of high-performance thermoplastic composites and have poor compatibility with those matrices.There is an urgent need to develop thermoplastic sizings.Thermoplastic polymers with similar structure to the matrix were applied as the main sizing content for the present thermoplastic sizings.However,due to the hydrophobicity,to retain a large amount of commercial surfactants in sizings is necessary,which causes the thermal instability and further produces interface defects and brings damage to the mechanical properties.To this end,three novel semi-aromatic waterborne poly(amide-imide)(PAI)containing hydrophilic pendant groups were designed and synthesized in this project,and surfactant-free self-emulsifying aqueous thermoplastic sizings forCF were prepared for the first time.The properties of fibers and composites with sizings and the effects of sizings on the interface were studied.A cysteine derivative(L-Cys-OA)containing polyethoxy pendant groups was synthesized by the Michael addition reaction of sulfhydryl and double bonds,and further synthesized with cyclohexanetricarboxylic anhydride to obtain aliphatic water-soluble diacid monomer containing imide(DA-OA),then polymerized with flexible aromatic diamine to obtain non-ionic poly(amide-imide)(PAI-OA),which combined excellent solubility(150 mg/ml)with heat resistance.Through the self-emulsification of the hydrophilic polyethoxy pendant groups,a surfactant-free aqueous sizing was prepared for the first time.The sizing with a small average particle size(76.54 nm)was storage-stable.And the organic solvent content was only 1.7 wt%.The sized carbon fiber(sCF-OA)had good processability.Compared with the Toray T300 carbon fiber composites(eCF/PEI),the interlaminar shear strength(ILSS),flexural strength and impact strength of the reinforced polyetherimide(sCF-OA/PEI)composite were 86.14 MPa,753.47 MPa,62.42 kJ/m~2,improved by 37.76%,35.21%and 12.86%,respectively.The hydrothermal aging retention rates above were also significantly promoted.The hydrothermal aging retention rate of ILSS was 95.07%,23.48%higher than that of eCF/PEI.Meanwhile,the mechanical properties and hydrothermal aging resistance of theCF reinforced poly(ether-ether-ketone)composites(sCF-OA/PEEK)with PAI-OA sizing were also considerably improved.Combined with the structural characteristics of PAI,the interfacial enhancement and its mechanism of the composites were analyzed by experiments and quantum chemical calculations.A novel cysteine derivative(L-Cys-A)containing quaternary ammonium salt pendant groups was synthesized by the click reaction of thiol and epoxy,and diacid monomers(DA-A)and ionic water-based poly(amide-imide)(PAI-A)was further synthesized,which was also soluble(150 mg/ml)and heat resistant.Through the ionization of quaternary ammonium salt side groups in water,a surfactant-free self-emulsifying aqueous sizing with a small particle size(45.42 nm)was prepared,which was more storage-stable than the non-ionic PAI-OA sizing.The sized carbon fiber(sCF-A)had good processability.Compared with eCF/PEI,the ILSS,flexural strength and impact strength of theCF reinforced poly(ether-imide)(sCF-A/PEI)composite were 92.98 MPa,713.9 MPa,62.11 kJ/m~2,increased by 45.46%,28.11%and 12.29%,respectively.The mechanical properties and hydrothermal aging resistance of sCF-A/PEEK were also improved.Similarly,the interfaces of the composites and their reinforcement mechanisms were analyzed by experiments and quantum chemical calculations.To further improve the interface bonding and mechanical performances,the diacid monomer containing reactive catechol groups was synthesized by the reaction of L-dopa and cyclohexane anhydride.The phenolic hydroxyl-containing multimonomer ionic poly(amide-imide)(PAI-D)with better solubility(200 mg/ml)and heat resistance was prepared.The self-emulsifying aqueous sizing was storage-stable and the organic solvent content was further reduced(1.2 wt%).The sized fiber(sCF-D)had excellent processability.The ILSS,flexural strength,and impact strength of sCF-D/PEI were significantly improved by 56.84%,47.24%,and 48.84%to 100.22MPa,820.52 MPa,82.32 kJ/m~2,respectively,compared to eCF/PEI.Similarly,the mechanical properties and hydrothermal aging resistance of sCF-D/PEEK were further promoted.The results show that the PAI-D sizing realized the chemical bonding of the thermoplastic sizing to theCF surface for the first time through the reactive catechol pendant groups,thereby further enhancing the interfacial bonding of the composites.Additionally,the interaction between the PAI-D sizing and the matrix was revealed by quantum chemical calculations.