Preparation And Properties Of 3D Printed Continuous Aramid Fiber Reinforced Polyetherimide Composites

Continuous fiber-reinforced thermoplastic composites(CFRTPCs)are widely used in aerospace,construction,and automotive fields by virtue of their high strength and lightweight properties.However,CFRTPCs are still mainly prepared by traditional manufacturing processes,which require the use of special molds and high manufacturing costs,and are not suitable for the manufacture of some highly customized parts.3D printing technology has unique advantages in the preparation of CFRTPCs,among which fused deposition molding(FDM),as a major molding process,has the advantages of high designability and easy operation,and is particularly suitable for the molding of thermoplastic resin-based composites.It is particularly suitable for the molding of thermoplastic resin-based composites.Polyetherimide(PEI),as a special engineering plastic with high temperature resistance and excellent mechanical properties,can meet the high standard of service requirements for material performance in the aerospace field,and is therefore chosen as a high-performance matrix material for FDM molding of CFRTPCs.However,PEI is an amorphous material,which results in low impact resistance,and suitable reinforcements need to be selected for toughening modification in the preparation of PEI resin-based composites.In addition,the 3D printing process of CFRTPCs has difficulties such as poor fiber-matrix interface bonding,many internal pores of the material,and susceptibility to interlayer failure,which can lead to low mechanical properties of the final molded products.To address the above problems,this paper used FDM process to print and prepare PEI products and study their impact properties,and selected continuous para-aramid fiber(CKF)as the reinforcing fiber,and prepared continuous para-aramid fiber reinforced polyetherimide composite(CKF/PEI)by in situ impregnation 3D printing process,and improved the mechanical properties of the composite printed products by adjusting the nozzle temperature and matrix flow rate,and the fiber surface plasma modification treatment.In this paper,the effects of printing speed,printing temperature,molding direction and annealing temperature on the porosity and impact properties of PEI printed parts were studied to provide a reference for the subsequent 3D printing of CKF/PEI composites.The study shows that increasing the printing speed can reduce the interfacial temperature difference between PEI extrudate and deposition layer,improve the interlayer bonding and thus improve the mechanical properties of the products,but too high printing speed will lead to uneven thickness of the extruded wire,resulting in the reduction of mechanical properties;increasing the printing temperature makes the PEI molten extrudate have enough heat transfer with the deposition layer,resulting in better interlayer bonding and improving the mechanical properties of the products.The mechanical properties of PEI products in different molding directions differ significantly,and the vertically molded parts mainly rely on the strength of the deposited layer to resist the impact load,so they have better impact properties;annealing and heat preservation treatment at a temperature slightly higher than the glass transition temperature(T_g)of the material can relieve the residual stress inside the products,thus improving the mechanical properties of the products.Secondly,three CKF-reinforced PEI matrixes with different bunch fiber denier were selected,and the effects of different bunch fiber grades of CKF,different nozzle temperatures and substrate flow rates,and different print layer thicknesses on the mechanical properties,interfacial bonding,and surface molding quality of CKF/PEI composites were investigated.The study shows that the 1667 CKF/PEI composite with 1667 dtex has the highest fiber content and therefore the best mechanical properties of the printed parts.The mechanical properties of the CKF/PEI composite were further improved by increasing the nozzle temperature and matrix flow rate.The surface roughness of 220 CKF/PEI obtained from the CKF with the smallest filament fibre has the highest surface quality.Finally,in order to further enhance the mechanical properties of CKF/PEI composites and improve the fiber-matrix interfacial bonding properties,CKF was subjected to oxygen plasma treatment.It was shown that the oxygen plasma treatment improved the chemical inertness of CKF by introducing oxygen-containing reactive groups on the fiber surface,and caused changes in the fiber surface roughness and increased the specific surface area of its interfacial contact.When the duration of oxygen plasma treatment was 30 min,the interfacial bonding and mechanical properties of the composites were best,and their interfacial shear strength,impact strength,bending strength,and interlaminar shear strength were 45.57 MPa,105.27 k J/m~2,157.06 MPa,and 7.05 MPa,respectively,which were improved by 42.90%,23.09%,and 19.31%compared with the CKF/PEI before modification treatment,23.09%,19.31%,and 15.36%,respectively,compared with the CKF/PEI before modification treatment.It indicates that the oxygen plasma treatment can improve the defects of poor interfacial bonding of the composites,thus improving the mechanical properties of 3D printed CKF/PEI to a certain extent,which makes the CKF/PEI composites expected to be used in aerospace and vehicle manufacturing in the future to meet the demand for high strength,high toughness and lightweight materials in these fields.