Preparation And Properties Of Carbon Fiber / Poly(Ether Ether Ketone) Composites Private For 3D Printing

3D-printing,one of the transformational technologies in Industry4.0,has brought brand new concepts to the manufacturing industry with superiorities in short design cycle,high material usage rate,unlimited material design,integrated moulding.Fused deposition molding(FDM)technology is a 3D-printing technology using thermoplastic resin as raw material,which has become one of the commonly used3D-printing technologies in industry due to its simple manufacturing process,high reliability and wide range of materials.With the advancing technology of FDM3D-printing,the performance of 3D-printing pure resin has approached that of injection molding grade products.However,in the face of the increasing requirements for material performance in aerospace and medical fields,the performance of pure resin materials for FDM 3D printing could no longer meet their demanding requirements,and there is an urgent need to develop a fiber-reinforced composite material suitable for 3D printing technology.At present,in the field of 3D-printing fiber-reinforced composites,the composite material performance is low due to the high viscosity of the composite melt,weak interfacial bonding between matrix and fiber,and poor interlayer fusion.In this thesis,a series of carbon fiber(CF)/ poly(ether ether ketone)(PEEK)composite materials was studied in 3D-printing.First,by regulation of fiber content,fiber length and melt flowability,mechanical properties varied and were optimized.Then,to improve the weak interfacial adhesion between carbon fiber and PEEK resin,a carbon nanotube reinforced and fluorene-containing PEEK was prepared.Finally,multiple interactions from nanoscale to micrometer scale between carbon fiber and carbon nanotube strengthened the composite resins.3D-printing parameter setting like printing nozzle and baseplate temperature was further optimized to achieve better mechanical properties.A sequence of CF/PEEK was firstly prepared by melt blending and different CF content,types,length were controlled and studied.Results shows that 10wt%CF/PEEK has the highest tensile strength at 92 MPa,close to pure PEEK.Tensile strength of the 10 wt%CF/PEEK with CF length at 200 μm reaches up to 120 MPa.However,increased melt viscosity caused by CF would bring more flaws into3D-printing sample pieces.To minimize the effect of melt fluidity,composite with a melt index of 55 g/10 min was prepared and its tensile strength was improved greatly compared with pure PEEK,reaching 136 MPa,although there is still a considerable performance gap between 3D-printed pieces and traditional injection molding pieces.A small amount of CNT was introduced aiming to improve the interfacial shear strength(IFSS)between CF and PEEK matrix,besides,CNT is expected to enhance mechanical properties.Nano packings like CNT aggregate badly,thus a low content of large conjugated fluorene functional group was further introduced for good CNT dispersion.As a result,the 1%CNT-2%FD-PEEK 3D-printed sample shows an improved bending strength at 138 MPa,tensile strength at 102 MPa,elongation at break at 77%.This is also explained and supported by micromorphology and thermal characterizationThe introduction of carbon nanotubes significantly improved the interfacial shear strength of CNT-2%FD-PEEK with carbon fibers,reaching 98 MPa,which is 96%higher than the shear strength with PEEK,and the improvement of interfacial properties is conducive to the enhancement performance of carbon fibers.On this basis,effects of multi-packing composites on 3D-printing was discussed.With the improvement in interfacial strength,printed samples shows rises in both X-axi sand Y-axis,146 MPa and 86 MPa respectively.After further optimization on printing parameters,such as baseplate temperature and nozzle temperature,and heat treatment condition,tensile strength of 3D-printing CF/CNT/2%-FD-PEEK in X-axis reaches155 MPa,17% improved compared with CF/PEEK,close to injection samples at 160 MPa.