Preparation And Performance Of 3D Printed Continuous Carbon Fiber Reinforced Poly-ether-ketone-ketone Composites

Continuous fiber reinforced thermoplastic composites(CFRTPCs)are important lightweight and high-strength composites wildly used in high technology such as aerospace.Currently,the main processes used to produce CFRTPCs are still focused on the manufacturing medium and large sheets,components and blocks,while the production of highly customized,geometrically complex and small parts is limited.3D printing technology has emerged to provide a new direction to solve this challenge.Among 3D printing technologies,fused deposition modeling(FDM)is specifically applicable to the manufacture of thermoplastic and thermoplastic composites and it has been gradually applied to produce CFRTPCs in recent years.However,among the studies conducted so far,the matrix materials are still mainly focused on conventional thermoplastics,which are with processing temperatures not exceeding 300°C.The research on the use of aerospace-oriented thermoplastic with high thermal performance as the matrix is still less,so there is an urgent need to supply new matrix materials in this field.In addition,the introduction of continuous fiber in 3D printing will increase the risks such as high porosity,interlayer delamination and anisotropy and decrease the mechanical performance of the product.Besides,the weak interface between commercial fibers and thermoplastic matrix is another factor limiting performance of the product.To address the problems above,poly-ether-ketone-ketone(PEKK),a high thermal performance thermoplastic,was used as the matrix in this paper,and continuous carbon fiber(CCF)was selected as reinforcement to prepare continuous carbon fiber/poly-ether-ketone-ketone composites(CCF/PEKK)by in-situ impregnation 3D printing and improved the mechanical performance of the fabricated parts by process optimization and the use of prepreg..Firstly,the effect of process parameters of 3D printing on the performance of CCF/PEKK was investigated to obtain the optimal process parameters before pretreating CCF,and to establish the process basis for 3D printing with CCF prepregs.The study showed that the effects of decreasing nozzle diameter and layer thickness reduced the porosity and increased the fiber content,and the effect of decreasing the layer thickness is more obvious.Increasing the flow ratio of the matrix improved the internal structure and mechanical performance,but it made the surface of the CCF/PEKK rough.Rising printing temperature improved the bonding between matrix and matrix and enhanced the impregnation while improving the crystallinity of the matrix,thus improving the mechanical performance of the part.However,the high molding temperature would destroy the crystal structure of the matrix and lead to the decrease of mechanical performance.The mechanical performance of CCF/PEKK with different build orientations differed,especially the interlaminar shear strength of the products with on-edge orientation was greatly reduced,which reflects the anisotropy of 3D printing.The optimized process parameters of CCF/PEKK were: nozzle diameter of 0.8 mm,layer thickness of 0.2 mm,flow ratio of 85%,printing temperature of 395°C and with flat build orientation,at which the flexural strength,modulus and interlaminar shear strength were increased by 164.2%,322.2% and 183.5% compared with those before process optimization,respectively.Then,to address the problems of poor resin impregnation and poor fiber-matrix interface,polyetherimide(PEI)was used as sizing agent to pretreat CCF by solution impregnation method to prepare PEI@CCF prepreg suitable for 3D printing,and the properties of PEI@CCF prepared with different concentrations of solution were investigated,including resin content,surface morphology,elemental groups and stability of 3D printing.The results showed that the resin content of the prepregs was effectively controlled by changing the concentration of sizing solution,and the PEI@CCF prepared with solution of 5 wt% PEI had the best coating uniformity.The results of EDS scanning and FT-IR showed that the typical elements and groups of PEI appeared on the surface of PEI@CCF,and the results of printing stability tests showed that the increase of PEI content increased the stiffness of PEI@CCF,resulting in a significant decrease in continuous operation time.At last,PEI@CCF/PEKK composites were prepared using different PEI@CCF with optimized process parameters,and the internal structure,thermal properties and mechanical performance of the composites were investigated.The results showed that PEI@CCF/PEKK still maintained excellent thermal stability and the melt and crystallization properties of the composites changed little.In addition,benefiting from the uniformity of the coverage of PEI,5PEI@CCF improved the interface and the impregnation of the product best,and the flexural strength,modulus and interlaminar shear strength of the parts with flat orientation prepared with 5PEI@CCF reached the highest value,which were 13.9%,27.6% and 12.4% higher than those of CCF/PEKK,respectively.The flexural strength,modulus and interlaminar shear strength of the parts with on-edge orientation were also improved by 9.2%,21.7% and 27.1% compared to CCF/PEKK,respectively,which indicated that PEI@CCF prepared by solution impregnation can improve the mechanical performance of 3D printed CCF/PEKK and make it possess the potential to become the mechanical part with complex structure.