Study On The Interlayer Reinforcement Modification Of Poly (Ether Ether Ketone) Resin For Fused Deposition Modeling 3D Printing

As industrial manufacturing technology advances,3D printing,as a cutting-edge technology relevant to many fields,has given renewed vitality into the traditional industries with its rapid prototyping,personalized customization and other advantages.And,Fused Deposition Modeling(FDM)technology has become one of the most widely used additive manufacturing technologies due to its advantages such as simplified process,cheap equipment and diverse printing materials.At present,with the upgrades of FDM equipment,optimization of printing parameters and filler enhancement modification,some of the performance of high-performance polymer 3D printed parts is close to those of traditional molding and injection molding.However,influenced by the FDM printing process,insufficient fusion between continuously extruded filaments and interlayer adjacent deposited filaments along the Z-axis direction lead to weak interlayer bond strength of 3D printed parts,which is a common problem in high-performance resin for FDM 3D printing technology and also one of the research hotspots in the field of 3D printing over the recent years.In this paper,Poly(ether ether ketone)(PEEK),with excellent mechanical and thermal properties,was used as the research object.Firstly,based on the improvement of resin melt flow,the resin melt flow was improved and printing defects were reduced by regulating the molecular weight of PEEK resin while ensuring the intrinsic strength and toughness of the matrix resin,which achieved both strength and toughness of 3D printed PEEK parts.Then,for the weak interlayer bond strength problem that still exists in the printed parts,amorphous poly(aryl ether ketone)(a PAEK)with good compatibility to PEEK resin was designed and synthesized,and the interlayer reinforcement of 3D printed PEEK parts was obtained by the diffusion of a PAEK in the blends between the layers during the printing process.To further improve the interlayer bond strength,rigid fluorene groups were introduced into the PEEK resin by copolymerization from the perspective of reducing the crystallization rate and increasing the interlayer fusion time.The crystallization properties of the PEEK copolymer were regulated by controlling the proportion of fluorene groups introduced,thus achieving both interlayer enhancement and X-and Y-axis mechanical properties of3D printed parts.Based on the above research,the mechanical strength of 3D printed PEEK parts was further improved by introducing a small amount of carbon nanotubes into the above resin using solution pre-dispersion combined with melt blending,and the main research results are as follows:(1)Based on the personalized characteristics of 3D printing equipment,the paper starts with a study of 3D printing process optimization conducted with commercial PEEK resin.And the results show the optimum performance of 3D printed PEEK parts with a[0]°orientation and a chamber temperature of 230°C and a nozzle temperature of 410°C.On this basis,the PEEK resin with a melt index of 34 g/10 min(PEEK-034)has optimal 3D printing performance with 3D printed X-axis tensile strength of 96 MPa,strain at break of 31%,flexural strength of 115 MPa,and flexural modulus of 3.7 GPa,which are close to the performance of injection molding parts.Nevertheless,the improving melt flow of the PEEK resin was not significant for the improvement of the interlayer bond strength in the Z-axis direction.The interlayer bond strength has only increased slightly from 8 MPa to 13 MPa,which still has a large gap compared to the X-axis direction and will surely limit the practical application of PEEK 3D printed parts.(2)For the weak interlayer bond strength of 3D printed PEEK parts,several a PAEKs containing different groups with good compatibility to PEEK were designed and synthesized from the perspective of enhancing interlayer molecular chain movement,and were used to blending modification of PEEK-034.The effects of chain stiffness,molecular weight,and blending content on the performance of 3D printed PEEK parts were systematically investigated,and the mechanism of enhancement of interlayer bond strength was clarified:The a PAEK,which is less confined to the crystalline region,enabling the diffusion and entanglement of interlayer molecular chains,thus effectively improving the interlayer bond performance.It was shown that the improvement of the interlayer bond strength was most obvious with the structure of bisphenol A amorphous polyaryl ether ketone(DPAPEEK)and a molecular weight(M_n)of 41.90 k Da.With the blending content to 20 wt%,the interlayer bond strength reaches35 MPa,which is 170%higher compared to the pure PEEK resin.However,due to the low intrinsic strength of a PAEK,the excessive introduction of a PAEK led to a decrease to the mechanical strength in the X and Y directions of the 3D printed parts.(3)To further enhance the interlayer bond strength,a series of amorphous polyaryl ether ketones(DPAFDx)with different fluorene contents were prepared by introducing rigid fluorene groups into the polymer chain segments based on the study in the previous chapter to improve the intrinsic mechanical strength of a PAEK.The effect of fluorene content,molecular weight,and blending content on the performance of 3D printed PEEK parts were investigated with the blend modification of PEEK-034.The introduction of the rigid fluorene group enhanced the intrinsic strength of DPAFDx,which increased from 58 MPa to 75 MPa at a fluorene group copolymerization content of 30 mol%.The increase in intrinsic strength resulted in an interlayer bond strength of41 MPa for the 20wt%-DPAFD30-2/PEEK,an increase of 17%compared to the DPAPEEK with bisphenol A group and an increase of 215%compared to the pure PEEK resin.However,the introduction of the 20 wt%amorphous polymer still resulted in a decrease in the X-and Y-axis strengths,with the tensile strengths in the X-and Y-axis directions decreasing to 88 MPa and 81 MPa,respectively.(4)During PEEK FDM processing,the rapid crystallization of the deposited filaments limited the diffusion of interlayer molecular chains,resulting in poor interlayer fusion,thus reducing the crystallization rate could promote more adequate diffusion of interlayer molecular chains,which in turn improved interlayer bond performance.Therefore,a series of PEEK copolymers(x-FD-PEEK)with different fluorene content were synthesized in the paper,and the effect of copolymerization group introduction on the intrinsic properties was reduced by controlling the percentages of copolymerization units.It was shown that the introduction of fluorene groups could significantly reduce the crystallization temperature and crystallization rate of x-FD-PEEK,increased the interlayer fusion time,and effectively promoted the interlayer fusion.As the fluorene content increased from 0 to 10 mol%and the half-crystallization time increased from 1.1 min to 2.5 min,and when the fluorine content increased to 15 mol%,the half-crystallization time increased to 3.1 min.The X-axis strength and Y-axis strength of the 3D printed 10%-FD-PEEK parts still reached 94MPa and 90 MPa,respectively,and the Z-axis interlayer bond strength reached 41 MPa.The Z-axis interlayer bond strength and strain at break of the 3D printed 15%-FD-PEEK parts were even higher at 67 MPa and 11.23%,an increase of 400%and 500%,respectively,compared to pure PEEK resin.(5)To further improve the strength of 3D printed parts,a further reinforcing filler was introduced based on the above study.In this paper,a series of masterbatches containing fluorene amorphous poly(arylene ether ketone)(DPAFD30)with different carbon nanotube contents were prepared by using multi-walled carbon nanotubes(MWCNTs)as reinforcing fillers and compounded with PEEK by melt blending to prepare MWCNTs/PEEK composites.However,it is found that MWCNTs not only restricted the migration and diffusion of DPAFD30,but also acted as heterogeneous nucleation to increase the crystallization rate of the composite,resulting in a significant reduction in the Z-axis strength of 3D printed parts.Based on this,we replaced the PEEK matrix with 10%-FD-PEEK resin,and the prepared composites with 1 wt%MWCNTs had a Z-axis interlayer bond strength of up to 35 MPa,while the tensile strength and strain at break in the X-axis direction were also improved to 97 MPa and41%,respectively,which further demonstrated that x-FD-PEEK could not only improve the performance of 3D printed parts,but also improve its composite effect with carbon nanotubes to further enhance the performance of the composites.