Polylactic acid (PLA) composites parts obtained by fused deposition modeling (FDM) three-dimensional (3D) printing have obvious fusion interfaces. The printed parts have low strength and poor plastic toughness, limiting their application in clinical degradable load-bearing implants. In this article, first, the nano-hydroxyapatite (n-HA) was modified by PLA to obtain a core-shell structure with PLA coating. The micron chopped carbon fiber (CF) was modified by nitric acid to obtain a rich oxygen-containing functional group structure. Second, the above two modified materials of n-HA and CF were coated on the surface of the PLA filament by ultrasonic impregnation to obtain the PLA/n-HA/CF composite filament. Finally, tensile samples were manufactured by FDM 3D printing with the PLA/n-HA/CF composite filament, and the tensile test was conducted. The results show that the surface-modified n-HA particles form a regular spherical core-shell structure with good dispersibility. It can be combined with a matrix of PLA filament by the PLA coating
Because of the apparent fusion interface, the Poly Lactic Acid (PLA) parts, obtained by fused deposition modeling 3D printing, have low strength and poor plastic toughness, which limit their applications. In this paper, to focus on the fusion interface bonding properties, firstly, the nano-hydroxyapatite (n-HA) was modified by PLA to obtain a core-shell structure with PLA coating, afterward, the modified n-HA was coated on the surface of the PLA filament by the ultrasonic dipping method to obtain the PLA/n-HA composite filament. Secondly, computational fluid dynamics (CFD) software was used to calculate and analyze the flowing state and printing parameters of PLA/n-HA composites based on the rheological experimental results. Finally, the PLA/n-HA composite tensile samples were manufactured by fused deposition modeling 3D printing, and the tensile test was conducted. The results show that after numerical calculation, the optimized printing temperature and printing velocity of PLA/n-HA composite was 210°C and 90 mm/s, respectively. Meanwhile, the modified n-HA had good dispersibility in the PLA_5% n-HA composite filament (the modified n-HA content is 5%), therefore, the 3D printed parts manufactured by PLA_5% n-HA composite filament obtained the best modified n-HA distribution in the interlayers, and the best reinforcement of interlayer bonding was obtained reasonably.
Due to its unique crystal structure and nano-properties, hydroxyapatite (HA) has become an important inorganic material with broad development prospects in electrical materials, for fire resistance and insulation, and in bone repair. However, its application is limited to some extent because of its low strength, brittleness and other shortcomings. Graphene (G) and its derivative graphene oxide (GO) are well known for their excellent mechanical properties, and are widely used to modify HA by domestic and foreign scholars, who expect to achieve better reinforcement and toughening effects. However, the enhancement mechanism has not been made clear. Accordingly, in this study, G and GO were selected to modify HA using the first-principles calculation method to explore the theory of interfacial bonding of composites and explain the microscopic mechanism of interfacial bonding. First-principles calculation is a powerful tool used to solve experimental and theoretical problems and predict the structure and properties of new materials with precise control at the atomic level. Therefore, the bonding behaviors of hydroxyapatite (100), (110) and (111) crystal planes with G or GO were comprehensively and systematically studied using first-principles calculation; this included analyses of the density of states and differential charge density, and calculations of interfacial adhesion work and elastic moduli. Compared to HA (100) and (111) crystal planes, HA (110) had the best bonding performance with G and with GO, as revealed by the calculation results. The composite material systems of HA (110)/G and HA (110)/GO had the smallest density of states at the Fermi level, the largest charge transfers of Ca atoms, the largest interfacial adhesion work and the most outstanding elastic moduli. These results provide a theoretical basis for the modification of HA to a certain extent, and are beneficial to the expansion of the scope of its application.
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