A surface modification of polylactic acid composites for additive manufacturing with modified chopped carbon fiber and modified nano-hydroxyapatite

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 layer, while a silane coupling agent combines the PLA coating layer and the core of n-HA. The modified chopped CF treated with 68% nitric acid for 6 h has an ideal etch pits with moderate depth and distribution producing firm combination with the PLA matrix. The surface of modified chopped CF has abundant -COOH and -OH functional groups. It can be combined with a matrix of PLA filament through an esterification reaction. Among all the tensile samples, PLA_5% n-HA_6% CF, with 5% modified n-HA and 6% modified chopped CF, respectively, improves the bonding strength between the fused interfaces with the two reinforcement materials well-distributed in the fuse interface area.