Effect of hot drawing on the properties of three-dimensional braided polylactic acid composites

Three-dimensional braided thermoplastic composites are characterized by easier recycling and shorter production cycles. Among them, polylactic acid (PLA) has received wide attention for its better biocompatibility and lower cost. The hot pressing (HP) process has a high degree of design freedom, however, the adoption of the HP process for the preparation of three-dimensional braided PLA composites may destroy the braided structure due to the extrusion of the preform during mold closure, resulting in the uneven distribution of the fibers, destroying the interfacial properties, and leading to the degradation of the mechanical properties. As a self-reinforcing technology, hot drawing (HD) can effectively improve the crystallinity of PLA and the mechanical properties of composites by applying a tensile force in the axial direction of the three-dimensional braided preforms based on the HP process. In this experiment, the glass fiber (GF) reinforced PLA composites were prepared and tested by two molding processes, HD and HP, respectively, and it was found that: The shear strength of HD composites compared with HP composites was 33.03% higher, the bending strength was 26.92% higher, the tensile strength was 39.67% higher, and the degree of crystallinity was increased by 20.03%, and the thermal stability was slightly improved. The hot drawing process promoted the orderly arrangement of PLA molecular crystals along the axial direction and the growth of nuclei, which led to a simpler arrangement of PLA molecular chains and improved the crystallinity of PLA, as well as the mechanical properties of the composites. Combining macroscopic as well as 3D profile observation, it is found that the HD process improves the problem of damage to the braided structure, ensures the integrity of the three-dimensional braided knots, and arranges the GF fiber bundles in an orderly manner, which is conducive to the improvement of the overall performance of the composites. © 2025 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.