Preparation And Properties Of Polylactic Acid Composite Reinforced With The Braided Structure Of Magnesium Wires

Polylactic acid (PLA) has poor toughness and degradation product is acidic, however, degradation rate of magnesium alloys is too fast despite of their high strength. Development of the composites with both magnesium alloys and PLA could solve these problems.In this paper, the PLA based composite reinforced with the 2D braided structure of magnesium wires was prepared through hot pressing process. The optimal processing condition was obtained. The influence of braided angle, the content of Mg wires and micro-arc oxidation (MAO) of Mg wires on mechanical properties of the composites was investigated. In addition, degradation properties of the composites in simulated body fluid (SBF) were explored.The 2D biaxial braided structure with 1×1 form of magnesium wires was determined by comparing the preparation process of PLA based composites with two kinds of braided structure. Based on the studies on the influence of hot processing condition on bending strength of the composites, the optimal processing condition is selected as the temperature 165℃, the pressure 2.6MPa and the time 20min.The braided angle and Mg content have important impacts on the mechanical properties of the composite. When braided angle is kept at 30°, the tensile strength, bending strength, horizontal shear strength and impact toughness increase with increasing the Mg content, which are 1.6,1.8,1.6 and 2.8 times of those of pure PLA respectively when volume fraction of Mg wires is 12%. When the volume fraction of Mg wires is kept at 10%, the tensile strength and bending strength decrease with the increase of braided angle, while the horizontal shear strength and impact energy increase firstly and then decrease. When braided angle is 45°, they can reach the peak value 75.6MPa and 0.23J, respectively. Compared with the directional reinforcement of Mg wires, the braided structure of Mg wires can improve the longitudinal shear strength of the composites. MAO treatment to magnesium wires can improve interfacial bonding properties. The tensile strength of the composites with a braided angle 30° and Mg content 12vol% reach 80.4MPa, which is 13.7MPa higher than that of the composites with untreated Mg wires.During 4 weeks immersion, pH value of soaking solution for pure PLA decreased. But the one for the composites decrease firstly and then increase at about 1 week, finally keep stable after 4 weeks. The residual bending strength of the composites with a braided angle 30° and Mg content 7vol% and pure PLA is 56MPa and 31MPa, respectively. The reducing extent of bending strength of the composites is lower. The corrosion of magnesium wires is not obvious, while the molecular weight of PLA matrix in the composite reduces from 5.5×104 to 3.9×104, which is higher than that of pure PLA (3×104). This demonstrates that the presence of magnesium wires can reduce the degradation rate of PLA.