Preparation And Degradable Properties Of PLA-based Composite Reinforced With Magnesium Alloy

Magnesium alloy/polylactic acid (Mg/PLA) composite material has the advantages combining the high strength of magnesium alloy and the controllable degradation behavior of polylactic acid. Meanwhile, the degradation products of magnesium alloy is alkaline, which can neutralize the partial acidity caused by PLA degradation. Hence, Mg/PLA composite material is an ideal resorbable orthopedic material. In this paper, Mg/PLA composite rods and sheets were fabricated by hot-pressing technique combining with hot drawing technique. Then the influences of drawing process, annealing treatment and the volume fraction of Mg wires on the properties of the composite were studied. On this basis, a systematic study on the degradation behaviors of pure PLA and the composite in simulated physiological environment (SPE) under the action of static compression stress. The conclusions are as following:Follow-up drawing process can significantly improve the crystallinity of PLA in the composite and the mechanical properties of the composite prepared by hot-pressing. After three times drawing, the crystallinity of PLA in the composite with 10vol% Mg wires increased by 50%. Its tensile strength and bending strength increases to 80 MPa and 194 MPa, respectively increased by 35.6% and 64.4%. The bending strength of drawing composite rod with 10vol% Mg could be increased by 15% to 20% using annealing treatment (up to 232 MPa). With the increase of the volume fraction of magnesium alloy wires, the strengths of the composite sheet increases and could reach 106MPa and 196MPa when the Mg volume fraction is 40vol%, which are increased by 104% and 70% compared with pure PLA respectively.In simulated physiological environment, the degradation of pure PLA resulting in the decrease of pH value of SPE, while that of the composite made the pH value of SPE increase. Increasing the environment temperature will accelerate the degradation of pure PLA and the PLA in the composite, resulting in the significant decrease of the viscosity average molecular weight of PLA and the bending strength of the composite, which could decrease by 33.2% and 25.8% respectively after soaked for 15 days when the environment temperature increased from 25℃ to 50℃. In SPE at 37℃, the applied static stress can significantly accelerate the degradation of pure PLA and the PLA matrix in the composite. With the stress increasing, the acceleration effect is more obvious. Compared with those under no stress, when the applied stress is 5MPa, the bending strength and the viscosity average molecular weight of the composites decreased by 19.7% and 28.8%, respectively, after soaked for 15 days.Synergy influences of the environment temperature and the static stress is more significant than that of the single factor on the degradation behaviors of pure PLA and the composite. With increasing the temperature and the applied stress at the same time, the bending strength and the viscosity average molecular weight of PLA and the composite decreased significantly and the rate of weight loss increases. In simulated physiological environment, increasing the environmental temperature and the applied stress will promote the corrosion and cracking of the micro-arc oxidation (MAO) ceramic coating on Mg surface in composites. However, after 15 days immersion, the magnesium alloy wire remain intact with no significant corrosion, which indicates the magnesium alloy wires are effectively protected by the MAO ceramic coating and the PLA matrix during the early degradation period of the composite.