Preparation, Interface Strength And Mechanical Properties Of PLA-based Composite Reinforced With Magnesium Alloy Wires

The biodegradable polylactic acid (PLA) has the poor strength and toughness, while the corrosion rate of medical magnesium alloys (Mg) in human body is too fast. These shortcomings limit their clinical applications. A new PLA-based composite reinforced with directional magnesium alloy wires was prepared by hot pressing. Meanwhile, the hot drawing process and annealing treatment was used to prepare the self-reinforced PLA-based composite. The influence and strengthening mechanism of micro-arc oxidation treatment (MAO) of Mg wires on the interface properties of the composites were investigated by single fiber pull-out test and molecular dynamics simulation method. The effects of MAO treatment of magnesium alloy wires, wire diameter size as well as the drawing process and annealing treatment on the mechanical properties of the composites were studied using tensile, bending and shear test.The experimental results show MAO treatment to Mg wires can significantly improve the interface bonding properties of the composite, which make the interface fracture change from the interface-controlled mode to the matrix-controlled one. As a result, the average interfacial shear strength increases by 369.8% and the critical embedment depth of the wire reduces by 77.4%. For the composite containing 6vol%Mg wires with a diameter of 0.3 mm, the bending strength of the composite with MAO-treated wires increase from 94 MPa to 110 MPa, which is 1.33 times of pure PLA. Under the same MAO treatment, the Mg wires with the diameters of 0.2 mm,0.3 mm or 0.45 mm can effectively strengthen PLA matrix. The average interfacial shear strength of the composite increases with increasing the wire diameter. However, the wire with a diameter of 0.68 mm has a poor reinforcement.The main interfacial strengthening mechanism of the composite is the combined effect of the mechanical inter-locking action formed by PLA matrix penetrating into the pores of MAO film and the improved interface friction resulted from the rough MAO surface. In addition, the increase of intermolecular forces is also a kind of interface strengthening mechanism which attributes to the adsorption orientation of H and O atom of PLA to with respect to O and Mg ions of MAO surface.It was found that the drawing process can greatly increase the crystallinity and elastic modulus of PLA in the composite. Accordingly, the tensile strength and bending strength of the composite with 20vol%MAO-treated Mg wires increase from 80 MPa and 145 MPa to 108 MPa and 237 MPa, respectively. However, the shear strength has a slight decrease. Annealing treatment could promote the preferential growth along (203) crystal plane of PLA crystallization phase. As a result, the bending strength of the drawed composite with 8vol% MAO-treated Mg wires increases by 24%～32% with the highest value of 180 MPa. Moreover, the mechanical properties of the composite tend to be stable with the increment of annealing temperature.