Standardized evaluations of mechanical properties of biodegradable Mg strengthened poly-lactic acid composite through interfacial Properties

Abstract

Event Abstract Back to Event Standardized evaluations of mechanical properties of biodegradable Mg strengthened poly-lactic acid composite through interfacial Properties Muhammadshoaib Butt1, Jing Bai1, Feng Xue1 and Cheng Chu1 1 southeast university, School of Material Science and engineering, China Introductions: Mg alloys, as prospective biodegradable orthopedic implants, are attracting wide attention. However, their high corrosion rate and hydrogen release during degradation leads to a potential limitation of application in future. Mg strengthened poly-lactic acid composite is a good attempt to integrate both their advantages and to avoid their weakness. Since there are many methods to prepare composite, it is necessary to develop a standardized system to evaluate the mechanical properties, especially the interfacial bonding strength during degradation. Materials and Methods: AZ31 alloy (96%Mg, 3%Al and 1%Zn) rod with diameter of 2.44mm, height 60mm and plate with dimension were 60mm×10mm×1.7mm (length ×width × height), were first prepared by smelting ,casting ,hot extrusion, wet drawing and annealing. Three surface treatment methods were performed for both Mg rod and plate, anodic oxidation (AO), micro-arc oxidation(MAO) and chemical conversion.These Mg rods and plates with and without surface coating were used to fabricate PLA/AO/Mg composite, rod with diameter of 4mm and height of 60mm, and plate with dimension of 60mm ×12.3mm ×3mm(length × width ×height), respectively (Fig. 1), by plastic injection molding (PIM) process. To evaluate the degradation performance of different composite, tensile tests, bending tests, degradation rate measurements, and interfacial morphology observations were carried out for these samples immersed in simulated body fluid (SBF) for different time. Results and Discussions: The mechanical testing results show the composites have significant higher bending and tensile strength than pure PLA[1]. For example, the average bending strength of rod samples improves from ~100MPa of pure PLA to ~175MPa of PLA/naked Mg composite, and further improve to ~190MPa of PLA/Mg with AO coating composite. The average tensile ultimate strength of rod samples improves from ~52MPa of pure PLA to ~95MPa of PLA/Mg with AO coating. Moreover, Mg with MAO coating can further improve strength[2] of composite than AO coating. From the samples after tensile test, it can be found that only outer PLA is broken during pulled out, while the Mg still can maintain structure integrity, indicating the interface of Mg and PLA is mechanical bonded and frictional force is an major factor to impact the interfacial bonding strength of Mg and PLA[3]. Additional, since there are two interface in these composites with surface treated Mg, namely Mg - coating interface and coating – PLA interface, both interfaces play important roles in influencing the mechanical properties of composite[4]. The present composites show good corrosion resistance during degradation, and there is no noticeable change after immersion for 1 month. Meanwhile, these composites also show good mechanical stability during degradation, and the average strengths are still more than half of their original strengths after 1-2 month immersion.[5] The decrease of strength is mainly attributed to the hydrolysis of PLA and the morphological changes of interfaces resulting from the corrosion. Conclusions: Biodegradable PLA/Mg composite were prepared by plastic injection molding(PIM). These composites show significant better mechanical properties than pure PLA, and with surface treatment of Mg the mechanical properties are further improved. Two interfaces between Mg and PLA play critical roles in influencing the mechanical properties of original composites as well as during degradation. Standardization to analysis the morphology and bonding strength was proposed and this is helpful to evaluate the mechanical properties of PLA/Mg composites during degradation. Programs Foundation of Ministry of Education of China (No. 20120092120048); The National Natural Science Foundation of China (No. 31570961)