Development of Polyoxymethylene/Polylactide Blends for a Potentially Biodegradable Material: Crystallization Kinetics, Lifespan Prediction, and Enzymatic Degradation Behavior

This paper reported the development of polyoxymethylene (POM)/polylactide (PLA) blends for a potentially biodegradable material. A series of POM/PLA blends at different weight ratios were prepared by melt extrusion with a twin-screw extruder, and their mechanical properties, crystallization behavior and kinetics, thermal degradation kinetics and stability, lifespan prediction and enzymatic degradation behavior were investigated extensively. POM and PLA were found to be partially miscible in the melt state at low temperature and become phase-separated at elevated temperatures, and their blends exhibited a typical lower critical solution temperature behavior. There were two distinct glass transition temperatures (T-g) observed for POM/PLA blends at any mass ratios when quenched from the homogeneous state, and both POM and PLA domains showed an apparent depression in their respective T-g's in the blends. Owing to the partial miscibility between two domains, the tensile strength and impact toughness of POM/PLA blends gradually decreased with an increase of PLA content, but their flexural strength and modulus presented an increasing trend with PLA content. The studies on non-isothermal and isothermal crystallization behaviors of the blends indicated that the crystallization rates of the blends decreased continually with increasing the PLA content, confirming that the crystallization of POM domain was controlled by the molecular-confined mechanism. The introduction of PLA into POM not only led to a slight increase of thermal stability of POM domain at low PLA contents but also shortened the lifespan of the blends, favoring the natural degradation of the blends. The POM/PLA blends exhibited an improvement in partially biodegradable performance with an increase of PLA content and their mass loss reached up to 25.3 wt % at the end of 48-h enzymatic degradation when 50 wt % of PLA was incorporated.