Thermal behavior of injection- and compression-molded custom-built polylactic acids

Abstract

In recent time, the quest for renewable materials for the development of packaging items is constantly increasing. The class of polylactic acids (PLAs) is the most promising one, although a broader scale commercial expansion of these polymers cannot leave unceasing enhancement of their functional properties aside, especially toughness and thermal stability. Similarly, continuous innovation in prototyping competitive easy-route solutions for material processing is another key to successful industrial applications of PLAs. In this respect, this study deals with the design and formulation of innovative custom-built PLAs for injection and compression molding, which are compostable, suitable for food contact, and characterized by a good compromise of mechanical properties and thermal resistance. Therefore, a commercial grade PLA was modified by reactive compounding extrusion with maleic anhydride (MAH)-grafted PLA (PLA-MA) and glycidyl methacrylate (GMA)-grafted PLA (PLA-GMA) and micro-lamellar talc. Material structure and thermal response of the compounds were evaluated by differential scanning calorimetry (DSC) and Fourier transform-infrared spectroscopy (FTIR). The experimental findings show that material structure and, especially, crystallization of the PLA can be controlled by fine-tuning the compound formulation. In addition, achievement of the appropriate crystallization degree in the polymer can lead to compostable composite materials with good thermal stability. Accordingly, the custom-built PLA formulations feature the potential to expand significantly the fields of application of compostable biopolymers, thus posing a valid alternative to both durable not compostable bioplastics and conventional plastics in injection and compression molding process.