Influence of moulding processing on poly (lactic acid) (PLA) semi-crystalline properties

Abstract

Poly (lactic acid) (PLA) is a bio-based and compostable polyester, widely employed in a variety of daily used products, being easily processed via the traditional manufacturing techniques, i.e., injection moulding (IM), compression moulding (CM), blow moulding (BM), etc. This study will be specifically focused on the impact of both IM and CM processing techniques on PLA characteristics, aiming to optimize these manufacturing procedures and ultimately improving its end-products features. By means of thermal, mechanical and microscopy analysis, the role of the different moulding techniques in influencing the PLA semi-crystalline development will be extensively investigated, also by correlating the related morphology with its macroscopical behavior. It will be observed that the polymer flow orientation during IM promotes the semi-crystalline development, as confirmed by Avrami analysis, XRD measurements, and TEM imaging. Moulded sample thickness, manufacturing pressure, and PLA granular consolidation that differ for the two moulding methodologies appear to be directly accountable for the detected faster crystallization kinetics during IM when compared to the CM one. Finally, by combining thermal information (Gibbs–Thomson equation), XRD data (Scherrer equation) and TEM imaging, the size of the crystalline lamellae during PLA crystallization will be sampled, also detecting the phenomenon of "lamellar thickening" as the crystalline content increases in both the injection and compression moulded samples.