Delving into Process–Microstructure–Property Relationships in Cast-Extruded Polylactic Acid/Talc Composite Films: Effect of Different Screw Designs

In the context of polymer-based composites, the knowledge of the correlations between the processing conditions, the microstructure, and the final properties is essential to tailor polymeric systems for specific applications. Specifically concerning the extrusion process, an accurate design of the screw profile allows for achieving composites with modulable microstructures, according to the specific properties required by the intended application. In this work, films of polylactic acid-based composites with 5 wt.% of talc were obtained by means of a single-screw extruder equipped with a flat die and a calender unit. Three different screw profiles, namely a general-purpose compression screw, a screw with a reverse flow zone, and a barrier screw, were employed for the production of films. The ability of the screw profile in varying the degree of filler dispersion and distribution was assessed through morphological and rheological analyses, demonstrating that the barrier screw is more able in disaggregating the talc lamellae. Due to the achieved microstructures, films produced using this screw profile exhibited superior barrier properties, with a decrease of about 27% in the oxygen permeability as compared to unfilled PLA. However, a concurrent decrease in material ductility as compared to the other films was observed. Finally, the thermoformability of the composites was assessed; also in this case, trays with more precise edges and corners were obtained for the film formulated through the barrier screw.