Production of Green Star/Linear PLA Blends by Extrusion and Injection Molding: Tailoring Rheological and Mechanical Performances of Conventional PLA

In this work, bio-based products composed of blends of a star-shaped poly(d ,l -lactide) (star-PDLLA) and a conventional linear poly(l -lactide) (linear-PLLA) are produced by typical large-scale manufacturing techniques for thermoplastic blends. In the first case, the two polymers are blended through melt extrusion, producing pellets that are subsequently compression-molded into the final bio-based polymer films. Alternatively, the star/linear poly(lactide) (PLA) materials are developed by direct blending through injection molding, a process that generally applies after a preblending extrusion step to ensure proper mixing. Thermomechanical degradation induced by the different processes is evaluated, and the performances of the final star/linear PLA products are thoroughly compared. The effect of the short-branched, amorphous, star polymeric component on thermal, mechanical, and rheological properties of the conventional PLLA is comprehensively investigated, revealing that the star-PDLLA incorporation promotes the formation of a more flexible and tougher material with reduced capability of crystallization. Most importantly, star-PDLLA decreases the melt viscosity of the final material, while increasing the shear-thinning behavior, hence facilitating melt flow during manufacturing. Such properties lead to enhanced material ductility and processability, with respect to typically brittle and viscous conventional PLLA-based materials. Moreover, the tuning of final material performances can be achieved by simply varying the star-PDLLA content.