Highly biodegradable, ductile all-polylactide blends

All-PLA blends have been fabricated by an easily scalable and green melt-blending of linear-PLLA and 3-armed star-shaped PDLLA at different proportions (100:0, 95:5, 90:10, 80:20, and 50:50, w:w). The fabrication process, carried out in a hot-press, consisted of three steps: an initial heating of the thoroughly blended polymer mixtures at 170 °C for 5 min, a second heating at 170 °C for 5 min with a pressure of 200 Pa, and a final cooling at room temperature during 20 min keeping the same pressure. This methodology resulted in very homogenous amorphous samples, as revealed by XRD and DSC. The incorporation of star-PDLLA toughened the polylactide matrix by a clear ductilization, opening opportunities for the expanded use of the developed blends in different applications, due to their increased processability. DSC analysis revealed indeed that by increasing star-PDLLA content it is possible to gradually reduce the Tg, as well as the capability of crystallization of the linear-PLLA component. Such properties determine a plasticizing effect on the final blends. The increased content of the star component turned the films from transparent to translucent and decreases the thermal decomposition temperatures, which remain in any case very well above room temperature. The water vapor transmission rates varied with the star-PDLLA content between values characteristic for isolating to breathable films, thus allowing the use of these blends in different applications such as food packaging and biomedical devices. Finally, no important changes of water contact angle and water uptake were observed between the different blends. Despite the negligible effect of seawater on the biodegradation of commercial PLA, star-PDLLA-containing blends showed high biodegradation rates at short-times in marine environments, reinforcing the environmentally friendly character of polylactide.