Solvent-Free Processing of i-P3HB Blends: Enhancing Processability and Mechanical Properties for Sustainable Applications

Poly(3-hydroxybutyrate) is a biobased and biodegradable polymer, produced via bacterial fermentation and characterized by an isotactic structure and mechanical properties similar to those of polyethylene and polypropylene. However, its brittleness-due to high crystallinity (~70%) and thermal degradation, starting at a temperature range of 180-190 °C near its melting point (175 °C)-makes its processing difficult and limits its applications. Most recent studies on modifying P3HB involved solution casting, typically using chloroform, which raises sustainability concerns. In this study blends of isotactic poly(3-hydroxybutyrate) (<i>i</i>-P3HB) with atactic poly(3-hydroxybutyrate) (<i>a</i>-P3HB) and poly(3-hydroxybutyrate-<i>co</i>-4-hydroxybutyrate) (P34HB) were prepared through solvent-free extrusion, and the thermal and mechanical properties of these blends were characterized. The obtained blends showed an extended processing window with reduced processing temperatures (150-160 °C), which were significantly lower than the onset of the decomposition temperature of <i>i</i>-P3HB, thereby avoiding thermal degradation. Furthermore, the crystallinity of these blends could be varied between 17 and 70%, depending on the polymer ratio, which allows for tailormade materials with tunable mechanical properties and an elongation at break up to 600%. Based on the results, the obtained blends in this study are promising candidates for various applications and processing techniques, such as injection molding, extrusion, and fiber spinning, offering a sustainable alternative to conventional plastics.