Levulinic acid-based bioplasticizers: a facile approach to enhance the thermal and mechanical properties of polyhydroxyalkanoates

Plasticizers are the most used polymer additives world-wide. Nowadays, conventional plasticizers (e.g. phthalates) do not meet the requirements in terms of renewability, biodegradability and cytotoxicity that have become necessary, especially if they are compounded with biopolymers. In this study, novel bioplasticizers are synthesized from levulinic acid via a protecting-group-free three-step process. After FT-IR and NMR characterization of the synthesized molecules, their plasticization effect has been tested with poly(3-hydroxybutyrate) (PHB) as a model semicrystalline biopolyester characterized by a narrow processing window, slow re-crystallization and high brittleness, which limit its processability and diffusion. The proposed bioplasticizers show remarkable miscibility with PHB and low leaching. The bioplasticizers also show a remarkable plasticization effect in terms of reducing the glass transition and melting temperatures (17 °C and 8 °C, respectively), which are comparable with the performance of the best commercially available green plasticizers. Furthermore, flexibility and crystallinity are positively affected, leading to an overall reduction in the typical brittleness of PHB. The observed effects result in an expansion of the temperature range in which PHB can be processed without thermal degradation. Moreover, the incorporation of the levulinic acid-based additives does not significantly affect the typical biodegradability and biocompatibility of PHB, showing their promising features as bioplasticizers for both environmental and biomedical applications.