Combined effect of glycerol/levulinic acid-based bioadditive on enzymatic hydrolysis and plasticization of amorphous and semi-crystalline poly(lactic acid)

Polylactic acid (PLA) is a widely used biopolymer, but its brittleness and limited biodegradability hinder its application as a standalone material. To enhance its properties, PLA can be compounded with plasticizers, ideally nontoxic and from sustainable sources. While phthalates remain the predominant plasticizers, their known harmful effects have led to the development of bio-based alternatives like glycerol trilevulinate (GT). This study investigates the plasticizing effect of GT on amorphous (aPLA) and semi-crystalline (cPLA) PLA, comparing it to the impact that can be achieved with a conventional plasticizer, diisononyl cyclohexane-1,2-dicarboxylate (DINCH). Specifically, GT added at 40 phr reduces the glass transition temperature of aPLA by 20 degrees C and the melting temperature of cPLA by 12 degrees C, whereas DINCH exhibited a more limited effect. Compared to DINCH, GT also demonstrated very low migration in terms of both leaching and volatility. Moreover, GT impacts on the enzymatic depolymerization of the prepared compounds. Specifically, enzymatic hydrolysis tests revealed an enhanced biodegradability of the aPLA/GT compounds, achieving complete degradation within 72 h of incubation, as confirmed by high performance liquid chromatography-based monomer quantification. The cPLA/GT formulations are also susceptible to hydrolysis, showing an increased weight loss from 18% to 31% when 20 phr of GT is added. These outcomes suggest that GT can be used not only to tune the thermal properties but also to significantly promote polyesters biodegradability, envisioning an environmentally friendly management of the PLA-based formulations.Highlights A bioplasticizer for amorphous and semi-crystalline PLA is proposed. Bioplasticizer reduces the glass transition and melting temperature of PLAs. Bioplasticizer also enhances the enzymatic degradation of semi-crystalline PLA. Bioplasticizer performance has been compared with a commercial plasticizer.