Development of a bioplasticizer to improve processing, thermal and mechanical properties of biopolyesters

Plasticizers are most used polymer additives worldwide. Nowadays, conventional plasticizers do not meet the renewability, biodegradability, and cytotoxicity requirements that have become necessary, especially if they are compounded with biopolymers. This study aimed to develop a sustainable bio-plasticizer using glycerol and levulinic acid to obtain high performing and environmentally friendly plasticizer. Glycerol trilevulinate (GT) was synthesized using biobased raw materials without using solvents and harsh conditions. After FT-IR and NMR characterization of the synthesized plasticizer, the reaction parameters were optimized in terms of temperature, time, and yield. The plasticization effect was assessed with poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a biopolyester characterized by a narrow processing window. Compounding was performed using extrusion by adding 2.5, 5, and 10 wt.% of GT to the polymer. Produced formulations were processed by injection molding and 3D printing to prepare samples whose performances were compared with blends produced with commercial green plasticizers, named diisononyl 1,2-cyclohexanedicarboxylic acid (DINCH) and acetyl tributylcitrate (ATBC). Mechanical tests showed an overall increase of the flexibility and decrease of the stiffness when PHBV was compounded with all GT concentrations. In addition comparison with DINCH and ATBC revealed that 5 wt.% GT formulation performed similarly and in some cases, even better than the commercial alternatives. For all formulations, by increasing the GT amount a positive effect on the thermal properties in terms of reduction of glass transition and melting temperatures was observed. Moreover, lowering of the crystallinity was detected, suggesting remarkable performances of GT as plasticizer compared with PHBV. Furthermore, 3D printing processing temperature of 5 wt.% GT formulation was lowered by 10°C extending the polymer's processability window while ensuring specimen's printability.