Anaerobic Fermentation of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) Plasticized with Glycerol Trilevulinate into Volatile Fatty Acids

Polyhydroxyalkanoates (PHAs) are a promising class of biobased and biodegradable polymers; however, their inherent brittleness and limited processability hinder widespread application. The glycerol trilevulinate (GT) bioplasticizer has been proposed to enhance the mechanical properties of PHAs without compromising their biodegradability. This study investigates the effect of GT at different concentrations on the anaerobic fermentation of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) to volatile fatty acids (VFA), focusing on microbial conversion efficiency. These VFA are platform chemicals serving various applications, including resynthesis of PHAs. PHBV/GT blends were characterized in terms of their thermal and morphological properties. The results show that the increased GT percentage reduces the crystallinity and melting temperature, thereby enhancing polymer flexibility. Anaerobic fermentation experiments were conducted using (i) prehydrolyzed PHBV/GT fermentation at fixed 10 wt % GT content and (ii) direct fermentation of PHBV/GT solid particles at different GT concentrations. The findings show that GT-plasticized PHBV was successfully converted into VFA, with acetate and n-butyrate being the predominant fermentation products. While low concentrations of hydrolysate (4-10 g SCOD/L) were efficiently converted, higher concentrations (20 g SCOD/L) did not lead to fermentation, suggesting potential microbial toxicity. The different contents of GT did not affect the microbial conversion process. These findings support the use of GT as plasticizer for PHA-based materials and development of renewable, biodegradable, and microbial recyclable plastic products.