Polyhydroxyalkanoates (PHAs) are a promising family of biodegradable and bio-derived thermoplastics. However, PHAs are often considered non-recyclable because of chain scission and loss of properties during thermal reprocessing. Here, we demonstrate for the first time the melt-state glycolysis of PHAs as a platform for reactive extrusion processing of PHAs, allowing, for example, block copolymer synthesis or a rapid, scalable and solvent-free strategy to facilitate recycling. Using ethylene glycol as a glycolytic agent and poly(3-hydroxybutyrate- co -4-hydroxybutyrate) (P3HB4HB, 15% 4HB) as the PHA feed, controlled depolymerisation yielded hydroxyl-terminated oligomers with molecular weights tuneable down to 2.3 kDa assisted by metal catalysts. Among the catalysts screened, dibutyltin dilaurate (DBTDL) exhibited the highest activity, producing the most pronounced reduction in M ¯ n . Quantitative 1 H and 31 P Nuclear Magnetic Resonance (NMR) spectroscopy confirmed the formation and abundance of hydroxyl end groups, enabling molecular weight estimation consistent with SEC analysis. The glycolysis products retained distinct thermal transitions, even at low molecular weight, and showed a significant reduction in melting temperature to 145 °C, representing a 27 °C decrease from the as-received material. These hydroxyl-functionalised oligomers provide reactive precursors for chain extension, crosslinking, or block copolymerisation, offering a modular route to functional, tuneable, and recyclable materials. This work establishes melt glycolysis of P3HB4HB as a practical pathway for advancing circularity in biodegradable polymers while creating potential value-added opportunities through tailored re-use.
Lawless et al. (Fri,) studied this question.