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Ball mill grinding enables sustainable polyester depolymerisation
Researchers have developed a mechanochemical approach to depolymerise post-consumer aliphatic polyesters such as PLA, PHAs and biodegradable multilayer flexible film packaging. The recovered monomers are converted in a one-pot process into α-lipoic acid-based photopolymer resins that form tunable, dynamic and degradable covalent adaptable networks.
Aliphatic polyesters such as poly(lactic acid) (PLA) and poly(hydroxyalkanoates) (PHAs) are inherently biodegradable and are typically collected and composted at end of life. However, this often prevents their recycling and repurposing into new materials. Chemical recycling offers an alternative route for the depolymerisation of polyesters and their packaging formats, including multilayer flexible packaging, but conventional processes frequently generate significant chemical waste in the form of solvents and excess reagents. To overcome these limitations, Skala and colleagues investigated ball mill grinding (BMG) as an operationally simple mechanochemical route for the aminolysis of polyester materials.
Using BMG, the researchers successfully depolymerised PLA, PHAs and a biodegradable multilayer flexible film packaging into their constituent monomers under mild and largely solvent-free conditions. The mechanochemical approach circumvents key drawbacks of conventional ester aminolysis and demonstrates the utility of BMG mechanochemistry for sustainable polymer recycling.
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One-pot conversion into dynamic covalent networks
Building on the depolymerisation step, the recovered monomers were directly esterified with α-lipoic acid (αLA) in a one-pot procedure to yield tunable αLA-based photopolymer resins. Upon photopolymerisation, these resins formed disulfide-based covalent adaptable networks (CANs). Investigation of structure-property relationships revealed a broad range of accessible mechanical properties, with the resulting materials being significantly softer than the original polyester film packaging.
Importantly, the αLA-based materials showed degradability via disulfide cleavage under conditions that mimic low oxidation-reduction potential (ORP) environments. The approach therefore combines sustainable depolymerisation of polyester waste with the synthesis of bio-based, dynamic and degradable photopolymer networks, opening up potential applications in adaptable coatings, adhesives and functional materials derived from plastic waste streams.
Source: Skala, M. E. et al., Tunable dynamic covalent networks from mechanochemical depolymerization of post-consumer aliphatic polyesters. Polymer Chemistry 17 (27), 2966–2977 (2026).
