Catalyst design for depolymerisation of oxygenated polymers to true monomers

Overview

This solution addresses one of the most pressing challenges in circular plastics: the efficient chemical recycling of polymer blends back to their true monomers. By applying rational catalyst design principles, the technology enables selective depolymerisation of polymer mixtures in the solid-state at elevated temperatures, eliminating the need for solvents and avoiding costly product separation.

The approach is particularly valuable for recycling poly(lactic acid) (PLA), polyhydroxyalkanoates (PHAs), and CO2-based polycarbonates, including their blends. The process yields monomers such as lactide, epoxides, and CO2, which can be repolymerised to produce virgin-quality plastics, enabling a genuine closed-loop plastics economy.

Technical specifications

Key features:

• Earth-abundant metal-based catalysts (Mg(II) and Zn(II)) operating at extremely low loadings (0.01 mol%)
• Solid-state depolymerisation at mild temperatures (100-160 °C)
• Selective recovery of monomers from polymer blends, enabling orthogonal chemical recycling
• Catalyst recyclability for at least four cycles without loss of productivity, activity, or selectivity
• Demonstrated multigram-scale operation (greater than 10 g of polymer)
• No solvent required, reducing environmental impact and processing costs
• Combined experimental and computational catalyst design methodology

The kinetics of depolymerisation are governed by temperature, catalyst, and polymer structure. By understanding these kinetics for homopolymers in the solid-state, reaction conditions can be optimised to selectively direct product formation toward monomer recovery and preferentially depolymerise one polymer over another in a blend.

Technology readiness level

The technology has been validated for PLA and related polyesters, as well as CO2-based polycarbonates, with three high-impact publications supporting the work. Current efforts are focused on expanding the scope to PHAs and developing a family of catalysts with orthogonal reactivity for PLA/PHA blends. Future validation includes computational modelling to understand reaction mechanisms, screening catalysts for PHA depolymerisation using thermogravimetric FTIR analysis, and scaling the process to laboratory level (10 g to 1 kg).