Open- and Closed-Loop Recycling: Highly Active Zinc Bisguanidine Polymerization Catalyst for the Depolymerization of...

Area of Science:

• Polymer Chemistry
• Catalysis
• Sustainable Materials

Background:

• Chemical recycling of polyesters is crucial for a circular economy.
• Developing efficient and selective catalysts for polyester degradation is an ongoing challenge.
• Current methods often require harsh conditions or yield low-value products.

Purpose of the Study:

• To introduce and evaluate a novel aliphatic N,N-bisguanidine zinc complex, [Zn(DMEG2ch)2](OTf)2·THF, for the chemical recycling of (bio)polyesters.
• To investigate the catalyst's activity in ring-opening polymerization (ROP) and depolymerization, particularly for polylactic acid (PLA) and polycaprolactone (PCL).
• To explore catalyst recyclability and the direct recovery of monomers for open- or closed-loop recycling.

Main Methods:

• Synthesis and characterization of the N,N-bisguanidine zinc complex.
• Kinetic and thermodynamic studies of PLA depolymerization via alcoholysis.
• Testing catalyst performance in degrading PLA, PCL, and their blends with PET.
• Investigating catalyst recycling using ethanol and monomer recovery.

Main Results:

• The zinc complex [Zn(DMEG2ch)2](OTf)2·THF exhibits high activity in ROP of lactide (LA) and ϵ-caprolactone (CL).
• Efficient depolymerization of PLA to high-value alkyl lactates under mild conditions was achieved.
• Successful catalyst recycling and direct LA recovery from PLA were demonstrated.
• Selective degradation of PLA from PLA/PET mixtures and a cascade recycling of PLA/PCL blends were accomplished.

Conclusions:

• The developed zinc catalyst is highly active and versatile for (bio)polyester chemical recycling.
• This catalyst facilitates the recovery of valuable monomers and enables both open- and closed-loop recycling pathways.
• The findings contribute to establishing a circular plastics economy and mitigating plastic pollution.