Improving Circularity via Chemical Recycling to all Rings

Area of Science:

• Polymer Chemistry
• Sustainable Materials Science
• Chemical Engineering

Background:

• Aliphatic polyesters offer competitive properties to conventional plastics like PE and PP.
• Chemical recycling to monomer (CRM) is a key advantage, but not all polyesters are amenable to this process.
• The thermodynamic feasibility of CRM is typically assessed by the change in free energy during ring-opening polymerization (∆G_ROP), which is a one-dimensional measure.

Purpose of the Study:

• To introduce a multi-dimensional concept for chemical recycling to all rings (CRR) by reaching ring-chain equilibrium (RCE).
• To demonstrate that the thermodynamic landscape of recycling is multi-dimensional, involving equilibria beyond just monomer-polymer.
• To enable CRR for polymers that are difficult to recycle via traditional CRM.

Main Methods:

• Development of a highly active catalytic system to achieve RCE.
• Thermodynamic analysis using the change in free energy during ring-chain equilibrium (∆G_RCE).
• Application of the CRR concept to poly(ε-caprolactone), poly(pentadecalactone), and mixed polymer systems.

Main Results:

• A multi-dimensional CRR approach was successfully implemented using a novel catalytic system.
• The thermodynamic driving force for CRR (∆G_RCE) differs significantly from that of CRM (∆G_ROP).
• Efficient CRR was achieved for polymers previously considered difficult to recycle, including poly(ε-caprolactone) and poly(pentadecalactone).

Conclusions:

• The study presents a new general concept for closing the material loop in polymer recycling.
• CRR, based on RCE and ∆G_RCE, offers a more comprehensive and effective strategy than traditional CRM.
• This work expands the scope of recyclable polymers and advances sustainable material management.