Effective Recycling Pathways of Commodity Polymers Enabled by Mechanoradical Capture

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Mechanical recycling of plastics faces challenges due to polymer chain degradation and reduced material properties.
• Reprocessing generates reactive mechanoradicals that lower molecular weight, limiting recyclability.

Purpose of the Study:

• To develop a value-preserving recycling strategy for polystyrene (PS) and poly(methyl methacrylate) (PMMA).
• To enable enhanced circularity and performance of mechanically recycled plastics.

Main Methods:

• Utilizing ball milling to induce polymer chain scission and generate mechanoradicals.
• Capturing mechanoradicals with bis(butyl trithiocarbonate) to yield polymers with trithiocarbonate (TTC) end groups.
• Employing TTC-functionalized polymers as macroinitiators for controlled polymerization or depolymerization.

Main Results:

• Mechanoradical capture successfully yielded TTC-functionalized polymers with significantly reduced molecular weight (≈90% lower).
• Chain extension restored or increased molecular weight, recovering entangled polymer properties and the rubbery plateau.
• The capture-and-repair strategy demonstrated robustness over three degradation-regeneration cycles.
• Ball milling alone reduced PMMA's thermal depolymerization temperature, enabling efficient depolymerization.

Conclusions:

• Mechanoradical capture is a promising approach for value-preserving plastic recycling.
• This strategy enhances the circularity and performance of recycled polymers.
• The method offers a pathway to overcome limitations in current mechanical recycling processes.