Multi-Generation Recycling of Thermosets Enabled by Fragment Reactivation

Area of Science:

• Polymer Chemistry
• Materials Science
• Sustainable Chemistry

Background:

• Thermosets offer excellent stability but lack chemical circularity due to cross-linked structures.
• Cleavable comonomers (CCs) enable thermoset deconstruction but recycling is limited to one cycle with low recycled content.
• Current recycling methods for thermosets are inefficient and do not fully address end-of-life challenges.

Purpose of the Study:

• To develop a novel "fragment reactivation" strategy for enhanced chemical recycling of thermosets.
• To improve the solubility and reactivity of deconstructed thermoset fragments for subsequent recycling rounds.
• To demonstrate the feasibility and efficiency of multiple-cycle recycling using this new approach.

Main Methods:

• Introduction of a siloxane-based cleavable comonomer (CC) into polydicyclopentadiene (pDCPD).
• Deconstruction of CC-enabled thermosets into oligomeric fragments.
• Activation of fragments via functional groups for improved solubility and reactivity.
• Demonstration of multi-cycle recycling using both two-step (deconstruction-reactivation) and single-step (deconstructive reactivation) processes.

Main Results:

• Two rounds of chemical recycling achieved with 40 wt % reactivated fragments in pDCPD.
• A single-step "deconstructive reactivation" process enabled three rounds of recycling with 40-45 wt % fragment incorporation.
• Key material properties and deconstructability were maintained throughout the recycling cycles.
• The lifespan of deconstructable pDCPD thermosets was extended by approximately 2.6 times.

Conclusions:

• Fragment reactivation significantly enhances the chemical recycling efficiency of thermosets.
• The developed strategy offers a promising and potentially generalizable approach for sustainable thermoset management.
• This method addresses limitations of previous CC-enabled recycling, paving the way for circular thermoset economy.