# Advancing aerogel recyclability through polyhexahydrotriazine reactivity

## TL;DR

Researchers developed recyclable organic aerogels using dynamic hexahydrotriazine chemistry, enabling sustainable reuse and property adjustments.

## Contribution

A novel dynamic chemistry approach for recyclable aerogels using hexahydrotriazine reactivity is introduced.

## Key findings

- Aerogels can be depolymerized into soluble oligomers using primary amines and reassembled into new networks.
- Amine feedstocks during depolymerization allow tailoring of aerogel properties like thermal conductivity and flame resistance.
- HT bond exchange enables transformation into thermoset-like films and back to aerogels under heat and pressure.

## Abstract

Organic aerogels have emerged as promising materials for advanced thermal insulation. However, their chemically robust covalent networks pose a major barrier for effective recycling. Introducing specific chemical bonds into the aerogel scaffold that enable on-demand reversibility offers a viable pathway to enhance recyclability and promote the sustainable use of these materials. In this work, we demonstrate that hexahydrotriazine (HT) units undergo nucleophilic attack by amines and engage in metathesis reactions, fundamentally redefining their reactive behaviors. Based on this, we introduce a waste-minimized, closed-loop chemical recycling process for highly porous, thermally superinsulating organic aerogels. These materials are partially depolymerized into soluble oligomers upon exposure to primary amines and can be reassembled into fresh polymer networks on demand. Additionally, by varying the amine feedstocks during depolymerization, we tailor key aerogel properties, such as thermal conductivity and flame resistance, beyond their initial synthesis. Under heat and pressure, HT bond exchange enables aerogels to transform into high-performance thermoset-like films, which can subsequently revert to aerogels. This breakthrough in HT chemistry sets a benchmark for atom-efficient recycling, reprogramming, and reprocessing of HT-based materials, providing a transformative foundation for a circular materials platform with broad impact.

The sustainable use of organic aerogels is limited by their non-recyclability owing to the covalently-crosslinked networks that constitute their structures. Here, the authors report on the dynamic chemistry of hexahydrotriazine units to develop recyclable aerogels.