You are invited to attend Zahra Rezaei's MASc oral exam, where she will discuss her research on the Recovery and Reuse of Nanomaterials from Radically Polymerizable Thermoset Nanocomposites; Towards A Circular Economy
Abstract:
The widespread adoption of thermoset nanocomposites has created significant end-of-life management challenges due to their permanent crosslinked networks, which resist conventional recycling methods and trap valuable nanomaterials within non-degradable matrices. This work presents a proof-of-concept study to assess a new approach for achieving a circular economy for thermoset nanocomposites; recovering and reusing nanomaterials from thermoset nanocomposites through the incorporation of cleavable comonomers into the polymer matrix, enabling controlled matrix degradation and nanofiller recovery at end-of-life.
Carbon nanotubes (CNTs) were selected as the nanofiller for this study due to their widespread use in nanocomposites and growing industrial significance, and a styrene/divinylbenzene (DVB) thermoset matrix was chosen as a model matrix for its chemical compatibility with CNTs. To enable controlled degradation at end-of-life and nanofiller recovery, comonomer additives that can install cleavable bonds into the matrix’s polymer network were systematically evaluated. Several candidates were investigated, including cyclic ketene acetal (CKA) (specifically 2-methylene-1,3-dioxepane, MDO), which underwent hydrolysis too rapidly and an unwanted ring-retaining side reaction for practical application, and thionolactones (specifically dibenzo[c,e]-oxepine-5(7H)-thione, DOT and 2-(isopropylthio)dibenzo[c,e]oxepine-5(7H)-thione, 2SiPrDOT), which was limited by the monomers’ solubility in the styrene/DVB system. Through this careful screening process, 2SiPrDOT was selected as the most suitable option, offering both chemical stability during processing and sufficient solubility in the system.
Comprehensive characterization of the primary nanocomposites using thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), electrical resistivity measurements, and hardness testing confirmed that 2SiPrDOT incorporation did not significantly alter the thermal, electrical, or mechanical properties of the material, preserving the high-performance characteristics essential for practical applications.
The thermoset matrix was then deconstructed through nucleophilic degradation, allowing recovery of finely distributed CNTs from the crosslinked network.
Analysis of recovered CNTs using energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and Raman spectroscopy revealed no significant changes in the nanofiller’s structure or surface chemistry, demonstrating the gentle nature of the recovery process. The recovered CNTs (68.7% yield) were subsequently re-embedded into a fresh styrene/divinylbenzene matrix and polymerized. Characterization of these secondary nanocomposites using the same characterization techniques showed properties comparable to the primary nanocomposites, confirming successful retention of nanofiller functionality through the recovery and reuse cycle.
This research demonstrates that strategic incorporation of cleavable comonomers into thermoset matrices offers a viable pathway toward circularity for high-performance nanocomposites. By enabling controlled matrix deconstruction while preserving nanomaterial quality, this approach addresses both environmental concerns associated with nanocomposite waste and the economic imperative to reclaim valuable nanomaterials. The demonstrated success with the styrene/DVB system suggests broader applicability of this methodology. As a general radical ring-opening polymerization strategy, this approach has the potential to be extended to other vinyl-based thermosets and diverse nanofillers, offering a promising foundation for developing next-generation recyclable composites across multiple industrial sectors.
Supervisor Professor Elisabeth Prince