A mechanochemical approach to recycle thermosets containing carbonate and thiourethane linkages

Abstract

Over the past decades, various industries shifted from traditional materials such as glass and metals to thermoset polymers due to their excellent chemical resistance, thermal stability, reduced weight, and affordability. However, at the end of their life cycle, these highly crosslinked polymers end up as environmental pollutants due to their non-recyclability. To tackle this issue, researchers are exploring vitrimer-type polymers with recyclable qualities, supporting a circular economy and sustainable management of thermoset wastes. This study investigates a new promising method of recycling two commonly used thermosets in commercial applications, poly allyl diglycol carbonate (PADC) and poly thiourethane (PTU), via a mechanochemical process known as vitrimerization. The process involves the cryogenic ball milling of the thermoset with a zinc-based catalyst and a hydroxyl-providing agent, followed by compression molding, enabling the thermoset conversion into a vitrimer. Rheological tests revealed the remarkable stress-relaxation capabilities of the vitrimerized networks, indicating the conversion of the initial permanent crosslinked structures into dynamic networks through vitrimerization. Dynamic mechanical analysis results show that the vitrimerized samples display a consistent rubbery plateau at high temperature, similar to that of permanently crosslinked networks, suggesting a fix crosslink density during the exchange reaction. Differential scanning calorimetry and thermogravimetric analysis results showed that the thermal properties of the vitrimerized samples closely resemble those of the original samples.