From network degradation to mechanical brittleness: The aging response of epoxy vitrimers

Abstract

The growing use of composite materials in engineering has intensified the need for sustainable alternatives to traditional thermoset polymers, which are difficult to recycle and contribute to environmental pollution. Vitrimers, a class of covalently adaptable network polymers capable of bond exchange reactions, offer a promising solution by combining the mechanical robustness of conventional thermosets with the potential for reprocessing and recyclability. However, their long-term stability under extreme environmental conditions remains underexplored. This study investigates the effects of oxidative and hydrolytic aging on a DGEBA-based vitrimer system formulated with glutaric anhydride and zinc acetylacetonate. By subjecting samples to accelerated aging conditions and analyzing changes in macromolecular structure, thermal behavior, and mechanical performance using FTIR, DMA, microscopy, nano-indentation, and tensile testing, we explored the degradation mechanisms that govern vitrimer durability in extreme environments and evaluated their potential for long-term structural applications. Although both oxidation and hydrolysis are identified as coupled diffusion-reaction processes in bulk polymers, their degradation mechanisms for the chosen vitrimer were found to differ significantly. Hydrolysis exhibited an initial period of mass gain due to water sorption, followed by a reaction-dominated phase characterized by substantial mass loss via bulk erosion. In contrast, oxidation, limited by the low diffusivity of oxygen at atmospheric pressure, did not show a diffusion-driven mass gain or an induction period. Instead, degradation initiated immediately, resulting in an overall mass loss and the localized formation of micro-pores near the material’s outer surface. While the two extreme environments provided two differing degradation mechanisms, they shared a similar macroscopic response of increased embrittlement as aging progresses, demonstrated by a significant reduction in peak stress and failure strain. These insights into the distinct degradation pathways and their converging mechanical consequences provide a critical foundation for evaluating the long-term viability of vitrimers in demanding structural applications and for guiding the design of more durable, recyclable polymer systems.