Predicting how polymers age far from equilibrium

Glassy polymers, even deep in the glassy state, are characterized by slow molecular rearrangements able to macroscopically reduce their volume. This relaxation phenomenon, known as physical aging, significantly alter material properties over time, in inert storage conditions. While current frameworks can satisfactorily reproduce the aging kinetics after small perturbations [1], they often fail to describe how polymers age in conditions similar to those of industrial processing [2], that is, after large temperature variations occurring within short intervals of time. By analysing the evolution of thermal barriers in glasses, we developed a model that predicts aging behaviour far from equilibrium across various temperatures and processing conditions. Our approach, requiring at most the outcome of just a single aging experiment, can predict the timescale at which materials start aging, even well below the glass transition temperature. These results provide new insight on the equilibration pathways of polymers and provide a framework to predict material performance under nonequilibrium condition where the structural relaxation requires geological times.

[1] B. Riechers et al. Sci. Adv. 8, eabl9809 (2022)

[2] V. Di Lisio et al., J. Chem. Phys. 159, 064505 (2023)