Supplementary material from "A multiple natural configuration framework for hydrolytic degradation in biodegradable polymers"
We developed a chemo-mechanical constitutive framework to model the response of viscoelastic biodegradable polymers undergoing hydrolysis. The framework integrates time-dependent fluid diffusion, scission kinetics with autocatalysis, monomer transport, volume changes and viscoelastic deformation. The framework is based on a multiple natural configuration theory that captures the continuous transformation of polymer networks from long-chain macromolecules to monomers, thereby enabling relaxation in the polymer owing to scission. Additionally, the model incorporates stress relaxation owing to the molecular network realignments (viscoelastic response) that evolve alongside the scission process. With the proposed framework, we study the intertwining among the multiple mechanisms that come into play during hydrolysis. We then use the framework to further explore the influence of geometrical features and boundary conditions of polymer solids on the biodegradation process that leads to the formation of residual stress and shape distortion (permanent set). The modelling framework is also capable of describing multiple physical mechanisms that are observed in experiments, such as multiple stress relaxation and the conversion of homogenous into heterogeneous polymers as they degrade.