Micromechanical modelling of biodegradable semi-crystalline polymers: The evolution of anisotropic mechanical properties during degradation

The mechanical properties of biodegradable polymers are strongly linked to molecular weight and crystallinity. In this study, our modelling approach is used to relate changes in physical properties (molecular weight, crystalline volume fraction and porosity) of a semi-crystalline PLLA during degradation to macroscopic mechanical properties (modulus). We create a database of mechanical behaviour based on possible values of these properties, which is then queried to quickly predict the modulus without the need for multiscale approaches. Initially, the semi-crystalline polymer is considered as an ensemble of crystalline amorphous regions with no preferential direction. In subsequent simulations, the effect of anisotropy is investigated by considering various orientations and dispersions of the crystalline phase. Theoretical bounds were calculated and compared to simulations and published data. The database of mechanical behaviour was modified to capture the emergence of porosity during degradation. These predictions are compared against previously published experimental values of Young's modulus for PLLA (Poly (L-lactide)) during degradation with good agreement. These simulations also provide insight into the transition to brittle behaviour during degradation.