The hydrolysis mechanism of polyglycolic acid under tensile mechanical loading: a density functional theory study

Abstract

The hydrolysis mechanisms of polyglycolic acid (PGA) under tensile mechanical loading were studied by the density functional theory (DFT) calculations for illustrating the enhancement of PGA hydrolysis by external mechanical loading found in previous experimental studies (Iran. Polym. J., 2008, 17(9), 691–701). Before the hydrolysis degradation begins, PGA firstly forms the PGA hydrolysis intermediate by combining one water molecule at the carbonyl carbon and then the C–O alkyl bond is ruptured after the hydrogen atom transfers from the carbonyl oxygen to the alkyl oxygen. Consequently, the effects of tensile forces imposed on the PGA and PGA intermediate were both studied. The variations of bending angle, torsion angle, and bond length as well as the electronic properties of PGA and its intermediate at different strains were presented. From the force–strain profiles of PGA and the PGA intermediate, the tensile force on the PGA can be relaxed once the PGA forms the PGA intermediate, leading to the stabilization of the PGA material under external mechanical loading. After the calculation using the nudged-elastic band (NEB) method, the results reveal that the energy barrier for the dissociation of the PGA intermediate into two PGA molecules significantly decreases under increasing force, which induces PGA hydrolysis. Our DFT calculation results have provided a clear explanation for the experimental observation, where the mechanical loading enhances the PGA degradation rate.