Deeper insight into hydrolysis mechanisms of polyester/cotton blended fabrics for separation by explicit solvent models

Abstract

Aiming to get a deeper and accurate understanding on separation of polyester/cotton blended fabrics in subcritical water, the hydrolysis mechanisms of cellulose and polyester were studied using dispersion-corrected density functional theory (DFT-D) method with and without explicit H₂O under the conductor-like screening model (COSMO) set. The number and locations of explicit H₂O were determined by their likely functions including being dissociation and solvent and catalyst. The calculations disclosed that explicit H₂O provide inductive activation on glycosidic bond of cellulose and ester groups at the center of polyester and the assistance on the transfer of proton as proton-carrier and as catalyst of proton shuttle, affecting the reaction and activation energies in a realistic manner. In addition, the number of explicit H₂O molecules functioning as catalyst of proton shuttle may also has a strong influence on catalytic activity. Based on the improved explicit solvation models, the overall activation energies of proposed hydrolysis mechanisms for cellulose and polyester are 14.81 and 21.46 kcal/mol respectively, which explains the preferential hydrolysis of cellulose from experimental results.

Keywords: Cellulose/PET hydrolysis mechanisms; Dispersion-corrected density functional theory; Explicit H(2)O.