Relationship of Surface Hydrophilicity, Charge, and Roughness of PET Foils Stimulated by Incipient Alkaline Hydrolysis

Abstract

An enhancement of wettability of PET foils pretreated hydrolytically by immersing in mild alkaline (NaOH) solutions has been documented by a descending sigmoidal dependence between the interfacial free energy γSL of the PET/water interface and the concentration of NaOH solution cNaOH. An increase in temperature of the NaOH solution below the glass-transition temperature of PET further promotes the hydrophilicity, resulting in a proportional shift of the γSL vs cNaOH dependence. The limiting hydrophilicity of PET is thermodynamically predicted to occur at γSL → 0, corresponding to the advancing water contact angle θa ≈ 50° (for 6% NaOH and 60 °C). The surface roughness due to the partial hydrolytic degradation as well as the weight loss (dissolution) of PET are found to reach a maximum value just when the latter dependence goes through its inflection. Assuming a general parallelism between the interfacial free energy and the dissolution kinetics, we propose the hydrolytically stimulated formation and growt...