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 γ SL of the PET/water interface and the concentration of NaOH solution c NaOH . 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 γ SL vs c NaOH dependence. The limiting hydrophilicity of PET is thermodynamically predicted to occur at γ SL f 0, corresponding to the advancing water contact angle θ a ≈ 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 growth of pits on the PET surface to cause the initial acceleration as well as subsequent retardation of dissolution as c NaOH increases, leading to the S-shaped γ SL vs c NaOH dependence with the inflection for a specific c NaOH . Moreover, the zeta potential measured by the streaming current method also attains a maximum at the same specific concentration of NaOH. It would indicate that the largest amount of electric charges is populated via polar carboxyl and hydroxyl groups created by chemical scissions of PET polymer chains when a change in the dissolution rate increases to the utmost. In such a way, partial hydrolysis restricted to the uppermost part of moderately hydrophobic surface of solid PET allowed us to better understand the intermingled role of thermodynamic and physical aspects in surface wettability itself.

Electrokinetic Potential and Other Surface Properties of Polymer Foils and Their Modifications

“…1) due to the pH dependence mentioned above. Zeta potential for PET was determined [50] to be about -40 mV (only approximate estimation from figure [50]) using the same instrument as we used (the same cell, electrolyte, concentration, pH=6), this value agrees well with the present one of -54.7 mV, obtained for pH=6.2. Some polymers inclusive PC and PS have also been measured in 0.001 mol/dm 3 KCl, but in different analyser [51] and the data are not comparable with present ones.…”

“…1, at these polymers are different difference between zeta potential determined and calculated by both of methods and equations. Possible explanation could be found in our previous study [50] and it can be connected with oxygen containing molecular segments oriented toward the polymer bulk and also with surface roughness.…”

Prewetting Induced Hydrophilicity to Augment Photocatalytic Activity of Nanocalcite @ Polyester Fabric

“…On acid prewetting of nanocalcite @ PF, the surface roughness due to kinks and corners appeared (Figure 4c). Similar results were obtained by other researchers on acid prewetting [53]. Upon basic prewetting surface roughness increased causing the appearance of fluffy and eroded boundaries of discs (Figure 4d).…”

Facile Preparation of Hydrophobic PET Surfaces by Solvent Induced Crystallization

“…This suggests, as it could also be intuited in the SEM micrographs, that, during the treatment, NaOH not only removes the skin by dissolution but also affects the underlying particulate substrate. Hydrolytic degradation by the effect of NaOH on PET flat foils has been seen to induce a slight increase in surface roughness parameters, which has been explained by the dissolution of hydrolysis reaction products [35]. This sample also is more scattered in all the roughness parameters compared to the sample in which the skin was removed by acetone spraying, Q-PET-DA.…”