Comparative Degradation Kinetics Study of Polyamide Thin Films in Aqueous Solutions of Chlorine and Peracetic Acid Using Quartz Crystal Microbalance

Polyamide thin film composite membranes are widely used in water reclamation. Peracetic acid (PAA) is an emerging wastewater disinfectant with a potential for membrane cleaning and disinfection; however, its interaction with polyamide remains poorly understood. This study employs quartz crystal microbalance with dissipation (QCM-D) to determine the PAA-induced degradation kinetics of polyamide thin films, in comparison with the conventional disinfectant-free chlorine (HOCl). Polyamide films showed a sorption phase followed by a degradation phase when exposed to PAA (1000 mg L^-1) and HOCl (100 mg L^-1) solutions. While the sorption phase in HOCl experiments was short (1.4-3.5 min) and followed a Boltzmann-sigmoidal model, it spanned over 3-33 h in PAA experiments and displayed a two-stage behavior. The latter kinetics are attributed to sequential processes of the physical sorption of PAA in polyamide films followed by PAA-induced polyamide oxidation. In the degradation phase, the HOCl-exposed films followed a rapid, two-step exponential decay reaching an equilibrium mass of ∼50% of the initial (wet) mass after ∼5 h of exposure. In contrast, the PAA-exposed films followed a Boltzmann-sigmoidal decay, with ∼80% of the initial (wet) mass remaining intact after >10 h of exposure. Fast force maps generated using atomic force microscopy showed a progressive increase in the morphological heterogeneity of the polyamide films in HOCl solution due to pitting, cracking, bulging, and eventual delamination under both flow and no-flow conditions. In contrast, PAA only formed small pits on the polyamide film under flow; in a stagnant PAA solution, the film had no visible changes even after ∼148 h of exposure. This is the first comparative study on the chemical and morphological changes in polyamide films induced by PAA and HOCl. The much higher compatibility of polyamide with PAA than with chlorine supports the potential of PAA being used as a halogen-free membrane cleaning/disinfecting agent.