Hypochlorite Cleaning Causes Degradation of Polymer Membranes |
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Authors: | Elizabeth Arkhangelsky Denis Kuzmenko Norm V Gitis Michael Vinogradov Suresh Kuiry Vitaly Gitis |
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Affiliation: | (1) Unit of Environmental Engineering, Ben-Gurion University of the Negev, PO Box 653, Beer-Sheva, 84105, Israel;(2) Center for Tribology, 1715 Dell Avenue, Campbell, CA 95008, USA |
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Abstract: | Polymer membranes are often used in water treatment industry, as a reliable economic solution for purification of surface
water streams. Among a variety of membrane processes the ultrafiltration (UF) membranes combine high pathogen removal ability
with minimal energy consumption. Since the membranes are considered to be chemically and mechanically stable, in-place cleaning
is routinely performed with strong oxidizing agents, such as hypochlorite. The results of the current study, however, clearly
indicate that the mechanical strength of UF membranes deteriorates upon hypochlorite cleaning. Values of ultimate tensile
strength, ultimate elongation and Young’s modulus decreased as the dose (concentration × contact time) of hypochlorite was
increased, with the decreases being more marked for cellulose acetate membranes than for polyethersulfone membranes. Scanning
probe microscopy showed membrane aging in response to hypochlorite treatment. The aging was related to gradual chain breaking
in membrane skin layer, as reflected by the disappearance of O–C–O and C–S absorbance peaks in ATR-FTIR spectra of treated
cellulose acetate and polyethersulfone membranes, respectively. Since the degree of scission was linearly related to the deterioration
in ultimate tensile strength, we here propose that ultimate tensile strength measurements can be used as a simple macroscopic
test for periodic inspection of the degree of degradation of UF membranes exposed to in-place chemical cleaning. |
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Keywords: | Cellulose acetate Hypochlorite Polyethersulfone Stress– strain diagram Ultimate elongation Young’ s modulus |
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