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Membrane Water Treatment
  Volume 3, Number 3, July 2012 , pages 169-179

Modification of polyamide reverse osmosis membranes seeking for better resistance to oxidizing agents
Lucinda F. Silva, Ricardo C. Michel and Cristiano P. Borges

    One of the major limitations in the use of commercial aromatic polyamide thin film composite (TFC) reverse osmosis (RO) membranes is to maintain high performance over a long period of operation, due to the sensitivity of polyamide (PA) skin layer to oxidizing agents, such as chlorine, even at very low concentrations in feed water. This article reports surface modification of a commercial TFC RO membrane (BW30-Dow Filmtec) by covering it with a thin film of poly(vinyl alcohol) (PVA) crosslinked with glutaraldehyde (GA) to improve its resistance to chlorine. Crosslinking reaction was carried out at 25 and 40oC by using PVA 1.0 wt.% solutions at different GA/PVA mass ratio, namely 0.0022, 0.0043 and 0.013. Water swelling measurements indicated a maximum crosslinking density for PVA films prepared at 40oC and GA/PVA 0.0043. ATR-FTIR and TGA analysis confirmed the reaction between GA and PVA. SEM images of the original and modified membranes were used to evaluate the surface coating. Chlorine resistance of original and modified membranes was evaluated by exposing it to an oxidant solution (NaClO 300 mg/L, NaCl 2,000 mg/L, pH 9.5) and measuring water permeability and salt rejection during more than 100 h period. The surface modification effectively was demonstrated by increasing the chlorine resistance of PA commercial membrane from 1,000 ppm.h to more than 15.000 ppm.h.
Key Words
    reverse osmosis; polyamide active layer; surface modification; chlorine resistance; poly(vinyl alcohol)
Lucinda F. Silva and Ricardo C. Michel : IMA/UFRJ, Federal University of Rio de Janeiro, 21941-598, Rio de Janeiro, RJ, Brazil
Cristiano P. Borges : PEQ/COPPE/UFRJ, Federal University of Rio de Janeiro, 21941-970, Rio de Janeiro, RJ, Brazil

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