Abstract
In water treatment process ozone is applied to disinfection and to remove organic pollutants. Membrane contactor devices are used as a physical barrier to separate two fluids without phase dispersion and it can be used to improve the ozonation efficiency. Polymeric materials are used in membrane contactors and they can react with ozone, suffering degradation and losing its mechanical properties. In this work, commercial polymeric membranes were selected to investigate their interaction with ozone in gaseous phase. It was evaluated changes in polymer structures and in membrane morphology by FTIR, DSC, TGA and SEM. It was observed preferential ozone attack to double carbon-carbon bonds in the main polymer chain for polyimide and polysulphone membranes. Polypropylene has single carbon-carbon bonds and its reaction with ozone was less intensive. For polydimethylsiloxane membranes the ozone attack seems to occur in the carbon-silicon bond, leading to loss of mechanical and thermal properties.
Highlights
Ozone is a gas of triatomic oxygen molecule with great oxidative power, characteristic odor and colorless, and it can react with a number of organic compounds
Many authors proposed a variety of ozonolysis mechanism in the last century[6], the ozonolysis mechanism proposed by Criegee[7,8,9,10] is the one currently used, where polymers with double carbon-carbon bonds in the main chain can react with ozone
Scanning Electron Microscopy (SEM), TGA, DSC, and FTIR analysis were used to characterize the samples and identify modifications that would be occurred by the oxidation process of the polymeric membranes, helping in the elucidation of ozone attack
Summary
Ozone is a gas of triatomic oxygen molecule with great oxidative power, characteristic odor and colorless, and it can react with a number of organic compounds. Many authors proposed a variety of ozonolysis mechanism in the last century[6], the ozonolysis mechanism proposed by Criegee[7,8,9,10] is the one currently used, where polymers with double carbon-carbon bonds in the main chain can react with ozone In this mechanism, an ozone molecule attacks a double bond of carbons in a dipolar cycloaddition process forming an unstable primary ozonide (molozonide). The molozinide cleaves the bond to form a carbonyl oxide (zwitterions) and a carbonyl compound Both generated molecules can be recombined creating a secondary ozonide, a trioxolane ring[11,12]. This work investigated the ozone resistance of polydimethylsiloxane, polypropylene, polytetrafluoroethylene, polyvinylidenefluoride, polyetherimide and polyethersulfone These polymers are frequently used in membrane contactors
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