Fluorination of polyhydrofluoroethylenes. II. Formation of perfluoroalkyl carboxylic acids on the surface region of poly(vinylidene fluoride) film by oxyfluorination, fluorination, and hydrolysis

Abstract

SynopsisOxyfluorination and postfluorination behaviors of poly(viny1idene fluoride) films, as well as hydrolysis of the films treated so far, have been studied by infrared (IR) spectrometry. By exposing the polymer film to a mixture of oxygen and fluorine at about 90°C acyl fluoride groups attendant on the scission of the polymer chains were formed. The oxyfluorinated molecules could be further perfluorinated with fluorine alone at about 90°C, leaving many of the acyl fluoride groups. When the properly oxyfluorinated and postfluorinated film was further treated with a hot 6M sodium hydroxide solution the opaque layer of perfluoroalkyl sodium carboxylate of high molecular weight was formed on the surface of the film, to about 3 pm in thickness, which behaved as a cation exchanger. This new type of cation exchanger of perfluoroalkyl carboxylic acid was significantly more acidic than the usual methacrylic acid exchanger. It was able to adsorb the sodium ions from a neutral sodium chloride solution up to about 70% of the exchange capacity and to keep the ions stable while washing them with water, though it could be regenerated to the hydrogen form with a dilute acetic acid solution. The nature of the new ion exchanger has been examined in some detail by IR spectrometry with Li+, Na+, and Cs+ ions.

Effect of non-solvent additives on the structure and performance of PVDF hollow fiber membrane contactor for CO2 stripping

“…The chemical stability of PVDF membrane is of particular concern as the polymer showed less tolerance to strong base solutions, esters and ketones [46]. This may be due to several degradation effects such as dehydrofluorination in polymer chain [47], chemical attack of sodium hydroxide in a conformation and discoloration upon immersion in sodium hydroxide solution [48]. Therefore, since diethanolamine is classified as a base solution, it was anticipated that deterioration of membrane performance which occurs after 10 h of operation is due to degradation of PVDF membrane with high temperature amine solution.…”

Effect of chemical cleaning conditions on the flux recovery of MF membrane as pretreatment of seawater desalination

“…Normally, chemical cleaning operated at pH higher than 12 which could damage the PVDF membrane. However, to investigate the effect of pH at harsh conditions, the experiment was still conducted even if the pH of the solution exceeds pH 12 [30][31][32].…”

Development of Anti-fouling Piezoelectric Polyvinylidene Fluoride Membrane

“…This would become an issue of concern where PVDF membranes are used in applications that are often exposed to strong alkaline solutions or chemical cleaning involving alkaline solutions. The poor chemical stability of PVDF in alkaline solution was reported in several early studies (Komaki, 1979;Shinohara, 1979;Nguyen, 1985). The darkening of oxyfluorinated PVDF was observed by Shinohara (1979) upon hot alkaline treatment.…”