PROCESS FOR REMOVING FLUORINATED EMULSIFIER FROM FLUOROPOLMER DISPERSIONS USING AN ANION-EXCHANGE RESIN AND A pH-DEPENDENT SURFACTANT AND FLUOROPOLYMER DISPERSIONS CONTAINING A pH-DEPENDENT SURFACTANT

Abstract

A process of reducing the amount of fluorinated emulsifiers in fluoropolymer dispersions by contacting the fluoropolymer dispersion with an anion exchange resin in the presence of a pH-dependent surfactant, and fluoropolymer dispersions containing the pH-dependent surfactant and uses thereof.

Description

[0001]The present invention relates to a process of reducing the amount of fluorinated emulsifier in fluoropolymer dispersions using anion exchange resins in the presence of one or more pH-dependent surfactants. The invention also relates to fluoropolymer dispersions containing the pH-dependent surfactants but containing no or only low amounts of fluorinated emulsifiers, and to uses of these dispersions.BACKGROUND[0002]Fluoropolymers, i.e. polymers having a fluorinated backbone, have been long known and used in a various applications because of their desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc. Various fluoropolymers are for example described in “Modern Fluoropolymers”, edited by John Scheirs (ed), Wiley Science 1997. The fluoropolymers may have a partially fluorinated backbone, generally at least 40% by weight fluorinated, or a fully fluorinated backbone. Particular examples of fluoropolymers include polytetrafluoroethylene (P...

AI Technical Summary

Benefits of technology

[0008]Additionally, there is a need to provide stable aqueous fluoropolymer dispersions containing no or only very low amounts of fluorinated surfactants allowing effective and easy coagulation of the fluoropolymer.

[0010]In the following there is provided a process for reducing the amount of fluorinated emulsifier in a fluoropolymer dispersion. The process comprising contacting the dispersion with an anion exchange resin in the presence of a pH-dependent surfactant. The pH-dependent surfactant attains either a cationic or a non-ionic form, depending on the pH of the dispersion in which it is present. The pH-dependent surfactant is capable of stabilising the dispersion when the surfactant is in its non-ionic form. The dispersion is contacted with the anion exchange resin at a pH at which the surfactant is in its non-ionic form.

Problems solved by technology

Fluorinated emulsifiers are generally expensive compounds and in several cases fluorinated emulsifiers have been found to be poorly biodegradable.

If the fluoropolymers can be collected from those poorly phase-separated mixtures at all, they typically contain rather large amounts of residual non-ionic surfactants and water, the presence of which impacts on the physical properties of coatings prepared from these poorly phase-separated fluoropolymers.

For example, due to the presence of the surfactants the fluoropolymer coating may adsorb water, for instance from ambient humidity, leading to poor properties as regards, for example, surface hardness, water resistance, self-lubrication or friction-resistance etc.

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