Method for reducing fluorinated emulsifiers from aqueous fluoropolymer dispersions using sugar-based emulsifiers

Process for upconcentrating an aqueous dispersion of a fluoropolymer selected from the group consisting of a polytetrafluoroethylene homopolymer, a polytetrafluoroethylene copolymer, and combinations thereof;

• comprising
• providing the aqueous dispersion of the fluoropolymer and a fluorinated polyether emulsifier having the general formula:
• [Rf—O-L-A]M
• with L being a fully perfluorinated or partially fluorinated alkylene group, Rf being a partially or fully fluorinated alkyl group wherein the alkyl chain is interrupted by at least one ether oxygen atom, A represents an acid residue and M represents the counterion or combination of counterions for the acid group A including a proton;
• and
• heat treating the dispersion in the presence of from about 1 to about 15% by weight based on the fluoropolymer content of that dispersion of a sugar-based emulsifier, wherein such heat treating induces phase separation into
• an aqueous fluoropolymer-enriched dispersion having
• a first amount of the fluorinated polyether emulsifier and
• a first amount of the fluoropolymer;
• wherein the first amount of the fluorinated polyether emulsifier is no greater than 500 ppm and the first amount of the fluoropolymer is at least 40% by weight, based on the total weight of the aqueous fluoropolymer-enriched dispersion, and
• an aqueous fluoropolymer-depleted phase having
• a second amount of the fluorinated polyether emulsifier and
• a second amount of the fluoropolymer, and
• further wherein
• the first amount of the fluoropolymer in the fluoropolymer-enriched phase is greater than the second amount of the fluoropolymer in the fluoropolymer-depleted phase;
• and
• the second amount of the fluorinated polyether emulsifier in the aqueous fluoropolymer-depleted phase is greater than the first amount of the fluorinated polyether emulsifier in the aqueous fluoropolymer-depleted phase.