Concentrated fluoropolymer dispersions stabilized with anionic polyelectrolyte dispersing agents
View Patent ↗An aqueous fluoropolymer dispersion comprising fluoropolymer particles having an average particle size of about 10 to about 400 nm. The dispersion has a solids content of at least about 35 to about 70 wt % and comprises about 0.03 wt % to about 10 wt % anionic polyelectrolyte dispersing agent based on the weight of fluoropolymer solids. The dispersion has a Gel Time of at least about 100 seconds.
1. A process for reducing the fluorosurfactant content of and concentrating an aqueous fluorosurfactant-containing fluoropolymer dispersion comprising:
stabilizing fluoropolymer dispersion comprising fluoropolymer particles having an average size of about 10 to about 400 nm and a solids content of about 15 to about 55 wt % with anionic polyelectrolyte dispersing agent;
contacting said stabilized fluorosurfactant-containing aqueous fluoropolymer dispersion with an anion exchange resin to reduce fluorosurfactant content to a predetermined level;
separating said anion exchange resin from said dispersion after the fluorosurfactant content has been reduced to produce a reduced-fluorosurfactant dispersion; and
concentrating said dispersion to at least about 35% by weight using a method which produces dispersion substantially free of nonionic surfactants; wherein said concentrated reduced fluorosurfactant dispersion comprises less than about 300 ppm fluorosurfactant.
2. The process of claim 1 wherein said concentrating is performed by adding acrylic polymer of acid content of 20% or more by weight to said reduced-fluorosurfactant dispersion in an amount of about 0.01 to about 1 wt % based on aqueous content of said dispersion and subjecting said dispersion to conditions causing said dispersion to separate into a lower phase high in fluoropolymer solids and an upper phase low in fluoropolymer solids and recovering said lower phase as concentrated reduced fluorosurfactant dispersion.
3. The process of claim 2 wherein the pH of said stabilized fluoropolymer dispersion is at least about 6 when said adding of acrylic polymer of acid content of 20% or more is performed.
4. The process of claim 2 wherein the pH of said stabilized fluoropolymer dispersion is at least about 9 when said adding of acrylic polymer of acid content of 20% or more is performed.
5. The process of claim 2 wherein the pH of said stabilized fluoropolymer dispersion is at least about 9.5 when said adding of acrylic polymer of acid content of 20% or more is performed.
6. The process of claim 1 wherein said concentrating is performed by electrodecantation.
7. The process of claim 1 wherein said concentrated reduced fluorosurfactant dispersion recovered has a solids content of about 35 to about 70 wt %.