# US 8,785,516 B2 · Fluoropolymer dispersion treatment employing ultraviolet light and oxygen source to reduce fluoropolymer resin discoloration

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- Number: US 8,785,516 B2
- Document ID: US8785516B2
- Status: Granted
- Kind: B2
- Application number: 13/875,316
- Filed: 2013-05-02
- Published: 2013-11-14
- Granted: 2014-07-22
- Earliest claimed: 2012-05-09
- Assignees: E. I. Du Pont de Nemours and Company
- Applicants: E I du Pont de Nemours and Company
- Inventors: Paul Douglas Brothers; Gregory Allen Chapman; Subhash Vishnu Gangal; Dipti Dilip Khasnis; Adam Paul Smith
- Web page: https://patentgrep.com/patent/US8785516B2

## CPC

- B01J 19/123: {Ultraviolet light}
- C08F 6/006: {Removal of residual monomers by chemical reaction, e.g. scavenging}
- C08F 8/06: Oxidation
- C08F 114/26: Tetrafluoroethene
- C08F 214/262: {with fluorinated vinyl ethers}
- C08J 3/28: Treatment by wave energy or particle radiation
- C08F 2800/20: as weight or mass percentages
- C08J 2327/18: Homopolymers or copolymers of tetrafluoroethylene
- B01J: CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- C08F: MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08J: WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H (working, e.g. shaping, of plastics B29)

## Abstract

Process for reducing thermally induced discoloration of fluoropolymer resin produced by polymerizing fluoromonomer in an aqueous dispersion medium to form aqueous fluoropolymer dispersion and isolating said fluoropolymer from said aqueous medium to obtain said fluoropolymer resin. The process comprises exposing the aqueous fluoropolymer dispersion to ultraviolet light in the presence of an oxygen source.

## Claims

### Claim 1

Process for reducing thermally induced discoloration of fluoropolymer resin, said fluoropolymer resin produced by polymerizing fluoromonomer in an aqueous dispersion medium to form aqueous fluoropolymer dispersion and isolating said fluoropolymer from said aqueous medium to obtain said fluoropolymer resin, said process comprising:
exposing the aqueous fluoropolymer dispersion to ultraviolet light in the presence of an oxygen source, wherein said aqueous fluoropolymer dispersion contains hydrocarbon surfactant which causes said thermally induced discoloration.

### Claim 2 (depends on 1)

The process of claim 1 wherein said process reduces thermally induced discoloration by at least about 10% as measured by % change in L* on the CIELAB color scale.

### Claim 3 (depends on 1)

The process of claim 1 wherein said fluoropolymer dispersion is polymerized in the presence of hydrocarbon surfactant.

### Claim 4 (depends on 1)

The process of claim 1 wherein said oxygen source is selected from the group consisting of air, oxygen rich gas, ozone containing gas and hydrogen peroxide.

### Claim 5 (depends on 1)

The process of claim 1 wherein said oxygen source comprises ozone containing gas.

### Claim 6 (depends on 1)

The process of claim 1 wherein said oxygen source comprises hydrogen peroxide.

### Claim 7 (depends on 1)

The process of claim 1 wherein the solids content of said dispersion during said exposing to ultraviolet light is about 2 weight % to about 30 weight %.

### Claim 8 (depends on 1)

The process of claim 1 wherein said ultraviolet light has a wavelength in the UVC band.

### Claim 9 (depends on 1)

The process of claim 1 wherein said exposing the aqueous fluoropolymer dispersion to ultraviolet light in the presence of an oxygen source is carried out at a temperature of about 5° C. to about 70° C.

### Claim 10 (depends on 1)

The process of claim 1 wherein the fluoropolymer resin has an initial thermally induced discoloration value (L*i) at least 4 L units on the CIELAB color scale below the L* value of equivalent fluoropolymer resin of commercial quality manufactured using ammonium perfluorooctanoate fluorosurfactant.

### Claim 11 (depends on 1)

The process of claim 1 wherein said hydrocarbon surfactant is selected from anionic surfactants represented by the formula R-L-M wherein R is preferably a straight chain alkyl group containing from 6 to 17 carbon atoms, L is selected from the group consisting of —ArSO3−, —SO3−, —SO4−, —PO3−, —PO4− and —COO−, wherein —ArSO3− represents aryl sulfonate, and M is a univalent cation selected from H+, Na+, K+ and NH4+.