---
kind: "section"
citation: "21 C.F.R. § 173.21"
title: "21"
number: "173.21"
heading: "Perfluorinated ion exchange membranes."
url: "https://uscodex.org/cfr/21/173.21"
---

# §173.21. Perfluorinated ion exchange membranes.


Substances identified in [paragraph (a)](#a) of this section may be safely used as ion exchange membranes intended for use in the treatment of bulk quantities of liquid food under the following prescribed conditions:

- (a) **Identity.** The membrane is a copolymer of ethanesulfonyl fluoride, 2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, with tetrafluoroethylene that has been subsequently treated to hydrolyze the sulfonyl fluoride group to the sulfonic acid. The Chemical Abstracts Service name of this polymer is ethanesulfonic acid, 2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-, polymer with tetrafluoroethane (CAS Reg. No. 31175-20-9).
- (b) **Optional adjuvant substances.** The basic polymer identified in [paragraph (a)](#a) of this section may contain optional adjuvant substances required in the production of such basic polymer. These optional adjuvant substances may include substances used in accordance with [§ 174.5](/cfr/21/174.5.md) of this chapter.
- (c) **Conditions of use.**
  - (1) Perfluorinated ion exchange membranes described in [paragraph (a)](#a) of this section may be used in contact with all types of liquid foods at temperatures not exceeding 70° (158 °F).
  - (2) Maximum thickness of the copolymer membrane is 0.007 inch (0.017 centimeter).
  - (3) Perfluorinated ion exchange membranes shall be maintained in a sanitary manner in accordance with current good manufacturing practice so as to prevent microbial adulteration of food.
  - (4) To assure their safe use, perfluorinated ionomer membranes shall be thoroughly cleaned prior to their first use in accordance with current good manufacturing practice.

## Notes

### Amendments

[59 FR 15623, Apr. 4, 1994]

### Authority

Authority: 21 U.S.C. 321, 342, 348.

### Source

Source: 42 FR 14526, Mar. 15, 1977, unless otherwise noted.

### Amendments

[59 FR 15623, Apr. 4, 1994]