§ 173.21 Perfluorinated ion exchange membranes.
Substances identified in paragraph （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） 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 of this chapter.
（c） Conditions of use. （1） Perfluorinated ion exchange membranes described in paragraph （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.
[59 FR 15623, Apr. 4, 1994]
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