Adhesion to Sodium Naphthalenide Treated Fluoropolymers. Part II. Effects of Treatment Conditions and Fluoropolymer Structure

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Abstract
Films of polytetrafluoroethylene (PTFE) and perfluorinated copolymers (PFA and FEP), with a range of fabrication histories, were exposed to sodium naphthalenide (Na/naphth) etchant so as to defluorinate the surface for improved wettability, and hence adhesion. The depth of defluorination was measured gravimetrically and the nature of the chemical functionalities determined spectroscopically. For smooth films, the fluoropolymer type and crystallinity had little effect on the defluorination process. Surface area was the major variable affecting defluorination rate, although the presence of surface defects and deformation in skived films also increased the rate of defluorination. For all but the skived PTFE, there was little change in surface texture either after defluorination or subsequent stripping of the defluorinated layer by an acid etch. Acid stripping of the defluorinated layer on skived PTFE left a porous surface texture. The chemical nature of the surface could be changed by modifying the post-etch treatment of the specimen, for example by modifying the rinse procedure and the storage history of the specimen before the adhesive bond is made.