Sodium naphthalene etch

Sodium naphthalene etching or Tetra Etch for PTFE improves the surface roughness and creates unsaturated bonds, carbonyl and carboxyl groups. 

Treated with sodium naphthalene etch solution. 

MPa for various KEL-F resins treated with sodium naphthalene etch solutions and also abraded. 

Chemical surface treatments vary with the type of plastic being bonded. These processes can involve the use of corrosive and hazardous materials. The most common processes are sulfuric acid-sodium dichromate etch (polyolefins) and sodium-naphthalene etch (fluorocarbons). Both of these processes are described in ASTM D-2093. 

The combination of properties that makes fluorocarbons highly desirable engineering plastics also makes them nearly impossible to heat or solvent weld and very difficult to bond with adhesives without proper surface treatment. The most common surface preparation for fluorocarbons is a sodium naphthalene etch, which is believed to remove fluorine atoms from the surface to provide better wetting properties. A formulation and description of the sodium naphthalene process can be found in another chapter. Commercial chemical products for etching fluorocarbons are also listed. 

Epoxy-polyamide and epoxy-polysulfide adhesives have been used successfully for bonding properly treated polychlorotrifluoroethylene (PCTFE). An epoxy-polyamide adhesive (Epon 828/Versamid 125 60 40 ratio) cured for 16 h at room temperature followed by 4 h at 74°C has given tensile-shear strengths of 19.6—20.8 MPa for various grades of PCTFE resins treated with sodium naphthalene etch solutions and also abraded [28,29]. 

Teflon and other fluorocarbon surfaces may be altered by chemical treatments using solvent solutions of sodium naphthalene complex or molten sodium. Teflon etchants, for example, Tetra-Etch , a tradename and product of W. L. Gore Associates, are effective in improving adhesion to Teflon. Oxidation treatments for metals such as copper or aluminum also produce highly polar oxide surfaces that are more easily bondable. The reader is referred to several sources for a more comprehensive... 

The fluorocarbon surface may be made more wettable by exposing it for a brief moment to a hot flame to oxidize the snrface. The most satisfactory surface treatment is achieved by immersing the plastic in a sodium-naphthalene dispersion in tetrahydrofuran. This process is believed to remove fluorine atoms, leaving a carbonized surface that can be wet easily. Fluorocarbon films treated for adhesive bonding are available from most suppliers. A formulation and description of the sodium-naphthalene process may be found in Table 7.10 (p. 7.37). Commercial chemical prodncts for etching fluorocarbons are also listed. 

Polytetrafluoroethene (Teflon) is etched, giving an active surface which can then be bonded strongly to an epoxy resin. With a source of acidic hydrogen such as water or an alcohol, sodium naphthalene affords 1,4-dihydronaphthalene. Polymers with functional groups at each end of the chain ( telechelic polymers) can be made by polymerization of styrene with sodium naphthalene. The anionic radical which is produced in the initiation step dimerizes to a dianion containing two propagating centres. 

Commercial solutions of etchant do not contain ammonia or tetrahydrofuran for safety and health reasons. For example, Tetra-Etch contains 25% by weight of sodium-naphthalene complex and 75% of ethylene glycol dimethyl ether. Fluoro Etch (offered by Acton Technologies, Inc., Pittston, PA) contains about 30% sodium-naphthalene complex and 70% of an ethylene glycol solvent. Acton Technologies has reported successful use of both ethylene glycol dimethyl ether and diethylene glycol dimethyl ether as solvents.OO... 

The radicals produced may react with molecules of solvent, hydrocarbon, hydrocarbon anion or may dimerize. Reaction with methyl iodide and subsequent determination of iodide anion in the aqueous extract is a recommended method for analyzing compounds like sodium-naphthalene. The etching of polytetrafluorethylene is an interesting example of the reduction of halides an active surface is produced which is then able to form strong bonds to an epoxy resin. The reducing action of hydrocarbon anions has been used in the preparation of metal carbonyls. In this it is commonly convenient to start from the salt of a metal in a +2 or +3 oxidation state, which must be reduced to the zero oxidation state both sodium-naphthalene and aluminium alkyls have been used in this connection. 

Sodium is the most economical choice, but it must be handled with utmost care. There are two ways to prepare solutions of sodium. It can be dissolved in anhydrous liquid ammonia or made into a complex with naphthalene followed by dissolution in an ether such as tetrahydrofuran or dimethyl glycol ether. Special precautions must be taken while working with sodium etching solutions. Fluoropolymers surface-... 

Sodium Etching - Sodium etching is a process by which the surface of fluoropolymers is rendered adherable. During etching, the fluoropolymer surface is brought into contact with a sodium solution (1 1) in naphthalene dissolved in tet-rahydrofiiran or an anhydrous solution of sodium in liquid ammonia. 

Prebonding etch is needed to activate the perfluoro surface of PTFE before it can be bonded with adhesives. This is typically a solution of sodium in naphthalene, which is extremely alkaline. It puUs some fluorine atoms off the surface, or even carbonizes ifi leaving a surface which is more ready to accept adhesives such as epoxy resins. 

Fluorocarbons Polychloro- trifluoroe- thylene, polytetra- fluoro- ethylene, polyvinyl fluoride, polymono- chlorotri- fluoro- ethylene Trichloro- ethylene 1. Wipe vrith solvent and treat with the following for 15 min at RT Naphthalene (128 g) dissolved in tetrahydrof uran (11) to which is added sodium (23 g) during a stirring period of 2 h. Rinse in deionized water, and dry in water air Sodium-treated surfaces must not be abraded before use. Hazardous etching solutions requirii skillful handling. Proprietary etching solutions are... 

The most difficult-to-bond plastics family is polytetrafluoroethylene and the other fluori-nated polymers which are the Teflon-like materials. The widespread use of these polymers as coatings for cookware is, of course, based on this property of nonsticking. The conventional methods of etching which can be useful with other difificult-to-bond plastics, like polyethylene and polypropylene, simply do not work on these fluorinated polymer surfaces. Instead the surfaces must be treated with an exotic mixture of metallic sodium and naphthalene in tetrahydrofuran.( 37,i38) More recently, ionized gases (plasma treatment) have also been used successfully. Once treated the surfaces become bondable using conventional two-part liquid... 

The treatment for fluorocarbon polymers is usually based upon metallic sodium dissolved in a solution of naphthalene in a polar aprotic solvent such as tetrahydrofuran, although other etch treatments such as a solution of alkali metal in liquid ammonia [12] have been reported [13]. Details for the preparation of the treatment solutions have been published [14] and solutions of sodium naphthalenide are commercially available, e.g. under the trade name Tetraetch from W. L. Gore Associates Inc. These commercial pretreatments are relatively easy and safe to operate and widely used in industry. Also, it is possible to purchase fluorocarbon polymers already treated by such chemical processes. 

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