Sodium etch

Meier, J. F., and Petrie, E. M., The Effect of Ultraviolet Radiation on Sodium Etched Polytetrafluoroethylene Bonded to Polyurethane Elastomer, Journal of Applied Polymer Science, vol. 17,1973, pp. 1007-1017. 

D.W. Dwight, W.M. Riggs, J. Colloid Interface Set 47 (1974) 650 (a) control, (b) Na/NHg sodium-etched surface, (c) melted polymer reciystallized against a gold substrate.. 

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-... 

Table 7.2 shows the effect of sodium etching on several fluoropolymers by Tetra-Etch on the surface composition and lap shear bond strength. In general, the data for various fluoropolymers indicate an increase in the adhesive bond strength with increasing fluorine and chlorine content. Kinetics of treatment is more favorable to perfluorinated PTFE than PVF that contains one fluorine per monomer unit according to the data in Table 7.2. 

Table 7.1. Effect of Sodium Etching on the Surface Compostiiton and Adhesion Bond Strength of Fluoropolymers ...

Plasma treatment is a dry process that does not utilize solvents and generates little waste compared to sodium etching. It is a more expensive process due... 

Fig 10.34) indicate that the PTFE surface is comprised of only carbon and fluorine. The energy shift can be curve-fitted by trial and error to determine the functional groups on the surface. The most simplified report that ESCA generates is the atomic composition of the surface elements with the exception of hydrogen. A helpful tool for investigating surface changes of a polymer is the ratio of other elements to carbon. Table 10.9 shows the effect of sodium etching on the surface composition of a few different fluo-ropolymers. 

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. 

Sodium etch Sodium hydroxide Sanitizing melamine or urea polymer, polyolefin, polyethylene oxide, polystyrene, polysulfone, and styrene-acrylonitrile (SAN) Fluoroplastics and some polyesters Polystyrene, polyesters, polyamide, and polysulfone Homopolymer polyacetal Developed by... 

Sodium etching is an extreme treatment technique that is suitable for surfaces that are very difficult to treat. Examples include fluoropolymers and thermoplastic polyesters. 

Dental ceramics consist mainly of metal oxides of silicon, aluminum, potassium, and sodium. Etching with an aqueous solution ofhydroflnoric acid roughens the ceramic surface. 

Table 14.3 contains data that compares the results of plasma treatment and sodium etching for four fluo-ropolymers. Peel strengths of untreated and treated samples were measured by bonding them into T-peel specimen using the flexibilized epoxy adhesive Scotch-Weld 3553 (available from 3M Corp.). The laminates were cured for several hours at 70°C and peel tested at 12.5 cm/min pull rate. Polytetrafluoroethylene does not accept plasma treatment as well as PEA and FEP, as indicated by its relatively low peel strength. Sodium etching is the only effective method of modifying the surface of PTFE. 

Surface preparation of fluoroplastics can be achieved by a number of methods.h i] The plastic surface can be roughened by blasting with water. Other methods include corona bombardment, cross-linking by activated inert gas species, molten metal alloy treatment, sodium hydride treatment, and sodium etching. The treated layer is at most 1 pm thick and does not alter the bulk properties of the fluoroplastic. Surface... 

Fluoroplastic films such as FEP can be metallized by vacuum deposition. Metal adhesion is enhanced if the surface has been treated for adhesion by sodium etching or other procedures. Untreated general purpose FEP film may be vacuum-metallized for some applications depending upon the specific metal and deposition process. Copper, aluminum, silver, gold, and some metallic oxides have been applied to FEP film by vacuum metallization.f ]... 

Plasma treatment does not impart sufficiently strong adhesive bonds in PTFE, the most common perfluoropolymer. Bond strengfli of plasma-treated PTFE is at best 60% of that obtained by sodium etching." ... 

Perfluorinated fluoroplastics are chemically unaffected by nearly all commercial chemicals. An exception is highly oxidizing substances such as element forms of sodium, potassium, and other alkaline metals. This is the basis for sodium etching of fluoroplastic parts, which is described in this section. 

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