Adhesive surface sodium treatment

The pre-treatment of a filler surface changes fhe interface, and thus it is expected to affect the properties of adjacent phases extending some way into the bulk. There are examples of using the various surface modifiers such are acids and acid precursors, alkoxysilanes, organofitanates and related compounds, stearic acid and others." How the surface pre-treatment of CaCOs filler by sodium stearate changed fhe adhesion parameters in the PVAc composite is illustrated in Table 1 The adhesion parameters could be used to relate the interactions at the interface to the mechanical properties of the composite. For example, the small absolute decreases in the work of adhesion after the pre-treatment can lead to the proportionate large absolute decreases in fracture energy. 

The fluoropol)mier needs to be in the solution for a brief duration ranging from 2-10 seconds.1 1 Ammonia rapidly volatilizes after the article is removed from the bath. Sodium can be removed by dipping the treated article into ethyl alcohol. Too long of an immersion time actually weakens the adhesive bond. The optimum time depends on the freshness ofthe etching solution. The treated fluoropolymer has a shiny dark brown color, which grows into a dull brown after exposure to air. Analysis of the baths shows the presence of fluoride and/or chloride ions suggesting defluorination and/or dechlorination of the surface during treatment (Table 14.1). 

Recently, acidified sodium hypochlorite solutions containing l-octyl-2-pyrrolidone as wetting agent have been successfully used for the treatment of TR rubber soles (Cepeda-Jimlnez et al. 2003a). The improved adhesion is due to improved wettability and creation of chlorine moieties on the rubber surface. The treatment is restricted to about 1 pm depth surface of TR rubber. Furthermore, aqueous solutions of sodium dichloroisocyanurate (DCI) (O Fig. 51.4) have been recently used to increase the adhesion of TR rubber soles (Cepeda-Jimenez et al. 2002). The chemical structure of DCI is somewhat similar to that of TCI and relatively concentrated DCI water solutions are necessary to obtain good peel strength values. 

The anodized surface is often subjected to additional treatment before the radiation-sensitive coating is appHed. The use of aqueous sodium siUcate is well known and is claimed to improve the adhesion of diazo-based compositions ia particular (62), to reduce aluminum metal-catalyzed degradation of the coating, and to assist ia release after exposure and on development. Poly(viQyl phosphonic acid) (63) and copolymers (64) are also used. SiUcate is normally employed for negative-workiag coatings but rarely for positive ones. The latter are reported (65) to benefit from the use of potassium flu o r o zirc onate. 

The chemical resistance of PTFE is exceptional. There are no solvents and it is attacked at room temperature only by molten alkali metals and in some cases by fluorine. Treatment with a solution of sodium metal in liquid ammonia will sufficiently alter the surface of a PTFE sample to enable it to be cemented to other materials using epoxide resin adhesives. 

Figure 9 shows a relationship between JTl and JTsc,ov for all salts. Any relationship between them is not clear on the whole. However, inversely proportional relationships are slightly observed for each group of barium salts and sodium salts. Considering such experimental result, it may be supposed that the adhesion force of remained clusters is controlled by more strong factors, such as a crack of the surface of nucleation agent occurred by the solid inclusion during the activation treatment. 

Metal ions that diffuse to the surface react with atmospheric gases to form hydroxides in a thin layer of high pH [36]. Fowkes improved adhesion of a basic polymer to glass with an acid wash [6, 7] a similar treatment also improved adhesion to epoxy [37], an acidic polymer. The former effect was attributed to replacement of sodium silicate with silanols by ion exchange the latter may result from removing a corrosive layer of metal hydroxides from the interface. IGC and PTD measurements in this study demonstrate a measurable basicity on bare fibers, which other investigators also noted [6,14,17],... 

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. 

---