Plastics sulfuric acid dichromate etch

Sulfuric acid-dichromate is the most commonly applied chemical etching treatment for many plastics. There are few hard rules to determine the composition of this treatment media, although ranges can be found (Table 3.3). The exact formulation should be determined by testing the adhesive bond strength for any given plastic. Combinations of chromic acid, sulfuric acid, and phosphoric acid have been successfully used. "... 

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. 

Epoxy and nitrile-phenolic adhesives have been used to bond these plastics after surface preparation. The surface can be etched with a sodium sulfuric-dichromate acid solution at elevated temperature. Flame treatment and corona discharge have also been used. However, plasma treatment has proven to be the optimal surface process for these materials. Shear strengths in excess of 3000 Ib/in have been reported on polyethylene treated for 10 min in an oxygen plasma and bonded with an epoxy adhesive. Polyolefin materials can also be thermally welded, but they cannot be solvent cemented. 

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