Surface treatment wetting

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Articles fabricated from FEP resins can be made bondable by surface treatment with a solution of sodium in Hquid ammonia, or naphthalenyl sodium in tetrahydrofuran (64) to faciUtate subsequent wetting. Exposing the surface to corona discharge (65) or amines at elevated temperatures in an oxidizing atmosphere (66) also makes the resins bondable. Some of the more recent work is described in References 67—69. 

Exact si2ing of mica products coupled with surface treatment procedures have led to a greater use for wet ground mica in plastic compositions, particularly automobile bodies. These quahty products demand a high dollar value. 

Although kaolins are easily wetted by both oil and water, surface treatment may sometimes be used to enhance the oleophilic properties. The kaolin in paint may represent 20—30% of the pigment. 

The dry powder process has several additional advantages over the wet process. For example, much less waste of enamel occurs because the dry over-spray is airborne and recycled in a closed system. No-pidde ground coats have broadened the apphcation of both wet-process and dry-process systems. These enamels are appHed over cleaned-only metal. Thus the problems of disposing of pickling acid wastes containing iron sulfates and nickel wastes are eliminated (see Metal surface treatments) (7). 

Cassie [39] extended Wenzel s treatment to composite surfaces. His treatment can be applied to a rough surface incompletely wetted by a liquid so that it consists of an area fraction f wetted and /2 unwetted surface. Then ... 

Spray Cleaning - Gas (Wet) Scrubbing - Gravel Washing - Vegetable Cleaning - Surface Treatment - Car Washing... 

Chemicals which are used to modify bulk sheet properties usually have to be added to the wet fibre suspension so that they become well distributed throughout the -direction of the sheet. Chemicals which are added as a surface treatment to the dry sheet are usually only able to influence surface properties. 

Low surface tension. Wetting of the surface is more difficult as the surface tension decreases. Surface treatments can improve the surface tension and the wettability. 

Surface treatments of carbon fibers can in general be classified into oxidative and non-oxidative treatments. Oxidative treatments are further divided into dry oxidation in the presence of gases, plasma etching and wet oxidation the last of which is carried out chemically or electrolytically. Deposition of more active forms of carbon, such as the highly effective whiskerization, plasma polymerization and grafting of polymers are among the non-oxidative treatments of carbon fiber surfaces. 

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