Penetrating finishes water repellents

Water Repellency and Water Resistance. Water repeUency is defined as the abihty of a textile fiber, yam, or fabric to resist wetting, whereas water resistance is a general term appHed to a fabric s abiUty to resist wetting and penetration by water (2). A third term, waterproof, is appHed to those fabrics that do not allow any water penetration at all. Waterproof fabrics are generally coated with an impermeable surface layer that does not allow air permeabihty. Water-repellent finishes are hydrophobic compounds that are appHed to fabrics to inhibit water penetration while still allowing air permeabihty. 

Penetrating finishes such as stains and water-repellent preservatives ( 7,8) leave little or no continuous coating on wood surface. Because there is no coating, there is no failure by blistering or peeling. These finishes are ideally suited for rough-textured surfaces difficult to paint effectively. 

Two basic types of finishes (or treatments) are used to protect wood surfaces during outdoor weathering those that form a film, layer, or coating on the wood surface, and those that penetrate the wood surface to leave no distinct layer or coating. Film-forming materials include paints of all description, varnishes, lacquers, and also overlays bonded to the wood surface. Penetrating finishes include preservatives, water repellents, pigmented semitransparent stains, and chemical treatments. 

Penetrating Finishes. Penetrating finishes, which do not form a film over the wood, include oils, water repellents, stains, preservatives, and surface treatments. 

Penetrating finishes such as stains and water-repellent preservatives leave little or no continuous coating on wood... 

Recent experiments by the authors studied the water repellence of PET fabrics (technical fabrics), photochemically treated in the presence of, e.g., 1,5-hexadiene, 1,7-octadiene, diallylphthalate (DAP) and l//,l//,2//,2H-perfluorodecyl acrylate (PFDA). Exemplary experimental data are summarized in Fig. 13 showing drop penetration times in excess of 1 hour (measurements were stopped after this time) and DuPont grading of up to 8. The relevant values for the untreated fabrics were drop penetration time approx. 20 s and a DuPont grading 0. Based on the well-known effect of heat treatments on long-chain fluoro compounds (cf. Sections 4 and 5.1), the samples treated with PFDA were also characterized following a further heat treatment. As was found in the case of wet-chemical finishes and plasma-deposited fluorocarbon thin layers, the water repellence of the samples could be further enhanced by heat treatment in this case also. 

The oldest repellent finish is to repel water. The purpose of this finish is self evident. Drops of water should not spread on the surface of the textile and should not wet the fabric. The drops should stay on the surface and easily drip off. Similarly, oil repellent finishes should prevent oily fluids from wetting treated textiles. In a similar manner, soil-repellent finishes should protect textiles from both dry and wet soils. In all cases, the air permeability of the finished fabric should not be significantly reduced. Waterproofing treatments will not be covered in depth. A waterproof textile should withstand the hydrostatic pressure exerted by a column of water from at least aim height before the first drops of water penetrate through the fabric. In practice this is mostly achieved with coatings which have the disadvantages of stiff handle, lack of air and vapour permeability and consequently poor wear comfort. 

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