Repellents with Hydrocarbon Hydrophobes

Repellents have hydrocarbon, polysiloxane. and/or fluorocarbon hydrophobes. Only fluorinated repellents are oleophobic and repel both water and oil. 

The stability of wax dispersions and the durability of wax-containing repellent finishes have been increased by formulating wax dispersions with polymers, such as poly(vinyl alcohol) [6], polyethylene [7], acrylic polymers, for example, poly (butyl acrylate) [8], copolymers of stearyl acrylate or stearyl methacry- 

The water repellents formulated with waxes and polymers are used as extenders for polymeric fluorochemical repellents. 

One of the oldest water repellents is aluminum acetate [1,4] hydrolyzed on fibers to basic aluminum acetates and hydroxides of undefined structure. The poor adhesion and dusting of the repellent was a major shortcoming of the finish. An improvement was made by applying a water-soluble soap to the fibers and precipitating it with an aluminum salt, such as the acetate, formate, or sulfate  

Instead of the two-bath treatment, aluminum soaps have been applied as solutions in an organic solvent or as aqueous dispersions. 

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In recent years, fluorochemical repellents have been coapplied mainly with wax dispersions made durable with cross-linking adjuvants. Although a variety of water repellents with hydrocarbon-type hydrophobes enhance the repellency and durability of fluoropolymer repellents, silicones may reduce their oil repellency... 

Fluorochemicals will remain the most effective, durable, and expensive repellents. The use of nonfluorinated extenders, where appropriate, will continue to improve the cost-effectiveness of fluorochemical repellents. Silicones and repellents with hydrocarbon-type hydrophobes will share the market where the perfor-mance/cost relationship is in their favor. 

The OH portion of an alcohol molecule tends to interact with water—it is hydrophilic. The hydrocarbon portion does not interact, rather it is repelled— it is hydrophobic. The larger the hydrophobic portion, the less soluble in water is the molecule. 

The reason for this behaviour is that the surfactant molecule contains two structurally distinct parts, one of which is hydrophilic while the other is hydrophobic. Oil-soluble surfactants have an oleophilic and an oleophobic part. In the great majority of surfactants, the hydrophobic part is a hydrocarbon chain, which usually has an average length of 12 to 18 carbon atoms and may include an aromatic ring. A single molecule in aqueous solution seeks the surface, because its hydrocarbon tail is repelled by the water, and it tends to remain there, with the hydrophobic part above the surface and the hydrophilic part below, i.e. in the water phase. Further molecules seek the surface or the walls of the vessel until both are full, at which point further additions result in the formation of micelles, which are clusters of molecules arranged with the hydrophobic parts towards the centre and the hydrophilic parts on the outside. 

Fluorochemical repellents differ from silicone- or hydrocarbon-based repellents in several aspects, of which oil repellency is the most important [311]. Repellents with a fluorocarbon chain repel both water and oil, whereas repellents with silicone or hydrocarbon hydrophobes repel only water. 

Fluorochemicals used in water- and oil-repellent finishes have been monomeric or polymeric. The first fluorochemical repellents used commercially were monomeric. In analogy to repellents with a hydrocarbon hydrophobe (see Section 12.1), perfluoroalkanoic acids, and phosphate esters have been applied as chromium complexes [121-123], zirconium or titanium alkoxides or salts [124-126] or have been converted to quaternary amines [127,128] ... 

Perfluoroalkyl or Polysiloxane Group The presence of either of these groups as the hydrophobic group in the surfactant permits reduction of the surface tension of water to lower values that those attainable with a hydrocarbon-based hydrophobic group. Perfluoroalkyl surfaces are both water- and hydrocarbon-repellent. 

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