Hydrophobic fibers

Early waterproofing treatments consisted of coatings of a continuous layer impenetrable by water. Later water-repellent fabrics permitted air and moisture passage to improve the comfort of the wearer. Aluminum and zirconium salts of fatty acids, siUcone polymers, and perfluoro compounds are apphed to synthetic as well as natural fibers. An increase in the contact angle of water on the surface of the fiber results in an increase in water repeUency. Hydrophobic fibers exhibit higher contact angles than ceUulosics but may stiU require a finish (142). 

There is Httle difference between the wet and the dry stress—strain diagrams of hydrophobic fibers, eg, nylon, acryHc, and polyester. Hydrophilic protein fibers and regenerated cellulose exhibit lower tensile moduH on wetting out, that is, the elongations increase and the strengths diminish. Hydrophilic natural ceUulosic fibers, ie, cotton, linen, and ramie, are stronger when wet than when dry. 

Hydrophobic fibers are difficult to dye with ionic (hydrophilic) dyes. The dyes prefer to remain in the dyebath where they have a lower chemical potential. Therefore nonionic, hydrophobic dyes are used for these fibers. The exceptions to the rule are polyamide and modified polyacrylonitriles and modified polyester where the presence of a limited number of ionic groups in the polymer, or at the end of polymer chains, makes these fibers capable of being dyed by water-soluble dyes. 

Phthalocyanine Dyes. The phthalocyanine molecule is much too big to be used on hydrophobic fibers and therefore is only used in its sulfonated form as the basis for direct and reactive dyes (see Phthalocyanine compounds). Its forces of attraction are different from a small linear yeUow a2o dye with which it is used to form bright greens. CompatibiHty between the two is likely to be a problem in practice and to overcome this, green dyestuffs containing a phthalocyanine dye linked via a saturated chromophore blocker (—x—) have been made, eg,... 

Freundhch isotherms are generally found with ceUulosic and other ionic hydrophobic fibers. 

If diffusion through the fiber is not carried out efficiendy then not only will the rate of dyeing be slow, with a chance that equihbrium between dye and fiber is not reached, but also the fibers will be dyed unevenly and possibly be ring dyed leading to poor fastness properties. Diffusion through the fiber is dependent on the actual dye and fiber chain molecular stmcture and configuration, and also, especially with hydrophobic fibers, the mobiUty of the chemical chain (7). 

Alliger (U.S. Patents 3,659,402,1972, and 3,905,788,1975) describes fiber-bed structures which are not random, but are rather built up from flat mesh sheets offset angularly from one layer to the next and then compressed and bonded. Such bonded beds of relatively coarse hydrophobic fibers both are remarkably flushable, to prevent fouling by insoluble solids, and have surprisingly high collection efficiency per unit pressure drop for submicrometer particles, approaching that of irrigated fine hydrophobic fiber filters such as described by Fair (U.S. Patent 3,135,592, 1964) and Vosseller (U.S. Patent 3,250,059, 1966). 

The absorption of disperse dyes by hydrophobic fibers such as polyesters is increased by the addition of dibenzothiophene 5,5-dioxide to the hot, aqueous dyebath. Presumably the sulfone behaves as a typical carrier acting as a mutual solvent for both fiber and dye. 

The Freundlich isotherm, where the dye in fiber D, is directly proportional to (D,)- and a plot of log D against log D, gives a straight line, is generally found with cellulosic and other ionic hydrophobic fibers. 

Disperse Dyes. These are substantially water-insoluble nonionic dyes for application to hydrophobic fibers from aqueous dispersion. They are used predominantly on polyester and to a lesser extent on nylon, cellulose, cellulose acetate, and acrylic fibers. Thermal transfer printing and dye diffusion thermal transfer (D2T2) processes for electronic photography represent niche markets for selected members of this class (see Chapter 6). 

The introduction of relatively low amounts of water when using hydrophobic fiber materials... 

Immobilized HRP on cellulosic fiber their decolorization ability by factor of 2.9 and 2.6, respectively, in 48 h More hydrophobic fiber surfaces result [56]... 

Disperse dyes were invented to dye the first hydrophobic fiber developed, namely cellulose acetate, and were initially called acetate dyes.25 The term disperse dyes is more appropriate, because these dyes are suitable for a variety of hydrophobic fibers and it is descriptive of their physical state in the dye-bath. Disperse dyes have extremely low water solubility and to be applied from this medium they must be (1) dispersed in water using a... 

CNC ARIDRY C is a water repellent designed primarily as semi-durable to durable water repellent for most hydrophobic fibers, especially nylon. This product is also an excellent extender for fluorochemical finishes. 

Disperse dyes. Disperse dyes are substantially water-insoluble nonionic dyes for application to synthetic hydrophobic fibers from aqueous dispersions. Disperse dyes are applied as very finely divided materials that are adsorbed onto the fibers with which they then form a solid solution. Dispersed dyes are primarily used for polyester and acetate fibers. Simple soluble azo, styryl benzodi furanone, and insoluble anthraquinone are the most common disperse dyes. Disperse yellow 3, disperse red 4, and disperse blue 27 are good examples of disperse dyes [5] ... 

---