Wetting in Woven Fibers and Papers

In the treatment of woven fabrics for dyeing, waterproofing, sizing, and other procedures, important criteria for evaluation are the speed and completeness of the wetting process. In the textile industry, wetting is taken to mean the submersion of the fabric in an aqueous treating solution, replacing all the air in the cloth structure with the solution. Obviously, if the treatment 

In aqueous systems, the range of surface tensions that will be encountered using common surfactants and practical concentrations is somewhat limited. In most practical cases, one might expect ctlv to be reduced to the range of 40 mN m l a change of a factor of 2 from that of pure water (72.8). Lower values are normally attained only with very high surfactant concentrations (which can introduce foaming problems), with purer, more expensive surfactants, or with special materials such as fluorocarbon or silicone surfactants. 

The presence of surfactants or wetting agents in textile treatment solutions can also introduce other complications in the understanding of the dynamics of the wetting process. Because surfactants adsorb at the SL interface as well as the LV interface, as the liquid front moves across fresh solid surface, adsorption processes will tend to deplete the concentration of available surfactant and may cause localized changes in both ctlv and 6. In many cases, however, adsorption rates at the SL interface is much slower than that at LV interfaces, so that such effects can be taken into consideration without too much difficulty. 

Of more direct practical importance to textile processing is the fact that it becomes increasingly more difficult to remove the last traces of air from the fiber system. Fiber bundles in yarn can produce quite complex capillary systems that provide ample opportunity for air entrapment in very inaccessible nooks and crannies. It is found, for example, that yarns made of smooth essentially cylindrical fibers are much easier to wet completely than those eomposed of 

TABLE 6.1. Effects of Change in Surface Tension triy (mN in and Contact Angle on Linear Rate of Flow in a Hypothetical Capillary System  

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