Substrate preparation, textile processing

Given the variable process control requirements for each of these fabric preparation techniques and the ecological issues associated with the volume of water consumed in washing and rinsing cycles, alternative methods to enhance dye uptake to prepared textile substrate surfaces are gaining ground. This is particularly true for synthetic, hydrophobic fibers, such as polyester. The ability of a large... 

Polyaniline has also been deposited by in situ polymerization (chemically or electrochemically) as thin films or coatings (in the form of ES) on a variety of substrates such as glass slides, metal films, natural or synthetic fibers, and textiles, [25,26]. In the chemical oxidation process, the substrate was immersed in a newly prepared aqueous acidic solution containing aniline and ammonium peroxydisul-fate. The material deposited during the first 1-2 min was in the highly oxidized state and later changed into the oxidation state of emeraldine salt after —10 min [26]. 

The optimum amount of UV absorber varies with each chemical type and application, but in most cases is in the 0.25-1.0% concentration range. Other factors to consider while selecting the proper type and amount of UV absorber are color contribution, FDA sanction for food packaging applications, and, of course, add-on cost. The UV absorbers are incorporated into plastic substrates by dry blending, extrusion compounding, and then conversion into the final product by various processes such as injection molding, blown film extrusion, multifilament spinning, and sheet extrusion. Also, UV absorber dispersions can be prepared and dyed onto textile fabrics, which will not only UV-stabilize the polsrmer substrate but also improve the color stability of the dyes used to color the fabric. 

Another widely used approach is the in situ polymerization of an intractable polymer such as polypyrrole onto a polymer matrix with some degree of processibil-ity. Bjorklund [30] reported the formation of polypyrrole on methylcellulose and studied the kinetics of the in situ polymerization. Likewise, Gregory et al. [31] reported that conductive fabrics can be prepared by the in situ polymerization of either pyrrole or aniline onto textile substrates. The fabrics obtained by this process maintain the mechanical properties of the substrate and have reasonable surface conductivities. In situ polymerization of acetylene within swollen matrices such as polyethylene, polybutadiene, block copolymers of styrene and diene, and ethylene-propylene-diene terpolymers have also been investigated [32,33]. For example, when a stretched polyacetylene-polybutadiene composite prepared by this approach was iodine-doped, it had a conductivity of around 575 S/cm and excellent environmental stability due to the encapsulation of the ICP [34]. Likewise, composites of polypyrrole and polythiophene prepared by in situ polymerization in matrices such as poly(vinyl chloride), poly(vinyl alcohol), poly(vinylidine chloride-( o-trifluoroethylene), and brominated poly(vi-nyl carbazole) have also been reported. The conductivity of these composites can reach up to 60 S/cm when they are doped with appropriate species [10]. 

With few exceptions, the mechanical properties of conductive polymers are rather poor. This is a result of the cross-linked nature and aromatic character of the backbone. One exception is polyaniline, which can be prepared as oriented crystalline fibers of excellent strength (see Chapter 18). The use of a textile substrate represents a convenient method of introducing mechanical strength, flexibility, and processibility to conducting polymers for practical applications. 

In order to conduct the processes associated with preparation, the textile substrate must effectively be wet out. Surfactants or surface active agents are used to lower the surface tension of water in relation to the fiber substrate so the water will wet the substrate. Surfactants are organic molecules that effectively bridge the transition between water and the more hydrophilic fiber surface through combination of a polar head and a hydrocarbon tail within a single molecule. 

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