Hydrophobicity, wool

Cleansing of materials (substrates) implies the removal of soil and stains. A wide variety of stains and substrates are encountered. For instance, textiles may be of natural origin such as cotton, wool, or natural silk, or are made of synthetic fibers, such as nylon, polyester, or polyacryl. Cotton is cellulose that has an intermediate hydrophobicity wool and natural silk are proteins, both rather hydrophobic and in most cases negatively charged. Synthetic fibers are usually polymers of which the backbone is characterized by a series of repeating units such as peptide units (in nylon), ester bonds (in polyesters), and cyan groups (in polyacryl). 

In fine wool such as that obtained from merino sheep, the cuticle is normally one cell thick (20 x 30 x 0.5 mm, approximate dimensions) and usually constitutes about 10% by weight of the total fiber. Sections of cuticle cells show an internal series of laminations (Figs. 1 and 2) comprising outer sulfur-rich bands known as the exocuticle and inner regions of lower sulfur content called the endocuticle (13). On the exposed surface of cuticle cells, a membrane-like proteinaceous band (epicuticle) and a unique hpid component form a hydrophobic resistant barrier (14). These hpid and protein components are the functional moieties of the fiber surface and are important in fiber protection and textile processing (15). 

Nylon is similar ia its general chemical stmcture to the natural fiber wool, and therefore all the previously described processes for wool are appHcable to dyeiag nylon with acid, metallised, and other dyes. There are, however, significant differences. Nylon is synthetic, it has defined chemical stmcture depending on the manufactufing process, and it is hydrophobic (see Fibers, POLYAMIDES). 

Other applications of filters include sterilization of venting or displacement air in tissue and microbiological culture (carbon filters and hydrophobic membrane filters) decontamination of air in mechanical ventilators (glass fibre filters) treatment of exhausted air ftom microbiological safety cabinets (HEPA filters) and the clarification and sterilization of medical gases (glass wool depth filters and hydrophobic membrane filters). 

Exploration of the use of liposomes in wool processing stems from the similarity that exists between the bilayer structure of the cell membrane complex of wool and that of the liposomes. Merino wool contains about 1% by weight of lipids, these forming the hydrophobic barrier of the cell membrane complex. Cholesterol is one of the main lipid... 

An interesting development is achieved by incorporating long hydrophobic hydrocarbon radicals, which yields dyes with neutral affinity to wool and very good wetfastness properties [6], Example C.I. Acid Red 138, 18073 [15792-43-5] (13) ... 

Bonding Forces Between Dye and Fiber. Dye anions can participate in ionic interactions with fibers that possess cationic groups. However, the formation of ionic bonds is not sufficient to explain dye binding, because compounds that can dissociate are cleaved in the presence of water. Secondary bonds (dispersion, polar bonds, and hydrogen bonds) are additionally formed between dye and fiber [47], Close proximity between the two is a prerequisite for bond formation. However, this is counteracted by the hydration spheres of the dye and of wool keratin. On approach, these spheres are disturbed, especially at higher temperature, and common hydration spheres are formed. The entropy of the water molecules involved is increased in this process (hydrophobic bonding). In addition, coordinate and covalent bonds can be superimposed on secondary and ionic bonds. 

The increase in the atomic concentration of oxygen (Table 1) suggests an increased amount of hydrophilic groups on the wool surface. This fact can be confirmed by the results of the contact angle measurements (Table 2). Following enzymatic treatment the contact angle is distinctly decreased, from 122.5° for untreated wool to 108° and even 102°, but the wool fabric surface is still hydrophobic (0 > 90°). The contact angle value obtained for wool after an intensive treatment (4% o.w.f. of enzyme) equals the one for wool samples with chitosan deposited. 

The mechanisms involved in the binding of Wool Fast Pink RL (Figure 1) to the protein molecule is as well not fully understood but probably involves a combination of ionic interactions between the charged groups on the dye and protein molescules, and hydrophobic interactions between the dye and protein molecules. 

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