Deep Dye Fibers

A common method to increase the dyeing rate is to inhibit the formation of crystalline regions during fiber manufacture. To this end, it suffices to break up 

The result is a fiber that is less crystalline and dyes more readily. The downside is an unavoidable reduction in transition temperatures, a less stable structure more prone to shrinkage, and the easier escape of dye molecules and oligomers which can deposit onto the surfaces of textile processing equipment. Depending on the level and type of comonomer used, increased problems with lightfastness or polymer degradation can also occur. 

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Figure 12.13 Structure of a PET copolymer with adipic acid, used for deep-dye fibers...

Chemically there arc important differences. There are no side chains and unlike wool the number of amino and carboxylic groups differs there is an excess of carboxylic groups. The numbers of amino groups can be changed by chemical modification, c.g.. in deep dyeing nylon, but for the most part nylon fibers can be considered lo have a limited number of sites, which can differ from one chemical type to another. 

In order to achieve a satisfactory color yield, suitable cationic precipitants which exhaust straight onto the fiber must be used for deep dyeings. These products precipitate acid dyes and simultaneously have a fixing action as the binding link between the fibers and dye molecules. 

Greater success was achieved by DuPont who copolymerized, the sodium salt of 5-sulfoisophthalic acid into PET to render the polymer dyeable with cationic (basic) dyes. Basic dyeable PET was successfully launched as Dacron 64 in the form of a low-pill staple product [64]. The presence of the sulfonate groups in the polymer chain also acts as an ionic dipolar cross-link and increases the melt viscosity of the polymer quite markedly. Thus, it is possible to melt-spin polymer with IV 0.56 under normal conditions, giving a low-pill fiber variant. The fiber also has a greater affinity for disperse dyes due to the disruption of the PET structure. Continuing this theme, there are deep dye variant PET fibers, often used in PET carpet yarns, which are copolymers of PET with chain-disrupting copolymer units like polyethylene adipate. They have less crystallinity and a lower Tg. therefore, they may be dyed at the boil without the use of pressure equipment or carrier at the cost of some loss of fiber physical properties. 

Deep-dyeing variants - ver-e-ont n. Polymers that have been chemically modified to increase their dyeability. Fibers and fabrics made there from can be dyed to very heavy depth. 

Dyes for polyesters or cellulose acetate fiber-, deep blue to greenish blue shades... 

Standard polyester fibers contain no reactive dye sites. PET fibers are typically dyed by diffusiag dispersed dyestuffs iato the amorphous regions ia the fibers. Copolyesters from a variety of copolymeri2able glycol or diacid comonomers open the fiber stmcture to achieve deep dyeabiHty (7,28—30). This approach is useful when the attendant effects on the copolyester thermal or physical properties are not of concern (31,32). The addition of anionic sites to polyester usiag sodium dimethyl 5-sulfoisophthalate [3965-55-7] has been practiced to make fibers receptive to cationic dyes (33). Yams and fabrics made from mixtures of disperse and cationicaHy dyeable PET show a visual range from subde heather tones to striking contrasts (see Dyes, application and evaluation). 

Water-insoluble vat dyes are converted to soluble anthrahydroquinones by reducing agents, such as sodium dithionite (hydrosulfite) in the presence of sodium hydroxide. The sodium salts of these mostly deep colored leuco compounds penetrate cellulose fibers. The insoluble dye is attached firmly to the fiber after reoxidation (see Section 4.5). Representative of a special form are the water-soluble sulfuric acid esters of the anthrahydroquinone compounds, namely, the leuco esters of vat dyes). 

An azo dye is formed from a Naphtol AS coupling component and a diazotized base (developing component) under suitable conditions (see Section 3.7). This coupling is carried out on the fiber itself. If components without solubilizing groups are used, the dye formed is an insoluble pigment, and dyeings with excellent fastness properties are achieved. Today, azoics are used primarily for deep clear shades, like red and purple. 

Disperse dyes can be used to produce light to medium deep shades on acrylic and modacrylic fibers [96, p. 639], The dyeing mechanism and process correspond to those used on PES and CA fibers (see Section 4.12). However, dyeing can be performed below 100°C. Addition of carriers is not required. The good migration properties of disperse dyes result in problem-free level dyeing. 

The complex formation of Cu (I) ions with nitrile groups has found an interesting application for dyeing acrylonitrile fibers with anionic dyestuffs. The copper ion is readily absorbed by polyacrylonitrile and copolymers thereof, which then acquire almost unlimited affinity for many anionic dyes, permitting dyeing to very deep shades, including black ... 

A pertinent example of the application of Werner s coordination complexes to the coloring of synthetic fibers is exhibited in the case of polypropylene fibers containing nickel. The minute nickel particles have been evenly dispersed throughout the fiber by a chelate stabilizer/ so that upon dyeing with azo disperse dyes bearing the same o-substituents, as noted above, a fast deep color is formed (4)- This example,... 

The simplest way of dyeing a fiber is by a direct dye. The dye is dissolved in water so that its concentration is about 0.02 to 0.1 per cent. The amount of dye depends on the weight of the cloth. For light shades the amount of dye is 0.05-0.3 per cent, and for deep shades 4-10 per cent, of the weight of the cloth. A small amount of sulfated alcohol soap is added to reduce the surface tension of the solution and thereby aid in the penetration of the dye. Inorganic salts are added to the dye bath, such as sodium chloride for cotton dyes and sodium sulfate for wool dyes, in amounts varying from 5 to 10 per cent. The fiber is steeped in the dye bath and heated at 80-100° until the proper shade has been... 

Fibers from copolyesters containing PAG dye to deep shades in a boiling bath of disperse colors also without carriers. The peparation of such copolyesters is, however, troublesome nce at the thermal conditions of polycondensation, e.g., at more than 270 °C, PAG tends to depolymerize so that the blodc-copolymers become copolymers with statistical distribution of the components te this way the decrease of the melting point of the resulting copolymer cannot be avoided. 

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