Dyebath control

In devising strategies to prevent insect attack on processed woolens, it is appropriate to aim only to protect processed wool goods and to control the principal domestic pest species. This is usually achieved by incorporation of an insecticide into those goods required to be protected, usually from the dyebath while the articles are being dyed, and methods for protection of wool goods have been reviewed (122). 

The heavier the depth of shade and closei to the saturation value for the fiber under its dyebath conditions (pH, electrolyte, etc), the more libely it is to obtain a level dyeiag. Thus for heavy shades relatively Htde control is needed ia the dyeiag process. 

Class B direct dyes have poor leveling power and exhaustion must be brought about by controlled salt addition. If these dyes are not taken up uniformly in the initial stages it is extremely difficult to correct the urdevelness. They are dyes that have medium—high affinity and poor diffusion. In their apphcation the cellulose is entered into a dyebath containing ordy dye. The salt is added gradually and portionwise as the temperature is increased and possibly the final additions made after the dyebath has come to the bod. 

Commercially viable systems for the decolorisation of spent dyebaths can be based on hydrogen peroxide treatment initiated by UV radiation. A representative selection of six disulphonated monoazo acid dyes and two disazo disulphonated types was exposed for various times in a pilot-scale photochemical reactor of this kind. The controlling parameters were dye structure, pH, peroxide dosage and UV light intensity [39]. In a wider survey of the response of various classes of dyes to the combination of UV radiation and hydrogen peroxide, viable candidates for further in-plant treatment trials were the water-soluble reactive, direct, acid and basic classes. On the other hand, water-insoluble colorants such as disperse and vat dyes did not appear to be viable [40]. 

As a general rule, the lower the dyebath pH the more rapid is the rate of initial adsorption by the amide fibre and the subsequent approach towards equilibrium exhaustion. Consequently, the attainment of a safely controllable rate of dyeing becomes easier the higher the pH at which dyeing begins. Eventually, however, a pH is reached at which the dyebath is no longer exhausted within a reasonable time. 

The electrolyte (i.e., sodium chloride or sodium sulfate), its concentration, and the speed of addition control the adsorptive behavior of the dyes and the degree of exhaustion. A high electrolyte content of the dyebath shifts the dyeing equilibrium toward the fiber. 

Unique dye carrier fully programmed one-product dyeing system for jets and beams produces superior dyebath oil emulsification and leveling properties, foam control, disperse dye dispersibility, and barre coverage. 

Put a 1 cm wide strip of multifiber fabric in your dyebath as an internal control. 

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