Dyebath pH control of dyeing machinery under dynamic conditions: Fact or fiction?

The incorporation of a method of closed loop feedback pH control into the automatic control of dyeing machinery was studied. The method was based on the use of preset pH profiles that either are linear, exponential, or quadratic in shape. An on-line pH meter and dosing pumps attached to a pilot-scale dyeing machine were used together with mathematical models that describe the conditions of the dye liquor at any given time. The temperature dependence of the system and the effect of electrolyte, dye, and other additives in the dyebath were studied for inclusion in the model. It was demonstrated that simplifications are required if this system is to be used under dynamic conditions. The results based on experiments however, demonstrate a relatively high degree of accuracy and reliability of pH control either according to preset dosing or to preset pH change profiles. This system was used for dyeing cotton with reactive dyes and can be used for dyeing wool with acid dyes as well as other pH dependent dyefiber combinations. The use of this system allows for a reduction in time and energy requirements, as well as an overall reduction in the level of environmental pollution.