Functions of Dyeing Assistants in the Dye Bath
(i) Acids
Acids are commonly used in apparel industry to dye protein structure based fibers such as wool. And acid dye also used to dye synthetic fibers such as nylon. In the dying process, acid will be added to improve substantitivity of dye and also to help the exahusion of the dye bath. Specially dye should be added when nylon dyeing process. Because nylon does not absorb dye in the normal situation. But when we add dye to nylon with acid, absorbency will high. Wool also increase dye absorbency when use acids with dye. But when we add dye to wool material we must careful about pH range and concentration of acid. Because protein molecules highly react with high concentrated acids and destroy molecular chains. Therefore fiber will be damaged. It is highly affect to quality of fabric and finished product.
(ii) Salts
Salts are commonly used in textile industry when dye all forms of dye with cellulose fibers. As we remember that our second lab class 1st practical ( direct dye ) we have seen salt used fabric sample were highly dye absorbed. Therefore salt can be used to obtain good colour appearance of output fabric. And also salt save cost of manufacturing. Because high absorbency of dye and increased and need not to use high concentration of liquor ratio.
(iii) Leveling Agents
Leveling agents are mostly used with vat dyes, disperse dyes and some acid dyes leveling agents are used to proper control dye absorbency process and help to uniform dye absorbency of each places. Sometimes absorbency sometimes uniforms absorbency. Because some fabric has higher and low absorbency area. After dyeing process some places appear ugly colour dots. To avoid this colour effect leveling against are very helpful.
(iv) Carriers
Carriers are commonly used in apparel industry to dye synthetic polymer fibers such as polyester. In the condition polyester fiber does not absorb water molecules. Therefore we cant dye directly. Because higher crystalline region, PET polymer area, continues filaments and non-poled bonds not attract water molecules. Therefore use carriers when synthetic fiber dyeing process. Main function of carriers can be explained as loosening the fiber structure and this process helps to the dye to have less restricted entry to fiber inside. Apart carriers we can dye fabrics using higher temperature and highest pressure. But it is high cost method.
(v) Reducing Agents
Reducing agents can be employed with vat dyes and sulphur dyes. The main function of reducing agents can be explained as level of alkali will be decreased insoluble vat dyes and also sulphur dyes to decrease from that is soluble and substantive. Therefore reducing agents are essential to apply for sulphur and vat dyes.
* In the vat dyeing process that we used Na2S2O4 ( Sodium Dithionate ) a strong reducing agents one with reduction potential.
Apart above five examples, we can see the most chemical fabric dyeing assistants in the textile industry. But I think my note will helpful to understand about basic dyeing assistants in the textile and clothing industry. This letter was written for Lab Class - II , TTX4232, The Open University Of Sri Lanka, Nawala, Nugegoda.
Author: K. K. T. Madhusanka