One of the most vital ingredients, Salt is used extensively for dyeing different substrates with various dyes. It plays a crucial role in transferring the dye from the solution to the substrate. This process is known as exhaustion.
Even though salt is extremely vital, it has multiple negative impacts. Having high salt concentration causes the exhaustion process to not complete. It leaves the dye bath with leftover dye and huge amounts of salt. In addition, it increases the raw material costs and reduces the efficiency of the process. Therefore, in order to achieve an excellent dye, the amount of salt use must be maintained. Below are four ways to reduce the amount of salt and still achieve a great dye.
Salt has a common ion effect that pushes the dye molecules on the substrate. Let us take the example of dyeing cotton with anionic dyes. Anionic dyes, when immersed in water, have negatively charged functional groups and cotton has a negative zeta potential. The affinity of the dye towards the substrate is reduced. This is because the similar charges of cotton and anionic dyes, repel each other during the dyeing process.
You can minimize the barrier by introducing cations such as quaternary ammonium salts on the substrate. They will increase exhaustion and the substantivity of the anionic dye towards cotton. Furthermore, they will reduce the amount of salt required.
The affinity of a dye towards the substrate relies on factors such as solubility, planarity, and formation of H-bonds with the molecular mass and substrate. A dye should have low solubility, high planarity, and functional groups that accelerate H-bonding in order to have a good affinity. The exhaustion rate is bound to be higher at a lower concentration of salt if the affinity is more. There are a variety of such low-salt dyes that have been introduced to the market and the above-mentioned attributes give them an upper hand while marketing such products.
Optimizing the dyeing conditions is another great way to minimize the amount of salt. Each class of dye has divergent affinity and characteristics for the substrate. The range of salt concentrations on exhaustion can be evaluated by setting up a design of experiments with different parameters such as temperature, pH and time. The salt concentrations can be minimized to 50% without changing the dyeing quality.
Reducing the material to liquor ratio (MLR) is a great way to reduce the salt quantity. However, a higher value of MLR does help create a uniform and level dyeing. It does have negative impacts on the energy, environment, and cost. In addition, high MLR volume will lead to a high requirement of energy to carry out the different processes. To overcome these drawbacks, it is best to lower the MLR to a level that won’t negatively impact dyeing quality. Are you on the lookout for stunning colorants that will produce striking effects on your leather, paper, cotton, polyamide, wood, inks, coatings substrates? If yes, then get in touch with Alps Chemicals, and bring your products to life by giving them an exuberant makeover!