Denim Fabric Dyeing Problems


Indigo, a special case

Denim takes a special place among modern textiles: The indigo-blue color and fashionable wash-out effects make all the difference

Dyeing jeans

The most difficult stage in the making of jeans is dyeing, a process which actually faces  two problems. Pulcra Chemicals offers solutions to both. Problem number one: With denim, only the warp yarn is dyed instead of the whole fabric. Up to 4,000 parallel fibers are simultaneously washed and then pass through several successive baths. Indigo is insoluble in water and will only take when the chemistry is right. The dyeing vats are injected with sodium lye and the reductant hydrosulfite, which converts the indigo into a soluble form and changes its color to yellow. Step by step, each single fiber is coated with six initially yellow, later green dye layers, with a light gray zone remaining in the center. Once the dye has been deposited on the fibers, the sodium lye and the reductant are removed from the bath and the initial blue color is restored.

The enzyme-based wash-out look

Problem number two: Because fashion demands it, after washing, sizing, and weaving, the dye has to be partially removed from the finished fabric. Which brings us to the wash-out look. Enzymes do the job better in every way. However, besides enzymes the process does require special softeners and smoothing agents. And it takes special expertise to apply these.

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