RESEARCH & DEVELOPMENT
The physical structure of woven denim does not change much. The basic 5-pocket jean is predominately open-end spun, with a 14-ounce weight fabric constructed in a 3x1 twill. Pre-treatments like sanding gives denim a worn look, but new chemistry usually provides consumers with innovative choices of fresh denim looks. To obtain that color of denim, the cotton yarn must first be dyed.

In 1989, Wolfgang A. Strahl, Cotton Incorporated's senior vice president of Textile Research & Implementation, initiated a project to develop a process that would dye garments with indigo dye, the dye used that gives denim its customary look. Up to that point, only two types of indigo dyeing processes existed, ball warp dyeing and warp sheet dyeing.

Normally, the reduced indigo dye is applied to cotton yarn in a ball warp or warp sheet arrangement by dipping them through boxes to layer the indigo dye on the outside of the yarn. The indigo dye is then air oxidized back to its insoluble form. Because an efficient garment dyeing process had never been developed, creating an improved process would give clothing manufacturers a valuable option in producing a variety of offerings, in various hues, that consumers would hopefully find appealing.

In 1993, Strahl hired an associate director. Technical Services, named David Vlaservich. Strahl challenged Vlaservich to perfect this indigo process that Strahl had originally started four years earlier. Indigo dye, in its pigment form, will not dissolve in water, and holds no natural affinity toward cotton. However, by reducing the dye and improving the dye-to-fiber affinity, Vlaservich obtained positive results by dyeing and extracting cotton garments in an inert oxygen-free atmosphere which prevents premature oxidation.

Because it is a cheap gas and heavier than oxygen, nitrogen was chosen to purge air from the dye machine, thereby providing an acceptable dyeing environment. After the dyeing cycle is complete, the nitrogen purge is again applied during the drain and extraction cycles where the excess dyebath is drained into a collection tank for reuse in other dyeing batches. The machine is then opened to the air and oxidation occurs, thus restoring the indigo color.

"This process promotes a uniform dye application, improves dye yield and colorfastness, allows manufacturers to re-use dyebaths and save money, while at the same time, remains environmentally friendly because no harsh chemicals or dye-stuffs are released down the drain," explains Vlaservich.