Preparation and Dyeing Techniques

Normally, dyehouses have standard preparation procedures and formulas that work very well in terms of removal of non-fibrous contaminants and natural fiber pigmentation. However, some fabrics can exhibit barré that is caused by either optical or dyeability issues. Often, the barré is not created in dyeing, but can be highlighted. In this scenario, the dyeing is not the cause but the “messenger” of the problem.

Typically, barré is not a problem in whites, only in dyed fabrics. Therefore, if a fabric is known to have barré, then that roll should be processed into a white.

Preparation can help “mask” barré, but cannot and will not eliminate it. The cause of the barré must be eliminated for future rolls to be free of the defect.

The scour and/or bleach procedure can be intensified to mask the barré. This can be done by combinations of using a higher temperature or longer processing times. Usually the chemistry will remain the same; however, in some cases, it may have to be increased or changed.

If any changes are made in the preparation procedure, the fabric and resultant shade will possibly change in whiteness, strength, and appearance. In fact, the whiteness will almost always change. If whiter, the old dye formula will need to be adjusted. The strength of the fabric may be affected to the point where it becomes a problem. Finally, the surface of the fabric may change so that it may not match previous lots. As a result of more aggressive preparation to cover barré, it is important to evaluate such changes on small samples in the lab or a sample machine.

Tension can play an integral role in not only the formation of the fabric, but also during preparation, dyeing, and finishing. As with all variables, it must be controlled to known parameters and be consistent. Any inconsistencies in tension could change the morphology of the cotton (i.e. during mercerization), level of dye pick-up, or surface appearance (i.e. during mechanical finishing such as brushing or sanding)