Professional guide

Bleaching and scouring

In the many steps of textile production, bleaching and scouring are two of the processes that many over-look. But since fibres generally are not perfectly white to start with, nor free of impurities; these are necessary and potentially environmentally harmful steps. Here are some innovative alternatives.

Today’s textile wet processing involves use of high alkalinity, high temperature and harsh chemicals for removal of impurities. This means excessive use of energy and water, as well as a high environmental burden in the form of non-biodegradable waste.

Desizing
Starch size, a coating used to strengthen and protect warp yarns during industrial weaving, must be completely removed prior to bleaching and dyeing or printing. This desizing step is critical to ensuring an even and consistent fabric finish. Desizing with Genencor’s amylase enzymes is much more effective, cost efficient, and eco-friendly for manufacturers than chemical desizing methods, such as treatment with acids, hot alkali, or oxidizing agents. The same goes for Novozymes Aquazym®, which is a powerful sustainable amylase enzyme that removes the size, and is easy to apply at a pH range from 5-10.

Scouring
Scouring allows for removing the protective pectin layer/non-cellulosic components found in native cotton while also getting rid of other impurities. This process allows producers to easily bleach and dye the fabrics. Novozymes’ Scourzyme® solution is an eco-friendly alternative that allows for bioscouring the fabrics with as little harm as possible to the environment. Scourzyme also does not annihilate as much raw cotton in this process as chemicals do, so producers are left with more cotton from their raw materials.

Bleach cleanup
After fabric or yarn bleaching, residues of hydrogen peroxide are left in the bath, and need to be completely removed prior to the dyeing process, using a step called bleach cleanup. Incomplete peroxide removal results in poor dyeing with distinct change of color shade and intensity, as well as patchy, inconsistent dye distribution. With a sustainability in mind, Novozymes’ catalase enzyme Terminox® for bleach clean-up ensures that residual hydrogen peroxide from the bleaching process is removed efficiently, and in an economical and environmentally friendly way.

Bleaching
When bleaching cotton, a lot of chemicals, energy and water are part of the process, and reducing the environmental impact of cotton production addresses these issues. The company Huntsman has developed a wetter/stabiliser that maximises the wetting and detergency of the bleaching process and a one-bath caustic neutraliser and peroxide remover in order to shorten the bleaching cycle, reduce energy and water required and deliver more consistent bleaching results. They have developed surfactants that are environmentally friendly (in that they do not contain Alkylphenol ethoxylates), and the system that is both Oeko-Tex and GOTS approved.

Cotton bleaching can be obtained without the use of harsh alkalis and requires a lot less water and energy

When it comes to bleaching of cellulosic fibres, Huntman’s enzymatic bleaching system enables bleaching at near-neutral conditions and at low temperatures without the use of sodium hydroxide. But, since the enzymes used are derived from GMOs, the process is not compatible with GOTS certification. However, with this system, cotton bleaching can be obtained without the use of harsh alkalis and requires a lot less water and energy. Additional benefits include softer handle, lower fibre weight loss, no neutralising required and no fibre damage. (Source: EcoTextileNews)

Huntsman Textile Effects has also partnered with textile enzyme supplier Genencor, a division of Danisco A/S. The move follows Genencor’s launch of the new “PrimaGreen” EcoFade LT100 which enables manufacturers to bleach fabrics at neutral pH and low temperature. By lowering the treatment and rinsing temperature considerable savings in water and energy consumption of up to 40% are said to be possible. “Gentle Power Bleach™” allows full white levels on regenerated cellulosic fibres and fabrics such as lyocell or Tencel® . PrimaGreen® Super, Ecofade and Ecolight are new biotech enzyme technologies for denim finishing. These enable creating a wide variety of denim shades and bleaching options, while preserving energy, water and natural resources.  PrimaGreen® Ecowhite is a biotech enzyme bleaching technology for all textile processing, reducing energy, increasing process efficiency and yielding better product results.