Bleichung

Bleichung is the process of removing color from materials or reducing color intensity, typically by oxidation, reduction, or enzymatic action. The term is used in textiles, paper production, food processing and cosmetics. In practice it refers to laboratory procedures and industrial operations that yield a lighter or white appearance.

Chemical bleaching uses oxidizing agents such as chlorine-based reagents (chlorine gas, calcium hypochlorite, sodium hypochlorite) and peroxide-based systems (hydrogen peroxide, sodium percarbonate, peracids). Chlorine-based routes were historically dominant in textiles and pulp, but can produce environmentally persistent byproducts; many modern processes favor chlorine dioxide or peroxide bleaching to reduce chlorinated waste. Enzymatic bleaching employs oxidative enzymes such as peroxidases or laccases in combination with mediators to decolorize textiles, sometimes at lower temperatures and with fewer harsh chemicals. Oxygen bleaching and ozone are also used in pulp production and textile finishing.

Applications include textiles to whiten cotton, viscose and blends; paper bleaching to achieve higher brightness; and certain food applications, such as whitening flour or starch. In cosmetics and personal care, decolorization steps are used to adjust color characteristics in some products. Industrial bleaching can also refer to the treatment of effluents to remove residual color and contaminants.

Historically, bleaching began with sunlight, heat and alkaline substances. The advent of chlorine-based bleaching in the late 18th and 19th centuries significantly expanded capabilities, leading to bleaching powders and industrial hypochlorite solutions. In recent decades, environmental concerns have driven the shift toward peroxide-based and chlorine-dioxide methods and toward totally chlorine-free processes. Safety and environmental controls are essential due to the caustic nature of reagents and potential byproducts.