Textile bleaching

• 1. Ancient Grassing Methods

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  An Egyptian list found in the tomb of Rekh-mi-re at Thebes mentions bleached linen as early as 1000 BC. This document proves that people removed natural color from fabric over two millennia ago. Wood ash, known as potash or impure potassium hydroxide, served as an early form of soap for this task. By 1 AD, communities were washing cloth in a solution of ashes called lye and leaving it exposed to sunlight. This process became known as Grassing because workers laid linens on grass fields for over seven days after boiling them with lyes. Bleachfields were open areas near watercourses where these textiles dried under the sun. Linen has long been bleached in Europe using this specific method. The Dutch began bleaching by about the 12th century and soaked their cloth in soured milk baths for five to eight days. This step softened and neutralized the harsh effects of the caustic lye used earlier.

• 2. Chemical Bleach Revolution

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  The French chemist Claude Louis Berthollet first demonstrated the bleaching properties of chlorine around 1789. His work marked the transition from outdoor grassing to indoor chemical treatments. James Watt brought this knowledge to Britain shortly thereafter. A fellow Scot named Charles Tennant patented a more practical bleaching powder that made chlorine-based methods commercially successful. Around 1756, Scottish doctor Francis Home proposed using a weak solution of sulphuric acid instead of sour milk. John Roebuck manufactured sulphuric acid commercially, which reduced soaking time to just twelve to twenty-four hours. Chemical bleaching rose above Grassing because it was quicker and possible indoors. The discovery of Chlorine in the late 18th century changed how industries approached textile manufacturing forever.

• 3. Industrial Regulation And Trade

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  The English East India Company imported bleached, painted, and printed calico from India during the 17th century. This trade disrupted existing English silk and wool markets significantly. Parliament passed the Encouragement of Manufactures Act 1698 to prohibit wearing printed calicos from China, India, or Persia. A second law in 1721 banned all printed, painted, stained, or dyed calicoes entirely. These restrictions stimulated demand for linen and fustian fabrics within England. The Calico Acts were finally repealed in 1774 when cloth could be made using imported cotton from America. Bleachfields became common features in and around mill towns during the British Industrial Revolution. These regulations shifted global trade patterns for cotton and linen while forcing domestic manufacturing growth.

• 4. Oxidative Versus Reductive Agents

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  Bleaching agents attack chromophores and alter the color absorbing properties of objects. Oxidative bleaching generally uses sodium hypochlorite, sodium chlorite, or sulfuric acid. Hydrogen peroxide serves as a major source of chemical bleaching for textiles and wood pulp globally. Around sixty percent of world hydrogen peroxide usage goes toward these specific applications. Oxygen acts as a degrading agent that destroys phenolic groups and carbon, carbon double bonds. Vegetable fibers like cotton, ramie, jute, and animal fibers such as wool are typically bleached with oxidative methods. Regenerated fibers including bamboo also fall into this category. Reductive bleaching employs sodium hydrosulphite, which is a powerful reducing agent. Fibers like polyamides, polyacrylics, and polyacetates can be treated using reductive bleaching technology instead.

• 5. Optical Brightening Technology

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  Optical brightening agents absorb light in the ultraviolet and violet region between 340 and 370 nanometers. They then re-emit light in the blue region typically from 420 to 470 nanimeters through fluorescence. These compounds make textile material appear more brilliant white after scouring and bleaching steps. OBAs come available in different tints such as blue, violet, and red shades. The term bleach originates from a French word signifying to whiten. Bleaching involves whitening by removing substances that impart color to the material undergoing treatment. This process decolorizes the material after it has been scoured. Optical brighteners function alongside traditional chemical methods to enhance visual brilliance.

• 6. Modern Continuous Processing Ranges

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  A continuous bleaching range consists of several compartments where fabric moves from one side to another. Guide rollers help transport the material through these machine sections. Fabric gets treated with chemicals, heated, rinsed, and squeezed during this cycle. Continuous bleaching is possible for fabrics in open-width or rope form. Scouring removes impurities like waxes and pectins while making textile material hydrophilic or water absorbent. This first step occurs at room temperature or suitable higher temperatures with wetting agents added. Alkali helps prepare the fiber before the actual bleaching begins. Modern machinery treats fabric through guided rollers, heating elements, rinsing cycles, and squeezing mechanisms simultaneously.