Textile manufacturers often bleach cotton fabric to remove color impurities before dyeing. This process commonly involves oxidizing the natural colorants in fiber with hydrogen peroxide under strong alkali conditions, and it can be accelerated by steaming the fabric after the chemicals are applied. But those harsh processing conditions can damage cotton fibers, and steaming times of as much as 50 minutes consume large amounts of energy.
Researchers from Jiangnan University and Nantong University report a method for bleaching cotton fabrics that achieves optimal whiteness in just four minutes of steaming time, with very little fiber damage (ACS Sustainable Chem. Eng. 2018, DOI: 10.1021/acssuschemeng.8b00912).
The method relies on a bleach activator, N-[4-(triethylammoniomethyl)benzoyl]caprolactam chloride (TBCC). Bleach activators react with hydrogen peroxide in aqueous solution to form peracids that are active at lower temperatures than hydrogen peroxide. Unlike other reported bleach activators, TBCC is cationic, so it is ideal for interacting with textile fibers that tend to develop a negative charge in water, says Peter Hauser, a retired professor at the North Carolina State University College of Textiles. Hauser was part of the NCSU team that invented and patented TBCC. He called the new paper “a pretty good step forward.”
The researchers report that fabric bleached using TBCC and a 4-minute steaming period was just as white as fabric steamed for 50 minutes without the use of a bleach activator, with no apparent chemical damage to the cotton fibers. Hauser says that although the chemical costs may be higher using this process, industrial users may find the improved production efficiency and higher-quality product to be worth that extra cost.
The rapid TBCC bleaching method incorporates sodium citrate for pH control, a less-harsh alternative to the sodium hydroxide commonly used in hydrogen peroxide bleaching processes.
The researchers are working to evaluate the environmental impact of the process, as well as to simplify the synthesis of TBCC to reduce its production cost.