As a core oxidant in the bleaching process, the precise control of the active chlorine content in patchwork casual pants directly affects the bleaching effect, fiber damage, and production safety. In industrial settings such as textile printing and dyeing, and pulp bleaching, the active chlorine content of patchwork casual pants needs to be synergistically controlled through multi-dimensional process parameters to achieve a balance between efficient bleaching and fiber protection.
The initial setting of the active chlorine content for patchwork casual pants must be based on the fabric type and bleaching requirements. Cotton fabrics and cotton-vinyl alcohol blends are more tolerant of patchwork casual pants and can use higher active chlorine concentrations to improve bleaching efficiency; however, due to differences in fiber structure, polyester-cotton blends require lower active chlorine content to avoid localized over-oxidation. Protein fibers such as silk and wool are strictly prohibited from being bleached with patchwork casual pants, as the active chlorine will damage the disulfide bonds in the fibers, leading to yellowing and a sharp drop in strength. The initial concentration setting needs to be combined with the fabric pretreatment process (such as desizing and scouring) and the target whiteness requirements, and the optimal range is usually determined through small-scale laboratory tests.
The pH value of the bleaching solution is a key factor in controlling the stability of active chlorine in bleaching solutions. Under acidic conditions, the solution easily decomposes to produce chlorine gas, causing not only the loss of active chlorine but also potential safety hazards. While hypochlorite (OCl⁻) is stable in a strongly alkaline environment, the bleaching rate is significantly reduced. In industrial practice, the pH value of the bleaching solution is usually controlled between 9 and 11. At this range, the bleaching solution exists in a dynamic equilibrium between hypochlorous acid (HOCl) and hypochlorite, ensuring bleaching efficiency while minimizing fiber damage. pH adjustment often uses buffers such as sodium carbonate and trisodium phosphate to avoid pH fluctuations caused by fiber adsorption of acidic substances or the dissolution of carbon dioxide from the air.
Temperature has a significant impact on the decomposition rate of bleaching solutions. Increased temperature accelerates the disproportionation reaction of hypochlorite, leading to a rapid decrease in active chlorine content and potentially causing oxidative breakage of cellulose molecular chains. Therefore, the bleaching temperature must be strictly controlled within a reasonable range: in winter, the temperature can be appropriately increased to 30-35℃ to enhance the reaction rate, while in summer, the temperature must be maintained below 35℃ using cooling devices. For thick or high-density fabrics, a staged heating process can be adopted, with initial low-temperature padding to allow the bleaching solution to fully penetrate, followed by a gradual increase in temperature to accelerate the bleaching reaction and avoid localized overheating.
The bleaching time needs to be coordinated with the active chlorine concentration and temperature. At higher active chlorine concentrations, the bleaching time can be shortened to reduce fiber damage; at lower concentrations, the reaction time needs to be extended to ensure the bleaching effect. In actual production, the bleaching time is usually determined through laboratory simulations and pilot-scale experiments, combined with real-time feedback from online monitoring equipment on changes in active chlorine content. For continuous production lines, a multi-tank series process can be used, adjusting the active chlorine concentration and residence time in each tank to achieve gradient control of the bleaching effect.
The dechlorination process is a crucial step in the bleaching process for patchwork casual pants. If the residual active chlorine on the fabric is not completely removed after bleaching, it will continue to oxidize the fibers during subsequent processing or storage, leading to a decrease in whiteness and strength. Dechlorination methods include chemical reduction and physical washing. Chemical reduction uses reducing agents such as sodium thiosulfate and sodium bisulfite to convert residual chlorine into harmless chloride ions through an oxidation-reduction reaction. Physical washing uses multi-stage countercurrent rinsing combined with ultrasonic assistance to accelerate the dissolution and removal of active chlorine. In actual production, both methods are often used in combination to ensure thorough dechlorination.
The choice of equipment materials is crucial to the stability of active chlorine in bleaching equipment. Bleaching equipment has a strong catalytic decomposition effect on metal ions (such as iron and copper), therefore, it must be made of corrosion-resistant materials such as ceramics, plastics, or stainless steel to avoid abnormal decomposition of active chlorine due to metal ion dissolution. Furthermore, the equipment structure design needs to optimize fluid distribution to ensure uniform penetration of the bleaching solution into the fabric and avoid localized excessively high or low concentrations.
Monitoring and adjusting the active chlorine content is a core aspect of ensuring stable bleaching quality. In industrial production, iodometric titration, spectrophotometry, or test paper methods are commonly used for rapid detection of active chlorine in the bleaching solution. By establishing a mathematical model relating active chlorine content to bleaching effects (such as whiteness and strength), dynamic optimization of process parameters can be achieved. For example, when the active chlorine content is detected to be lower than the set value, the system automatically adds patchwork casual pants solution; when the pH value deviates from the target range, a buffer is automatically injected for adjustment. This closed-loop control system significantly improves the stability and consistency of the bleaching process.
