| Bleaching process is an important stage in pretreatment of cotton fabric, which isresponsible for remove coloring matter and some other impurities, providing a white substratefor the subsequent dyeing and finishing. Bleach with hydrogen peroxide (H2O2) istraditionally carried out under alkaline conditions at temperatures higher than95oC. This notonly consumes extensive energy, but also gives rise to severe fiber damage. By adding aso-called cationic bleach activator, namely N-[4-(triethylammoniomethyl)benzoyl]caprolactam chloride to H2O2solution, an activated peroxide system can be formed andapplied for low-temperature bleaching. Therefore, the TBCC-activated peroxide system hasadvantages of saving energy and reducing fiber damage.Normally, TBCC are synthesized in two steps using two baths:1) caprolactam and4-chloromethylbenzoyl chloride were added to toluene for reaction at reflux for about5hoursto give the intermediate products;2) an intermediate product and triethylamine were added toacetonitrile for reaction at reflux for about4hours to give final product. This synthesismethod involves complex operations and extensive energy consumption. In this project, it wasproposed that TBCC were synthesized in two steps but in one bath. Using this method,caprolactam,4-chloromethylbenzoyl chloride and triethylamine were added to acetonitrile,firstly reacting at room temperature to give intermediate product, and then reacting at reflux togive the final product. TBCC was synthesized by this method with a yield of up to94.7%,while the two-bath two-step method provided a yield of only58.4%.In order to understanding the influence of the alkyl chain length on the bleachingperformance, N-[4-(dimethylalkylammonio)benzoyl]caprolactam chlorides were designed andsynthesized with various length of alkyl chains. These new cationic bleach activators wereconfirmed using1H NMR,13C NMR and LC-MS. Activated peroxide system were establishedusing these new bleach activators for cotton bleaching at50oC and pH7.2. Experimentalresults showed that the bleaching performance was slightly enhanced as the alkyl chain lengthincreased from C2to C8while the bleaching performance was significantly reduced as thealkyl chain length increased from C8to C16. When the alkyl chain length was lower than C8,the increase in the alkyl chain length was beneficial to enhance the interaction between thecationic bleach activator and cotton fibers, resulting a better bleaching performance; however,when the alkyl chain length was greater than C8, the increase in the alkyl chain length led tostearic hindrance which limited cationic bleach activators penetrated into cotton fibers,thereby resulting in a reduced bleaching performance. |
