Process And Mechanism Of Impart Wettability To Desized Cotton Canvas Without Alkali

The pretreatment of cotton fabric includes singeing, desizing, scouring and bleaching. The main purpose of pretreatment is to remove impurities, improve the wettability and whiteness of fabric, and get a better performance in order to meet the requirement of following dyeing and finishing. The traditional pretreatment of cotton fabric usually use caustic soda and hydrogen peroxide, and the treatment process is under high temperature and high pH value. The traditional pretreatment can bring good performance to the cotton fabric, but it has many disadvantages. For example, strong alkaline solution causing excessive decreased fiber strength, high energy and water consumption, the BOD and COD value of wastewater being too high, and pollution of the environment.This study was based on the existing work of our research group. By researching key affection factors that effect on the water absorption of desized cotton fabric, we aimed at to develop one pretreatment process which can save energy and reduce wastewater discharge, and finally achieve good social and economic benefits.All the researches were around the wettability of desized cotton fabric. By the reproducibility experiments and the extraction of wax and pectin, we analyzed the main factors impacted the wettability of cotton fabrics from the angle of mechanism. On the point view of cotton fabric itself, the content of cotton wax and the distribution of wax and pectin were the main factors which impact the wettability of cotton fabric. On the point view of pretreatment process, the residual surfactant on the fabric and drying method of the treated fabric also affected the evaluation of fabric wettability.Study about the effect of surfactant on the wettability of cotton fabrics showed that if washing wasn't sufficient, the residual surfactant on the fabric made the fabric have a "false capillary effect". The best washing method that could totally remove the surfactant from the fabric was to wash the fabric in boiling water for three times with 10min each time, then to wash in cold water for three times.The distribution of wax on the fabric would affect the wettability of the fabric. After cotton wax was partially removed, the distribution of wax was discontinuous which benefit to wicking. When the drying temperature exceeded the melting point of wax, wax inside the cotton fiber would swim to the surface of the fiber to form a continuous film, and affected on the wettability of the fabric.To extract wax and pectin respectively and tested the capillary effect of the fabric, the results showed that the content of cotton wax and the distribution of wax and pectin were the main factors which impacted wettability of cotton fabric.Through the orthogonal experiments studying on the impregnation process of cotton fabric pretreatment, the optimal combination of high-temperature oxidation one-step process was obtained as follows:treated in the boiling water for 10min, and then in the bath of H2O2 5.0g/L, NW800 1.5g/L, liquor ratio 1:20, PH value 11, temperature 90℃, for 60 min. The capillary effect of treated fabric was up to 12.9cm, and the whiteness was about 76.3. Both the wettability and whiteness were better than the effect by traditional alkali-peroxide one-bath pretreatment. The loss rate of warp yarn strength was 11%.We also obtained the optimal combination of two-step impregnation process which was accomplished by H2O2/TAED system bleaching without alkali under low-temperature after the pectinase souring. The optimal parameters of pectinase scouring was pectinase 2g/L, NW800 1.5g/L, pH value for 8, firstly treating in 55℃with 30min and then heating to 90℃and dealing with 20min. The optimal parameters of H2O2/TAED system bleaching without alkali under low-temperature was H2O2 4g/L, TAED/H2O2 molar ratio of 2:1, sodium pyrophosphate concentration of 3g/L, NW800 1g/L, pH value of 9, temperature 70℃, time for 45min. The capillary effect of treated fabric was up to 13.8cm, and the whiteness was about 73.4. The loss rate of warp yarn strength is 15.2%.In order to achieve continuous mass production, this paper also studied the feasibility of the padding process (pad- stack process, pad-steam process, and pad-stack-steam process). Because all the treatments were without alkali, wax could only be removed by emulsion. However, due to the fabric carrying little liquid after padding, there was no enough water as the dispersion medium. So the emulsion could not proceed effectively, and the wax could not be removed. All of these resulted in that the wettability of cotton fabric could not be improved. Even if increasing the processing temperature or extension the treatment time, it didn't work in improvement of the fabric's wettability.