Abstract:

Objective Lyocell fibers are prone to high fibrillation owing to the friction under alkaline condition. In order to reduce the fibrillation behavior, herein, the effects of pretreatment process, like cold pad-batch desizing, hot-alkali desizing, enzyme desizing, bleaching, and mercerizing on the fibrillation phenomenon were investigated. The relationship between chemicals such as NaOH, H₂O₂, as well as treatment conditions like time and temperature, and fibrillation generation process was analyzed. Then, the pretreatment conditions and process of Lyocell woven fabric were optimized.
Method In this paper, in order to investigate the effect of desizing process on fibrillation phenomenon, cold pad-batch desizing, hot-alkali desizing, and enzyme desizing were conducted, respectively. Then, the desized Lyocell woven fabric was bleached and mercerized. The treatment conditions like time, pH value, temperature and the chemical concentration were determined. The capillary effect and whiteness were measured. The fibrillation behavior was determined using Martindale abrasion machine and observed with scanning electron microscope. From the comparison of the fabrics after the treatment of deszing, bleaching and mercerizing, the pretreatment process and conditions were optimized.
Results The effects of desizing processes on the properties of capillary effect, whiteness, and fibrillation behavior were investigated. In the cold pad-batch desizing of Lyocell fabrics, capillary effect and whiteness increased as the NaOH concentration increased from 10 to 30 g/L (Fig. 1 and Fig. 2). However, when the concentration of NaOH was above 25 g/L, the pilling grade decreased and fibrillation appeared. Comparatively, the pilling grade of the Lyocell fabric decreased from significantly when the concentration of NaOH is above 20 g/L using hot-alkali desizing (Fig. 5). It means that low temperature desizing could avoid the generation of fibrillation phenomenon to a certain extent. In enzyme desizing, the fabric obtained satisfactory capillary effect and whiteness at the enzyme concentration of 8 g/L with a batching time of 12 h. Moreover, the pilling grade maintained at 4 and no obvious fibrillation phenomenon appeared when the enzyme desizing condition varied. It was indicated that enzyme desizing was a good choice for good capillary effect and whiteness with lower fibrillation behavior. The influence of bleaching treatment on fibrillation behavior was presented (Fig. 13 and Tab. 3). In can be seen that, increasing the H₂O₂ concentration could significantly increase the whiteness, but fibrillation appeared when the H₂O₂ concentration was above 3 g/L and the treatment time was above 30 min. The effect of mercerizing on fibrillation was also investigated (Fig. 15 and Fig. 16). The result shows that, when the concentration of NaOH was above 125 g/L and the treatment time was above 1 min, serious fibrillation appeared on Lyocell fabric surface. The reason is that alkali treatment could cause obvious fiber swelling, then Na⁺ carried a large number of water molecules into the amorphous region of the fiber, resulting in the decrease of fiber lateral force.
Conclusion In the pretreatment process of Lyocell fabrics, obvious swelling and fibrillation could be caused by NaOH. From the comparison of cold pad-batch desizing, hot-alkali desizing and enzyme desizing, the last method could effectively reduce the fibrillation behavior of the Lyocell fabrics because there is no alkali consumed. H₂O₂ bleaching can further improve the whiteness of the fabric, but when the concentration is higher, the fabric of Lyocell will be slightly fibrillated. In addition, because Lyocell fabrics have less impurities than cotton, light bleaching process can be used to obtain higher whiteness. In addition, alkali mercerization can cause serious fibrillation, so mercerization was not suggested to be conducted in the pretreatment process. Therefore, in order to reduce the fibrillation tendency in Lyocell woven fabric pretreatment, low temperature, low alkali consumption or enzyme treatment was suggested.

Key words: Lyocell woven fabric, fibrillation, desizing, bleaching, mercerizing