Abstract:

Objective Cotton fiber is a natural cellulose fiber with a wide range of applications. Cotton spunlace nonwovens as a cotton fiber product are widely used in medical textile and personal protection. However, for degreasing and bleaching of cotton spunlace nonwovens, the conventional cold pad-batch process faces the problems of long processing time and low production efficiency. Therefore, novel technologies need to be developed to reduce cold pad-batch time and improve production efficiency.

Method The cotton spunlace nonwovens were plasma treated using PG-10000F plasma equipment, and the treatment solution prepared from 4 g/L NaOH, 6 g/L H₂O₂, 2 g/L tetraacetylethylenediamine(TAED), and 2 g/L fatty alcohol polyoxyethylene ether was stirred evenly by magnetic stirring. After plasma treatment, the cotton spunlace nonwoven was immediately put into a self-sealing bag containing hydrogen peroxide activation solution with a bath ratio of 1∶20, then reacted within a certain time from 0 to 24 h at 30 ℃. The cotton spunlace nonwoven was then soaked in warm water at 60 ℃, and washed with water twice for removing impurities. Finally, the degreased/bleached cotton nonwoven fabric was obtained after drying in an oven at 40 ℃ for 4 h.

Results The pores formed by plasma treatment were properly eliminated in the bleaching process (Fig. 3). Plasma treatment and hydrogen peroxide activation treatment were adopted to smooth the fiber surface (Fig. 4), while the plasma treatment removed lipid substances from the surface of cotton fibers and improve the hydrophilicity of cotton fibers (Fig. 5). Plasma treatment time and cold pad-batch time were unchanged for all samples, and the material whiteness was the highest when the plasma treatment power was at 2 kW (Fig. 6(a)) and the plasma treatment time was 10 s (Fig. 6(b)). Plasma treatment power and plasma treatment time remained unchanged, and there was no significant change in whiteness after 6 h of cold pad-batch time (Fig. 6(c)). As the plasma treatment power increased, the water absorption showed an upward trend, and gradually flattened after the power reached 2 kW (Fig. 7(a)). The plasma treatment time had little influence on the water absorption of the material (Fig. 7(b)). The water absorption showed an upward trend with the increased cold pad-batch time, and the first 2 h increased the fastest (Fig. 7(c)). The plasma treatment power displayed no significant influence on the material strength (Fig. 8(a)). With the prolongation of plasma treatment time, the strength showed a decreasing trend, and had no significant change after 15 s (Fig. 8(b)). With the prolongation of cold pad-batch time, the material strength decreased rapidly within 4 h, and then gradually flattened (Fig. 8(c)). According to response surface analysis, plasma treatment power and plasma treatment time showed no significant influence on the whiteness of cotton spunlace nonwovens (Fig. 9). The cold pad-batch time had the greatest influence on the whiteness of nonwovens, and the whiteness increased rapidly at first and then decreased slowly with the increase of the cold pad-batch time (Fig. 10). The whiteness increases first and then decreased with the plasma treatment time, and the increased and decreased proportion of whiteness was almost the same (Fig. 11). When the whiteness of the response value was set to the maximum (76%), the optimal condition from the response surface optimization implied the plasma treatment power was 1.828 kW, and the plasma treatment time was 10.804 s. When the cold reactor time was 6.454 h, the whiteness was 75.872%, R²=0.923 5, indicating an accurate model.

Conclusion In summary, plasma treatment could moderately remove the cotton seed shell and other foreign impurities on the surface of cotton spunlace grey nonwoven fabrics. At the same time, lipid substances were removed from the surface of cotton fiber after plasma treatment, the number of hydrophilic groups such as hydroxyl increased, and the water absorption of cotton spunlace nonwovens were improved. Plasma treatment could promote the degreasing and bleaching process. Although the plasma cold pad-batch treatment process could hardly increase the treated cotton spunlace nonwovens whiteness, the cold pad-batch time were shorted from 8 h to 6.5 h compared with the conventional cold pad-batch process, which could improve the production efficiency.

Key words: response surface method, plasma technology, cold pad-batch, cotton spunlace nonwoven, degreasing and bleaching process, spun reinforcement