Abstract:

Objective Fabrics made of viscose fibers are very popular because of their good hygroscopicity and breathability, as well as wearing comfort. However, the conventional printing on viscose fabrics with reactive dyes is both water and energy intensive. In addition, huge amount of urea is consumed to absorb moisture from the steam, assisting the dissolution of dyes and swelling of fibers, which is not environmentally friendly. In order to reduce the water, energy and urea consumptions in printing viscose fabrics with reactive dyes, a urea-free printing process based on the foam-assisted alkali feeding and wet steaming procedures is proposed.

Method In this study, the alkali agent was applied onto a viscose fabric printed with reactive dyes by pre-wetting with foam, and the moisture absorption function of urea was replaced by utilizing the steam condensation to produce water on the viscose fabric with low wet pick-up during steaming. The alkali-resistant stability of foam prepared by using sodium dodecyl sulfate (SDS) as the foaming agent and sodium alginate (SA) as the foam stabilizer was investigated. The influence of different factors on the color strength of viscose fabric printed with Reactive Red 24 was studied, and the comprehensive printing effects were also analyzed.

Results The drop emergence time (DET, t₀) and half-life period of decay (HPD, t_1/2) of the foam prepared with 4 g/L of SDS and 12 g/L of SA can reach 14.30 min and 80.67 min respectively, even when the mass concentration of sodium carbonate in the foaming stock solution was 90 g/L with a pH value of 11.51, indicating a good alkali-resistant stability. When the viscose fabrics printed with 3% (mass fraction) of Reactive Red 24 were screen printed with foam prepared with the foaming stock solution containing 4 g/L of SDS, 12 g/L of SA and 30 g/L of sodium carbonate, and then directly steamed at different temperatures for certain time without intermediate drying, the prints can obtain highest K/S value when steamed at 115 ℃ for 13 min. For the viscose fabrics printed with 3% (mass fraction) of Reactive Red 24, screen printed with foam prepared with foaming stock solution containing 4 g/L of SDS, 12 g/L of SA and 10-70 g/L of sodium carbonate, and then steamed at 115 ℃ for 13 min, the K/S value of the prints reached the highest when the concentration of sodium carbonate was 30 g/L. For the registration pattern on viscose fabrics printed with both 3% (mass fraction) of Reactive Blue 19 and Reactive Red 24 in sequence, followed by screen printing with foam prepared with foaming stock solution containing 4 g/L of SDS, 12 g/L of SA and 30 g/L of sodium carbonate, and then steamed at 115 ℃ for 13 min, the outline of the pattern was found clear and smooth, and no obvious bleeding was observed, indicating acceptable pattern sharpness. For the viscose fabrics printed with 1%, 3% and 5% (mass fraction) of Reactive Red 24 using the proposed foam-assisted alkali feeding-wet steaming procedure and the conventional all-in method, the color build-up property was good for both of them, the color levelness of the prints obtained from the proposed printing process was a bit poorer than that from the all-in method, the color fastness to dry rubbing of the prints both reached grade 4-5 or above, and the wet rubbing fastness of the prints obtained from the proposed process was a bit better than that from the all-in method, with a grade of 4 or above for the former.

Conclusion The foaming stock solution formulated with SDS as foaming agent and SA as foam stabilizer has good alkali-resistant stability, with DET and HPD of 14.30 min and 80.67 min, respectively, even when the mass concentration of sodium carbonate was 90 g/L and the pH of 11.51, with 4 g/L of SDS and 12 g/L of SA in the solution. The appropriate conditions for printing viscose fabric with 3% (mass fraction) of Reactive Red 24 using the foam-assisted alkali feeding-wet steaming process are 30 g/L of sodium carbonate, steaming at 115 ℃ for 13 min. The printed viscose fabrics using the developed process have acceptable pattern sharpness with no obvious bleeding, good color build-up property, the color fastness to dry and wet rubbing can respectively reach up to grade 4-5 or above as well as grade 4 or above. In general, although attempts are needed to improve the color levelness, the proposed printing process has the potential to reduce the water, energy and urea consumption in printing of viscose fabric with reactive dyes.

Key words: urea-free printing, reactive dye, viscose fabric, foam stability, feeding alkali with foam system, wet-steaming fixation