Abstract:

Objective Alkali-agent degumming printing is a traditional craft with significant cultural value. However, its contemporary development is constrained by technical bottlenecks such as limited pattern precision and low efficiency. To address these challenges, this study explores a novel alkali gel degumming process. Through scientific and quantitative research, it aims to resolve existing technical limitations and promote the modern preservation and innovation of this traditional technique.

Method To achieve rapid and refined degumming of raw silk fabrics, this study developed an alkali gel printing process based on the synergistic effect of alkali, water, and heat. The gel was formed by the reaction between sodium hydroxide and sodium polyacrylate, and its high viscosity enables precise localization of degumming conditions. The optimal process parameters were determined by characterizing the degummed samples using scanning electron microscopy and infrared spectroscopy.

Results The experimental results indicated that sodium hydroxide concentration, hot-pressing temperature, and hot-pressing time all significantly affected the degumming rate of silk fabric. The degumming rate increased with higher sodium hydroxide concentration, showing a positive correlation. This is because the alkali moves sericin away from its isoelectric point, enhancing its swelling and dissolution. The degumming rate also got higher with increasing hot-pressing temperature. When the temperature increased from 60 ℃ to 100 ℃, the degumming rate improved from 25.63% to 27.12%, with consistent gains for every 10 ℃ increment. It was also showed that heat promoted the transfer of alkali through moisture in the gel to the silk fiber surface, creating a synergistic alkali-water-heat condition essential for degumming. However, excessively high temperatures caused rapid moisture evaporation, leading to premature drying and suppressed degumming. The effect of hot-pressing time on degumming rate followed an initial increase followed by a decrease. Extending the time from 30 s to 90 s led to rise of the degumming rate from 25.31% to 26.67%, during which sericin swelled and separated from fibroin. Further extension to 120-150 s reduced the degumming rate to 24.53%, due to moisture loss causing re-solidification of sericin and adhesion to fibroin. Orthogonal tests showed the following influencing factors ranking, which is sodium hydroxide concentration > hot-pressing temperature > hot-pressing time. FTIR analysis confirmed that the chemical structure of fibroin remained unchanged under optimal degumming conditions, with its conformation still dominated by β-sheets, β-turns, α-helix, and random coils.

Conclusion The alkali degumming of raw silk fabric relies on the synergistic effect of alkali, water, and heat. This study developed an alkali gel by neutralizing sodium polyacrylate with sodium hydroxide, which can precisely provide the necessary conditions for localized degumming. Experimental results verified that under the optimized parameters - 3% sodium hydroxide mass fraction, 90 ℃, and 120 s, effective degumming was achieved, resulting in a smooth fiber surface with intact chemical structure. Furthermore, by controlling the mass fractions of sodium hydroxide and sodium polyacrylate within 3%-3.5% and 8%-9%, respectively, optimal pattern contour precision was obtained. The alkali gel process developed in this study enables rapid and precise degumming printing on raw silk fabric, overcoming the limitations of traditional alkali boiling and steaming methods in terms of pattern flexibility and fineness, thereby providing a new technical approach for modern silk degumming and printing.

Key words: alkaline gel, degumming printing, raw silk fabric, fineness, microstructure, printing, pre-treatment, degumming