The bio-enzymatic degumming process for mulberry silk fabric achieves efficient removal of sericin while preserving the fiber's natural luster to the maximum extent through precise control of enzymatic hydrolysis conditions. The core of this process lies in utilizing proteases to selectively hydrolyze the structural differences between sericin and fibroin. Simultaneously, by optimizing parameters such as temperature, pH, enzyme concentration, and reaction time, excessive hydrolysis of the fiber surface is avoided, resulting in a rough texture and maintaining its smooth and translucent properties.
The key to bio-enzymatic degumming is the specificity of the enzyme. Although both sericin and fibroin are proteins, the former has a globular structure containing a large number of polar side-chain amino acids, making it easily recognized and hydrolyzed by proteases; the latter has a linear crystalline structure, mainly composed of non-polar amino acids such as alanine and glycine, exhibiting natural resistance to enzymatic hydrolysis. This structural difference allows proteases to precisely target sericin, while the fibroin fiber remains intact. For example, the 2709 alkaline protease can efficiently decompose sericin in an environment of pH 9.0, while causing almost no damage to the fibroin, thus ensuring that the fiber surface remains smooth after degumming.
Temperature control is the core element in preserving luster. The activity of proteases is closely related to temperature; excessively high temperatures lead to enzyme denaturation and inactivation, while excessively low temperatures reduce reaction efficiency. Typically, papain reaches its optimal activity balance at 70℃, and alkaline protease 2709 at 45-50℃. Within this temperature range, enzyme molecules can fully bind to sericin and catalyze hydrolysis, while avoiding thermal shrinkage or surface swelling of the silk fibers caused by high temperatures, thus preventing a decrease in luster. For example, after 4 hours of treatment with alkaline protease 2709 at 45℃, the residual sericin rate of tussah silkworm cocoons can be reduced to below 3%, while the fiber surface remains smooth.
Precise pH adjustment directly affects the enzymatic hydrolysis effect. Sericin easily swells and dissolves in an alkaline environment, but excessive alkalinity will damage the fibroin structure. Biological enzymatic degumming typically controls the pH within a weakly alkaline range of 7.0-10.0 to ensure enzyme activity while avoiding fiber damage. For example, papain can effectively decompose sericin under neutral conditions, while alkaline protease 2709 exhibits the highest activity at pH 9.0. Maintaining pH stability by adding a buffer ensures a uniform enzymatic hydrolysis process, preventing fiber roughness caused by localized over-hydrolysis.
Synergistic optimization of enzyme concentration and reaction time is crucial for preserving luster. Too low an enzyme concentration leads to incomplete degumming, leaving residual sericin that affects luster; too high a concentration may cause slight hydrolysis of the fibroin surface, reducing fiber strength. Typically, papain concentration is controlled at 0.5-6 g/L, while alkaline protease 2709 is most effective at 4-6 g/L. Reaction time needs to be adjusted according to fiber thickness, with a single treatment of 40-150 minutes, or using staged degumming (e.g., 40 minutes + 20 minutes) to improve efficiency. For example, after treating silk fabrics with 2.0-2.5 g/L protease at 40-50℃ for 40-45 minutes, the wicking strength can be increased to 12.5 cm while maintaining a smooth surface.
The combination of pretreatment and post-treatment processes further enhances the luster retention effect. Pretreatment involves soaking in a weak alkaline solution to fully swell the sericin, weakening its binding force with fibroin and promoting uniform enzymatic hydrolysis. Post-treatment involves multiple washes to remove residual enzyme solution and sericin hydrolysis products, preventing yellowing and hardening over time. For example, irregular fuzz easily appears on the fiber surface after soap-based scouring, while the surface is smooth and glossy after enzymatic scouring, thanks to the precise coordination of pretreatment and post-treatment.
Innovative applications of composite processes provide new ideas for luster preservation. Ultrasonic-assisted enzymatic hydrolysis accelerates sericin removal through cavitation effects, while reducing enzyme dosage and reaction time. For example, adding ultrasonic treatment to papain solution can reduce the sericin content to 0.57% and improve the material's thermal stability. Furthermore, low-temperature bleaching technology utilizes mild oxidants such as peracetic acid to further remove residual pigments after enzymatic hydrolysis, avoiding damage to fibers caused by traditional bleaching agents, thus ensuring a lasting luster.
The bio-enzymatic degumming process achieves efficient sericin removal and perfect preservation of fiber luster through precise control of enzymatic hydrolysis conditions. Its core lies in utilizing the specificity of enzymes, optimizing reaction parameters, coordinating pretreatment and posttreatment, and enhancing the effect through composite processes. This technology not only meets the high requirements of mulberry silk fabric for luster but also aligns with the trend of green and environmentally friendly production, providing an ideal solution for the processing of high-end silk products.
