Mulberry silk fabric is highly prized for its natural luster, soft touch, and elegant drape. However, its protein fiber structure results in weak dye-fiber bonding, making colorfastness a key factor limiting its quality improvement. Colorfastness enhancement through compounding fixatives, which synergistically strengthen the chemical bond between dyes and fibers, is a core approach to improving the colorfastness of Mulberry silk fabric.
Traditional colorfastness enhancers often rely on single components. For example, cationic colorfastness enhances wet fastness by electrostatically adsorbing and binding with dye anions, but its direct binding force to fibers is limited. Modern colorfastness enhancement through compounding fixatives with different mechanisms of action creates a multi-dimensional bonding network. For instance, compounding cationic polymers with reactive colorfastness allows the former to rapidly adsorb dyes via ionic bonds, while the latter forms a stable structure with fibers and dyes via covalent bonds. This synergistic effect significantly improves wash fastness and rubbing fastness.
Reactive colorfastness enhancers play a crucial role in compounding systems. The active groups in its molecules (such as epoxy groups and chlorotriazine groups) can covalently react with the amino and carboxyl groups of silk fibers, while simultaneously forming cross-linked structures with the hydroxyl and amino groups of dye molecules. This dual bonding mode transforms dye adsorption into chemical fixation, significantly reducing the risk of dye detachment during washing or rubbing. For example, fixing agents containing multiple active groups can simultaneously form multiple covalent bonds with fibers and dyes, constructing a three-dimensional network structure and improving color fastness.
The addition of metal ion complexing fixing agents can further enhance the effectiveness of the compounding system. Rare earth elements (such as lanthanum and cerium) have large ionic radii and high charge densities, enabling them to form stable complexes with coordinating groups (such as hydroxyl and carbonyl groups) in dye molecules, while simultaneously binding with carboxyl groups in fibers, forming a "dye-metal-fiber" ternary complex structure. This structure not only improves the dye's resistance to hydrolysis but also reduces the thermal motion of dye molecules through steric hindrance, thereby improving light fastness and perspiration fastness.
The compounding application of bio-based color-fixing agents provides a green solution for mulberry silk fabric. Natural polyphenols such as tannins contain multiple catechol groups, which can bind to fibers through hydrogen bonds and simultaneously form hydrophobic stacks with dye molecules, reducing dye leaching. Compounding them with reactive color-fixing agents creates a bio-chemical dual-layer protective film on the fiber surface: the inner layer fixes the dye through covalent bonds, while the outer layer blocks external erosion through hydrogen bonds and physical adsorption. This composite structure improves color fastness while preserving the natural feel and breathability of mulberry silk.
The color-fixing agent compounding process must balance chemical action and physical penetration. The dense structure of mulberry silk fibers requires color-fixing agent molecules to have suitable size and charge distribution. Small-molecule reactive color-fixing agents can quickly penetrate into the fiber interior, while large-molecule cationic polymers can form a dense protective layer on the fiber surface. By controlling the molecular weight and charge density of each component in the compounding system, a synergistic effect of "internal fixation and external protection" can be achieved. For example, using a small-molecule fixing agent for internal cross-linking followed by surface sealing with a large-molecule polymer can significantly improve wash fastness.
Fixing agent compounding technology also needs to consider compatibility with the dyeing process. Mulberry silk dyeing often uses acidic or reactive dyes, and residual electrolytes, pH values, and unreacted dyes on the fiber surface after dyeing can all affect the fixing effect. Compound fixing agents need to have anti-interference capabilities, such as stabilizing the system's pH value by introducing buffer groups or removing metal ion interference through chelation. Furthermore, the timing of fixing agent addition and temperature control are crucial. Fixing after dyeing and before soaping can prevent excessive dye swelling; while low-temperature fixing (e.g., below 60℃) can reduce fiber damage while ensuring sufficient covalent bond formation.
The improvement in color fastness of mulberry silk fabric relies on multi-dimensional innovation in fixing agent compounding technology. By leveraging the chemical bonding of reactive fixing agents, enhancing the complexation of metal ions, promoting the green synergy of bio-based components, and precisely controlling process parameters, a stable composite system of dye-fixing agent-fiber can be constructed. This technological approach not only resolves the contradiction between fastness and hand feel in traditional fixing methods but also provides technical support for the high-end application of mulberry silk fabric, driving its continued development towards durable vibrancy and eco-friendliness.
