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1. Impact of Bioregeneration Cotton Yarn Fiber Properties on Color Absorption Uniformity
Bioregeneration cotton yarn, also known as bioregenerated cotton yarn, exhibits exceptional dyeing properties due to its unique fiber structure. Compared to traditional virgin cotton, bioregenerated cotton yarn is typically composed of two main types of fibers: regenerative cotton or recycled cotton.
1.1 Morphological Heterogeneity of Recycled Fibers
For bioregenerated cotton yarn derived from recycled cotton, the raw materials undergo mechanical or chemical decomposition and respinning. This process results in irregular fiber length, varying maturity, and varying damage.
In the dyeing solution, these morphologically diverse fibers exhibit distinct adsorption kinetics and diffusion rates. Mechanically regenerated staple fibers often expose more cellulose hydroxyl groups at their ends, but they may also experience some exfoliation of the cuticle or primary wall. This results in localized fluctuations in color absorption capacity.
The core challenge of color absorption uniformity lies in the fact that the physical or chemical stresses introduced during the regeneration process alter the fiber's microporous structure. If pre-treatment fails to fully homogenize the fiber's hydrophilicity, the resulting dyed yarn or fabric is prone to exhibiting streaky or skittery colors, shade variations, or tailing-leading differences.
1.2 The Compatibility Advantages of Regenerative Cotton
Yarn derived from regenerative cotton, due to its cultivation practices that promote healthy soil, has a fiber structure more similar to high-quality virgin cotton and exhibits less morphological heterogeneity. This type of cotton fiber exhibits improved initial affinity and equilibrium uptake for color absorption, laying a solid foundation for uniform dyeing.
2. Color Fastness Performance and Chemical Structure Challenges
Color fastness is a key indicator of a textile's ability to maintain color stability against external factors (such as washing, friction, and light). The color fastness performance of bioregenerated cotton yarn is closely related to the dye class and fixation efficiency used.
2.1 Direct and Reactive Dye Selection
Direct dyes and reactive dyes are primarily used for cotton fibers.
Direct dyes bind to cellulose molecules through van der Waals forces and hydrogen bonds, resulting in a simple fixation mechanism, but generally exhibit low wet fastness. For regenerated cotton fibers containing more amorphous regions, direct dyes may adsorb more rapidly, but desorption may also be faster.
Reactive dyes form chemical bonds with cellulose hydroxyl groups through covalent bonds, resulting in excellent washing and rubbing fastness. However, due to micro-cracks on the surface of regenerated cotton fibers, the effective collision rate (ER) between dye molecules and active sites and the fixation rate (FR) may be affected. The use of fixing agents or cross-linking agents is a key finishing step in improving the wet fastness of reactive dyes.
2.2 Relationship between Cellulose Degradation and Light Fastness
Some regenerated cotton may undergo a certain degree of cellulose depolymerization during the recycling process, resulting in a decrease in the degree of polymerization (DP). A decrease in DP value makes the fiber more sensitive to UV radiation and oxidizing agents.
This sensitivity may indirectly affect light fastness. Under light, the damaged cellulose structure is susceptible to degradation, and the dye molecules, as chromophores, are also susceptible to structural disruption or redox reactions, leading to fading or shifting of color. The application of antioxidants or UV absorbers in the finishing stage is an effective technical approach to improving light fastness.
3. The Synergistic Effect of Finishing Technologies on Performance
High-quality bioregenerated cotton yarn or fabric relies on a meticulous finishing process.
Softening is essential for improving the feel of regenerated cotton yarn. Due to the roughness and unevenness of regenerated fibers, hydrophilic softeners that do not affect color fastness are required to prevent the formation of a hydrophobic film, which in turn reduces the fabric's breathability and washability.
Shrinkage control is crucial for cotton fabrics. Resin finishing can improve dimensional stability. However, formaldehyde emissions from the resin must be strictly controlled, especially for bioregeneration cotton products that prioritize sustainability and biosafety. The selection and implementation of finishing technologies are crucial factors in determining whether bioregenerated cotton yarn can meet the quality requirements of the high-end textile market.
