Abstract:

Objective Wool fibers feature a scaly cuticle layer, rendering wool fabrics prone to felting shrinkage during washing, wet-heat treatment, or mechanical action. This felting results in dimensional shrinkage, stiff hand feel, and reduced elasticity, significantly compromising fabric quality. To overcome limitations of traditional methods, such as complex two-bath processes and significant fiber damage, this study explores a simplified, low-damage one-bath finishing approach. Specifically, we developed a novel, eco-friendly single-bath finishing process utilizing green agents L-cysteine and bromelain under mild conditions. This single-step process efficiently disrupts the wool scale structure, effectively balancing anti-felting performance with tensile strength retention. It also enhances functional properties like dyeability and wettability, while substantially streamlining processing and reducing chemical consumption.

Method Fabrics were initially degreased using sodium dodecyl sulfate. Subsequently, the degreased wool fabrics underwent a novel one-bath, one-step anti-felting treatment employing a solution containing L-cysteine and bromelain. To evaluate the treatment efficacy and potential fiber damage, we measured: felting shrinkage using an automatic shrinkage tester; breaking strength with a fabric strength tester; alkali solubility; and surface thiol content. Additionally, surface morphology was examined by scanning electron microscopy, and chemical structural changes were analyzed by Fourier transform infrared spectroscopy. Furthermore, fabric wettability, hand feel, and dyeing properties were characterized using a contact angle meter, fabric style tester, and computer color matching system, respectively.

Results The synergistic one-bath one-step system integrating L-cysteine (L-cys) and bromelain (BRM) effectively addressed the limitations of low efficiency in single-protease systems and operational complexity in conventional two-bath bio-anti-felting processes. Mechanistic studies confirmed that L-cys selectively cleaves disulfide bonds within the scale layer, creating reactive sites that significantly enhance the proteolytic accessibility of BRM. This sequential mechanism (disulfide reduction followed by peptide hydrolysis) enables thorough scale exfoliation of cuticle scales while preserving the wool fiber integrity. Performance metrics indicated that felting shrinkage decreased dramatically from 23.12% in untreated fabric to 2.98% in treated samples, accompanied by a controlled breaking strength loss of merely 10.80%. Quantitative biochemical analyses further validated the mechanism, where alkali solubility was increased from 13.41% to 18.30%, indicating modified keratin solubility due to structural disruption, while surface thiol content surged from (1.43 ± 0.05) μmol/mg to (3.42 ± 0.06) μmol/mg, providing direct evidence of disulfide bond cleavage and cooperative interaction between the agents. Morphological characterization via scanning electron microscopy corroborated efficient and uniform scale removal, with no observable fibrillation or cortical damage. Fourier transform infrared spectroscopy analysis confirmed that the treatment exclusively targeted disulfide bonds and surface-exposed peptide linkages with no irreversible hydrolysis of the keratin polypeptide backbone, thereby minimizing core fiber damage. Functionally, the process enhanced multiple fabric properties, with wettability improved markedly (contact angle reduced from 136° to 80° and wetting time shortened to 120 s), and dyeing performance intensified (dye uptake rates reached 88.11% for Lanasol Golden Yellow and 58.64% for Acid Red B, with corresponding K/S values substantially exceeding untreated controls). Tactile attributes were optimized (softness increased to 87.53, smoothness elevated to 79.04, stiffness reduced to 14.41). These multidimensional improvements demonstrate the system's capacity to deliver high-efficiency anti-felting with minimal fiber compromise while concurrently upgrading functional performance.

Conclusion This study establishes a synergistic L-cysteine/bromelain one-bath system that achieves low-damage anti-felting finishing for wool textiles. The mechanism involves L-cysteine-mediated selective disulfide bond cleavage in the scale layer, which exposes reactive sites for bromelain to hydrolyze peptide bonds. This sequential action enables profound scale exfoliation while maintaining the structural integrity of the fiber cortex, reducing felting shrinkage to 2.98% with only 10.80% breaking strength loss. Optimal parameters (3.0 g/L L-cysteine, 60 U/mL bromelain, pH 7.0, 55 ℃, 90 min) balance anti-felting efficacy and mechanical integrity. The treatment concurrently enhances functional properties of wool fabric, where alkali solubility is increased and thiol content confirms structural modification, while scale removal improves dye uptake and wettability with elevated softness and smoothness indicating improved hand feel. Compared to traditional two-bath or chemical-intensive methods, this one-bath approach simplifies production flows, eliminates hazardous reagents, and reduces environmental footprint. Consequently, the L-cysteine/bromelain system establishes an eco-efficient industrial bio-anti-felting strategy that delivers superior performance with minimal fiber damage, demonstrating strong potential for green textile applications.

Key words: anti-shrinkage finishing, wool fabric, L-cysteine, bromelain, bio-enzyme, one-bath process