An eco-friendly rapid shrink-proofing finishing of wool fibers by protease based on substrate activation strategy

The protease method of wool shrink-proofing finishing is challenging to apply industrially due to its low efficiency and prolonged treatment time. In this study, the activator P[(CH 2 ) n OH] 3 , n∈(1, 10) and protease Savinase 16 L were combined and used in the same bath to rapidly degrade wool scales to achieve the target of machine washable for wool. The activator significantly improved the degradation efficiency of 16 L on wool's high-sulfur scale tissue, reducing the wool shrink-proofing treatment time to 100 s. The treated wool samples' area shrinkage, strength, elasticity, length, fineness, and directional friction effect were evaluated. The results showed that the activator combined with Savinase 16 L could rapidly hydrolyze wool fiber scales, and the wool area shrinkage was 1.65 % without excessive damage to the original properties of wool fibers. Furthermore, the reaction mechanism of wool scale degradation by protease and the activator was confirmed by Raman spectroscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results showed that the activator worked by activating the wool high-sulfur scale layer, thereby increasing the efficiency of the protease degradation of wool. It had no activating effect on the protease molecule. The activator opens the disulfide bonds on the wool scales while transforming the β-thinning and β-rotation in the scales to α-helix or random curling. It could promote protease adsorption and reaction on wool. Under pH 8.0 and 50℃, 2 g/L of activator could increase the adsorption of 16 L on wool by 12.7 times and increase the hydrolysis activity of 16 L on wool by 1575 times. After treatment with this technology, the content of -NH2, -COOH, and -SOx on the surface of wool was increased. Furthermore, a continuous multiple-padding wool shrink-proofing production line was designed, including a treatment liquid circulation and heat preservation systems. Stable industrial production applications were realized.