Development of processes using modified proteases for the reduction of felting and shrinkage of wool textiles
Four commercial proteases were characterised in terms of their activities, protein concentrations, optimum application conditions (pH and temperature) and suitable buffer systems in order to obtain maximum performance on wool. Different wool pre-treatments using oxidising or reducing agents in aqueous and solvent media were investigated. Effects of different types of surfactants on the activity of the protease Esperase were studied. Both non-ionic surfactant (Fabriwet NW) and anionic surfactant (Fabriwet AW) were compatible with Esperase and a specific type of anionic surfactant was found to significantly promote protease Esperase activity. Scanning electron microphotographs were used to monitor the degradation level of enzyme-treated wool samples as well as measurements of weight loss, tensile strength and shrinkage. Esperase was then covalently coupled to reversibly soluble-insoluble polymer Eudragit SI00 and LI00. Different coupling reactions in terms of polymer concentration, different washing methods to remove unmodified protease, presence or absence of l-Ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride (EDC) crosslinking agent and protease addition methods were investigated. The presence of EDC in the coupling reaction was confirmed to increase covalent fixation of the Esperase to the Eudragit and dropwise addition of enzyme also allowed more efficient covalent coupling. Washing of modified Esperase with acetate and phosphate buffer followed by Tris-Triton buffer was shown to give efficient removal of unmodified enzyme. The modification of proteases in this way not only increased their size so that they work on the surface of the wool cuticle but also increased their stability which is an important benefit from an industrial point of view. Results show that modified Esperase had a higher thermal stability than native Esperase at both 55 °C and 65 °C. Wool fabric was treated with modified Esperase and native Esperase at similar activity levels. Both showed similar improvement in wool shrink-resistance, however, wool fabric treated with modified Esperase presented less damage than that treated with native Esperase. Bio-scouring of wool fabric with modified Esperase improved fabric whiteness and it was possible to dye bio-scoured fabric at a lower temperature. Colourfastness was not affected. Pilot and bulk trials of production of modified Esperase were performed. These verified that modification of Esperase was able to control the reaction of the enzyme with the wool, and in all cases less degradation of the wool occurred than in similar treatments with the native Esperase. The dyeing properties of wool fabrics appear to be unaffected by treatment with modified Esperase and dyed fabrics show good colourfastness properties. All these results showed that use of the modified Esperase can be a promising alternative to the chlorination plus polymer treatment for wool shrink-resistance.
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