Extremozymes for improving wool properties
Introduction
Hand and dyeing behaviour are important quality aspects for wool. Common finishing processes, such as oxidation of the wool surface by means of chlorination to increase the dyeing affinity or application of softening agents to modify the handle, improve these properties. A great disadvantage of these processes is the environmental pollution, e.g. AOX.
Enzymes can be used in order to develop environmentally friendly alternative processes. Since wool mainly consists of proteins and lipids especially proteases and lipases have been investigated for wool fibre modification. The ability of protease-catalysed processes to improve wool properties was the subject of former research projects at DWI. Wool treatment with mesophilic proteases leads to a reduced felting tendency and an increased dyeing affinity (DWI, Aachen, 1997; Heine et al., 1998). Both the cuticle and the cortex of the fibre are modified by proteolytic enzymes. Moreover, the handle of wool top and yarn can be improved by the reduction of the bending modulus as a result of a partial hydrolysis caused by proteases (Bishop et al., 1998).
Enzymes from extremophilic micro-organisms (extremozymes) such as thermo-, halo-, psychro-, alkali-, or acidophilic micro-organisms perform best under the corresponding extreme conditions (Sunna et al., 1996; Sunna and Antranikian, 1997). Therefore, the industrial use of extremozymes is regarded as promising. Aqueous treatments under constant temperature and pH conditions are most suitable for application of these enzymes. In the textile industry alkaliphilic enzymes could be used in alkaline washing processes and thermophilic and/or acidophilic enzymes under high temperature conditions and in acid dyeing processes respectively. A positive side effect of the high process temperatures suitable for thermophilic enzymes is the elevated diffusion rate. For economical reasons it is aimed at combining the extremozyme treatment with the procedures already established in the textile industry. A typical dyeing process on a winch beck at the cloth fabric Westmark (Mönchengladbach, Germany; TW) is used as a basis for the integration of a protease treatment. The dyeing process is conducted after a pre-washing step. Treatment conditions such as temperature and pH value are controlled.
Experimental series on a Turbomat laboratory dyeing machine (AHIBA) on wool top showed that the conditions of the pre-washing step are suitable for a thermo- and alkaliphilic protease. To minimize the fibre damage the added amount of protease was optimized accordingly.
Section snippets
Wool
Merino wool top, average fibre diameter 21.3 μm. Blended cloth with 70% wool, 20% polyester, 10% polyamide, atlas weave, weft higher amount of wool than warp (fabric 1). Wool twill cloth, average fibre diameter 23.16 μm (fabric 2). Wool twill cloth, average fibre diameter 22.26 μm (fabric 3).
Enzyme
Esperase 8.0 L, type A (Novo Nordisk) 8.0 U g−1 resp. 7.8 U ml−1.
Pre-washing on turbomat laboratory dyeing machine (AHIBA)
Fig. 1 shows the conditions of the dyeing process on a winch beck (TW). The enzyme treatment was integrated into the pre-washing step under
Degree of whiteness
Wool top and fabric were treated under the conditions of the pre-washing step on the AHIBA laboratory dyeing machine either with or without adding protease. The degree of whiteness of the wool samples increases with the amount of protease used. The reference wool top and reference fabric show the lowest degree of whiteness (Table 1).
The difference between the degree of whiteness of references and samples is significant. Increasing the amount of protease from 9.8 to 19.5 mU g−1 does not
Conclusion
The amount of protease used on the AHIBA and the winch beck does not result in an increased damage on wool fabric compared to the usual process conditions. This can be concluded from the results of the alkali solubility testing, the SEM pictures and the tensile strength measurements. Even though smaller amounts of protease cause loss in tensile strength on wool top.
The positive effects on the degree of whiteness, the felting tendency and the dyeability should become even more distinctive by
Acknowledgements
We would like to thank the German Federal Foundation Environment (DBU, Osnabrück, Germany) for their financial support of this project.
References (5)
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The use of proteolytic enzymes to reduce wool fibre stiffness and prickle
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(1998) - DWI, Aachen. 1997, Final Report of the AiF Research Project. ‘Entwicklung eines enzymatischen Verfahrens zur...
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