Low temperature water-saving bio-degumming of natural silk using thermophilic protease

Abstract

Degumming of natural silk is energy and water-consuming process which is usually carried out at the boil for 3 h in three consecutive water baths or by using alkaline soapy solutions. Herein, we adopted an energy and water-saving green method for degumming of raw natural silk by the thermophilic protease enzyme (TPE) from Bacillus safensis FO-36bMZ836779 strain. Bio-degumming of natural silk was carried out using different enzyme concentrations, temperatures, duration and pH. The dyeability of the conventionally and bio-degummed natural silk towards acid dye was investigated. To save more energy and water, a one-bath degumming and dyeing of natural silk was conducted in two successive steps. The chemical, physical and mechanical properties of the bio-degummed silk fibers were studied using amino acid analysis, SDS-PAGE electrophoresis, scanning electron microscopy, X-ray diffraction pattern, whiteness index, and tensile strength. The chemical and biological oxygen demand as well as the total dissolved and suspended salts of the bio-degumming effluent were measured. Results of study show this that the amount of sericin obtained from bio-degumming of silk at the optimum conditions (50% v/v at 55 °C for 3 h) is very close to that obtained by the energy and time-consuming conventional degumming process. The degree of whiteness of the bio-degummed natural silk was highly improved without any negative impact on dyeability and mechanical properties. No severe deterioration of the bio-degummed fibre surface was detected by the SEM micrographs. The molecular weight of sericin extracted by degumming process is lower than that obtained by conventional degumming of natural silk.