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

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 degrees 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.

Automated summary

In this study, a green method for degumming natural silk using a thermophilic protease enzyme was adopted, which resulted in a high degree of whiteness of the silk fibers without compromising dyeability and mechanical properties. Additionally, the degumming process extracted sericin with a lower molecular weight compared to conventional methods.