What is degumming of silk?

The degumming process of silk is also known as the scouring of silk. About 25% of the raw silk consists of undesirable constituents which is known as ‘silk gum’ or ‘sericin’. Sericin is a sticky substance produced by the silkworm that holds the strands of silk together. The process of removal of this silk gum or sericin from silk fibers is called degumming. Degumming of silk improves the sheen, color, hand, and texture of the silk fibers.

Removing the gum improves the sheen, color, hand, and texture of the silk. Because the gum can serve as a protective layer, it is typically left on the silk until it is ready to dye. In some cases, the fabric is woven to completion, and then degummed, to protect the yarn from abrasion on the loom. The process involved to remove these impurities is called ‘degumming’ or ‘scouring’ of silk. After the removal of gum from silk fibers around one-third of the weight of silk fibers may be lost.

The raw silk which contains the gum is called ‘Hard silk’ while the degummed silk after the removal of gum is called ‘soft silk’. The process of degumming also removes accompanying substances like fats, oils, natural pigments, and mineral components. The sericin covers the fibrous material and fibroin of silk and makes the surface of silk harsh, hence it must be removed to provide lustre and softness to the fiber. The degumming process brings out the supple and lustrous qualities of silk.

Degumming process is done by boiling the raw silk in soap solution at a temperature of 90°C to 95°C. Hence the main degumming agent is soap. The concentration of soap solution is around 20%–30% of the weight of the material. As per the quality of fiber, along with soap solution alkali can also be added. But, the degumming process can also be done by treating raw silk with different alkaline, neutral and enzymes such as acid proteases. This process is called enzyme degumming. This process is very famous in China. For enzyme degumming, proteolytic enzymes such as trypsin (of animal origin), pepsin, and papain (of vegetable origin) are used. In enzyme degumming, the gum must be swollen before the enzyme treatment, after which mild alkali is added to remove natural waxes, soil, and lubricant oils.