Degumming Process of Silk Fibre

Posted by Default on December 27, 2018 in

Silk degumming: 
Degumming is the process of removing the sericin, or silk gum, from silk. The main objective of silk degumming process is to impart soft handle and lustre to silk by removing sericin, any impurities picked up during reeling throwing etc. Sericin is the important element of silk. You can see chemical composition of silk below section. Degumming can be carried out on yarn or fabric, in manually or mechanically operated machines. Mechanisms of degumming remain to be investigated.


Raw silk does not possess the luster and softness for which this fiber is known. The gummy substance called sericin (about 20%–25% in mulberry silk and about 15% in wild silk) covering the fibrous material, fibroin, imparts a harsh handle and must be removed in order to bring out the supple and lustrous qualities. Although sericin and fibroin, the two components of raw silk are both proteins, they differ considerably in their relative compositions of various amino acids and accessibility. Degumming also removes accompanying substances such as fats, oils, natural pigments, and mineral components. The thorough and uniform removal of these impurities are important not only for uniform dyeing, but also particularly for good printing results. The process for removal of sericin is known as degumming, boiling off, and less commonly scouring.

Figure: Degumming process: (a) silk in first degumming solution, (b) silk in second degumming solution, (c) neutralization silk fibers, (d) degummed silk fibers before drying, (e) degummed silk fibers after drying. (Image courtesy: https://www.researchgate.net)

Chemical composition of silk fiber:

The composition of raw silk is as follows: 

• Fibroin - 70-80%
• Sericin - 20-305
• Waxy matter - 0.4-0.8%
• Carbohydrates - 1.2-1.65
• Inorganic matter - 0.7%
• Pigment - 0.2%

Degumming methods: 
There are some methods of degumming of silk. Following are the main degumming processes: 

1. Extraction with water.
2. Boil-off in soap.
3. Degumming with alkalies.
4. Degumming with acids.
5. Degumming with enzymes.
6. Degumming with organic amines.

The conventional working method for degumming or boiling off mulberry silk is as follows: 

1. Soaking overnight or for 6 h in a bath with 3–5 g/L Marseilles soap and 1–2 g/L wetting agent.
2. Boiling off for 2–6 h at 90°C−95°C in a bath containing 8–10 g/L Marseilles soap at pH 9.5 with soda ash.
3. Repeat the treatment in a second bath similar to the first one for 2 h, if necessary.
4. Rinsing first at 50°C with ammonia and then followed by two rinsing, one at 40°C and another at room temperature.

A rapid method of degumming with soap is to treat for 1–2 h at 90°C–95°C at pH 9.5–10 in the following bath: 

• 8–10 g/L Marseilles soap
• 1–2 g/L wetting agent
• 1 g/L soda ash
• 1 g/L sodium tripolyphosphate.

The wild silk (e.g., Tussah or Tussar) requires an initial scouring in a liquor: material ratio of 30:1 (minimum) and 10% (by weight of silk) soda ash. 

References: 

1. Textile and Clothing Design Technology Edited by Tom Cassidy and Parikshit Goswami
2. http://textilelearner.blogspot.com/2012/03/degummingscouring-process-of-silk.html
3. http://nptel.ac.in