Silk cocoon degumming | The process sequence of silk cocoon degumming

 

Silk cocoon degumming

Silk cocoon degumming

Silk is a natural protein filament that can be converted into textiles by weaving or knitting techniques. Silk protein fibers/filaments are mainly composed of fibroin and some insect larvae are produced to make cocoons. For commercial use, it belongs almost exclusively to the filament from cocoons produced by various moth species of caterpillars, which belong to the genus Bombyx and are commonly referred to as sericulture.

Silks are the only natural filament or solid fiber and the filaments are 300-1800 yards long. Silk fiber has a double rod-like structure, it is covered with gum glue. The wild silk fiber is very irregular and flat, with wavy ribbons resembling longitudinal marks. Cultivated silk is smooth, cylindrical, and usually uniform in thickness like glass rods.

Silk fiber contains about 20-25 percent sericin gum. Sericin is a group of soluble glycoproteins that are expressed in the middle silk glands of the Bombay Mori. Silk excreted by silkworms consists mainly of two proteins, sericin, and fibroin; the structural center of the fibroin silk and the sericin gum coating the fibers and allowing them to stick together.

Natural glue, sericin is usually left on the silk during reeling, throwing, and weaving. It acts as a size that protects the fibers from mechanical injury. Once the insects are out the cocoons must be degummed before they can be spun into yarn.

The process sequence of silk cocoon degumming

Process sequence of silk cocoon degumming


i. Removing short threads

Each cocoon is surrounded by a short thread that the silkworm supports its structure. These threads tend to be inferior so it is best to remove them before degumming. They pull off quite easily.

ii. Degumming supports silk

Support silk is degummed and can be used.

iii. Removal of larvae and pupal skins

Thereafter, larval and pupal skins must be removed from the inside of the cocoon. A pair of hemostats comes in handy for this step. The cocoon fills the water and floats the skins on top and prevents them from getting inside.

iv. Treat with soap solution

Fill a pot with water and add the same amount of soap - about 1/2 cup in 100 cocoons. It is important for us to use only natural soaps instead of detergents that may contain harmful enzymes for silk or sodium lauryl sulfate. Some recipes call for soda and/or lye washing but we have gotten good results using only soap. Boil the cocoons until they fall to themselves and lose their shape. It can take anywhere from 30 minutes to a few hours depending on the species of silk. Make sure the cocoons are not boiled as this can cause them to tangle and mat.

v. Extracting water, and Drying

They are sufficiently degummed when they look like fluffy cotton balls. Protein fibers are best in acid conditions so add a splash of vinegar or acetic acid to the final rinse water. About 1/4 cup per gallon of water. Rinse and gently remove excess water and hang to dry.

vi. Pulling apart

They will look good on the skin when dry, but we should be able to separate and avoid them with our fingers. If not, repeat the degumming process. They are now ready to spin.

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