Degumming with soap

Enzymatic degumming was first introduced by Lurgi as the EnzyMax technology. " Reduced gum volume due to formation of water-soluble lyso-phosphatide, avoidance of soap stock formation, hence increased oil yield, and reduced environmental impact have made enzymatic degumming based on phospholipase enzyme an alternative to conventional degumming with increasing commercial interest (Figure 9.1.8). ... 

The apphcation of a protease treatment to silk was introduced as an alternative to the degumming process using alkaline soap solutions (Freddi et al., 2003 Gulrajani et al., 2000). Alkaline soap has a deleterious effect on the silk, resulting in a harsh feel to the material. Enzyme degumming with protease removes the sericin without damaging the fibre. Results of enzyme treatment have shown that the fibre is stronger than that obtained by traditional alkaline soap treatments. 

Silk consists of 70 to 80% of fibroin and 20 to 28% of sericin, the silk gum. The sericin of natural silk is removed by boiling with soap and chemicals. Both flosses of the silk are covered with silk gum. Non-degummed silk is yellow to yellow-greenish and has a faint appearance. In addition, it feels hard and dry. After the degumming it has a soft and lithesome feel and a superior sheen. Degumming provides the fibers with a higher absorbency, which increases the dye absorption. 

Silk in iis raw siaie is coated with scricin. It is necessary to remove this gum in order to develop ihe silk luster and dyeability. Synthetic detergent systems, such as higher alcohol sulfaies, and soda ash and boric acid have replaced soap to a large extent for degumming. 

A flow sheet for a semi-continuous interesterification line with postbleaching ability is shown in Fig. 34.27. The oil must be degummed, well-refined (<0.05 percent FFA), and free from peroxides and moisture that causes production of soaps. Palm oil stearin and completely saturated (<5 IV) Cl 8 hydrogenated fats generally are trans free and may be used as part of the feed. Reactions are run under vacuum, and oil is best stored under nitrogen between processes.44... 

The silk fabric selected for this work was an unweighted plain woven Chinese silk habutae (Testfabrics, style 605) having 126 ends/in. (37.6 denier) and 117 picks/in. (32.1 denier) and weighing 1.11 oz/yd2. The fabric as received had been degummed, as was confirmed by extraction with a soap solution. Fabric samples were obtained at two different times and are identified as Lots 1 and 2 to distinguish between them. 

Degumming is effected by careful treatment of silk with high pressure water, acids, alkalies, soaps and synthetic detergents. Chemical dissolution of sericin is obtained partly by hydrolysis and partly by dispersion, independent of the method used. Soap works mainly by dispersion whilst alkalies have a strong hydrolytic effect [57]. 

Silk yam is normally degummed in the hank form. In the pack (beck), the hanks are normally hung on polished wood or metal rods which are submerged in the bath and turned by hand. Alternatively, hank and spray dyeing machines can also be used for degumming of silk in yam form. In the foam boiling process foam produced by soap bath comes m contact with silk and thus causes degumming. 

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