Partial degumming

Depending on the nature of silk, it is treated for 1-3 h at boiling temperature. The weight loss with half boiled silk lies in the range of 6-12% on the original raw weight. 

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Both degumming and partial degumming are only suitable for reeled silk (greige). These finishing processes are insignificant where schappe and bourette silks are concerned, since these are freed from their gum in the early stages of preparation before spinning [66]. 

The use of expanders does have an impact on the quality of the oil that the integrated processor should be aware of. An interesting phenomena of the expander is that while phosphorous levels in the extracted crude oil are normally increased over traditional flake extraction (typically as much as 200 ppm as P in soybean oil), nonhydratable levels in the degummed oil are normally lower. It is postulated that partial inactivation of the lipase enzyme (blamed for conversion of nonhydratable phosphatides) occurs in the expander and, while the crude oil has a higher neutral oil loss, the quality of the degummed oil is higher. In fact, one processor reported that despite aU efforts to make a soybean oil physical refining plant function, the oil was of substandard quality until the plant installed expanders. Once installed, the plant could consistently produce a quality physical refined oil (4). 

Semi-pilot plant scale trials with crude oils containing 220-580 ppm phosphorous (28) show that nonaqueous UF separations might be used to degum and partially decolorize cmde domestic oils before physical refining. No permeates from two commercially available membranes contained phosphorous, thus indicating complete removal of hydratable and nonhydratable phospholipids (28). 

Modified acid-degumming is a physical refining pretreatment that incorporates the benefits of caustic soda neutralization. This physical refining preparatory process treats the oil with a degumming acid and then partially neutralizes it with NaOH in solution. The amount of NaOH used is limited to prevent soap formation. The metal-phospholipid complexes are dissociated by the acid into insoluble metal salts and phospholipids in their acid form, which are still soluble in oil. The NaOH addition raises the pH and converts the phospholipids into sodium salts that are hydratable. The hydrated salts can be centrifuged for separation or dried to form agglomerates for adsorption on silica for removal with filtration. 

Degumming Hydratable non glyce-ridic lipids, such as phospholipids, partially removed... 

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