water extraction method
When reeling, about 1 to 3% of the sericin in the cocoon silk is dissolved in the water in a hot water bath at 50 to 60°C. Put this raw silk into hot water, sericin will dissolve intermittently. To completely remove sericin, you must use 120℃ hot water for 4 times of 2h extraction. The advantage of using high temperature and high pressure scouring without scouring agent is: Silk sericin is recovered from the refining waste liquid and is easy to recycle (the recovered sericin can be used as food additives and cosmetic additives). After a short period of high temperature and high pressure scouring and then enzymatic scouring, the silk feels soft and does not turn yellow easily.
soap scouring
Refining action Soap is hydrolyzed in the bath: RCOONa+H2O→RCOOH+NaOH
Fatty acids recombine with soap to form fatty acid soap colloid (acid soap):
RCOOH+RCOONa→RCOONa·RCOOH
The alkali generated in the process chemically combines with sericin to form sericin sodium salt, which is called “puffing”. The expanded sericin interacts with the generated acidic soap and undecomposed soap to separate from the silk, which is called “degumming” and is separated from the silk in the bath. Sericin is dispersed in water through the emulsification of soap and is no longer adsorbed to silk. Part of the sericin is decomposed under the action of the base in the bath.
The soap used for degumming should be easily soluble in water and colorless. Its 1% solution will not gel at room temperature. Marseille soap (olive oil soap) and oleic acid soap are more effective. The refined silk has high quality, luster and good hand feel. In addition, , domestically selected various vegetable oils, the silk soap made after decolorization and refining is also good. The soap has a mild effect, high permeability, is not easy to be over-refined and stained, and has good bulking, drape, whiteness and gloss. , and prevent the occurrence of wrinkles and scratches.
The disadvantage is that it has strong adsorption to silk and is difficult to clean. The residual soap will cause stains, yellowing, embrittlement, etc. The soap is not resistant to hard water and has a high cost. You can add base (Na2SiO3, Na2SiO3, NaHCO3, Na3PO4), both the degumming rate and the soap dosage.
Alkali refining
Mechanism: Base attacks the peptide bond and hydrolyzes sericin. The reaction is non-specific. The main amino acids are cysteine, serine, threonine and arginine.
When degumming, the pH value of the scouring bath is 8.8~10.5, preferably buffer solution, K2CO3/NaHCO3
Advantages: The degumming rate is higher than that of soap, it is resistant to hard water, and the residue is easy to wash off after training.
Disadvantages: poor softness, whiteness, gloss, lack of bulk, and poor body structure.
acid refining
After research, pH 1.5 to 2 is relatively safe (the strength of silk exceeds soap degumming). The hydrolysis of sericin by acid breaks the peptide bonds between aspartic acid and glutamic acid.
(1) It is easy to control the degumming rate with acid scouring agents, and the degree of removal can be partially degummed to meet certain special needs in the market (so-called three-point scouring, five-point scouring, seven-point scouring, etc.)
(2) A method of simultaneously scouring and dyeing in an organic acid (malic acid, tartaric acid, succinic acid, etc.) acid bath under high pressure. Energy saving, dyeing fastness is higher than normal pressure dyeing method.
enzyme refining
Proteolytic enzymes are used for refining. Advantages: good bulking, no lint, no damage to silk fibroin, etc. It can also remove dirt caused by dead cocoons.
Main enzymes: trypsin (pH 7-9), papain (pH 5-7.5, active at 70-90°C), bacterial enzyme (pH 9.60°C), 2709 enzyme, 209 alkaline protease, etc. Extended reading: https://www.alltextile.cn/product/product-0-985.html
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