Formation Mechanism Of Gummed Canton Silk And The Interaction Between Silk Protein And The Pigment From Root Of Dioscorea Cirrhosa Lour

Gummed Canton silk is a unique silk product in southern China, which is famous for its special fabric style and clothing properties. This fabric had many advantages suitable for the use in environment with high humidity and hot conditions, such as unique hand, high moisture and air premature, good wash and wear property, and good antioxidant and antibacterial properties. These characteristics of the gummed canton silk are originated from the special processing technique. Griege silk fabric is firstly dip-dyed with a plant dye from root of Dioscorea Cirrhosa Lour and then exposure to sunlight, after repeated this procedure for about 15 times, the dyed fabric was coated with mud. After washing, black coating on the surface of the fabric forms. Currently, gummed Canton silk can only be produced manually with the plant dye and river mud, due to the lack of knowledge of the formation mechanism of gummed Canton silk. Therefore, investigation of the fundamental scientific issue involved in the production is necessary.In this study, the chemical composition of the aqueous pigment extract and the surface of gummed Canton silk have been investigated. The interactions between the purified pigment and silk fibroin/sericin, and the dyeing behavior of the pigment toward degummed and undegummed silk fabrics were studied. The antibacterial mechanism of the dye and the antibacterial properties of dyed silk fabrics were also investigated. The main results of this study are as follows:(1) The pigment extract was isolated, qualification and quantification. The results showed that the extract mainly contained 82.9% w/w of polyphenols and 11.1% w/w of polysaccharide. As a part of the polyphenols, the pigment substance was identified as condensed tannins with degree of condensation of 2~5, which accounted for 57.5% w/w of the amount of the extract. The polysaccharide was mainly pectin and starch. There were 6.0% w/w of unknow compositions and 25.4% w/w of other polyphenols, which needed to be further investigation. The gel filtration chromatography method used in this study could prepare pure pigment substance, and this method lays the foundation for the further research.(2) Repeated light exposure did not cause significant change in the composition of pigment on the dyed fabric. Covalent bonding interaction between the mud compositions and pigment were not found after the dyed fabric coated with mud. The light exposure probably only acted as a process for drying the pigment extracts. XPS analysis showed that high-contect chacateristic humic substances and tiny amounts of metallic ions present on the surface of gummed Canton silk, indicating that humic substace was one of the main substances in the river mud which led to formation of the fabric. Gummed Canton silk formed through the synergistic reaction of the pigment extract, mud compositions(humic substances and metallic ions) and silk fabrics.(3) The intermolecular interaction between silk proteins and the pigment were analyzed. The binding between silk proteins and the pigment, which depended on hydrophobic interaction, was a spontaneous, entropy-increase and exothermic process. The interaction between silk fibroin/sericin and the pigment led to the formation of insoluble silk protein–pigment complex. In dry state, ―multiple hydrogen bonding‖ formed between the hydroxyl groups of the pigment and the carbonyl groups of silk chains, which led to formation of physically cross-linked web structure. The binding ability of the tannin pigment toward silk proteins was strong, which were significantly stronger than the pigment in the naturally yellow-colored silk fiber and also stronger than some polyphenols which were repored to be strong protein-binding compounds. The process for the pigment adsorpt on undegummed and degummed silk fabric meets the pseudo-second order model and Langmuir + Nernst bigram model. Nernst adsorption contributed more than the Langmuir during the dyeing process. This indicated that hydrogen binding and hydrophobic interaction were the main interaction force for the pigment dyeing silk fiber. The dyeing process was spontaneous, entropy-increase and endothermic. The equilibrium adsorption amount, dyeing affinity and the heat of dyeing for the pigment dyeing undegummed silk were significantly higher than those of degummed silk.(4) The pigment showed significant inhibition activity against Gram positive bacteria species via destroying the cell membranre of bacteria, but it showed no antibacterial activity toward Gram negtive species. However, the antibacterial activity of the pigment was adversely affected by the treatment with metallic ions, light exposure and repeated laundering.