A Study On The Properties Of Silk Treated By Steam Explosion And The Developing Of Super-fine Silk Powder

Silk as high quality natural protein fiber has been widely used in textile field for thousands years for its characteristic features such as moderate moisture absorption and retention properties, excellent slip properties on the skin, and adequate ultraviolet absorption properties. However, silk fabric has some innate shortcomings such as yellowing, poor wearability, low wet-crease resistance and dye fastness which prevent silk from further application. Therefore researchers have devoted in improving the performance of silk fiber, especially tapping its application in other fields since 1980s. So far, the study of the modification of silk fabric is concentrated on acquiring better performance by treating silk with the chemical ways such as grafting, crosslinking and sericin fixation. As for the study of silk in other fields, which include cosmetic and food industry, medicine and biomaterial, is focused on the production and application of silk powder and film. So far, people have invented some means to make protein powder, including mechanical method and chemical-mechanical way. However it is unexpectedly difficult to produce fine silk powder directly by mechanical processing in the form of fiber because of its high mechanical strength. Thus, silk fibroin powder has been produced by employing special chemical pretreatment on silk fibroin fibers, which involves enzyme treatment, redox and dissolution-separation way, to destroy chemical bonds and decrease crystallinity of fibers. Nevertheless these ' pretreatments require complicated processes that are inefficient and un-ecological to the environments. Then it is necessary to explore better pretreatment to produce finer silk powder.Firstly, in order to make it easier to produce fine silk powder, we try to use steam explosion in pretreatment of silk in this research and present the character of treated silk fiber such as surface configuration, structural characteristics, thermal properties, mechanical properties, moisture regain and solubility. In the experiments, silks were treated by steam explosion with different pressure in machine self-made. Applying scanning electron micrograph, infrared spectra, x-ray diffraction and thermal analysis to study the configuration and morphology of silks treated by steam explosion, results indicated that while the macromolecular conformation of silks remained β-configuration ,the morphology of surface and the degree of crystallization of silks had changed much: binding force of microfibril became weaker ,specific area of surface -was enlarged and crystallinity took on declining. The rearrangement of macromolecular structure also happened in some extent. After treatment, fiber's stability to heat and affinity to water were also weakened. And an experiment was carried out to test the dissolvability of silk sample. It turned out that the solubility of silk in calcium chloride and ethanol aqueous solution was enhanced. To sum up, the steam explosion can provide an effective pretreatment way for silk and make it easier to produce fine silk powder with mechanical way.Secondly, the silk treated by steam explosion was pulverized into fine powder with particle size of 1.829 m, and ulteriorly the feasibility of the application of protease treatment to produce finer and more uniform silk powder was investigated. The results indicated that after enzymatic treatment, the mean diameter of silk powder was reduced from 1.829 to 1.546 and the equivalent diameter distribution became more concentrated, then the uniformity of particles was improved. The infrared' spectra analysis demonstrated the effective removal of sericin did little damage to fibroin. That is, the silk powder remained sheet crystalline structure. And x-ray diffraction analysis showed the crystal degree of silk powder was strengthened. The amino acid analysis indicated that though Alcalse digested some polar amino acid in sericin, the kinds and major parts of amino acid hadn't changed. In addition, owing to the loss of some amino acid with polar side chains, moisture...