Research On The Degradation Mechanism And The Chemical Restoration Of Archaeological Silk Textiles And Waterlogged Wooden Artifacts

Archaeological silk textiles and wooden artifacts (e.g. lacquerware and bamboo strips with literature) are the important parts of the cultural heritage of China. Large numbers of fabulous archeological silk fabrics and wooden artifacts were excavated in China. Affected by various environmental factors during the long time of burial, most of them suffered degradation to different extent and the physical and chemical properties changed. When suffered serious degradation, the silk textiles turned brittle and the wooden artifacts became waterlogged and the mechanical properities of both became poor, which was unfavorable for the research and preservation. Thus the primary object of the preservation of archaeological silk textiles and waterlogged wooden artifacts is to make them return to the normal state without further injury and to delay the degradation process as much as possible. However, at the present, whether the research about the degradation mechanism or the research about the restoration method is not systematic and far from guiding the heritage conservation practice. Under this situation, we further investigated the degradation mechanism and the conservation method of the archaeological silk textiles and the waterlogged on the basis of the reported literatures. The main work of this dissertation is summarized as follows:1. The degradation mechanism of archaeological silk textiles. Silk textiles are naturally not resistant to light, heat, moisture and microorganism due to its protein composition. Most of the excavated silk textiles were at poor physical and chemical state and needed conservation. However, due to the complex hierarchical structure of silk fibroin protein, the degradation mechanism of silk textiles is still not clear. Most of the reported literatures focused on the investigation of change of one certain kind of structure or some certain parameters, ignoring the inherent relation between the hierarchical structures. In this work, the morphology, the primary structure, the secondary structure and the crystalline structure of the archaeological silk textiles were characterized with SEM, TEM, amino acid analysis, FTIR, XRD, SAED and DSC and compared to the fresh silk. The relation between the hierarchical structure was discussed and a possible degradation mechanism of silk fibroin was proposed.2. The effect, mechanism and reversibility of the bacterial cellulose restoration of the vulnerable archaeological silk textiles. Biotechnology was applied to the restoration of the archaeological silk textiles for the first time by Jingzhou Preservation Center of Cultural Relics, using the bacterial cellulose. Compared with the traditional chemical restoration method, the biological method has the advantage of non-toxicity, good compatibility and degradability. In this work, the chromaticity, morphology, molecular structure, crystalline structure, thermal stability and mechanical properties of the artificial aged silk specimens, the bacterial cellulose restored specimens and the light aged bacterial cellulose restored specimens were compared. It was found that the reinforcement effect of the bacterial cellulose restoration might be attributed to the good compatibility between the silk matrix and the bacterial cellulose and the high elastic modulus and crystallinity of the bacterial cellulose. Bacterial cellulose restoration could greatly enhance the mechanical properties and improved the crystallinity and the thermal stability of the archaeological silk textiles, without changing the original appearance. The bacterial cellulose could be removed by light aging without injury to the silk matrix. Thus the bacterial cellulose restoration method is reversible and has good potential in the preservation of archaeological silk textiles.3. Research on the silk fibroin/chitosan blend restoration of vulnerable archaeological silk textiles. Bacterial cellulose restoration has good effect, but the demands at restoration condition and facilities are high, which make it not suitable for the restoration at large scale. In the principle of’the original compensation’, the silk fibroin protein, which also has the advantage of high elastic modulus, non-toxicity, good compatibility, excellent mechanical properties and degradability, was selected to restore the vulnerable silk textiles. Due to the brittlement of the pure silk fibroin material, the silk fibroin/chitosan blend was adopted. The artificial aged silk specimens were restored with the solution with different silk fibroin/chitosan ratios. The mechanical properties, morphology, molecular structure, crystalline structure, thermal stability of the restored and the light aged restored silk specimens were investigated. The results suggested that the silk fibroin/chitosan restoration could greatly enhance the mechanical properties of the vulnerable silk textiles and could be removed by the light aging without injury to the silk matrix, which meant the method was reversible. The interaction between the silk fibroin and the chitosan played an important role in the restoration process.4. Degradation mechanism of the waterlogged bamboo strips. The degradation of waterlogged wood has been widely researched, while the research about waterlogged bamboo is quite limited. Compared to wood, bamboo has relatively high content of starch, sugar and protein and relatively low content of resin, wax and tannin, which make it more susceptible to the attack of microorganisms and insects and excavated at poorer state. Under this situation, research into the degradation mechanism of waterlogged bamboo was performed. The lignin and hemicelluloses were isolated from the waterlogged archaeological bamboo strips of different periods and the fresh bamboo. The chemical structure and the anatomical structure were thoroughly compared and the effect of the chemical degradation and the anatomical deterioration on the weakening of the mechanical properties of the waterlogged archeological bamboo strips were discussed for the first time. The results indicated that the degradation degree of the cellulose and the hemicelluloses increased with increasing age and the lignin was relatively chemical stable. But chemical linkage between the lignin and the carbohydrates was also changed, which might facilitate the degradation. The degradation of both the cellulose microfibrils and the ground tissue led to the weakening of the mechanical properties.5. Research on the restoration of waterlogged archaeological wood with organosiloxane via sol-gel method. The dehydration and the reinforcement is the key point of the restoration of the waterlogged archaeological wood. The traditional restoration method with alum, sucrose, resin, PEG and glyoxal has the disadvantage of deliquescence, mildew, poor permeability, low strength and toxic respectively. In this work, the organosiloxane including the WD-801and the WD-802were selected to restore the waterlogged archaeological wood via sol-gel method, due to the good permeability, high hydrophobicity, good antibacterial property and excellent aging resistance. The restoration effect and restoration mechanism at different treatment condition were investigated. The results suggested that the restoration of the waterlogged archaeological wood with organosiloxane could obtain satisfying results. The enhancement of the mechanical properties increased with increasing weight gain ratio, which was related to the rate of hydrolysis and condensation of the organosiloxane.