Research on Ageing Characterization of Chinese Historic Silk by Infrared Spectroscopy and X-ray Diffraction Methods

Author:Zhang Xiao Ning

Supervisor:gong de cai


Degree Year:2019





Ancient silk is one of the most valuable materials in the study of cultural heritage,representing the highest achievements of ancient China in the fields of art and textiles.Ancient silk fabrics are natural product composed of amino acids sequence.Structural changes occurred in ancient silk during the ultra-long and complex burial conditions resulting in greatly loss of strength and great affects on the value of cultural relics.Therefore,it is a fundamental and challenging work to study the degradation process and degradation products of ancient silk fabrics,introducing new technologies and methods for analysis,revealing the ageing mechanism and providing theoretical basis for the conservation and restoration of historical silk.The study on the aging of ancient silk fabrics is often one of the most fundamental and challenging jobs.First,ancient silk simples are difficult to obtain due to its rareness and preciousness.Second,the microstructure is very complicated and varies by unearthed from different periods and burial environments.Third,the limitation of sample size and quantity leads to the lack of systematic research.In order to study the degradation process of ancient silk,evaluate the degradation status and provide suggestions for the preservation of ancient silk(such as cleaning procedure),artificial aged silk should be prepared for simulating the aging process of ancient silk.Artificial aged silk are generally simulated according to the preservation environment of ancient silk.The dry-heat ageing was adopted as the preparation method was simple,the mechanical strength and the microstructure was similar to the ancient silk with corresponded degradation level.In this thesis,infrared spectroscopy and X-ray diffraction methods were applied as main research means.Initially,this research focuses on the primary structure,secondary structure,crystallinity,molecular orientation and thermal stability of thermal-aged samples.Through establishing the relationship between these parameters,interpreting the degradation mechanism of heat aging silk and providing a systematic study method of the ancient silk degradation behavior,this research aim is to provide reference for understanding the aging mechanism of ancient silk.On that basis,ancient silks unearthed from different archaeological sites in south China were investigated,dated from the Spring and Autumn period,Warring Sates period,Han dynasty,Song dynasty and Ming dynasty.The original infrared spectra,the secondary derivative spectra,primary structure,secondary structure,molecular orientation and the aggregation state of ancient silk were studied.The aging history and the aging stages of ancient silk fabrics were systematically inferred by comparison with the ageing behavior of thermal-aged silk.Combined with surface morphology by SEM,crystallinity,crystal size and thermal stability of unearthed silk fabrics,this research furtherly proves the microstructure of ancient silk with corresponding aging history and the aging stage.Furthermore,the ageing mechanism of ancient silk was proposed.Deuterium oxide was used to probe the interaction between peptide chains for historic silk.It showed that the interaction strength of polypeptide chain within crystallization region formed by beta-sheet chain and the amorphous region formed by random coil both decreased significantly during the natural aging process.Therefore,we believe that the loss of rigidity and elasticity of ancient silk is related to the change of that,as well as associated with the characteristics of degradation products in crystal region and amorphous region.This research could be assisted to explain the mechanical strength of ancient silk basically loss.Based on the fact that ageing started from single fiber and then spread to the whole fabrics.Synchrotron radiation-based Fourier transformed infrared(FT-IR)was applied to study the fresh silk as controlled sample with Nanling and Yinwan samples non-destructively.Nanling and Yinwan sample were chosen due to their similar thermal stability.Besides,the quantity of Yinwan sample is too limited to be analysed by traditional X-ray diffraction examination and other tests.Therefore,the secondary structure distribution,together with the distribution of beta-sheet crystallites orientation were thoroughly studied.Based on the comparative study of two ancient samples,the aging characteristics and aging stages of Nanling and Yinwan sample were inferred.SR-XRD was employed to characterize the microstructure of ancient silk with fresh silk as controlled sample,and the distribution of crystallinity index and molecular orientation were revealed.Combined with previous morphology study by Scanning Electron Microscopy(SEM),Optic Microscopy(OM)and thermal-stability by Thermogravimetry(TG),the deterioration status of ancient silk was inferred.The comparison study between SR-XRD and conventional XRD of ancient silk were also performed to prove the representativeness of the distribution of crystallinity index from single fibers.Additionally,the degradation characteristic of crystallinity index from thermal-aged silk was assisted in clarifying the degradation path of ancient silk.This research provides a systematic method for uncovering the aging characteristics,aging mechanism and aging evaluation of ancient silk.It also establishes the correlation of the microstructure of ancient silk with the loss of physical strength.It also provides the explanation of the strength failure of ancient silk caused by the deterioration of microstructure in molecular level.This research summarizing the common and diversity in ageing characteristic of ancient silk from different periods and burial conditions.Those were the keys to "cure the disease" of the ancient silk,providing a theoretical basis for the effective preservation and conservation of ancient silk,especially for the biochemical reinforcement method.