| Ancestors of China learnt to use plants to make tools for living and production at a quite early time.And excavation of ancient plant relics especially bamboo and wooden slips provided large amounts of material data for the studies of economic development and social change of the ancient society,which was quite meaningful.Due to the characteristics of lignocellulosic materials,plant relics could be easily influnenced by many different factors and seriously degraded during the burial process underground,which made them weaker and darker.In addition,some relics would suffer severe color change in a very short time after being excavated and exposed in air.In order to provide more specific conservation services,we studied the characteristics of the materials and degradation mechanisms of the ancient plant relics in this research.And this research would be a quite efficient supply for the insufficient of the study in the field of ancient plant relics in China as well.The excavation of Mauquis Haihun in Nanchang was one of the most important excavations in recent years in China.Lots of precious ancient relics have been unearthed from this tomb,which should be quite important and helpful for the study of ancient culture.In this research,two kinds of typical plant seeds including hemp seeds and melon seeds excavated from the tomb of Marquis Haihun were chosen as study objects together with several broken pieces of straw mat which suffered a severe color change soon after being excavated.Many different analytical methods were applied in this research to study the material characteristics and degradation mechanism of the samples,including wet chemistry analysis,ultimate analysis,thermogravimetric analysis(TG),X-ray fluorescence spectroscopy(XRF),atomic absorption spectroscopy(AAS),Fourier transform infrared spectroscopy(FT-IR),ultraviolet-visible spectroscopy(UV-Vis),nuclear magnetic resonance(NMR),thermogravimetry coupled with Fourier transform infrared spectroscopy and mass spectrometry(TG-FTIR-MS),electron paramagenetic resonance(EPR),and X-ray photoelectron spectroscopy(XPS).In addition,the reference value of the study on ancient plant seeds for the studies on other precious relics made of lignocellulosic materials was furtherly discussed a well.Results of the compositional and structural analysis showed that main constituents of the ancient hemp seed,melon seed and straw mat were hemicellulose,cellulose and lignin.The samples of ancient hemp seed and straw mat were seriously degraded with a big decrease in the contents of hemicellulose and cellulose.In contrast,the melon seed sample were relatively well preserved with little content change.In addition,the analytical results presented that lignin in all the three samples showed some indications of being oxidized at different levels.The results of thermal analysis showed that the pyrolysis processes of the three samples were similar,and the temperature ranges of pyrolysis of the samples at same heating rate were nearly the same,which lay at 200-600 ?.In addition,analytical results showed that the gaseous products of pyrolysis of the three samples were nearly the same as well.Majority of the products was composed of CO2,CO,moisture,alkenes,alchols,aldehydes and phenols,and among them CO2 occupied the leading role.In addition,the results of kinetic study presented that all the pyrolysis processes of the three samples followed the mechanism of nucleation and growth,however,the specific parameters of each sample showed some differences.Results of the EPR analysis of the straw mat indicated that stable carbon radicals existed in the sample with a relatively high concertration.Meanwhile,the analysis of burial environment found that large amount of microoganisms which could decompose organics including carbohydrates and lignin existed in the soil of the tomb.In addition,the analytical results of degradation products of the hemp seed and straw mat suggested that humic acid or humic-acid-like substances were generated during the degradation of the the samples.However,the degree of humification of the products was quite low as limited by the burial environment.Besides,the straw mat was discolored by Na2S2O4,and the analytical results presented that the discoloration was quite efficient with little structural change of the sample.In addition,the concentration of free radicals decreased after the discoloration.The analytical results of ancient hemp seed and straw mat have been cpmpared at different aspects,and the comparison results showed that tendency of the change of different components in the samples was the same together with the degradation products.Meanwhile,the pyrolysis process of the two samples were quite similar.The gaseous products of their pyrolysis were the same in kinds,and the relative amount of different specific products were quite close.In addition,pyrolysis of the two samples followed the same mechanism function,and the kinetic parameters were close as well.Ancient carbonized millet straw was analyzed in this research,and the results showed that free radicals existed in the sample as well,and the radicals had higher aromatic-condensed structure than those in the straw mat.However,the structures of carbohydrate and lignin in the sample were completely destroyed by high temperature,which made it quite different from the natural degraded sample in component and structure.In this research,part of the plant relics excavated from the tomb of Marquis Haihun was used as samples,and the characteristics and degradation mechanisms of the samples had been deeply and systematically studied,which provided efficient supply for the study in the field of ancient plant relics.Meanwhile,we studied the ancient plant seeds from the view of materials science,which broadened the usages of these samples and made them more useful in scientific studies.In addition,the study of characteristics of the excavated plant seeds would provide reference for the study of other lignocellulosic relics in this tomb,and it could provide data support for the conservation works of precious relics which could not be sampled from.Besides,mechanisms for the fast color change of plant relics after being excavated and exposed in air had been explored as well in this research,which made it beneficial for the pratical conservation of wooden and bamboo relics. |
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