Abstract：The conservation and protection of archaeological wood requires scientific protection schemes based on the knowledge of the main chemical components degradation process, such as the selection of reinforcements, treatment time and temperature. In this paper, four coffin samples were selected, which were excavated from Xuzhou Wanda Han dynasty tombs. These wood samples were identified as four different wood species, namely the hard pine (Pinus sp.), phoebe (Phoebe sp.), catalpa (Catalpa sp.) and zelkova (Zelkova sp.). By Attenuated Total Reflection Fourier Transform IR (ATR-FTIR) and Thermal Gravimetric Analysis (TGA), the chemical properties and fast pyrolysis behavior of the archaeological wood and corresponding sound woods are characterized. The results showed that the absorption peaks of CO stretching vibration from the acetyl group in the infrared spectrum of the archaeological pine, phoebe, catalpa and zelkova almost disappeared near 1 730 cm-1, while the relative peak intensity of the lignin benzene ring skeleton around 1 500 cm-1 was increased. These results reflect the serious degradation of hemicellulose in archaeological wood, while lignin preserved better. The absorption peak of acyloxy bond (—COO) at 1 238 cm-1 in hemicellulose was not found in the samples of archaeological wood holocellulose, but it was detected in the infrared spectra of all modern wood holocellulose except modern phoebe holocellulose, which indicated that the hemicellulose in archaeological wood suffered degradation more seriously than cellulose, and this result indicated that the acyloxy bonds content in phoebe hemicellulose was low. Compared with the acid-insoluble lignin samples of archaeological wood, the intensity of absorption peak near 1 459 cm-1 (methyl and methylene C-H bending vibration) is stronger than that of archaeological wood, indicating that there are more methyl, methylene and side chains in acid-insoluble lignin of modern wood. In the ATR-FTIR spectra of archaeological acid-insoluble lignin, the absorption peak intensity of lignin in the vicinity of 1 028 cm-1 is lower than that of modern health wood, indicating that the acid-insoluble lignin of archaeological wood contains few C—O bonds. Comparing the pyrolysis behavior of archaeological wood and referenced wood of different tree species found that the archaeological wood has slower pyrolysis rate, low initial temperature of the rapid pyrolysis stage and higher residue mass. The difference in pyrolysis behavior between archaeological wood and modern wood is mainly related to the massive degradation of holocellulose and the increase of relative lignin content in the archaeological wood. Among the four archaeological wood samples, the residual mass rate of archaeological phoebe is the lowest, which indicates that the relative content of lignin in archaeological phoebe is lower and holocellulose preserved better. Hence, its natural durability is the best among the four tree species. In addition, the pyrolysis rate of archaeological acid-insoluble lignin is slower than reference acid-insoluble lignin due to the low amount of side chains and methoxy groups. The above results show that both infrared spectroscopy and thermogravimetric analysis can be used to analyze the degradation progress of archaeological wood, and provide a scientific basis for the timely conservation of cultural relic.
袁 诚，翟胜丞，章一蒙，张耀丽. 红外光谱结合热重法对考古木材降解状况的分析[J]. 光谱学与光谱分析, 2020, 40(09): 2943-2950.
YUAN Cheng, ZHAI Sheng-cheng, ZHANG Yi-meng, ZHANG Yao-li. Simple Evaluation of the Degradation State of Archaeological Wood Based on the Infrared Spectroscopy Combined With Thermogravimetry. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(09): 2943-2950.
