Abstract:

Objective: This study aims to investigate the degradation and variation regularity of chemical composition on the shallow surface of Larix gmelinii (larch) wood used in ancient buildings in different periods, and provide theoretical support for the deterioration assessment and scientific protection of ancient wooden buildings. Method: Larch, a common tree species used in ancient wooden buildings, was taken as the research object. The shallow surface layer of the wood was divided into the primary degradation layer (layer Ⅰ, radial direction 0?3 mm), the secondary degradation layer (layer Ⅱ, radial direction 3?6 mm), and the weak degradation layer (layer Ⅲ, radial direction 6?9 mm), and the research was conducted based on the chronological line of “the Qing Dynasty-the Republican Period-the Morden Period-fresh wood”. The chemical extraction, Fourier transform infrared spectrometer (FTIR) and X-ray diffraction (XRD) techniques were used to investigate the changes in the chemical composition content and crystallinity of cellulose on the shallow surface of larch wood used in ancient buildings in different period. Result: Compared with the fresh wood (22#), the lignin and holocellulose on the shallow surface of larch wood used in ancient buildings in different periods exhibited significant degradation, and the degree of lignin degradation was more significant than that of holocellulose. Some wood used in ancient buildings had more significant degradation of hemicellulose. Due to the degradation of chemical composition in the amorphous region of cellulose, the crystallinity of cellulose increased to a certain extent compared with the fresh wood. The comprehensive degradation degree of chemical composition on the shallow surface of larch wood used in ancient buildings in different periods was as follows: Qing Dynasty (17#) > Republican Period (3#) > Morden Period (15#). In the same period, the degradation degree of larch wood used in ancient buildings from the shallow surface layer Ⅰ to shallow surface layer Ⅲ showed a downward trend. The degradation degree of the wood during the Qing Dynasty in the shallow surface layer Ⅰ (17-1#) was the most severe. The lignin and holocellulose content of the wood during the Qing Dynasty (17-1#) were 0.72 and 0.87, respectively, of the fresh wood (22#), and the crystallinity of cellulose increased by 17.80% compared with the fresh wood (22#). The wood during the Morden Period (15#) had the least degradation degree. The lignin and holocellulose content in the shallow surface layer Ⅰ (15-1#) were 0.94 and 0.86, respectively, of the fresh wood (22#), and the crystallinity of cellulose increased by 11.28% compared with the fresh wood (22#). The test results of the service wood components of ancient buildings confirmed that the degradation of chemical composition on the shallow surface of larch wood used in ancient buildings increased over time. Compared with the fresh wood (N1), the crystallinity of cellulose the larch wood during the Qing Dynasty (Oj1) and the Morden Period (Oj2) had increased by 32.39% and 28.95%, respectively. Among them, the degradation of eave columns (Oy1) was more severe than that of golden columns (Oj1), and the crystallinity of cellulose in eave columns and golden columns had increased by 35.51% and 32.39% respectively. Conclusion: Compared with the fresh wood, the chemical composition on the shallow surface of larch wood used in ancient buildings in different periods has significantly degraded. The degree of degradation gradually increases over time, and the comprehensive degradation degree shows a downward trend from shallow surface layer Ⅰ to shallow surface layer Ⅲ in the same period. There are significant differences in the radial deterioration of the shallow surface layer of larch wood used in ancient buildings. By analyzing the changes in the chemical composition on the shallow surface, the radial evolution of chemical composition of wood can be explored, providing a technological support for on-site deterioration assessment of wooden composition used in ancient buildings.

Key words: ancient architectural wood, Larix gmelinii, shallow surface, natural aging, chemical composition