Degradation Mechanism of Material Performance of Guhuaxuan Wood Components: Synergistic Effects of Chemical Composition and Microstructure

The material properties of ancient timber structural components exhibit strong dependencies on the temporal variations in their chemical composition and microstructural characteristics. To elucidate the degradation mechanisms, this study conducted a systematic investigation on the wooden elements of Guhuaxuan in the Forbidden City. Through an integrated multi-scale analytical approach incorporating Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM), we quantitatively characterized the deterioration patterns of cellulose, hemicellulose, and lignin, while establishing their structure-property relationships with key macroscopic parameters including apparent density and dynamic modulus of elasticity ( E _d ). Key findings reveal that surface-exposed regions (designated as A2, D2, G2) subjected to prolonged photo-thermal-hygric aging exhibited substantial depletion of carbohydrate polymers, with 20%-45% reductions in cellulose and hemicellulose content. In contrast, the interior D1 region demonstrated superior lignin preservation (30.29% residual content), attributable to microenvironmental heterogeneity within the timber matrix. Mechanistic analysis identified α-cellulose crystallinity as the predominant governing factor for mechanical performance (with a correlation coefficient of R ²  = 0.82 for E _d ), where crystalline domain disintegration directly drives the coordinated deterioration of density and E _d . This study advances the synergistic chemical-microstructural degradation mechanism of wood components and proposes a quantitative evaluation framework for ancient architecture restoration based on cellulose crystallinity and chemical degradation.