Effects of environmental factors on natural aging of timber members of ancient buildings: Ultraviolet radiation, temperature and moisture

The main objective of this study was to investigate the effects of environmental factors on natural aging and the mechanism on larch (Larix principis-rupprechtii Mayr) timber. Firstly, 130 specimens were processed in the sapwood area of wild forest larch timber to investigate the effects of ultraviolet (UV) irradiation time and the number of dry and wet (D-W) cycle on color, physical and mechanical properties of timber specimens. And then a multifactor level tests were designed according to the response surface methodology (RSM) to analyze the compound effects of each factor on the natural aging of timber based on the established artificial accelerated aging device. Finally, the changes in the chemical composition and microstructure of timber and the natural aging mechanism were investigated by infrared (IR) spectral analysis and scanning electron microscopy (SEM) observation. The results showed that the color of wood was significantly affected by UV and DW cycle aging, in addition, the density and bending properties of wood decreased significantly in DW cycle, while the effect of UV irradiation was weak. In addition, the effects strengths of environmental factors of wood aging were UV, temperature and relative humidity by RSM analysis, and there were obvious temperature and moisture dependence of UV aging of timber. IR and SEM analyses showed that the characteristic peaks representing cellulose and hemicellulose were weakened and the microstructure was impaired after natural aging, which is similar to the trend of analyses and observations of approximately 600 years old timber members obtained from ancient architecture in Beijing. The conclusions show that temperature and humidity accelerate UV radiation aging of timber, and that the D-W cycle has a significant effect on the physical and mechanical properties of timber. •Effects of environmental factors on natural aging of timber members.•Influence mechanism of environmental factors on natural aging.•Temperature, moisture dependence of natural aging.