| Summary: | 博士 === 國立中興大學 === 森林學系 === 91 === Wood is a major material for traditional architectures. Wood exposed to the weather environment undergoes degradation due to the combined effects of sunlight, rainfall, humidity, oxygen, heat, environmental pollutions and certain microorganisms. The data regarding estimation of weather on wood construction materials of the historical architectures in Taiwan is scarce. There are no actual records or analysises for weather degradation to find out the degraded characters of wood construction materials used under the weather environments. Such information is urgently needed for accurate repair work on damaged wood constructions.
The purpose of this research was focused on the investigation of the characters of weather degradation of the wood construction materials. Moreover, wood specimens collected from traditional architectures in Taiwan were evaluated for their surface characteristics, chemical properties and dimensional stability.
The wood utilization and wood species appeared to have very significant relation. The surface color of wood specimens was clearly affected by sunlight exposure, compass reading, location or geographic environment of the construction. When wood exposed in an environment with high humidity, its wood surface developed an appearance of dark brown, dark blue or blue color. In the case where the granite base has been deteriorated, the degraded products from granite would cause whitish appearance near the pedestal potion of post.
When the surface of China fir wood column exposed to outdoor, although causing the effects of sunlight and water, resulting in occurring of heart crack in wood, particularly the sunlight irradiation on the wood surface. However, this defect has not occurred in the column of Taiwan incense cedar and Camphor wood. This result, however, it demonstrates that the place of crack is the factor that clearly related to the irradiation of sunlight and utilization of wood.
On the other hands, the surface checks of softwoods mainly belong to the longitudinal check. In contrast, check in the hardwoods appeared to have the cave type rift on their surface. It is also possible that the properties of wood would affect the cracking behavior. In addition, the destruction of checking was affected by wood surface, knot and place of wood construction. The surface of China fir purlin specimens exhibited a better color stability than sound wood and fresh wood specimens after natural weathering for 30 days. However, China fir purlin specimens displayed more distinct color changes after water soaking at 25 ℃ for 24 hours.
The extractive content (%) of hot water and 1% NaOH solution from weathered wood specimens is apparently higher than those of aged, sound and fresh wood specimens. The high extract content in weathered wood is probably due to the cell wall degradation. By estimation of chemical component and FTIR, it showing that the hemicellulose and lignin of weathered and aged wood specimens has been conspicuously degraded.
According to the analysis of element composition, it revealed that the ratios of C/N and O/C changed significantly, implying possible photo- and bio-degradation. In water traces, sunlight-shaded or aged wood specimens, the ratio of C/N was obviously higher than O/C. Moreover, the degree of deterioration in specimens varies with the position.
The values of αR of weathered and aged wood specimens was higher than those of sound or fresh wood specimens when wood specimens were exposed under the 40 ℃ and 90% relative humidity for 72 hours conditions. When the weathered and aged wood specimens have been exposed in the water they would have greater water absorption due to the increased check and loss in extractives of wood surface. Moreover, it also apparently increased the shrinkage property in these specimens.
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