Vliv stáří dřeva na jeho vlastnosti

Abstract

The submitted Doctoral thesis focuses on comparing the structure and properties of centuries old wood which was obtained from constructions of historical buildings in the re-gion of the Beskydy Mountains with the recently cut wood. A goal of the thesis is to verify the prerequisite that technical properties and the structure of historically old wood meet the requirements for secondary use of this material in constructions, particularly of cultural mon-uments, while preserving the original structures and materials and thus the historical value of the respective monument. Experimentally, the thesis is divided to two parts and the verifica-tion of the set goals is carried out on fir wood (Abies alba). The first part focuses on the anal-ysis of the anatomic structure and chemical composition of wood of different ages and ascer-taining its selected physical and mechanical properties. The obtained values are compared with the values of the wood which has not been subject to the aging process in the thesis. The second part purposely focuses on the analysis of the structure and ascertaining the aforemen-tioned properties of thermally stressed wood. A thermal load simulates an environment wood is exposed to at dry-heat sterilisation of constructions. The anatomic structure of examined samples did not show any signs which would in-dicate that morphological changes had occurred during the aging process. The results of chemical analyses showed that no significant changes in cellulose occurred during the aging process, which was also confirmed by results of strength tests which did not get worse due to cellulose degradation compared with the recent wood. Experimental results thus confirmed that the wood strength was not influenced by natural aging, but by the secondary action of biotic elements. It can be of various intensity in the old as well as younger wood and depends on conditions which wood was exposed to. There was a significant drop in the content of hemicelluloses. Furthermore, a drop in the quantity of terpenes which can serve as attractants for wood-destroying insects was found. The said drop in terpenes can be considered the rea-son for a higher resistance of historical wooden structures to some kinds of wood-destroying insects.