CHEMICAL CHANGES IN FIR WOOD FROM OLD BUILDINGS DUE TO AGEING

摘要

Wood is a biological material and changes in its molecular structure during exposures usually have a negative influence on its strength and other mechanical and physical properties. In this work, wet chemical and physico-chemical methods have been used to determine the changes in the cellulose, hcmicelluloses, lignin and extractives of the 108 to 390-year-old visually undamaged fir wood taken from beams situated in the Rychvald castle in Czech Republic. Natural ageing of the fir wood without activity of biological agents caused a significant increase of the extractives content (twofold, or for the oldest beam, even fourfold) and a decrease of the hemicelluloses (by maximum 24%), while the amounts of lignin and holocellulose were quite stable (decreased only by 4%). The molecular weights, respectively, degrees of polymerization, were stable in cellulose, decreased in hemicelluloses, while in lignin increased due to condensation reactions.