Production of Wood Fibers from Thermally Treated Wood

The reduction of the hygroscopicity of wood fibers was investigated through a Thermal Treatment(TT)on wood chips performed before the defibering process.The TT and defibering tests were both carried out on a continuous pilot at semi-industrial scale.The thermal treatment study of wood chips,equivalent to a low temperature pyrolysis,was achieved for four conditions(280°C–320°C)for a duration of 10 min.Mass quantification of solids,condensables and gases(FTIR)at the outcome of the thermal treatment allowed to achieve the mass balances for each condition.The increase of the reactor temperature from 280°C to 320°C leads to a lower solid yield(94%–82%)while gaseous(1%–3.8%)and condensable(3%–11%)products increase significantly.Thermally treated wood samples were afterwards successfully defibered in different conditions to produce suitable fibers for insulation panel production.The aim of the study is also to evaluate the effects of the TT on the lowering of energy consumption necessary for the defibering process while producing good quality fibers.Energy consumption during defibering process shows a significant decrease with the increase the TT severity.Fiber morphology is affected by TT and the morphological quality of the fibers decreases as TT severity increases.The mass percentage of dust was also quantified as a quality marker of produced fibers.Measurements of equilibrium moisture(at 20°C and 65%RH)of the different materials(wood chips before and after TT,produced fibers)show a significant effect of the TT on wood chips hygroscopicity(8.2%for untreated wood to 4.1%for TT at 320°C).However,the effect of the TT on the hygroscopicity reduction of thermally treated wood fibers is drastically less significant due to breaking of the wood structure during defibering process.

Mechanical Characteristics of Chemically Degraded Surface Layers of Wood

The aim of this research was to find out whether the effect of chemical corrosion changes mechanical characteristics of surface layers of wooden construction elements. Degradation of the surface layers of wood was caused by chemical reactions of the basic substances of wood mass with compounds contained in antifire coatings. Fire retardants containing corrosive substances were often and repeatedly used in the Czech Republic on many wooden building constructions. This process of chemical corrosion is in practise called as ＂surface defibering of wood＂. This contribution presents standard and special experimental methods used for measuring the selected mechanical characteristics （compression strength, tension strength, bending strength, hardness and impact resistance） in the damaged surface layer of wooden construction elements. The material for experimental measuring was a construction element removed from a historical roof （ca 150 years old）. Mechanical characteristics of the surface layer of the defibered element were compared with the values measured in the deeper subsurface layer of non-damaged wood. The results of the experiments proved loss of cohesive strength and decrease of mechanical characteristics of wood only in a thin surface layer.