Changes in the Physical and Chemical Properties of Alder Wood in the Process of Thermal Treatment with Saturated Water Steam

Abstract

The paper presents changes in color and selected physico-chemical properties of alder (Alnus glutinosa) wood during the process of thermal treatment of the wood with a saturated steam-air mixture or saturated water steam in the temperature range t = 95–125 °C for τ = 3 to 12 h. During the process of thermal treatment of alder wood, the original light white-gray color changes depending on the temperature and time of modification to soft reddish-brown to dark brown color shades. Color changes of alder wood expressed in the form of the total color difference are in the range of values ∆E* = 2.7–31.7. Measurements of the density of thermally treated alder wood in the dry state indicate that due to the thermal treatment of alder wood, the density decreases by ρ ≤ 4.6% compared to the average density of native alder wood. Due to the hydrolysis of hemicelluloses, in the process of thermal treatment of wet alder wood, its acidity changes in the range of values: pH = 4.9 to 3.1. Analyzes of ATR-FTIR spectroscopy indicate changes in alder wood extractants and hemicellulose degradation. A decrease in unconjugated and an increase in conjugated carbonyls was observed at all temperatures of thermal modification of alder wood. Measurements indicate changes in the lignin of alder wood and the fact that as the temperature increases, the formation of new carbonyls increases, which is reflected in the change of the chromophoric system.

The Effect of Steaming Beech, Birch and Maple Woods on Qualitative Indicators of the Surface

“…When the average value of the roughness of unsteamed beech wood is Ra = 6.5 µm, and the value of of steamed beech wood's saturated water steam is at the saturated temperature of t = 135 ± 2.5 • C and an average value of Ra = 5.4 µm, then the roughness of steamed wood is 16.9% lower, that of birch wood is 13.4% lower and that of maple wood is 15.8% lower. The stated findings are not in agreement with the work of the authors from [26] who state that surface roughness decreases with an increase in density. On the contrary, the authors from [43][44][45] state that the surface roughness is more affected by the technical-technological parameters of woodworking, such as removal, feed speed and revolutions of the cutting tool, than by the density of the wood.…”

“…Coatings 2024, 14, 117 9 of 11 steaming wood using regime III. with saturated steam at a temperature of t = 135 ± 2.5 • C reduces the density of beech wood by 1.8%, birch wood by 4.4% and maple wood by 5.3% [25][26][27]. When the average value of the roughness of unsteamed beech wood is Ra = 6.5 µm, and the value of of steamed beech wood's saturated water steam is at the saturated temperature of t = 135 ± 2.5 • C and an average value of Ra = 5.4 µm, then the roughness of steamed wood is 16.9% lower, that of birch wood is 13.4% lower and that of maple wood is 15.8% lower.…”

Influence of UV Radiation on the Color Change of the Surface of Steamed Maple Wood with Saturated Water Steam

“…The color of wood changes in thermal processes, such as wood drying, wood steaming, and thermo-wood production technologies. The wood darkens more or less and, depending on the wood, acquires color shades of pink, red, and brown to dark brown-gray color [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 ].…”

Effect of Two Different Ageing Exposures on the Colour Stability of Transparent Polyurethane Finishing

“…The different behaviour of the wood species studied may be related to the differences in their chemical composition, especially lignin and extractives content. Wood extractives are an important factor affecting wood colour, while also playing an important role in the wood photodegradation process [ 23 , 26 , 27 , 28 ]. Different sizes of colour differences of the surface finish in the dark from those in the light point to the significant influence of light.…”

“…But we know from practice that not always the entire surface of a wood product (e.g., floor, shelf, table) is exposed to light. Many scientific works deal with the change in wood colour [ 22 , 23 , 24 , 25 , 26 , 27 ] or the change of surface finishes on wood in the interior due to the influence of light [ 17 , 28 , 29 , 30 ] or after accelerated weathering [ 9 , 13 , 31 , 32 , 33 , 34 , 35 , 36 ]. However, the effect of visible light from short waves (violet-blue) and the thermic effect of the infrared components of natural light passing through window glass [ 36 , 37 , 38 ] have to be considered as indoor ageing factors [ 25 , 39 , 40 ].…”