Impact of thermal modification on color and chemical changes of African padauk, merbau, mahogany, and iroko wood species

Thermal modification is an environment-friendly technology for improving various wood properties, especially the dimensional stability, decay resistance, and color homogeneity. In this work, four tropical wood species (African padauk, merbau, mahogany, and iroko) were thermally modified by the ThermoWood process. The influence of heat treatment on the color and chemical changes of wood was studied by spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, and wet chemistry methods. As the temperature increased, a decrease in lightness (L*) and a simultaneous decrease in chromatic values (a*, b*) were observed, indicating darkening and browning of the wood surface. As a result of the heat treatment, the relative content of hemicelluloses decreased the most in merbau and mahogany, while the thermal stability of iroko and African padauk was higher. All examined wood species showed a strong correlation between the lightness difference value (ΔL*) and the content of hemicelluloses (r = 0.88-0.96). The FTIR spectroscopy showed that the breakdown of C═O and C═C bonds in hemicelluloses and lignin plays an important role in the formation of chromophoric structures responsible for the color changes in the wood.O

The Effects of Propagation Techniques on Cell Wall Chemistry and Wood Anatomy in Micropropagated and Grafted Plants of the Dutch Elm Hybrid 'Dodoens'

Determination of wood anatomy traits and the chemical attributes of plant cell walls is of great importance for the evaluation of both the effects of hybridization and the results of breeding strategies within the genus Ulmus, because these are both aimed at an enhanced tolerance to dutch elm disease (caused by Ophiostoma ulmi and O. novo-ulmi) and to the improvement of trees having desired mechanical properties. The objective of this study was to determine whether the routinely applied vegetative propagation techniques of in vitro micropropagation or grafting would result in any change to lignin monomer composition and content, macromolecular traits of cellulose, neutral sugar composition, or the vascular and fiber anatomy traits in the stems of the dutch elm hybrid cultivar Dodoens (i.e., open-pollinated Ulmus glabra 'Exoniensis' × U. wallichiana P39). Propagation techniques appeared to have no direct effect on lignin monomer composition. The differences in the relative proportion of guaiacyl units in lignin between the stock types were not significant, showing that no advantage could be attributed to either stock type toward an enhanced tolerance to dutch elm disease. The micropropagated plants reached significantly higher values for 13 traits (32.5%), primarily associated with the relative proportion of d-glucose and the macromolecular traits of cellulose to compensate for a lower content of holocellulose. The grafts reached higher values for 10 traits (25%), including the relative proportions of d-xylose, d-mannose, and d-galactose. The effect of the rootstock might contribute to different amounts of these cell wall substances in the grafts. The grafts also reached a higher lignin content, which may provide minor advantages in terms of mechanical and physical properties to the cell walls of this stock type. Similarities between the stock types were found for 17 traits (42.5%). Both stock types formed compact homogeneous clusters clearly separated from each other in the multivariate wood trait analysis

Effect of thermal modification on properties and milling behaviour of African padauk (Pterocarpus soyauxii Taub.) wood

The purpose of this study was to analyze the effect of thermal treatment on chemical changes, mechanical properties and machining behavior of African padauk wood. Thermal modification of padauk wood was carried out at 3 different temperatures (160 °C, 180 °C, and 210 °C). Effect of modification temperature on chemical constituents and bending properties of padauk wood were ascertained. Thermally modified and un-modified samples were subjected to milling operation with combination of various processing parameters such as cutting speed (20, 30, 40 m/s), feed speed (4, 8, 11 m/min) and rake angle (15°, 20°, 25°), to obtain the optimum combination in terms superior surface quality (surface roughness and surface waviness) and minimum energy consumption. Cellulose and lignin proportion increased while hemicellulose proportion reduced significantly following thermal modification. Modification temperature, particularly 210 °C, had significant effect on the chemical constituents and bending strength of padauk wood. Modification up to 180 °C did not cause any significant loss in bending strength and bending stiffness, but the strength and stiffness loss was significant when samples were modified at 210 °C. Best surface quality with minimum energy consumption was obtained in African padauk wood thermally modified at 210 °C and milled with a cutting speed of 20 m/s, rake angle of 20° and feed rate of 4 m/min

Characterization of manmade and recycled cellulosic fibers for their application in building materials

The aim of this study was to characterize two types of cellulosic fibers obtained from bleached wood pulp and unbleached recycled waste paper with different cellulose content (from 47.4 percent up to 82 percent), to compare and to analyze the potential use of the recycled fibers for building application, such as plastering mortar. Changes in the chemical composition, cellulose crystallinity and degree of polymerization of the fibers were found. The recycled fibers of lower quality showed heterogeneity in the fiber sizes (width and length), and they had greater surface roughness in comparison to high purity wood pulp samples. The high purity fibers (cellulose content > 80.0 percent) had greater crystallinity and more homogeneous and smooth surfaces than the recycled fibers. The presence of calcite and kaolinite in all of the recycled cellulosic fibers samples was confirmed, whereas only one wood pulp sample contained calcite. The influence of the chemical composition was reflected in the fiber density values. Changes in the chemical composition and cellulose structure of the fibers affected the specific surface area, porosity and thermo physical properties of the fibers. More favorable values of thermal conductivity were reached for the recycled fibers than for the wood pulp samples. Testing the suitability of the recycled fibers with inorganic impurities originating from the paper-making processes for their use as fillers in plastering mortars (0.5 wt.% fiber content of the total weight of the filler and binder) confirmed their application by achieving a compressive strength value of 28 day-cured fiber-cement mortar required by the standard as well as by measured more favorable value of capillary water absorption coefficient.Web of Science7111145112

Chemical Profiles of Wood Components of Poplar Clones for Their Energy Utilization

Selected and tested poplar clones are very suitable biomass resources for various applications such as biofuels, the pulp and paper industry as well as chemicals production. In this study, we determined the content of lignin, cellulose, holocellulose, and extractives, syringyl to guaiacyl (S/G) ratio in lignin, and also calculated higher heating values (HHV) among eight examined clones of Populus grown on three different experimental sites. The highest lignin content for all the examined sites was determined in ‘I-214’ and ‘Baka 5’ clones, whereas the highest content of extractives was found in ‘Villafranca’ and ‘Baka 5’ clones. The highest S/G ratio for all the examined sites was determined in ‘Villafranca’ and ‘Agathe F’ clones. The chemical profiles of main wood components, extractives, and the S/G ratio in lignin were also influenced by both the experimental site and the clone × site interaction. Higher heating values, derived from calculations based on the contents of lignin and extractives (or lignin only), were in close agreement with the previously published data. The highest heating values were found for ‘Baka 5’ and ‘I-214’ clones. The optimal method of poplar biomass utilization can be chosen on basis of the lignocellulosics chemical composition and the S/G ratio in lignin

Colour and Chemical Changes of Black Locust Wood during Heat Treatment

Black locust is a fast-growing deciduous tree species with multiple industrial purposes due to its valuable traits. However, the heterogeneity of colour distribution between sapwood and heartwood limits its application. Thermal modification is an environment-friendly technology for improving various wood properties, especially dimensional stability, decay resistance, and colour homogeneity. In this work, black locust (Robinia pseudoacacia L.) wood samples were thermally modified at temperatures of 160, 180, and 210 °C. Extractives and main wood components were analysed by wet chemical methods, colour was measured by spectrometry, and structural changes by Fourier transform infrared spectroscopy. The obtained results show that the darkening of black locust wood, unlike other wood species of the temperate zone, is mainly caused by changes in extractives. Their content decreases during thermal treatment, but new chromophores are formed, especially in quinones. Degradation of hemicelluloses and the partial degradation of cellulose also contribute to colour changes. At higher temperatures, condensation reactions can occur in lignin, leading to the formation of some chromophores. Statistical analysis confirmed that temperature can be considered a very significant factor affecting the colour of the wood surface

Release of Terpenes from Fir Wood during Its Long-Term Use and in Thermal Treatment

Building structures made from fir wood are often attacked by wood-destroying insects for which the terpenes it contains serve as attractants. One of the possibilities for extending the lifetime of structures is to use older wood with a lower content of terpenes and/or thermally modified wood. The study evaluated the levels of terpenes in naturally aged fir wood (108, 146, 279, 287 and 390 years) and their decrease by thermal treatment (the temperature of 60 °C and 120 °C, treatment duration of 10 h). Terpenes were extracted from wood samples by hexane and analyzed by gas-chromatography mass-spectrometry (GC-MS). The results indicate that recent fir wood contained approximately 60 times more terpenes than the oldest wood (186:3.1 mg/kg). The thermal wood treatment speeded up the release of terpenes. The temperature of 60 °C caused a loss in terpenes in the recent fir wood by 62%, the temperature of 120 °C even by >99%. After the treatment at the temperature of 60 °C the recent fir wood had approximately the same quantity of terpenes as non-thermally treated 108 year old wood, i.e., approximately 60–70 mg/kg. After the thermal treatment at the temperature of 120 °C the quantity of terpenes dropped in the recent as well as the old fir wood to minimum quantities (0.7–1.1 mg/kg). The thermal treatment can thus be used as a suitable method for the protection of fir wood from wood-destroying insects

Structural Changes of Oak Wood Main Components Caused by Thermal Modification

Thermal modification of wood causes chemical changes that significantly affect the physical, mechanical and biological properties of wood; thus, it is essential to investigate these changes for better utilization of products. Fourier transform infrared spectroscopy and size exclusion chromatography were used for evaluation of chemical changes at thermal treatment of oak wood. Thermal modification was applied according to Thermowood process at the temperatures of 160, 180 and 210 °C, respectively. The results showed that hemicelluloses are less thermally stable than cellulose. Chains of polysaccharides split to shorter ones leading to a decrease of the degree of polymerization and an increase of polydispersity. At the highest temperature of the treatment (210 °C), also crosslinking reactions take place. At lower temperatures degradation reactions of lignin predominate, higher temperatures cause mainly condensation reactions and a molecular weight increase. Chemical changes in main components of thermally modified wood mainly affect its mechanical properties, which should be considered into account especially when designing various timber constructions

The Impact of Thermal Treatment on Structural Changes of Teak and Iroko Wood Lignins

Thermal modification is an environmentally friendly method to improve dimensional stability, durability, and aesthetic properties of wood. Changes in lignin as one of the main wood components markedly influence wood product properties and recycling possibilities of thermowood at the end of its life cycle. Teak and iroko wood samples were thermally treated at the temperatures of 160 °C, 180 °C and 210 °C following the Thermowood process. Dioxane lignin was isolated from treated and untreated wood and analysed by nitrobenzene oxidation (NBO), size exclusion chromatography (SEC) and Fourier transform infrared spectroscopy (FTIR). The yields of both acid-insoluble and dioxane lignins increased with an increasing treatment temperature. Dioxane lignins are GS-types containing more guaiacyl units compared to syringyl ones with S/G ratios of 0.91 and 0.84, respectively. In the process of thermal modification, several degradation and condensation reactions were observed. The cleavage of methoxyl groups and side chains, oxidation reactions, cleavage of the β-O-4 ether linkage and cross-linking radicals arising at higher temperatures were all confirmed. However, during the thermal treatment, teak lignin changed in a different way than iroko lignin, e.g., the molecular weight of iroko lignin decreased at all applied temperatures while it increased at 180 °C and 210 °C in teak lignin, and the change in S/G ratio and the cleavage of alkyl-aryl bonds are different in both wood species