Changes In Wood Structure Research Articles

Study of the effect of heat temperature on the chemical changes and hygroscopicity of eucalyptus wood by FT-IR and prediction of mechanical properties by the MLR regression method

This study describes the effect of heat treatment on some physical, chemical, and mechanical properties of Eucalyptus Camaldulensis (EC) wood at different temperatures and treatment times (200 °C–260 °C for 5, 60, and 90 min). The evaluation of hygroscopic properties was determined by relative humidity, mass loss, dimensional stability tests, and density. The results showed that the heat treatment leads to an increase in mass loss of 5.2 %–11.9 % at 200 °C. The density changed significantly for this studied species as well as the dimensional stabilization. Chemical changes in wood structure were assessed by Fourier Transform Infrared Spectroscopy.To verify the validity of the superposition “Mass loss-Density-water absorption” on the mechanical properties (modulus of elasticity (MOE) and modulus of rupture (MOR)) during heat treatment, we have developed a mathematical model based on Multiple Linear Regression (MLR), in order to establish a relationship between the independent parameters and the dependent parameters (MOE and MOR). The evaluation of the quality of the models developed was based on several statistical tools, namely R = 0.99, R2 = 0.99, R2adj = 0.98, and F = 132.33. The results demonstrated that elaborate models of mechanical properties have a high predictive capacity (MOR and MOE). The wood’s carbohydrates (particularly hemicelluloses) are then degraded during the heat treatment. The % of carbon increases from 47.8 to 49.8 %, which is proportional to mass loss, while the % of oxygen decreases by 46.1 %, which is inversely proportional to mass loss. Furthermore, FTIR analysis revealed that the effect of heat-treated wood chemical changes was related to the hydroxyl OH function of cellulose, functional groups, and aromatic system of lignin. In conclusion, the results demonstrated that at 200 °C, heat treatment caused a 5.2–11.9 % increase in mass loss; dimensional stability and density underwent considerable changes. FTIR spectroscopy confirmed the chemical changes in the wood structure during heat treatment. Furthermore, the “MLR” mathematical model showed that density contributed to the increase in MOR and MOE properties, while water absorption and mass loss contributed to the decrease in MOR and MOE properties. Finally, the % of oxygen decreased by 46.1 %, which is inversely proportional to the loss of mass, and the % of carbon increased from 47.8 % to 49.8 %, which is proportional to the loss of mass.

Understanding the mode of action of sorbitol and citric acid (SorCA) in wood

ABSTRACT In recent years, a wood treatment system based on sorbitol and citric acid (SorCA) has emerged as a promising alternative to already commercialized modification processes of European-grown wood species. The improvement of dimensional stability and biological durability have been reported. However, the mode of action behind the changes in wood structure leading to these improvements has not been well defined yet, as the research was based on the infrared spectroscopy, which cannot distinguish nor compare the effect of cell wall bulking (CWB), covalent bonding and cross-linking. Moreover, most of the assumptions regarding the reaction mechanism have resulted from the studies of citric acid reactions with wood and wood-based products. Therefore, in this study different analytical chemistry methods have been used to explain the interaction between SorCA and wood at two polymerization temperatures (120 and 140°C). It has been confirmed that the curing temperature is a crucial parameter for achieving the desired fixation. Subsequently, liquid chromatography-mass spectrometry (LC-MS), cross-polarization/magic angle spinning (CP/MAS 13C-NMR) spectroscopy and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) have been used to determine the contribution caused by an in-situ formation of high molecular-weight SorCA polyesters (resulting in CWB) and a higher rate of esterification of wood polymers.

The Possibility of Propolis Extract Application in Wood Protection

Nowadays, there is a growing interest in extending the service life of wood and wood products by applying natural substances that are harmless to humans and the environment. In this paper, propolis was used as an eco-friendly wood preservative. The aim of this study was to determine the resistance of Scots pine wood treated with the propolis extract against brown-rot fungus Coniophora puteana. The wood biodegradation was assessed by gravimetric method, as well as by the analysis of ergosterol concentration in decayed wood and by the determination of changes in the wood structure by means of Fourier transform infrared spectroscopy. The results indicated that the impregnation of wood with propolis extract above 12% concentration limited fungal decay. The mass loss of wood treated with 18.9% propolis extract was 2.3% and was over 21 times lower than that for untreated wood. The analysis of ergosterol content and the changes in wood structure also confirmed that the propolis extract above 12% concentration protected wood against decay caused by C. puteana. Moreover, the propolis extract used in wood impregnation was rich in phenolic compounds, mainly chrysin, pinocembrin and galangin, which possess antimicrobial activity. The obtained results indicate that the extract of Polish propolis can be a promising natural wood preservative, safe for humans and the natural environment.

Severe insect defoliation at different timing affects cell wall formation of tracheids in secondary xylem of Larix kaempferi

Severe insect defoliation induced non-lignified tracheids and thin-walled latewood tracheids in the defoliation year in Larix kaempferi. These anomalous tracheids had heterogenous lignin deposition of S2 layer. Severe insect defoliation induces the formation of light ring consisted of thin-walled latewood tracheids in larch trees, which would affect wood quality. However, the identity of the secondary wall layers affected by insect defoliation remains unclear. The aim of this study is to clarify the effects of insect defoliation on the formation of secondary cell walls of tracheids in Larix kaempferi with focus on the defoliation timing. We observed by light microscopy and transmission electron microscopy (TEM) the secondary cell walls of tracheids produced in a defoliation year in L. kaempferi trees on which needles were attacked in July (gypsy moth, GM samples) or August (larch sawfly, LS samples). Light microscopy observations revealed that GM samples produced non-lignified tracheids in the transition zone between earlywood and latewood, as well as thin-walled latewood tracheids, and non-lignified tracheids were observed near the cambial zone in LS samples following defoliation for two consecutive years. TEM observations revealed that the tracheids in both samples had anomalous layers in secondary walls such as thin S2 layers with heterogeneous lignin deposition. The production of non-lignified tracheids corresponded to defoliation date in both samples, unlike changes in the layer composition of anomalous tracheids. Our study suggests that changes in wood structure depend on the date of insect defoliation and that insect defoliation affects the formation of secondary cell walls of tracheids, presumably in response to inadequate photosynthate supply as a result of defoliation.

Using FTIR to Study the Chemical Degradation of Archaeological Wood in EL-Moez Street

Despite the complex structure of wood, it is a very sensitive material easy to degrade for several factors. FTIR spectroscopy is an excellent analytical method to characterize wood degradation by revealing chemical changes in wood structure in terms of the oxidation or hydrolysis mechanisms in the basic components: cellulose, hemicellulose and lignin. This paper presents assessing the different degradation types of archaeological wood in Historic Cairo as well as suggests a proposal schema in order to treat degraded wood.

VLIV MIKROVLNNÉ PLASTIFIKACE, PLOŠNÉHO SLISOVÁNÍ A VYSOKOTEPLOTNÍ ÚPRAVY NA ROVNOVÁŽNOU VLHKOST A SESÝCHÁNÍ DŘEVA SMRKU ZTEPILÉHO (Picea abies (L.) KARST.)

The wood is heterogenous material compound from substance of cell walls and air. It is colloidal ca­pil­la­ry-cellular material with ortogonal anisotropy (Babiak, 1976). The wood has possibility to bound liquids and gases into the structure. Due to this the wood is hygroskopic material leads to changes in dimensions and volume of wood generating at adsorption and desorption of water molecules into the wood. The dimentional changes evoked by changes in moisture content (bounded water) during shrinkage and sweeling have the biggest importance. Shrinkage is making the linear dimensions, area and volume shorter and smaller (Požgaj a kol., 1997). Hygroscopicity and dimensional instability is possible to affect by drying or modification (Horáček, 2004).Wood modification is a process where it causes improvement in material properties. Aimed changes in chemical structure of wood leads to change in material properties. The aim of modification is to reduce negative properties and to improve positive properties. Wood with changed properties has different parameters which it is necessary to investigate.Plasticization as temporary modification of material properties leads to softer wood due to release of intercellular bonds mainly in middle lamela. It makes subsequent processing as areal compression possible (Bouajila et al., 2006). To ther plasticization is necessary to heat up the wood on the certain temperature. The microwave heating is very useful for this heating. It has smaller expenses and time consumption.Pressing or areal compression perpendicular to the gain in radial direction presses the wood and makes it’s density bigger. Areal compression is responsible for changes in submicroscopic, microscopic and makroscopic levels of wood structure. Changes in wood structure leads to changes in li­near directions during shrinking.Plasticizated and compressed wood has many of excellent properties, but it has some negative pro­per­ties too that high temperature treatment reduces.The aim of this article is to find and compare equilibrium mositure content, linear shrinkage in radial, tangential and longitudinal direction of the native spruce wood (Picea abies L. Karst.) with the same values of microwave plasticizated, areal compressed in radial direction perpendicular to the gain and high temperature treated Spruce wood.

Duration and extension of anatomical changes in wood structure after cambial injury

Cambial injury has been reported to alter wood structure in broad-leaved trees. However, the duration and extension of associated anatomical changes have rarely been analysed thoroughly. A total of 18 young European ash (Fraxinus excelsior L.) trees injured on the stem by a spring flood were sampled with the aim of comparing earlywood vessels and rays formed prior to and after the scarring event. Anatomical and hydraulic parameters were measured in five successive rings over one-quarter of the stem circumference. The results demonstrate that mechanical damage induces a decrease in vessel lumen size (up to 77%) and an increase in vessel number (up to 475%) and ray number (up to 115%). The presence of more earlywood vessels and rays was observed over at least three years after stem scarring. By contrast, abnormally narrow earlywood vessels mainly developed in the first ring formed after the event, increasing the thickness-to-span ratio of vessels by 94% and reducing both xylem relative conductivity and the index for xylem vulnerability to cavitation by 54% and 32%, respectively. These vessels accumulated in radial groups in a 30° sector immediately adjacent to the wound, raising the vessel grouping index by 28%. The wound-induced anatomical changes in wood structure express the functional need of trees to improve xylem hydraulic safety and mechanical strength at the expense of water transport. Xylem hydraulic efficiency was restored in one year, while xylem mechanical reinforcement and resistance to cavitation and decay lasted over several years.

Characterisation of the initial degradation stage of Scots pine (Pinus sylvestris L.) sapwood after attack by brown-rot fungus Coniophora puteana

In our study, early period degradation (10 days) of Scots pine (Pinus sylvestris L.) sapwood by the brown-rot fungus Coniophora puteana (Schum.: Fr.) Karst. (BAM Ebw.15) was followed at the wood chemical composition and ultrastructure-level, and highlighted the generation of reactive oxygen species (ROS). An advanced decay period of 50 days was chosen for comparison of the degradation dynamics. Scanning UV microspectrophotometry (UMSP) analyses of lignin distribution in wood cells revealed that the linkages of lignin and polysaccharides were already disrupted in the early period of fungal attack. An increase in the lignin absorption A(280) value from 0.24 (control) to 0.44 in decayed wood was attributed to its oxidative modification which has been proposed to be generated by Fenton reaction derived ROS. The wood weight loss in the initial degradation period was 2%, whilst cellulose and lignin content decreased by 6.7% and 1%, respectively. Lignin methoxyl (-OCH3) content decreased from 15.1% (control) to 14.2% in decayed wood. Diffuse reflectance Fourier-transform infrared (DRIFT) spectroscopy corroborated the moderate loss in the hemicellulose and lignin degradation accompanying degradation. Electron paramagnetic resonance spectra and spin trapping confirmed the generation of ROS, such as hydroxyl radicals (HO∙), in the early wood degradation period. Our results showed that irreversible changes in wood structure started immediately after wood colonisation by fungal hyphae and the results generated here will assist in the understanding of the biochemical mechanisms of wood biodegradation by brown-rot fungi with the ultimate aim of developing novel wood protection methods.

Microwave Wood Modification Technology and Its Applications

The use of microwave (MW) technology is growing in all industries. This increased use has resulted from the high efficiency of converting electricity into MW energy; energy savings associated with rapid, in-depth heating of materials; specific interactions that can be achieved between MW energy and materials; radical acceleration of technological processes; reductions in MW equipment costs; and improvements in the reliability of industrial MW equipment. The new technology of MW wood modification is based on the supply of high-intensity MW power, up to 135,000 kW/m3 at frequencies of 0.922 and 2.45 GHz. Such power induces significant changes to the microstructure of wood and a dramatic increase in wood permeability. A number of commercial applications have been developed based on the fundamental changes in wood structure. These include the treatment of refractory wood species with preservatives, rapid drying of hardwoods, relief of growth and drying stresses in timber, manufacture of the new wood materials Torgvin and Vintorg, and modification of logs, sawn timber, and woodchips for pulping. MW equipment and processing parameters have been developed for three applications that are ready for commercial use. The technology provides significant material and energy savings and will give a new impetus to product development in a very traditional industry. The costs of microwave timber processing range from AU$22 to AU$69 per m3. These costs are acceptable to industry and potentially provide wide appeal for use in the timber, biocomposite, and pulp and paper industries.

Detection of fungal decay by high-energy multiple impact (HEMI) testing

Abstract The suitability of a previously described high-energy multiple impact (HEMI) test for the detection of early fungal decay was examined. The HEMI test characterises the treatment severity of thermally modified wood by stressing the treated material by thousands of impacts of pounding steel balls. This method differentiates between heat treatment intensities, which are manifest as structural changes in the wood. Similar changes in wood structure are known for wood decayed by fungi. Pine (Pinus sylvestris L.) decayed by brown rot and beech (Fagus sylvatica L.) decayed by white rot were tested. Mass loss caused by fungal decay and resistance to impact milling (RIM) determined in HEMI tests were found to be highly correlated. Testing of non-degraded pine, beech, and ash (Fraxinus exelsior L.) showed only marginal effects of wood density on RIM. Furthermore, annual ring angles and RIM of spruce (Picea abies Karst.) were not correlated. Accordingly, the detection of RIM reduction in decayed wood is not masked by variations in density and orientation of the annual rings. Previous results showed no adverse effects of weathering on RIM. Thus, the detection of fungal decay with HEMI tests is feasible not only for laboratory purposes, but also for wood in outdoor applications that has already undergone weathering.

Structural changes in activated wood-based carbons: correlation between specific surface area and localization of molecular-sized pores

Abstract Samples of maple were pyrolyzed and subsequently activated by carbon dioxide at different temperatures for various dwell times. The changes in wood structure were characterized by nitrogen adsorption isotherms, transmission electron microscopy (TEM) with selected-area electron diffraction (SAED), and scanning electron microscopy (SEM). Increasing pyrolysis temperatures promoted increased crystallization of graphitic wood components and mineral-like phases. The average pore diameter derived from nitrogen adsorption isotherms approximately correlated with the results obtained by high-resolution SEM and TEM. The highest surface area was found for samples containing considerable amounts of nanoperforated pit membranes located in intervascular pitting. High-resolution TEM examinations of membrane regions showed foam-like clusters with an average size of 1.7 nm, which are attributed to the selective influence of CO2 activation on pyrolyzed cellulose and lignin.

Slow initial decomposition and fungal colonization of pine branches in a nutrient-rich lowland stream

Mass loss, fungal colonization, and chemical changes of submerged pine (Pinus sylvestris) branches were monitored in a nutrient-rich lowland stream. Branches retrieved from the stream were analyzed for water-soluble substances to assess mass loss by leaching. Concentrations of substances soluble in hot 1% NaOH were determined in order to detect changes in wood-tissue structure indicating microbial degradative activity, and fungal colonization was estimated as ergosterol concentration. Decomposition of the pine branches was slow, with a mean mass loss of 8.3% within 13 months and an overall decay coefficient, k, of 0.074·year–1. Concentrations of water-soluble substances in wood decreased from 2.8% to 1.7% after 5 weeks and in bark from 5.6% to 3.8% within 2 weeks. No further losses were noted, nor were significant changes observed in concentrations of substances soluble in hot dilute NaOH. Fungal biomass in bark increased within the first 5 weeks (14–69 µg ergosterol·g–1dry mass) but was invariably low in wood. These results indicate that decomposition of intact fully corticated pine branchwood in streams proceeds very slowly, with little fungal colonization and no notable changes in wood structure occurring after more than a year even when dissolved nutrients in stream water are readily available.

Industrial Kiln Drying and its Effect on Microstructure, Impregnation and Properties of Scots Pine Timber Impregnated for Above Ground Use. Part 1. Effects of Initial, Final Dryings and Preservative on Impregnation and Timber Quality

Summary Scots pine (Pinus sylvestris L.) planks were dried in industrial progressive, conventional batch and high temperature kilns. The quality of drying was assessed by measuring the final moisture content and its gradient, deformations, checks and internal stress of planks. The timber was rearranged in three charges and impregnated in an industrial autoclave with copper-based preservatives for above ground use (class AB):Kemwood ACQ 1900, Tanalith E and Wolmanit CX-8. The moisture content was determined after impregnation and the planks were divided into two charges; the first was dried in an industrial conventional batch kiln while the second was air dried. Assessment of the final product quality after kiln and air drying was carried out as after the initial drying. The penetration of preservatives was measured as well. The data were analysed by a statistical mixed model to ascertain the effects of drying and preservatives on the impregnation and timber quality. A strong relationship was found between the initial drying of Scots pine timber and its quality after impregnation and drying. The conventional batch and high temperature kiln drying ensured similar drying quality regarding the final moisture content and gradient, bow, twist and checks, but the high temperature drying provided significantly better (94.4%of the total sapwood area) penetration of the preservatives tested. It is suggested that changes in wood structure could be provoked during the high temperature drying, thus improving the subsequent impregnation and secondary drying. The progressive and conventional batch kiln drying led to similar penetration of the preservatives; the conventional batch kiln drying ensured significantly lower final moisture content, less twist and surface checks of the timber than the progressive kiln drying. Wolmanit CX-8 penetrated significantly better into the pine sapwood (96.3%) than Kemwood ACQ 1900 and Tanalith E (83.5 and 88.5%, respectively). The planks impregnated with Wolmanit CX-8 achieved the best quality regarding the final moisture content, its gradient and cup. The planks impregnated with Kemwood ACQ 1900 and Tanalith E showed similar quality regarding the penetration and some deformations after drying, but Kemwood ACQ 1900 impregnated planks had highest moisture content and gradient.

The use of gray scale images when evaluating disturbances in cutting force due to changes in wood structure and tool shape

A method is presented for studying the effect of momentary disturbances due to variations in wood structure on the cutting force near the cutting edge. Force and density measurements are converted to a gray scale image. This method is very effective as regards the evaluation of experimental tests.

Dating of Events from Tree Growth and Wood Structure

Changes in wood structure, with growth ring counts, may be used to estimate the date of events affecting tree growth. Two cases are quoted in which changes in wood structure helped to establish the date of events of forensic interest. Some of the possibilities and dangers of this method of dating are discussed.