NIR detection of non-recoverable collapse in sawn boards of Eucalyptus globulus

NIR predictions of cellulose content and stiffness (modulus of elasticity, MOE) from spectra collected from the radial longitudinal surface of Eucalyptus globulus wood were found to be reliable indicators of zones of non-recoverable collapse associated with the presence of tension wood. Radial sections from 25 quarter-sawn boards cut from plantation-grown E. globulus trees in Spain were scanned to generate radial profiles of NIR-predicted wood properties at 2 mm increments. These boards manifested a range of non-recoverable collapse features, from no collapse to one or more severe collapse bands. Collapse bands occurred where NIR-predicted cellulose content and MOE exceeded threshold levels of 50 % and 25 GPa, respectively for more than four consecutive millimetres. A non-recoverable collapse indicator provided a clear predictor of non-recoverable collapse. A NRCI value ≥100 for a consecutive interval of at least 4 mm successfully predicted all ten NRC bands with shrinkage ≥10 % of board thickness. The potential applications of this tension wood detection method are discussed.     

Estimation of physical and mechanical properties of agro-based particleboards by near infrared spectroscopy

Partial least square regression (PLS-R) calibrations based on near infrared (NIR) spectroscopic data were developed in order to predict mechanical and physical properties of agro-based particleboards. The panels were manufactured using Eucalyptus and Pinus wood particles and sugar cane bagasse. The following panel properties were evaluated according to standard methods: modulus of elasticity (MOE), modulus of rupture (MOR), internal bonding (IB) strength, water absorption (WA24H), and thickness swelling (TS24H) after 24 hours of immersion. NIR spectra information was measured on samples cut from each particleboard and correlated with their physical and mechanical properties by PLS-R to build predictive NIR models. The NIR models for IB, WA24H and TS24H presented satisfactory coefficient of determination (0.73; 0.72 and 0.75, respectively.) The key role of resins (adhesives), cellulose, and lignin for NIRS calibrations of mechanical and physical properties of the particleboards is shown. These models can be useful to quickly verify such properties in unknown agro-based particleboards.     

Quality assessment of heat-treated wood by NIR spectroscopy

NIR spectroscopy was tested for predicting the properties of heat treated wood using pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) woods with two types of treatment: in oven and in a steam autoclave. Mass loss, equilibrium moisture content, dimensional stability, MOE, bending strength, colour CIELAB parameters and extractives content were determined. NIR spectra were obtained using a fibre probe on the radial surface of the samples. NIR models for mass loss showed very high coefficients of determination (R²) for cross validation ranging from 96–98%. The models obtained for wood properties were in general good with coefficients of determination ranging from 78–95% for equilibrium moisture content, 53–78% for dimensional stability, 47–89% for MOE, 75–77% for bending strength and 84–99%, 52–96% and 66–98% for colour parameters L, a^* and b^*, respectively. R² of the models for extractive content varied between 41.9–79.8% for pine and between 35.3–82.2% for eucalypt wood. NIR spectroscopy showed a good potential for quality control and characterization of heat treated woods.     

Swelling restraint of thermally modified ash wood perpendicular to the grain

The paper reports on creep of ash wood (Fraxinus excelsior L.) thermally modified at 180 and 200 °C, and subsequently subjected to compression in tangential and radial directions and simultaneously wetted, from the moisture content (MC) of 6% to above the fibre saturation point (FSP). The compressing load made 0.00, 0.25, 0.50 and 0.75 of impact stress at the proportional limit (R_c). The compression stress needed to restrain the swelling of wood, the so-called swelling pressure, was indirectly determined from isochrones of mechano-sorptive creep. The most important finding was that thermal modification reduces the strain of ash wood subjected to compression perpendicular to the grain to a degree proportional to the mass loss. The compression stress needed to restrain the swelling of thermally modified wood is ca. 10 and 20% smaller in the tangential and radial directions, respectively. This effect leads to a reduction in the anisotropy of swelling pressure of thermally modified wood perpendicular to the grain. Moreover, although upon thermal modification the mass loss of wood takes place, at the MC of 6% it shows practically the same modulus of elasticity (MOE) and Rc as the unmodified wood. After wetting to MC higher than the FSP, the thermally modified wood at 200 °C shows significantly higher MOE and Rc than the wood modified at 180 °C and untreated wood. Reduction of wood hygroscopicity, an inevitable effect of thermal modification, also reduces the range of changes in mechanical properties of wood caused by the increase in its MC to the FSP.     

Improvement of termite resistance,dimensional stability and mechanical properties of pine wood by paraffin impregnation

Paraffin has been used as surface protection of wood throughout the ages but its use for impregnation to improve wood resistance to biodegradation is recent. This study determined the main improvements on wood properties with paraffin impregnation. Healthy Pinus pinaster Ait. wood was impregnated with paraffin at different levels using a hot–cold process. Weight gain, equilibrium moisture content and dimensional stability (ASE) at 35 and 65 % relative humidity, termite durability against Reticulitermes grassei (Clément), bending strength, bending stiffness (MOE) and Janka hardness were determined. Density increased from 0.57 to 0.99, ASE ranged between 38–96 % and 16–71 % for 35 and 65 % relative humidity, respectively. Equilibrium moisture content decreased from 9.9 and 12.0 % to 0.8 and 3.6 % for 35 and 65 % relative humidity. Termite durability improved from level 4 to level 3 of attack, and higher termite mortality was found in treated wood (52 % against 17 %). Bending strength (MOR) increased with paraffin weight gain, reaching a 39 % increase. MOE also increased by about 13 % for wood with a weight gain around 80 %. Janka hardness increased significantly reaching about 40 % for wood with 80 % weight gain. Paraffin impregnated wood has improved properties with regard to equilibrium moisture content, dimensional stability and density, bending strength and Janka hardness, and resistance against termites.     

Relationship between transverse shrinkage and tension wood from three provenances of Eucalyptus globulus Labill

was studied using 12 mm increment cores taken from straight, vertical and dominant trees of three provenances from a plantation near Tarpina, South Australia. Tension wood fibre percentages were determined from microscopic examination of stained transverse sections and transverse shrinkage was measured from cores dried to 17% equilibrium moisture content. Shrinkage before and after steam reconditioning, as well as associated collapse, were related to the proportions of tension wood. Contrary to normal expectations, high levels of tension wood produced greater shrinkage in the sapwood than in the heartwood in material from all provenances. Collapse was significantly greater in material from the Jeeralang and Western Tasmania provenances than in the King Island provenance. While the mean proportion of tension wood was highest (4.3%) in material from Jeeralang and least from King Island (2.4%), no significant difference among the three provenances was evident for proportions of tension wood fibres when considering only the last year's growth. Variation in the width of the gelatinous layer (G-layer) was recorded for the tension wood fibres. Fibres with thin walled G-layers were usually scattered among normal fibres and collapsed regions containing such material generally recovered after reconditioning. On the other hand, regions containing the more typical tension wood fibres, with thick walled G-layers, exhibited high levels of shrinkage and collapse, and poor recovery after reconditioning.     

Relationship between transverse shrinkage and tension wood from three provenances of Eucalyptus globulus Labill

Eucalyptus globulus was studied using 12 mm increment cores taken from straight, vertical and dominant trees of three provenances from a plantation near Tarpina, South Australia. Tension wood fibre percentages were determined from microscopic examination of stained transverse sections and transverse shrinkage was measured from cores dried to 17% equilibrium moisture content. Shrinkage before and after steam reconditioning, as well as associated collapse, were related to the proportions of tension wood. Contrary to normal expectations, high levels of tension wood produced greater shrinkage in the sapwood than in the heartwood in material from all provenances. Collapse was significantly greater in material from the Jeeralang and Western Tasmania provenances than in the King Island provenance. While the mean proportion of tension wood was highest (4.3%) in material from Jeeralang and least from King Island (2.4%), no significant difference among the three provenances was evident for proportions of tension wood fibres when considering only the last year's growth. Variation in the width of the gelatinous layer (G-layer) was recorded for the tension wood fibres. Fibres with thin walled G-layers were usually scattered among normal fibres and collapsed regions containing such material generally recovered after reconditioning. On the other hand, regions containing the more typical tension wood fibres, with thick walled G-layers, exhibited high levels of shrinkage and collapse, and poor recovery after reconditioning.

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The Effect of Path Length on the Measurement Accuracies of Wine Chemical Parameters by UV,Visible, and Near-Infrared Spectroscopy

The use of spectral measurements using either UV, visible (VIS), or near-infrared (NIR) spectroscopy to characterize wines or to predict wine chemical composition has been extensively reported. However, little is known about the effect of path length on the UV, VIS, and NIR spectrum of wine and the subsequent effect on the performance of calibrations used to measure chemical composition. Several parameters influence the spectra of organic molecules in the NIR region, with path length and temperature being one of the most important factors affecting the intensity of the absorptions. In this study, the effect of path length on the standard error of UV, VIS, and NIR calibration models to predict phenolic compounds was evaluated. Nineteen red and 13 white wines were analyzed in the UV, VIS, and NIR regions (200–2500 nm) in transmission mode using two effective path lengths 0.1 and 1 mm. Principal component analysis (PCA) and partial least squares (PLS) regression models were developed using full cross validation (leave-one-out). These models were used to interpret the spectra and to develop calibrations for phenolic compounds. These results indicated that path length has an effect on the standard error of cross validation (SECV) absolute values obtained for the PLS calibration models used to predict phenolic compounds in both red and white wines. However, no statistically significant differences were observed (p > 0.05). The practical implication of this study was that the path length of scanning for wines has an effect on the calibration accuracies; however, they are non-statistically different. Main differences were observed in the PCA score plot. Overall, well-defined protocols need to be defined for routine use of these methods in research and by the industry.     

Effect of microwave heating on the near infrared spectra and on the prediction accuracy of chemical parameters in red grape homogenates

This study reports the effect of microwaving on the chemical composition [pH, total soluble solids (TSS), dry matter (DM) and total anthocyanins extraction], and the visible (VIS) and (NIR) spectra of red grape homogenates. It was observed that microwaving red grape homogenates prior to analysis improved the NIR calibrations for total anthocyanins (SECV: 0.21?C0.13 mg g^?1) and TSS (SECV: 0.89?C0.54 °Brix), however no improvements in the NIR calibrations for DM were observed. Microwaving red grape samples prior to NIR scanning also caused an increased in absorbance for samples heated for up to 3 min, particularly in those wavelengths associated with water (1400 nm and 1930 nm). The practical implication of this study is that microwaving of red grape samples prior to scanning did not improve the NIR calibration statistics for the most common chemical parameters measured in red grapes.     

Effect of grain orientation and surface wetting on vertical density profiles of thermally compressed fir and spruce

The effects of grain orientation and surface wetting on wood densification by compression in a hot press were evaluated for two commercial Canadian wood species, balsam fir (Abies balsamea) and black spruce Picea mariana. The vertical density profiles (VDP) of wood densified at 180 °C could be engineered to achieve different properties depending on press closing rate, wood permeability and annual ring orientation. The lower permeability of spruce caused it to split frequently during hot pressing. For balsam fir, at a press closing time of 2 min, the compressed wood with an original grain angle of 0° (radial compression) shows widened high density bands due to collapse of low density earlywood adjacent to the dense latewood. All grain orientations show higher density areas close to the wood surfaces similar to those of wood-based composites. However, when wood was preheated without pressure for 5 min followed by a press closing time of 2 min, water migrated to and plasticized the board centre causing it to be densified while the surface density remained low. Wood surface plasticizing with water or urea solution causes some localized surface densification, but the effect was not great.     

Some physical and mechanical properties of thermally modified juvenile and mature black pine wood

In this study, test samples of juvenile and mature black pine wood were treated for 3 h at temperatures of 140, 170, and 200 °C. Mass loss, density, equilibrium moisture content (EMC), modulus of rupture (MOR), modulus of elasticity, and impact bending strength (IB) of the separate samples were determined. The purpose of the tests was to determine how heat treatment at the three temperatures influenced the properties of the juvenile and mature wood. The results showed that heat treatment had greater effects on mass loss, EMC, and density of juvenile wood than of mature wood. The results also showed that heat treatment had lesser effects on the MOR, modulus of elasticity, and IB of juvenile wood than of mature wood. The results clearly indicated that heat treatment had different effects on the properties of juvenile and mature black pine wood.     

Effect of tannin on increasing UF adhesive performance at high temperature investigated by TMA and TGA analysis

Tannins have been largely studied as wood additives and wood adhesives. In a perspective of a desirably increased utilization of natural raw material in the wood timber industries, this study provides further and specific information on the use of condensed tannins to improve the heat resistance of urea–formaldehyde (UF) resins. The results obtained by thermomechanical and thermogravimetric analyses show that high percentage (33 and 50 %) of quebracho tannin in UF-tannin blend dramatically improves the overall UF thermal resistance, but 50 % of tannin decreases the maximum value of modulus of elasticity (MOE) of the bonded joint. The best balance between mechanical performance and decreased degradation at high temperature is obtained with 33 % of quebracho tannin. The MOE value of UF + 33 % of quebracho tannin at 260 °C is seven times greater than MOE of UF control. Thermograms show that quebracho tannin has a beneficial effect on increasing the resistance of glue-mix to degradation induced by temperature. When the content of tannin in the glue-mix is increased up to 50 %, the resin degrades completely at about 670 °C, i.e. more than 50 °C higher than neat UF resin. This improvement is related mainly to the resorcinol-type ring structure of tannin and the alkaline pH of UF + quebracho tannin glue mix that confer a higher resistance against joint degradation to UF even at elevated temperatures.     

Thermal modification of OSB-strands by a one-step heat pre-treatment – Influence of temperature on weight loss, hygroscopicity and improved fungal resistance

Thermal modification of wood leads to improved resistance against fungal decay and decreased moisture uptake. Polyoses contribute most to the sorption behaviour of wood and act as main nutrition source for fungi. Thus, especially the conversion of polyoses has major impact on the degree of improvement. Thermal decomposition of wood is accompanied by weight loss. In this work the influence of temperature on weight loss, resulting equilibrium moisture content (EMC) and fungal resistance of OSB-strands is shown. It was found that EMC reaches a constant level, indicating completed reduction of free accessible hydroxyl groups. The levelling was ascertained to be irrespective of the temperature and duration of the pre-treatment. An improved fungal resistance according to durability class 3 and better was found for samples pre-treated above 200 °C. The presented correlation between reduced EMC and improved fungal resistance provides a tool for efficient determination of the durability of thermally modified wood.     

Selected properties of gas phase ammonia treated wood

Changes of physical wood properties after ammonia gas phase treatment were tested. In order to cover the wide variability of the investigated parameter, nineteen different wood species were investigated. While density is more or less not affected, equilibrium moisture content at standard climate increases significantly for almost all species. Changes of differential shrinkage and swelling in radial and tangential direction are specific to species. While some species show increased swelling or shrinkage, for other species these values decline. In most cases, ammoniation leads to increased dimension stability in radial direction but to a reduction in tangential direction. So, anisotropy of swelling and shrinkage in general increases due to ammoniation. These results show that changed physical properties of such wood have to be considered concerning conditioning and dimensioning products therefrom.     

Potential of near infrared spectroscopy to assess hot-water-soluble extractive content and decay resistance of a tropical hardwood

The ability to identify both low- and high-durability samples in a population of naturally durable samples would allow more rational use of these materials, for example, using samples in the lower ranges of durability in non-soil contact. One possible method for rapidly assessing differences in heartwood characteristics related to durability is near infrared spectroscopy (NIR) coupled with multivariate statistical methods. A number of recent studies suggest that NIR can be related to a variety of wood properties, including extractive content. There are, however, few data on the ability of this technique to assess decay resistance, especially in hardwoods or species with high natural durability. In this report, the ability of NIR to predict both extractive content and resistance to fungal attack in Goncalo alves (Astronium graveolens) was assessed. NIR spectra accurately predicted hot-water-soluble extractive content of A. graveolens and its susceptibility to the white rot fungus Trametes versicolor. A. graveolens was very resistant to attack by the brown rot fungus Gloeophyllum trabeum and NIR spectra were not useful predictors of weight loss. NIR spectroscopy may be a useful tool for rapidly assessing the extractive content and decay resistance of naturally durable wood.     

Mechanical and physical properties of thermally modified Scots pine wood in high pressure reactor under saturated steam at 120, 150 and 180 °C

Scots pine sapwood and heartwood were thermally modified under saturated steam at 120, 150 and 180 °C in a high pressure reactor. Mechanical properties such as dynamic and static modulus of elasticity (MOE), static modulus of rupture (MOR), Brinell hardness and impact toughness were evaluated. The static MOE for sapwood did not decrease substantially (approximately 1 %), not even with a high mass loss of more than 12 %, when the wood was modified at 180 °C. Static MOE of the wood increased approximately 14 %, when modified at 150 °C. Surprisingly, MOR increased by 15 %, when modified at 150 °C with mass loss of 2.3 %. Whereas impact strength and hardness decreased somewhat, when modified at 180 °C. Moreover, high anti-swelling efficiency values were obtained (60 % for sapwood and 52 % for heartwood) when modified at 180 °C.     

Prediction of MOE of eucalypt wood from microfibril angle and density

Small clear specimens of 30×30×450 mm were prepared from plantation-grown Eucalyptus globulus, E. nitens and E. regnans that were between 15 and 31 years of age. Their modulus of elasticity (MOE) and modulus of rupture (MOR) were determined using static central-point-loading bending tests. Their microfibril angle (MFA) and density were determined using SilviScan on strip samples removed from the intact portion of the specimens after the bending tests. It was found that MFA alone accounted for 87 percent of the variation in MOE, while density alone accounted for 81 percent. Together, MFA and density (as Density/MFA) accounted for 92 percent of the variation in MOE. The MFA impact diminishing point appears to be 16 degrees for the wood material of three eucalypt species in this study. Density alone accounted for 80 percent of the variation in MOR, whereas MFA had little independent influence on MOR.

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Vorhersage des MOE von Eukalyptusholz aus Fibrillenwinkel und Dichte

Zusammenfassung  Kleine fehlerfreie Proben (30×30×450 mm) wurden aus 15 bis 33 Jahre alten Eucalyptus globulus, E. nitens und E. regnans aus Plantagenanbau geschnitten. Deren MOE und MOR wurden unter statischer zentraler Belastung im Biegetest bestimmt. Außerdem wurden der Mikrofibrillenwinkel (MFA) und die Dichte bestimmt, und zwar mittels SilviScan an Probestreifen, die nach dem Biegetest aus intakten Probeteilen geschnitten wurden. Es zeigte sich, daß allein der Mikrofibrillenwinkel zu 87 Prozent für die Variation des MOE verantwortlich ist, die Dichte für sich allein nur für 81 Prozent. MFA und Dichte zusammen (als Quotient Dichte/MFA) erklären 92 Prozent der Variation des MOE. Die Grenze des negativen Einflusses des Mikrofibrillenwinkels scheint für das vorliegende Probenmaterial bei 16 Grad zu liegen. Im Falle des MOR ist die Dichte allein für 80 Prozent der Variation verantwortlich, wogegen der MFA nur einen geringen unabhängigen Einfluß auf den MOR hat.

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Der Einfluss der Temperatur auf die Biegefestigkeit und den Elastizitätsmodul bei verschiedenen Holzwerkstoffen

The influence of temperature on the bending strength (MOR) and the modulus of elasticity (MOE) of eight different wooden materials (2 MDF, 1 OSB, 2 particle boards, beech and spruce plywood, solid wood panel) was tested at temperatures between -20 °C and +60 °C. Thereby a reduction of MOR of 12–39% and of MOE of 14–46% was measured in the range of 20 °C and 60 °C. The work to maximal load varied within a large range. Depending on the wooden material there was an increase of up to 48% or a reduction of up to 31% between 20 °C and 60 °C. Between 20 °C and -20 °C the MOR increased 5–22% and the MOE 3–27%. Only the MOE of the solid wood panel in fibre direction decreased by 6%. The work to maximal load ranged between a reduction by 19% and an increase by 10%.     

Evaluation of density and strength of Norway spruce wood by near infrared reflectance spectroscopy

The non-destructive evaluation of wood properties by Near Infrared Reflectance Spectroscopy (NIR) has been assessed. The surfaces of specimens of clear wood (Picea abies) were NIR-scanned, and the results compared to such properties as moisture content, density, compression strength and chemical and biological degradation. In addition, the NIR-scans of clear wood specimens were compared to the bending strength of the structural timber from which it had been cut. The NIR dependency of surface roughness was investigated and found to be of minor importance. NIR calibrations for moisture content (MC<30%), density, compression strength and chemical degradation proved that the NIR technique is an excellent non-destructive method (r ²≧0.9; independent test set). Even biological degradation was determined with a most promising accuracy (r ²=0.75; independent test set). For the prediction of the bending strength of timber NIR proved less efficient. However, NIR still contributed to timber strength prediction at the same level as annual ring width, the parameter which is presently visually assessed by timber graders. It is concluded that the NIR method is very versatile in the non-destructive evaluation of wood. The results merit further investigations in order to develop proper models and instrumentation for commercial use.