J. Van den Bulcke

Quantitative measurement of the penetration of water-borne coatings in wood with confocal lasermicroscopy and image analysis

Due to European environmental regulations, solvent-borne wood coating systems have to be replaced by water-borne and high solid coatings. Thorough research is yet needed to replace the traditional solvent-borne systems by water-borne paints and stains for exterior wooden joinery. In this article the penetration of paint primers and wood stain base-coats (solvent-borne and water-borne as well as high solids and hybrid systems) in wood is discussed. Penetration is an important factor for the durability of a coating and thus the protection of the wood. For the image capturing a confocal scanning lasermicroscope (CSLM) was used. Penetration was measured using two methods. Further statistical analysis was done to determine the factor that influenced the penetration the most.ZusammenfassungGemäß europäischer Umweltverordnungen müssen Farben auf Lösemittelbasis durch Anstriche mit Wasser als Lösemittel und hochfestem Anstrich ersetzt werden. Gründliche Forschung ist jedoch notwendig, um die traditionellen Systeme auf Lösemittelbasis zu ersetzen durch wasserlösliche Anstriche und solche für Außenverwendung. In diesem Beitrag wird die Eindringtiefe der Grundierungen und Anstrichsysteme in Holz diskutiert (Anstriche auf Lösemittelbasis, wasserlösliche Systeme sowie hochfeste und Hybridsysteme). Eindringtiefe ist ein wichtiger Faktor für die Dauerhaftigkeit einer Farbschicht und somit für den Schutz des Holzes. Für die Bilderzeugung wurde ein konfokales Lasermikroskop verwendet. Die Eindringtiefe wurde unter Anwendung zweier Methoden gemessen. Weitere statistische Analysen wurden durchgeführt, um den Faktor zu bestimmen, der die Eindringtiefe am stärksten beeinflusste.

Automated image-based analysis of spatio-temporal fungal dynamics.

Due to their ability to grow in complex environments, fungi play an important role in most ecosystems and have for that reason been the subject of numerous studies. Some of the main obstacles to the study of fungal growth are the heterogeneity of growth environments and the limited scope of laboratory experiments. Given the increasing availability of image capturing techniques, a new approach lies in image analysis. Most previous image analysis studies involve manual labelling of the fungal network, tracking of individual hyphae, or invasive techniques that do not allow for tracking the evolution of the entire fungal network. In response, this work presents a highly versatile tool combining image analysis and graph theory to monitor fungal growth through time and space for different fungal species and image resolutions. In addition, a new experimental set-up is presented that allows for a functional description of fungal growth dynamics and a quantitative mutual comparison of different growth behaviors. The presented method is completely automated and facilitates the extraction of the most studied fungal growth features such as the total length of the mycelium, the area of the mycelium and the fractal dimension. The compactness of the fungal network can also be monitored over time by computing measures such as the number of tips, the node degree and the number of nodes. Finally, the average growth angle and the internodal length can be extracted to study the morphology of the fungi. In summary, the introduced method offers an updated and broader alternative to classical and narrowly focused approaches, thus opening new avenues of investigation in the field of mycology.

Potential of X-ray computed tomography for 3D anatomical analysis and microdensitometrical assessment in wood research with focus on wood modification

Abstract Studying structure and chemistry of wood and wood-based materials is the backbone of all wood research and many techniques are at hand to do so. A very valuable modality is X-ray computed tomography (CT), able to non-destructively probe the three-dimensional (3D) structure and composition. In this paper, we elaborate on the use of Nanowood, a flexible multi-resolution X-ray CT set-up developed at UGCT, the Ghent University Centre for X-ray Tomography. The technique has been used successfully in many different fields of wood science. It is illustrated how 3D structural and microdensitometrical data can be obtained using different scan set-ups and protocols. Its potential for the analysis of modified wood is exemplified, e.g. for the assessment of wood treated with hydrophobing agents, localisation of modification agents, pathway analysis related to functional tissues, dimensional changes due to thermal treatment, etc. Furthermore, monitoring of transient processes is a promising field of activity too.

Envelope treatment of wood based materials with concentrated organosilicons

Counteracting moisture ingress in wood and wood based products is crucial for service life prolongation. The use of solvent- as well as water-based organosilicons as envelope treatments on such materials is investigated. Therefore, organosilicons were applied onto four different substrates like OSB and MDF as well as solid wood and plywood. Both treated as well as untreated materials were subjected to a series of floating and imbibition protocols in combination with artificial weathering in order to quantify their hydrophobing action. Envelope treatments of organosilicons show potential in improving water repellent characteristics of solid wood and plywood but have a reduced effectiveness after artificial weathering. The wood based panels OSB and MDF behave opposite. Further research is needed to validate hypotheses on this.ZusammenfassungUm die Nutzungsdauer von Holz und Holzwerkstoffen zu verlängern, ist es wichtig, der Aufnahme von Feuchtigkeit entgegenzuwirken. Untersucht wird die Verwendung von lösemittel- sowie wasserbasierten Organosiloxanen zur Oberflächenbehandlung dieser Materialien. Dazu wurden Organosiloxane auf vier verschiedene Werkstoffe, nämlich OSB und MDF sowie Massivholz und Sperrholz, aufgetragen. Sowohl behandelte als auch unbehandelte Proben wurden einer Reihe von Wasserlagerungs- und Tauchversuchen und künstlicher Bewitterung unterzogen, um die hydrophobierende Wirkung zu bestimmen. Die Oberflächenbehandlung mit Organosiloxanen zeigte Potential, die wasserabstoßenden Eigenschaften von Massivholz und Sperrholz zu verbessern, allerdings mit reduzierter Wirkung nach künstlicher Bewitterung. OSB und MDF verhalten sich entgegengesetzt. Zur Bestätigung dieser Hypothesen sind weitere Untersuchungen erforderlich.

X-ray computed microtomography characterizes the wound effect that causes sap flow underestimation by thermal dissipation sensors

Insertion of thermal dissipation (TD) sap flow sensors in living tree stems causes damage of the wood tissue, as is the case with other invasive methods. The subsequent wound formation is one of the main causes of underestimation of tree water-use measured by TD sensors. However, the specific alterations in wood anatomy in response to inserted sensors have not yet been characterized, and the linked dysfunctions in xylem conductance and sensor accuracy are still unknown. In this study, we investigate the anatomical mechanisms prompting sap flow underestimation and the dynamic process of wound formation. Successive sets of TD sensors were installed in the early, mid and end stage of the growing season in diffuse- and ring-porous trees, Fagus sylvatica (Linnaeus) and Quercus petraea ((Mattuschka) Lieblein), respectively. The trees were cut in autumn and additional sensors were installed in the cut stem segments as controls without wound formation. The wounded area and volume surrounding each sensor was then visually determined by X-ray computed microtomography (X-ray microCT). This technique allowed the characterization of vessel anatomical transformations such as tyloses formation, their spatial distribution and quantification of reduction in conductive area. MicroCT scans showed considerable formation of tyloses that reduced the conductive area of vessels surrounding the inserted TD probes, thus causing an underestimation in sap flux density (SFD) in both beech and oak. Discolored wood tissue was ellipsoidal, larger in the radial plane, more extensive in beech than in oak, and also for sensors installed for longer times. However, the severity of anatomical transformations did not always follow this pattern. Increased wound size with time, for example, did not result in larger SFD underestimation. This information helps us to better understand the mechanisms involved in wound effects with TD sensors and allows the provision of practical recommendations to reduce biases associated with wounding in field sap flow measurements.

Modelling three-dimensional fungal growth in response to environmental stimuli.

Most fungi grow by developing complex networks that enable the translocation of nutrients over large distances. Spatially explicit mathematical models are able to capture both the complexity of the fungal network and the biomass evolution, as such providing a powerful alternative to classical modelling paradigms. Unfortunately, most of these models restrict growth to two dimensions or confine it to a lattice, thereby resulting in unrealistic representations of fungal networks. In addition, interactions between fungi and their environment are often neglected. In response, this work presents a lattice-free three-dimensional fungal growth model that accounts for the interactions between the in silico fungus and different substrates and media. A sensitivity analysis was carried out to identify the key model parameters for future calibration. Finally, a scenario analysis covering a variety of growth conditions was conducted to illustrate the broad scope of the model and its ability to replicate in situ growth scenarios.

Comparison of species classification models of mass spectrometry data : kernel discriminant analysis vs. random forest : a case study of Afrormosia (Pericopsis elata (Harms) Meeuwen)

RATIONALE The genus Pericopsis includes four tree species of which only Pericopsis elata (Harms) Meeuwen is of commercial interest. Enforcement officers might have difficulties discerning this CITES-listed species from some other tropical African timber species. Therefore, we tested several methods to separate and identify these species rapidly in order to enable customs officials to uncover illegal trade. In this study, two classification methods using Direct Analysis in Real Time (DART™) ionization coupled with Time-of-Flight Mass Spectrometry (DART-TOFMS) data to discern between several species are presented. METHODS Metabolome profiles were collected using DART™ ionization coupled with TOFMS analysis of heartwood specimens of all four Pericopsis species and Haplormosia monophylla (Harms) Harms, Dalbergia melanoxylon Guill. & Perr. Harms, and Milicia excelsa (Welw.) C.C. Berg. In total, 95 specimens were analysed and the spectra evaluated. Kernel Discriminant Analysis (KDA) and Random Forest classification were used to discern the species. RESULTS DART-TOFMS spectra obtained from wood slivers and post-processing analysis using KDA and Random Forest classification separated Pericopsis elata from the other Pericopsis taxa and its lookalike timbers Haplormosia monophylla, Milicia excelsa, and Dalbergia melanoxylon. Only 50 ions were needed to achieve the highest accuracy. CONCLUSIONS DART-TOFMS spectra of the taxa were reproducible and the results of the chemometric analysis provided comparable accuracy. Haplormosia monophylla was visually distinguished based on the heatmap and was excluded from further analysis. Both classification methods, KDA and Random Forest, were capable of distinguishing Pericopsis elata from the other Pericopsis taxa, Milicia excelsa, and Dalbergia melanoxylon, timbers that are commonly traded.

Investigating plywood behaviour in outdoor conditions

Moisture behaviour of plywood is investigated in combination with detailed structural analysis. In the lab, neutron radiography and X-ray computed tomography (X-ray CT) were used to map the moisture distribution and internal structure of plywood respectively. In an outdoor natural weathering test, the average moisture content (MC) and moisture distribution of plywood were monitored using a continuous moisture measurement set-up and an adapted electrical method, respectively. The structural changes of the specimens during weathering were recorded by using X-ray CT. Based on the interrelationship of moisture behaviour and structure, suggestions are given for improving the water resistance of plywood by optimising structure.

Tree rings show a different climatic response in a managed and a non-managed plantation of teak ( Tectona grandis ) in West Africa

Establishing large-scale plantations of teak could reduce the pressure on natural forests and sequester atmospheric carbon into durable wood. Understanding the growth dynamics of this species in plantations, outside its natural distribution area, is crucial for forest management. Stem discs of teak were collected in Ivory Coast at two sites, a non-managed plantation (Gagnoa) and a managed plantation (Seguie). All stem discs were processed using the standard dendrochronological methods in order to unravel the relationships between growth and climate. Results showed that growth is slower in Gagnoa compared to the Seguie plantation that is being thinned regularly. In Gagnoa, trees responded positively to April rainfall, i.e., during the early stage of tree-ring formation, and negatively to September-October rainfall, i.e., during the short dry period. In Seguie, trees responded positively to July rainfall, i.e., during latewood formation, under decreasing rainfall. At both sites, tree growth was influenced by sea-surface temperature anomalies during the summer in the Gulf of Guinea. Teak growth in Seguie could be additionally linked to El Nino events, specifically during three major episodes (1976–77, 1982–83 and 1997–98).