Beate Buchelt

Furfuryl alcohol impregnation for improved plasticization and fixation during the densification of wood

Abstract The densification of wood leads to better mechanical properties, e.g., an increased hardness and dimensional stability. However, densified or shaped wood in contact with water springs back into its original shape without fixation. Hence, the aim of this study was the development of a combined densification and fixation procedure. Beech wood samples (Fagus sylvatica L.) were impregnated with a solution consisting of furfuryl alcohol and maleic anhydride. The compression of these impregnated samples to approximately 30% followed by a curing process in a heating press resulted in a significant increase of hardness and dimensional stability. The spring-back-effect was clearly reduced by the in situ polymerization of the furfuryl alcohol solution to furan resins.

Material behaviour of veneer during multidimensional moulding

During the coating of multidimensional moulded surfaces the coating material suffers different stresses, which limit the possible mould. The behaviour of veneer as a thin coating material is discussed in the following article. The investigations were carried out with veneers of beech (Fagus sylvatica L.), sycamore maple (Acer pseudoplatanus L.) and American walnut (Juglans nigra L.) of different thicknesses. The anisotropy of the material is analysed concerning the various structure of the considered wood species. Feasibilities and limits of a three dimensional moulding are presented and conditions for a plastic deformation are discussed. ZusammenfassungBeim Beschichten mehrdimensional geformter Flächen erfährt das Beschichtungsmaterial verschiedene Beanspruchungen, die die mögliche Form begrenzen. Im folgenden Artikel wird das Verhalten von Furnier als dünnes Beschichtungsmaterial beim Verformen diskutiert. Für die Untersuchungen wurden Furniere von Rotbuche (Fagus sylvatica L.), Bergahorn (Acer pseudoplatanus L.) und Amerikanischem Nussbaum (Juglans nigra L.) unterschiedlicher Dicke verwendet. Die Anisotropie des Materials hinsichtlich der unterschiedlichen Struktur der betrachteten Holzarten wird analysiert. Es werden Möglichkeiten und Grenzen bei einer dreidimensionalen Formung aufgezeigt und Bedingungen für eine plastische Verformung diskutiert.

Testing of set recovery of unmodified and furfurylated densified wood by means of water storage and alternating climate tests

Abstract Densification is a well-known method for improving the mechanical properties of wood. In the present study, unmodified and furfurylated wood samples were densified and submitted to cyclic water storage tests and cyclic alternating climate tests. Swelling coefficients and spring-back data were determined for the evaluation of the quality of densification. The study shows that results depend on the test method applied. Simple water storage tests do not reflect the behavior of densified wood in the high humidity range. The spring-back data of unmodified samples are more influenced by the testing method than those of the furfurylated ones.

Comparative analysis of thermally modified and native spruce loaded perpendicular to the grain

The aim of this work was to analyse the material behaviour of thermally modified and native spruce by load applied perpendicularly to the grain. Therefore, thermally modified and native samples were prepared for bending tests with the load in tangential direction. The bending strength in radial direction decreases significantly with the thermal treatment. The fracture surfaces in the tangential section of the bending samples after testing were analysed with a scanning electron microscope. For native samples, the typical failure was found in the intercellular area. For thermally modified samples, failure of the entire cell wall was observed. The material behaviour is more brittle, as demonstrated by the load-deflection curves, but also by anatomical studies of the fracture surfaces.ZusammenfassungZiel dieser Arbeit war es, das Materialverhalten thermisch modifizierter und nativer Fichte bei Beanspruchung quer zur Faserrichtung zu analysieren. Hierfür wurden thermisch modifizierte und native Proben in Biegeversuchen in tangentialer Belastungsrichtung geprüft. Durch die thermische Behandlung sinkt die Biegefestigkeit in radialer Richtung signifikant. Die Tangential-Bruchflächen der Biegeproben wurden nach dem Test mit einem Rasterelektronenmikroskop untersucht. Bei nativen Proben wurde das typische Versagen im interzellulären Bereich gefunden. Bei thermisch modifizierten Proben wurde dagegen ein Versagen der gesamten Zellwand beobachtet. Das Materialverhalten thermisch modifizierter Hölzer ist spröder als das von nativen Hölzern, wie die Last-Verformungs-Kurven, aber auch die anatomischen Untersuchungen der Bruchflächen gezeigt haben.

Influence of wood specimen thickness on its mechanical properties by tensile testing: solid wood versus veneer

No abstract available

New Biocomposites for Lightweight Structures and their Processes

The development of new biocomposites and efficient manufacturing methods that are suitable for series processing is the purpose of the current sub-project C4 of the Excellence Cluster MERGE, sponsored by DFG (Deutsche Forschungsgemeinschaft). Two different types of materials are combined: bio-based thermoplastic polymers such as bio-polyethylenes or bio-polyamides and renewable reinforcing materials such as thin wood veneer or unidirectional flax fibers. To achieve a high-efficiency in terms of mass-production, reproducibility and flexibility, it is required to perform several steps in the realization of semi-finished and final products. The improvement of the adhesion at the interface of the components, the implementation of continuous processes, in order to increase energetically the yielding, and the final design, through several methods, for future potential applications are so many perspectives to achieve.

Macroscopic and microscopic monitoring of swelling of beech wood after impregnation with furfuryl alcohol

Wood furfurylation is a modification method that improves several wood properties. Thereby wood is impregnated with a solution of furfuryl alcohol, catalysts and water, in general. The objective of this study was to understand the penetration of furfuryl alcohol into wood. Furthermore, a possible relationship between the substance amount and the swelling behaviour should be determined. To this end microscopic investigations were conducted to describe the temporal process of penetration and swelling. It was found that the swelling coefficients differ at the microscopic and macroscopic level. The microscopic swelling can reach twice the values of macroscopic swelling.ZusammenfassungDie Furfurylierung von Holz ist eine Modifikationsmethode zur Verbesserung verschiedener Holzeigenschaften. Dazu wird Holz im Allgemeinen mit einer Lösung aus Furfurylalkohol, Katalysatoren und Wasser imprägniert. Um das Penetrationsverhalten zu beschreiben wurden mikroskopische Untersuchungen an imprägnierten Proben durchgeführt. Des Weiteren wurde der Einfluss der Furfurylalkoholkonzentration auf das Quellverhalten untersucht. Es konnte festgestellt werden, dass sich die Quellungskoeffizienten im mikroskopischen und makroskopischen Bereich stark unterscheiden. Der mikroskopische Quellungskoeffizient kann doppelt so hoch sein wie der äußere, makroskopische Wert.

Influence of the slicing technique on mechanical properties of the produced veneer

The aim of this investigation was to compare the mechanical behaviour of lengthwise and plain sliced veneer of the species beech (Fagus sylvatica L.). Therefore, tension tests parallel and perpendicular to the grain were carried out. The results were evaluated using the variance analysis (ANOVA). As a result it can be stated that lengthwise sliced veneers exhibit significantly higher strength and better mechanical characteristics than plain sliced veneers. The checks parallel to the grain which occurred by manufacturing at that side of the veneer leaf which faces the cutting edge and which is stressed in tension are to be considered as reason therefore. In contrast to the tests parallel to the grain the modulus of elasticity perpendicular to the grain shows significantly lower values for lengthwise sliced veneers than for plain sliced veneers. Due to their higher strength values lengthwise sliced veneers are considered better base materials for engineered wood products than plain sliced veneers.ZusammenfassungZiel dieser Untersuchungen war der Vergleich des mechanischen Verhaltens von längs- und quergemesserten Furnieren der Holzart Rotbuche (Fagus sylvatica L.). Dazu wurden Zugversuche parallel und senkrecht zur Faserrichtung durchgeführt. Die Ergebnisse wurden mit der Varianzanalyse (ANOVA) verglichen. Längsgemesserte Furniere zeigen eine signifikant höhere Festigkeit und bessere mechanische Eigenschaften als quergemesserte Furniere. Als Grund dafür werden herstellungsbedingte Risse parallel zur Faser bei quergemesserten Furnieren angesehen. Längsgemesserte Furniere weisen senkrecht zur Faserrichtung überraschenderweise einen signifikant geringeren E-Modul auf als quergemesserte Furniere. Aufgrund ihrer höheren Festigkeitseigenschaften sind längsgemesserte Furniere besser für die Herstellung neuartiger Furnierwerkstoffe, wie Engineered Wood Products, geeignet als quergemesserte Furniere.

New method for determination of shear properties of wood

A new method for the determination of shear modulus and shear strength is presented in this study using a shear or picture frame. A shear frame in accordance with DIN SPEC 4885 is in other fields, such as fibre reinforced composites, state of the art. Here, a square test specimen with recessed corners is held in the shear frame and subjected to a quite uniform shear deformation state. To determine the shear modulus and the shear strength, tensile load acting on the shear frame and the associated shear strain are measured. This method has the advantage of simultaneous determination of the shear modulus and the shear strength. Thin square wooden plates of European beech (Fagus sylvatica L.) were tested in all anatomical directions. The results show good accordance with literature values. The highest values of shear modulus and shear strength were yielded for the LR plane, followed by the values in the LT plane. The tests in the RT plane clearly resulted in the lowest values.

The potential of phenol–formaldehyde as plasticizing agent for moulding applications of wood veneer: two-dimensional and three-dimensional moulding

Two phenol–formaldehyde resols, namely a low and a medium molecular weight phenol–formaldehyde, were investigated for their applicability as plasticizers in moulding of European beech veneer (Fagus sylvatica L.). Therefore, beech veneers specimens were impregnated with both phenol–formaldehyde resol types in various concentrations. Subsequently, two-dimensional mouldability of the veneer was tested in a three-point-bending test along and perpendicular to the grain. Additionally, three-dimensional moulding of the phenol–formaldehyde impregnated veneer was tested throughout a modified Erichsen cupping test, where the veneer is pressed through a circular shaped coining die. The obtained results indicate a significantly improved mouldability of the treated beech veneers compared to untreated, water-saturated control specimens. Even at low phenol–formaldehyde concentrations plasticizing effects were detected in longitudinal direction and perpendicular to the grain. These findings are substantiated by results from three-dimensional moulding. Furthermore, the low molecular weight phenol–formaldehyde treated veneers displayed a higher mouldability than medium molecular weight phenol–formaldehyde specimens at similar phenol–formaldehyde concentration.