Alexander Petutschnigg

Impregnation of Scots pine and beech with tannin solutions: effect of viscosity and wood anatomy in wood infiltration.

The impregnation process of Scots pine and beech samples with tannin solutions was investigated. The two materials involved in the process (impregnation solution and wood samples) are studied in depth. Viscosity of mimosa tannin solutions and the anatomical aspect of beech and Scots pine were analysed and correlated. The viscosity of tannin solutions presents a non-newtonian behaviour when its pH level increases, and in the case of addition of hexamine as a hardener, the crosslinking of the flavonoids turns out to be of great importance. During the impregnation of Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.), the liquid and solid uptakes were monitored while taking into consideration the different conditions of the impregnation process. This method allowed to identify the best conditions needed in order to get a successful preservative uptake for each wooden substrate. The penetration mechanism within the wood of both species was revealed with the aid of a microscopic analysis. Scots pine is impregnated through the tracheids in the longitudinal direction and through parenchyma rays in the radial direction, whereas in beech, the penetration occurs almost completely through longitudinal vessels.

Microstructure of viscoelastic thermal compressed (VTC) wood using computed microtomography

The paper describes for the first time the analysis of the structure of compressed wood using computed tomography. The anatomical structures of Douglas-fir and hybrid poplar before and after densification with the viscoelastic thermal compression (VTC) process were described by pore size distributions and mean pore sizes and compared. The compression of Douglas-fir mainly affected earlywood, while the compression of hybrid poplar mainly occurred in the vessels. In both wood species, the densification resulted in a significant decrease in the pore volumes. The porosity decreased to less than half of the original value for Douglas-fir earlywood and to approximately one-quarter for the vessels in hybrid poplar. The relevant mean pore sizes also decreased dramatically to about one-quarter compared to the original values. In contrast, latewood in Douglas-fir and libriform fibers in hybrid poplar are quite stable under compression. Douglas-fir latewood retained its original structure after compression and did not show any reduction in pore size. The results confirmed that the anatomical structure of VTC densified wood can be described by pore size distributions and mean pore sizes. However, in the case of broad or bimodal distributions, the mean pore sizes are of less significance.

Determination of the Microstructure of an Adhesive-Bonded Medium Density Fiberboard (MDF) using 3-D Sub-micrometer Computer Tomography

The microstructure of a medium density fiberboard (MDF) has attracted much interest, because it determines most of the properties during production as well as during use of this type of board. In this paper the sub-micrometer computer tomography (sub-μm-CT) with very high resolution was used in order to investigate an industrially produced MDF. The data obtained were analyzed using mathematical morphology and image analysis in order to obtain information on the distribution of voids and the fiber material. Resulting distributions were found to follow Γ-law which was confirmed using the maximum likelihood estimation. Eventually, good correlations between void distribution and local density as well as between the proportion of cell wall material and local density were found in this investigation.

Surface properties of tannin treated wood during natural and artificial weathering

Abstract Tannins are the natural substances that plants use to protect wood. Novel tannin based formulations were tested to evaluate their efficacy in preventing weathering degradation of the surfaces. Scots pine and European beech specimens were treated with flavonoid based wood preservatives and exposed to artificial and natural weathering. The surface properties of the samples before and after weathering were evaluated using contact angle and colour measurements. Tannin treated samples showed a moderate resistance against discoloration and greater wettability than untreated samples. ATR-FT-MIR and FT-NIR spectroscopies combined with principal component analysis (PCA) revealed that weathering mainly degrades the aromatic component of wood. Because the protective tannin network is nothing more than an aromatic polymer, it suffers a similar degradation of lignin. Although the higher amount of aromatics leads to higher degradations, it is still possible to observe via vibrational spectroscopies that the flavonoid enriched surfaces contain more aromatics also after weathering.

Beech wood shrinkage observed at the micro-scale by a time series of X-ray computed tomographs (μXCT)

Abstract The shrinkage behavior of European beech wood was successfully observed on a time series of images obtained by high resolution X-ray computed tomography (μXCT). The calculated measures for shrinkage and shrinkage anisotropy are consistent with published data. Evidence was provided for the ‘ray restraint’ theory of shrinkage anisotropy. This technique has a high potential for the study of dynamic processes in wood at the micro-scale, though the resolution of the images is lower and the measurement times are longer in comparison to synchroton radiation μXCT.

A Simple Approach to Distinguish Classic and Formaldehyde-Free Tannin Based Rigid Foams by ATR FT-IR

Tannin based rigid foams (TBRFs) have been produced with formaldehyde since 1994. Only recently several methods have been developed in order to produce these foams without using formaldehyde. TBRFs with and without formaldehyde are visually indistinguishable; therefore a method for determining the differences between these foams had to be found. The attenuated total reflectance infrared spectroscopy (ATR FT-IR) investigation of the TBRFs presented in this paper allowed discrimination between the formaldehyde-containing (classic) and formaldehyde-free TBRFs. The spectra of the formaldehyde-free TBRFs, indeed, present decreased band intensity related to the C–O stretching vibration of (i) the methylol groups and (ii) the furanic rings. This evidence served to prove the chemical difference between the two TBRFs and explained the slightly higher mechanical properties measured for the classic TBRFs.

Sustainable Phenolic Fractions as Basis for Furfuryl Alcohol-Based Co-Polymers and Their Use as Wood Adhesives

Furfuryl alcohol is a very interesting green molecule used in the production of biopolymers. In the present paper, the copolymerization in acid environment with natural, easily-available, phenolic derivatives is investigated. The processes of polymerization of the furfuryl alcohol with: (i) spent-liquor from the pulping industry and (ii) commercial tannin from acacia mimosa were investigated though viscometry and IR-spectroscopy. The curing kinetics of the formulations highlighted the importance of the amount of furfuryl alcohol and catalyst as well as the effect of temperature for both phenolic-furanic polymers. Evidence of covalent copolymerization has been observed through infrared spectrometry (FT-IR) combined with principal component analysis (PCA) and confirmed with additional solubility tests. These bio-based formulations were applied as adhesives for solid wood and particleboards with interesting results: at 180 °C, the spent-liquor furanic formulations allow wood bonding slightly with lower performance than PVA in dry conditions, while mixed formulations allow the gluing of particleboard with only satisfactory internal bonding tests.

Analyzing wood bark insulation board structure using X-ray computed tomography and modeling its thermal conductivity by means of finite difference method

The continuous trend to energy saving and sustainable constructions in buildings leads to an increasing demand of efficient and sustainable thermal insulation materials. One promising development is the usage of the natural “tree insulation material,” namely bark, for building insulations. Insulation boards out of larch bark were scanned with an industrial computed tomograph in order to study the structure of the boards. The computed tomograph images were segmented using a categorization algorithm based on ANOVA. Apart from gaining knowledge about panel porosity, understanding of the inhomogeneous bark boards was enhanced by finding that two main components are prevalent. That knowledge of the boards microstructure enabled the application of a numerical model for thermal conductivity based on the finite difference method. These findings give the direction for further developments of efficient bark insulation panels with well-defined pore structure.

Tree Log Identification Based on Digital Cross-Section Images of Log Ends Using Fingerprint and Iris Recognition Methods

Tree log biometrics is an approach to establish log traceability from forest to further processing companies. This work assesses if algorithms developed in the context of fingerprint and iris recognition can be transferred to log identification by means of cross-section images of log ends. Based on a test set built up on 155 tree logs the identification performances for a set of configurations and in addition the impacts of two enhancement procedures are assessed.

Laser Treatment of Wood Surfaces for Ski Cores: An Experimental Parameter Study

Recently, the production of skis with wooden cores has increased due to changes in customer awareness concerning ecological issues and rising raw material costs for mineral oil resources. The preparation of ski surfaces is one of the main expense factors in the production of skis. Thus, one perspective of the AMER SPORTS CORPORATION is to treat wood surfaces with laser beams to develop new aesthetic possibilities in ski design. This study deals with different laser treatments for samples from various wood species: beech, ash, lime, and spruce. The parameters investigated are laser beam intensity and number of laser points on the surface. To evaluate the aesthetic changes, the CIELab color measurements were applied. Changes in the main wood components were observed by the Fourier transform infrared spectroscopy (FTIR) using an ATR (attenuated total reflectance) unit. The results show that the laser treatments on wood surfaces have an influence on wood color and the chemical composition. Especially the intensity of laser beams affects the color changes in different patterns for the parameters observed. These findings will be useful to develop innovative design possibilities of wood surfaces for ski cores as well as for further product design applications (e.g., mass customization).