Volume 75, Issue 8

Microfibril angle (MFA) is a key biological trait contributing to wood stiffness, which is a common breeding objective for solid wood products in many tree species. To explore its genetic architecture, area-weighted MFA was measured in two Eucalyptus nitens progeny trials in Tasmania, Australia, with common open-pollinated families. Radial strips were extracted from 823 trees in 131 families and MFA assessed using SilviScan-2 ® . Heritability, genotype-by-environment interaction and inter-trait genetic correlations were evaluated to examine the genetic variability and stability of MFA and its relationships with other solid wood and pulpwood selection traits. Significant family variation was found for MFA in both trials. There was no significant genotype-by-environment interaction and the across-site narrow-sense heritability was 0.27. MFA was genetically independent of basic density, growth, and tree form. However, MFA was strongly and favourable genetically correlated to acoustic wave velocity in standing trees, modulus of elasticity and kraft pulp yield (KPY). The present study has shown that genetic improvement of E. nitens for pulpwood selection traits is unlikely to have adversely affected MFA, and thus timber stiffness. Rather these results suggest the possibility that selection for increased KPY may have indirectly improved MFA favourably for solid wood products.

This study proposes a new fractal model to improve the accuracy of equivalent thermal conductivity (ETC) prediction for wood and determine how the wood’s pore structure influences ETC. Using fractal theory and mercury injection porosimetry data, a fractal model for the geometry of the wood’s pore structure was built. The geometric model was then transformed into an equivalent thermal resistance model to calculate ETC. The calculations produced an explicit expression for ETC derived from the wood’s structural parameters including the minimum and maximum pore apertures, aperture distribution, porosity, and fractal dimension. The model also includes a probability factor. The simulated ETC produced by the model was validated by experiments and it was found to be in good agreement with these. These simulation results will be used to study the influence of several factors on ETC. The proposed model has the potential to be able to predict and analyzing other wood properties such as its electrical conductivity, diffusivity, and permeability and the model can likely also be used to analyze other porous materials.

Oak heartwood usually darkens during and after drying. This darkening can be heterogeneous, leaving non-colored areas in the wood board. These light discolorations have been linked to heterogeneous distribution of tannins, but compelling evidence on the microscale is lacking. In this study Raman and fluorescence microscopy revealed precipitations of crystalline ellagic acid, especially in the ray cells but also in lumina, cell corners and cell walls in the non-colored areas (NCA), which also had higher density. In these denser areas free water is longer present during drying and leads to accumulation of hydrolyzed tannins. When eventually falling dry, these tannins precipitate irreversible as non-colored ellagic acid and are not available for chemical reactions leading to darkening of the wood. Therefore, pronounced density fluctuations in wood boards require adjusting the drying and processing parameters so that water domains and ellagic acid precipitations are avoided during drying.

This research work presents a modelling strategy to analyse thermal conversion rates of two thermal wood modification processes based on time-temperature superposition method. It gathers in a single study different original and bibliographic experimental works analysing the dry mass variation that occurs during thermal and hydro-thermal wood modification processes. The mass loss kinetic was successfully modelled using a modified Arrhenius approach. The time-temperature superposition method allowed to define for each wood modification process a master curve and its time shift depending on the treatment temperature. The analysis of ventilated oven and saturated steam treatments pointed out the existence of a continuous single kinetic for the ventilated oven which became more complex for saturated steam since a second kinetic stage appeared. This kinetic difference was sustained by infrared spectra chemical analysis which showed that hemicelluloses degraded much faster in presence of steam while lignin degradation occurred in both conditions.

The moisture-dependency of the fracture energy for unmodified and acetylated Scots pine ( Pinus sylvestris L.) and birch ( Betula pendula Roth) has been investigated. Specimens were conditioned at relative humidity levels of 20, 75, and 97%, as well as dry and water-saturated. At moisture contents below 15%, the fracture energy increased with increasing moisture content for both unmodified and acetylated wood, while it decreased for untreated wood at higher moisture contents. A significant difference in moisture-dependency was found, indicating higher fracture energy for unmodified wood compared to acetylated wood at similar moisture contents. Additionally, to assess the impact of the increased brittleness for structural applications, the fracture energy was compared at equal relative humidity levels. The largest difference was seen at 75% relative humidity with approximately 50% lower fracture energy for acetylated wood. No significant differences were found for water-saturated samples. The moisture-dependency of the fracture energy, combined with the reduced hygroscopicity of acetylated wood, is suggested to be one, but not the only, contributing factor to the lower fracture energy of acetylated wood compared to unmodified wood at equal humidity levels. These observations have importance for structural design since design codes often assess material parameters based on ambient humidity.

In this paper, voxel-based finite element modelling based on spatial geometry and density data is applied to simulate the detailed stress and strain distribution in a large wood element. As example, a moulded wooden tube with a length of 3 m and a diameter of 0.3 m is examined. Gamma-ray computed tomography is used to obtain both, its actual geometric shape and spatial density distribution. Correlation functions (R 2  ≈ 0.6) between density and elastic material properties are experimentally determined and serve as link for defining the non-uniform distribution of the material properties in the finite element model. Considering the geometric imperfections and spatial variation of the material properties, a detailed analysis of the stress and strain distribution of a wood element is performed. Additionally, a non-destructive axial compression test is applied on the wooden tube to analyse the load-bearing behaviour. By means of digital image correlation, the deformation of the surface is obtained, which also serves for validation of the finite element model in terms of strain distributions.

Alkaline delignification of wood tissue is the core of the global pulping technology and the most prominent large-scale separation of the main wood components. This work aims at improved understanding of the interplay between the topochemistry of alkaline pulping and the associated morphological changes. Morphology and chemical structure of partially soda-delignified wood chips were studied combining X-ray tomography (XRT), X-ray diffraction analysis and compositional characterization (lignin and carbohydrate content). The XRT studies of wet samples (providing 3D structural information without interfering drying effects), allowed observation of the cell wall separation as an increasing amount of lignin was removed with the increasing pulping time. Comparison between the microstructure of the surface and the central parts of the treated chips showed a more delignified microstructure at the surface, which highlights the dependence of the delignification process on the mass transport (hydroxide ions and lignin fragments) through the wood tissue. The crystallite size of cellulose increased in the <200> crystal planes during the early stage of pulping while there was little effect on the <110> plane.

A lignin-based gel (AL-PE gel) was obtained from hardwood acetic acid lignin (AL) and poly(ethylene glycol) diglycidyl ether (PE) as a cross-linker at a high AL concentration, while the reaction at a lower AL concentration yielded an amphipathic derivative (am-AL-PE). The gel has been reported to swell in aqueous ethanol but shrink in pure water and ethanol. In the present work, swelling behaviors in other aqueous binary solvents and the swelling mechanism were investigated to explore novel lignin-based functional materials, such as stimuli-and/or environment-responsive gels. The AL-PE gel swelled in aqueous methanol, isopropanol, acetone, and tetrahydrofuran, and the order of swelling in the solvents was consistent with that of the am-AL-PE. Spin-spin relaxation time ( T 2 ) measurements with 1 H NMR analysis of the gel in aqueous acetone revealed that gel swelling was closely related to an increasing T 2 of acetone bound to the gel network. The nature of the lignin moiety in the gel also enabled a pH response, and the amphipathic nature of the gel provided it with a function as an absorbent for cationic surfactants. The results of this study can contribute to the valorization of lignin as a main component for solvent sensors and environmental purification materials.

Lignin is thought to be covalently bound to carbohydrates like hemicellulose during biosynthesis to form a lignin-carbohydrate complex (LCC). However, successive polymerisation with monolignols after the formation of LCC has not yet been clarified. To investigate the reaction of LCC, its enzymatic dehydrogenative polymerisation was conducted using deuterium-labelled coniferyl alcohol and model compounds, i.e., a lignin model ( β - O -4 dimer model) compound (LM) and an LCC model (benzyl ether type) compound (LCCM). The obtained polymers (DHPs) were methylated and subjected to thioacidolysis, and the degradation products were quantified by gas chromatography-mass spectrometry (GC-MS). The results showed that the amount of coniferyl alcohol connected to the LCCM via β - O -4 binding was almost the same as that bound to the LM. However, the amount of unreacted LCCM was larger than that of LM, suggesting that the LCCM is less likely to form condensed structures, i.e., 5-5, β -5, and 4 -O -5 structures. This could be due to the steric hindrance of the carbohydrate at the benzylic position.