Emil Engelund Thybring

The role of chemical transport in the brown-rot decay resistance of modified wood

Chemical modification of wood increases decay resistance but the exact mechanisms remain poorly understood. Recently, Ringman and coauthors examined established theories addressing why modified wood has increased decay resistance and concluded that the most probable cause of inhibition and/or delay of initiation of brown-rot decay is lowering the equilibrium moisture content. In another recent study, Jakes and coauthors examined moisture-induced wood damage mechanisms, including decay and fastener corrosion, and observed that these mechanisms require chemical transport through wood cell walls. They proposed that chemical transport within wood cell walls is controlled by a moisture-induced glass transition in interconnected networks of hemicelluloses and amorphous cellulose. This paper shows how these models jointly suggest mechanisms by which wood modifications can inhibit brown-rot. Alternative mechanisms are also discussed. These models can be used to understand and further improve the performance of wood modification systems.

The mechanisms of plant cell wall deconstruction during enzymatic hydrolysis

Mechanical agitation during enzymatic hydrolysis of insoluble plant biomass at high dry matter contents is indispensable for the initial liquefaction step in biorefining. It is known that particle size reduction is an important part of liquefaction, but the mechanisms involved are poorly understood. Here we put forward a simple model based on mechanical principles capable of capturing the result of the interaction between mechanical forces and cell wall weakening via hydrolysis of glucosidic bonds. This study illustrates that basic material science insights are relevant also within biochemistry, particularly when it comes to up-scaling of processes based on insoluble feed stocks.

Characterization of moisture in acetylated and propionylated radiata pine using low-field nuclear magnetic resonance (LFNMR) relaxometry

Abstract Moisture in radiata pine (Pinus radiata D. Don) earlywood (EW), which was acetylated or propionylated to various degrees, was measured by low-field nuclear magnetic resonance (LFNMR) relaxometry. Spin-spin relaxation times (T2) were determined for fully saturated samples at 22 and −18°C. T2 values for EW lumen water increased with increasing acetylation weight percentage gain (WPG), perhaps caused by the less hydrophilic acetylated wood (AcW) surface. Cell wall water (WCW) and the water in pits and small voids also showed increasing T2 values as a function of WPG but with a weaker tendency. A possible explanation is the counteracting effects of decreased hydrophilicity and reduced moisture content (MC) of these water populations at higher levels of acetylation. The evaluation of propionylation on WCW T2 data was complicated by peak splitting in the relaxation spectrum. Constant T2 values for void water populations at various WPG levels for propionylated samples indicate a modification gradient in the cell wall. Fiber saturation point (FSP) was significantly reduced by both modifications. Slightly higher FSP values for propionylated samples suggest that physical bulking is not the only factor causing moisture exclusion in AcW. But this interpretation is tentative because of the possibility of cell wall damage caused by propionylation.

Experimental techniques for characterising water in wood covering the range from dry to fully water-saturated

Water plays a central role in wood research, since it affects all material properties relevant to the performance of wood materials. Therefore, experimental techniques for characterising water within wood are an essential part of nearly all scientific investigations of wood materials. This review focuses on selected experimental techniques that can give deeper insights into various aspects of water in wood in the entire moisture domain from dry to fully water-saturated. These techniques fall into three broad categories: (1) gravimetric techniques that determine how much water is absorbed, (2) fibre saturation techniques that determine the amount of water within cell walls, and (3) spectroscopic techniques that provide insights into chemical wood–water interactions as well as yield information on water distribution in the macro-void wood structure. For all techniques, the general measurement concept is explained, its history in wood science as well as advantages and limitations.

Synergistic effects of enzymatic decomposition and mechanical stress in wood degradation

Wood mechanical properties deteriorate due to formation of cracks caused by mechanical loading and due to the loss of structural polymers as a result of enzymatic activity. How these processes contribute to wood degradation and whether the interaction between mechanics and enzymes accelerate wood degradation was studied. Lignocellulolytic enzymes and dynamic mechanical loading, either alone, in combination or successively were applied to native and hydrothermally modified Scots pine (Pinus sylvestris L.) veneers. Tensile testing was employed to evaluate the changes in mechanical properties of the specimens. Fibre saturation point and hydroxyl group accessibility before and after hydrothermal modification and subsequent enzymatic hydrolysis were assessed by differential scanning calorimetry and dynamic vapour sorption techniques. The study revealed that simultaneous mechanical and enzymatic treatments lead to a significant reduction in Scots pine tensile strength while successive application of the two treatments did not reduce wood tensile strength to the same extent. The finding points towards the importance of synergy between abiotic and biotic factors in wood deterioration. Further, hydrothermal modification, unlike enzymatic hydrolysis, significantly affected wood hygroscopicity, but did not influence how the wood reacted to the mechanical and enzymatic treatments.

Hydroxyl accessibility in wood by deuterium exchange and ATR-FTIR spectroscopy: methodological uncertainties

The accessibility of wood hydroxyls to water is commonly studied by infrared spectroscopy after deuteration where water-interacting hydroxyls have their H exchanged for D. In this study, the hydroxyl accessibility is determined with ATR-FTIR spectroscopy after deuteration of specimens with liquid D2O. Several factors are examined to reveal the uncertainties involved in the accessibility determination. Despite the fact that specimens were able to interact with water vapour after deuteration and drying, producing a freshly cut surface just before measurement limited the effect of re-exchange of hydroxyls and gave for most batches reproducible results.

Scanning or desorption isotherms?: Characterising sorption hysteresis of wood

Sorption isotherms describe the relation between the equilibrium moisture content of a material and the ambient relative humidity. Most materials exhibits sorption hysteresis, that is, desorption give higher equilibrium moisture contents than absorption at equal ambient climate conditions. Sorption hysteresis is commonly evaluated by determination of an absorption isotherm followed by desorption starting from the highest relative humidity used in the absorption measurement (typically 95%). The latter is often interpreted as the desorption isotherm but is in fact a scanning isotherm, i.e. an isotherm obtained from neither dry nor water-saturated state. In the present study, we investigated the difference between desorption isotherms and scanning isotherms determined by desorption from different high relative humidity levels reached by absorption and how this difference influenced the evaluation of sorption hysteresis. The measurements were performed on Norway spruce (Picea abies (L.) Karst.) using automated sorption balances. Hysteresis evaluated from desorption isotherms gave linear absolute sorption hysteresis for the studied relative humidity range (0–96%), whereas hysteresis evaluated from scanning isotherms gave non-linear curves with a peak between 50 and 80% relative humidity. The position of this peak depended on the relative humidity from which desorption was initiated. Consequently, understanding and evaluation of sorption hysteresis might be challenging if scanning isotherms are used instead of desorption isotherms, hereby increasing the risk of misinterpreting the results.Graphical Abstract