How accurate are automated sorption balances? An analysis of errors in wood moisture content from uncertainties in the conditioning environment

Automated sorption balances are increasingly used to determine sorption isotherms of hygroscopic materials like wood. The sorption isotherms are constructed based on a number of equilibrium states between a specimen and the surrounding conditioning environment. In recent years, the uncertainty of these equilibrium states has been thoroughly discussed related to the time at constant environmental conditions needed to reach an adequate mass stability. However, uncertainties related to the conditioning environment are rarely discussed. This study describes a framework for analyzing and quantifying the effect of these uncertainties on the error in determined equilibrium moisture content. Various effects of the conditioning environment are analyzed, and the most important effects relate to the relative humidity (RH) in the instruments, both in terms of fluctuations in RH and an offset from the target value. The moisture error for these effects was found within the range 0.001–0.01 g g−1

Studying amount, location and state of water in modified wood at moisture levels relevant for fungal degradation

Water is an essential parameter for fungal degradation of wood, but degradation primarily occursat high moisture levels at water potential in the range of -4 to -0.1 MPa, which corresponds to 97-99.9% relative humidity. At these moisture levels, water is present in the wood structure both inand outside of cell walls. The majority of previous studies on the interaction between wood andwater for untreated as well as modified wood has, however, focused on the moisture range 0-95%relative humidity and mainly on water in cell walls. In this paper, we give examples of how preciseconditioning of specimens using the pressure plate technique can be combined with otherexperimental techniques in order to get information on interactions between wood and water athumidity levels relevant for fungal degradation. We show examples of how pressure plateconditioning can be combined with Differential Scanning Calorimetry (DSC) and Low FieldMagnetic Resonance (LFNMR) to get information not only about amount of water, but also aboutlocation and state of water in untreated and modified wood. Further use of such combination oftechniques has potential to give valuable pieces of information on the role of water in degradationprocesses for untreated as well as modified wood

Explaining the heat capacity of wood constituents by molecular vibrations

The heat capacity of wood and its constituents is important for the correct evaluation of many of their thermodynamic properties, including heat exchange involved in sorption of water. In this study, the dry state heat capacity of cellulose, hemicelluloses and lignin are mathematically described by fundamental physical theories relating heat capacity with molecular vibrations. Based on knowledge about chemical structure and molecular vibrations derived from infrared and Raman spectroscopy, heat capacities are calculated and compared with experimental data from literature for a range of bio- and wood polymers in the temperature range 5-370K. A very close correspondence between experimental and calculated results is observed, illustrating the possibility of linking macroscopic thermodynamic properties with their physical nano-scale origin

Hydroxyl accessibility in wood cell walls as affected by drying and re-wetting procedures

The first drying of wood cell walls from the native state has sometimes been described as producing irreversible structural changes which reduce the accessibility to water, a phenomenon often referred to as hornification. This study demonstrates that while changes do seem to take place, these are more complex than what has hitherto been described. The accessibility of wood cell wall hydroxyls to deuteration in the form of liquid water was not found to be affected by drying, since vacuum impregnation with liquid water restores the native cell wall accessibility. Contrary to this, hydroxyl accessibility to deuteration by water vapour was found to decrease to different levels depending on the drying conditions. Vacuum drying at 60 °C for 3 days reduced the accessibility more than drying for 1 day at 103 °C without vacuum. Drying for 3 days at 103 °C increased the hydroxyl accessibility compared to 1 day. Moreover, the decrease in hydroxyl accessibility to deuteration by water vapour induced by the first drying could be at least partially erased by subsequent vacuum impregnation with liquid water, indicating reversibility. For the drying of solid, non-degraded wood cell walls the results challenge the often supposed process of hornification, understood as a permanent decrease in hydroxyl accessibility to water.ISSN:1572-882XISSN:0969-023

Dialog-baseret undervisning i forelæsninger om træ som materiale

My project concerns the development of dialogue-based teaching withinwood materials science for civil engineers. Teaching was done over two course dates at the Technical University of Denmark in Spring 2018 where about 50 students attended each time. Teaching was organised with two hours of lectures in a lecture hall followed by two hours of supervised classroom exercises (calculation assignments). The aim of my project was to improve the learning outcome of students by having teaching revolving around discussions rather than a monologue lecturing. This was particularly challenging as my contribution to the course involved only a small fraction of the teaching and the students were used to traditional lecturing with very little student involvement in the teaching. Thus, a specific aim at the beginning of my first teaching date was to re-negotiate the didactical contract between me and the students by signalling that I expected them to be active and participate in the discussions. While the location and the curriculum for my teaching wereset, I was free to choose how I taught the curriculum. Therefore, I organised my teaching into a string of didactic loops according to the framework of the Theory of Didactic Situations. In each loop, the students were presented a minimal amount of information before they were given a question and time to reflect and discuss with their neighbour. Evaluation of the teaching method was done by the studentsreplying anonymously to an online questionnaire with three questions: 1) Rate the connection between lectures and classroom exercises? (Score 1 to 7), 2) Did discussing with your neighbour aid your understanding of the topic? (Score from 1 to 7), 3) Any further comments? (Written answers, multiple answers possible). The students were generally satisfied with the dialogue-based teaching and they found the teaching useful for classroom exercises based on the ratings of questions 1 and2. However, the third question was the most useful for me in improving my teaching in the future. From my own experience in the lecture hall as well as the students’ input it was clear that the re-negotiation of the didactical contract was not fully successful. As a result I will try to improve my future teaching by being more explicit in informing the students what is going to happen in the next session and why

Kinetics of Water Vapor Sorption in Wood Cell Walls:State of the Art and Research Needs

Water vapor sorption is the most fundamental aspect of wood-moisture relations. It is directly or indirectly related to the physical properties of wood and the onset of wood-damage mechanisms. While sorption properties of cellulosic materials have been utilized since antiquity, the time-dependent transition from one moisture content to another (i.e., sorption kinetics) has received much less attention. In this critical review, we present the state-of-the-art of water vapor sorption kinetics in wood. We first examine different experimental methods that have been used to measure sorption kinetics, from the quartz helix vacuum balance beginning in earnest in the 1930s, to automated sorption balances used recently. We then give an overview of experimental observations and describe the physical phenomena that occur during the sorption process, which potentially govern the following kinetics: boundary layer mass transfer resistance, heat of sorption, cell wall diffusion, swelling, and polymer mobility. Finally, we evaluate theoretical models that have been proposed for describing sorption kinetics, considering both experimental data and the physical processes described in the previous section. It is clear that no previously developed model can phenomenologically describe the sorption process. Instead, new models are needed. We conclude that the development of new models will require more than simple gravimetric measurements. In addition to mass changes, complementary techniques are needed to probe other important physical quantities on multiple length scales

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

AbstractMoisture in radiata pine (Pinus radiataD. 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.T2values 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 increasingT2values 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 WCWT2data was complicated by peak splitting in the relaxation spectrum. ConstantT2values 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.</jats:p

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