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Thermally modified wood (TMW) is widely used in outdoor applications due to its advanced properties towards weathering stresses. Although the structure changes of TMW from weather factors have been reported, investigation of the quantitative analysis of water states and cell wall structure of TMW after weathering is limited. In this work, the amount of bound water, fiber saturation point (FSP), cell wall pores, and free water distribution of thermally modified Scots pine, Norway spruce, and European ash were measured before and after a 2-year natural weathering via NMR relaxometry, cryoporometry, and magnetic resonance imaging. The results show that weathering increased T2 relaxation time of lumens, indicating the degradation of tracheids and vessels, especially in TMW compared to unmodified wood. The amounts of bound water, FSP value, and cell wall pores were increased after weathering; however, an increase in thermal modification intensity resulted in lower FSP and limited the increase in number of pores. In summary, TMW showed better performance than unmodified wood after weathering. [ABSTRACT FROM AUTHOR]

In this research, the measurement fundamentals of fiber saturation point (FSP) using differential scanning calorimetry (DSC) method were explained. This method is based on the assumption that free water is frozen but bound water remains unfrozen in low temperatures. Thus, the FSP can be calculated by measuring the enthalpy of melting of frozen wet samples. This method measures the amount of energy absorbed or released by a sample when it is heated or cooled. Results showed that the DSC method may yield a higher FSP value compared to the widely accepted value of 30%, depending on the wood species. Both thermal and chemical (acetylation) modification methods reduced the FSP but in the acetylation method, there was no linear correlation between the weight gain percentage (WPG) and FSP.

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 WCWT2 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. [ABSTRACT FROM AUTHOR]

This paper deals with the determination of the capillary pore-size distribution (CPSD) and equilibrium moisture content (EMC) of untreated and thermally modified (TM) Norway spruce [ Picea abies (L.) Karst.] by means of the pressure plate technique (PPT). Desorption experiments were conducted at very high values of relative humidity (RH) in the range between 99.2% and 100%. The thermal modification of spruce results in an alteration of the CPSD, owing to the formation of intercellular cracks in the middle lamella, as a result of cell-wall compression. The desorption curves for both untreated and TM spruce show an extremely upward bend at 99.97% RH. This step reflects an EMC of 38.1% for untreated spruce and 33.8% for TM spruce. None of the samples shrunk during the PPT measurements. Following desorption experiments at 97.4% RH, all samples shrunk. This step reflects an EMC of 27.9% for untreated spruce and 21.7% for TM spruce. [ABSTRACT FROM AUTHOR]

Removing water from wood is a critical requirement for applications in building and construction and for chemical modifications. Normally, green radiata pine ( Pinus radiata D. Don) timber, with a moisture content (MC) range at harvest between 150% and 200%, is kiln dried to below fiber saturation point (FSP) to 10-14% MC. In the present work, a physical-chemical-mechanical dewatering process is presented, which involves pressure cycling with supercritical CO2 to remove water to near the FSP. When the CO2 was cycled from ∼4 MPa into the supercritical state, at pressures up to 20 MPa, specimens of cross-sectional dimensions of up to 52 mm were successfully dewatered from a MC of 174%, typical of the green state, to approximately 39% in seven cycles. The specimens with the smallest cross-sectional dimensions dewatered more slowly than the larger specimens. Preheating the green wood before loading it into the dewatering vessel increased the rate of dewatering. The final MCs were similar in all experiments and were independent of specimen dimension (15-52 mm) or preheating temperature between 40°C and 60°C. Pressure-temperature phase diagrams show that it is necessary to compress the CO2 to the supercritical state for efficient dewatering. Diffusion rates and solubility of CO2 in sap were important, but channel opening within specimens was proposed to be a critical factor in the dewatering process. The reason why pressure-based experiments remove water from wood to an MC greater than the established FSP of 30% is not yet clear. [ABSTRACT FROM AUTHOR]

Some of the most important indoor wood-decay basidiomycetes were investigated in Erlenmeyer flask experiments, in which 50 Pinus sylvestris sapwood samples with moisture content (MC) of 16% were piled, in view of the parallel influence of wood moisture and temperature on decay in buildings. In the piles, the moisture flow from the liquid at the bottom was interrupted by a metal ring at layer 7. Laboratory incubations with Antrodia xantha, Coniophora puteana, Donkioporia expansa, and Gloeophyllum abietinum over the temperature range of 10°C-25°C showed that fungi are able to colonize, moisten, and thereafter degrade wood samples below fiber saturation, if a moisture source nearby is available. In extreme cases, mycelium grew on wood with 17.4% final MC, and wood mass loss of more than 2% occurred at 24.6% moisture. [ABSTRACT FROM AUTHOR]

Distributions of nuclear magnetic resonance (NMR) relaxation times provide detailed information about the moisture absorbed in wood. In this work, T2*, T2, and T1 distributions were recorded from fresh sapwood and heartwood samples of pine ( Pinus sylvestris) and spruce ( Picea abies) at various temperatures. Below the melting point of bulk water, free water is frozen and its signal disappears from the distributions. Then, the low-temperature distributions of the unfrozen bound water contain more information about its components, because the large free water peaks hiding some smaller bound water peaks are absent and the exchange between free and bound water is prevented. Comparison of the total moisture signal integrals above and below the bulk melting point enables the determination of fiber saturation point (FSP), which, in this context, denotes the total water capacity of cell wall. T2*, T2, and T1 distributions offer different kinds of information about moisture components. All the peaks in the distributions were assigned, and it was demonstrated that the accessible hydroxyl site content and the amount of micropores can be estimated based on the peak integrals. [ABSTRACT FROM AUTHOR]

The macroscopic formulation of moisture transport in wood below the fiber saturation point has motivated many research efforts in the past two decades. Many experiments demonstrated the difference in steady state and transient moisture transport and the inadequacy of models derived for steady state transport when used to describe transient processes. A suitable modeling approach was found by distinguishing between the two phases of water in wood, namely bound water in the cell walls and water vapor in the lumens. Such models are capable of reproducing transient moisture transport processes, but the physical origin of the coupling between the two phases remains unclear. In this paper, the physical background on the microscale is clarified and transformed into a comprehensive macroscopic description, ending up with a dual-scale model comprising three coupled differential equations for bound water, water vapor, and internal energy, as well as a simplified microscale model for determination of the coupling term. [ABSTRACT FROM AUTHOR]