| 1. |
- Fredriksson, Maria, et al.
(författare)
-
Water sorption in wood cell walls–data exploration of the influential physicochemical characteristics
- 2023
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 30:3, s. 1857-1871
-
Tidskriftsartikel (refereegranskat)abstract
- The material properties of wood are intimately tied to the amount of moisture contained in the wood cell walls. The moisture content depends on the environmental conditions, i.e. temperature and relative humidity, but also on material characteristics of the wood itself. The exact mechanisms governing moisture equilibrium between wood cell walls and environmental conditions remain obscure, likely because multiple material characteristics have been proposed to be involved. In this study, we used a data exploration approach to illuminate the important wood characteristics determining the cell wall moisture content in the full moisture range. Specimens of nine different wood species (two softwoods and seven hardwoods) were examined in terms of their material characteristics at multiple scales and their cell wall moisture content was measured in equilibrium with both hygroscopic conditions and at water-saturation. By statistical analysis, the chemical composition was found to be the most important predictor of the cell wall moisture content in the full moisture range. For the other wood characteristics the importance differed between the low moisture range and the humid and saturated conditions. In the low moisture range, the cellulose crystallinity and hydroxyl accessibility were found to be important predictors, while at high moisture contents the microfibril orientation in the S1 and S3 layers of the cell walls was important. Overall, the results highlighted that no single wood characteristic were decisive for the cell wall moisture content, and each of the predictors identified by the analysis had only a small effect in themselves on the cell wall moisture content. Wood characteristics with a major effect on the cell wall moisture content were, therefore, not identified.
|
|
| 2. |
- Ringman, Rebecka, et al.
(författare)
-
The importance of moisture for Brown Rot degradation of Modified Wood : A critical discussion
- 2019
-
Ingår i: Forests. - : MDPI AG. - 1999-4907. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of wood modification on wood-water interactions in modified wood is poorly understood, even though water is a critical factor in fungal wood degradation. A previous review suggested that decay resistance in modified wood is caused by a reduced wood moisture content (MC) that inhibits the diffusion of oxidative fungal metabolites. It has been reported that a MC below 23%-25% will protect wood from decay, which correlates with the weight percent gain (WPG) level seen to inhibit decay in modified wood for several different kinds of wood modifications. In this review, the focus is on the role of water in brown rot decay of chemically and thermally modified wood. The study synthesizes recent advances in the inhibition of decay and the effects of wood modification on the MC and moisture relationships in modified wood. We discuss three potential mechanisms for diffusion inhibition in modified wood: (i) nanopore blocking; (ii) capillary condensation in nanopores; and (iii) plasticization of hemicelluloses. The nanopore blocking theory works well with cell wall bulking and crosslinking modifications, but it seems less applicable to thermal modification, which may increase nanoporosity. Preventing the formation of capillary water in nanopores also explains cell wall bulking modification well. However, the possibility of increased nanoporosity in thermally modified wood and increased wood-water surface tension for 1.3-dimethylol-4.5-dihydroxyethyleneurea (DMDHEU) modification complicate the interpretation of this theory for these modifications. Inhibition of hemicellulose plasticization fits well with diffusion prevention in acetylated, DMDHEU and thermally modified wood, but plasticity in furfurylated wood may be increased. We also point out that the different mechanisms are not mutually exclusive, and it may be the case that they all play some role to varying degrees for each modification. Furthermore, we highlight recent work which shows that brown rot fungi will eventually degrade modified wood materials, even at high treatment levels. The herein reviewed literature suggests that the modification itself may initially be degraded, followed by an increase in wood cell wall MC to a level where chemical transport is possible.
|
|
| 3. |
- Thybring, Emil Engelund, et al.
(författare)
-
How much water can wood cell walls hold? : A triangulation approach to determine the maximum cell wall moisture content
- 2020
-
Ingår i: PLOS ONE. - : Public library science. - 1932-6203. ; 15:8
-
Tidskriftsartikel (refereegranskat)abstract
- Wood is a porous, hygroscopic material with engineering properties that depend significantly on the amount of water (moisture) in the material. Water in wood can be present in both cell walls and the porous void-structure of the material, but it is only water in cell walls that affects the engineering properties. An important characteristic of wood is therefore the capacity for water of its solid cell walls, i.e. the maximum cell wall moisture content. However, this quantity is not straight-forward to determine experimentally, and the measured value may depend on the experimental technique used. In this study, we used a triangulation approach to determine the maximum cell wall moisture content by using three experimental techniques based on different measurement principles: low-field nuclear magnetic resonance (LFNMR) relaxometry, differential scanning calorimetry (DSC), and the solute exclusion technique (SET). The LFNMR data were furthermore analysed by two varieties of exponential decay analysis. These techniques were used to determine the maximum cell wall moisture contents of nine different wood species, covering a wide range of densities. The results from statistical analysis showed that LFNMR yielded lower cell wall moisture contents than DSC and SET, which were fairly similar. Both of the latter methods include factors that could either under-estimate or over-estimate the measured cell wall moisture content. Because of this and the fact that the DSC and SET methods are based on different measurement principles, it is likely that they provide realistic values of the cell wall moisture content in the water-saturated state.
|
|
