| 1. |
- Digaitis, Ramunas, PhD, et al.
(författare)
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Investigating the role of mechanics in lignocellulosic biomass degradation during hydrolysis : Part II
- 2021
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Ingår i: Biotechnology progress (Print). - : John Wiley & Sons. - 8756-7938 .- 1520-6033. ; 37:1
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Tidskriftsartikel (refereegranskat)abstract
- Lignocellulose breakdown in biorefineries is facilitated by enzymes and physical forces. Enzymes degrade and solubilize accessible lignocellulosic polymers, primarily on fiber surfaces, and make fibers physically weaker. Meanwhile physical forces acting during mechanical agitation induce tearing and cause rupture and attrition of the fibers, leading to liquefaction, that is, a less viscous hydrolysate that can be further processed in industrial settings. This study aims at understanding how mechanical agitation during enzymatic saccharification can be used to promote fiber attrition. The effects of reaction conditions, such as substrate and enzyme concentration on fiber attrition rate and hydrolysis yield were investigated. To gain insight into the fiber attrition mechanism, enzymatic hydrolysis was compared to hydrolysis by use of hydrochloric acid. Results show that fiber attrition depends on several factors concerning reactor design and operation including drum diameter, rotational speed, mixing schedule, and concentrations of fibers and enzymes. Surprisingly, different fiber attrition patterns during enzymatic and acid hydrolysis were found for similar mixing schedules. Specifically, for tumbling mixing, slow continuous mixing appears to function better than faster, intermittent mixing even for the same total number of drum revolutions. The findings indicate that reactor design and operation as well as hydrolysis conditions are key to process optimization and that detailed insights are needed to obtain fast liquefaction without sacrificing saccharification yields.
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| 2. |
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| 3. |
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| 4. |
- Fredriksson, Maria, et al.
(författare)
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Artifacts in electrical measurements on wood caused by non-uniform moisture distributions
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 75:6, s. 517-525
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Tidskriftsartikel (refereegranskat)abstract
- This paper examines how the moisture conditioning method affects the electrical conductance of wood. A widely used dataset was acquired by Stamm in 1929 who used a method of conditioning where water-saturated wood specimens were partially dried, sealed and left for a period of time for moisture to be redistributed before the electrical conductance was measured. However, more recent measurements combined conditioning above saturated salt solutions and pressure plate/pressure membrane techniques to obtain equilibrium moisture contents at constant relative humidity levels in the full moisture range. In this paper, the electrical conductance as a function of moisture content was compared for these two conditioning methods. When the specimens were conditioned to constant relative humidity levels, the data obeyed a percolation model better than when the conditioning procedure by Stamm was used. This was attributed to that Stamm's method gives moisture gradients through the specimen because of sorption hysteresis effects, even though the wood is conditioned to a steady-state moisture content. Equilibration to constant relative humidity levels thus provided more well-defined moisture states and that the data followed a percolation model indicates that the mechanism of electrical conduction in wood does not change, even at high moisture contents.
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| 5. |
- Fredriksson, Maria, et al.
(författare)
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Modelling over-hygroscopic wood sorption isotherms based on quantitative wood anatomy
- 2017
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Ingår i: ; , s. 142-147
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A sorption isotherm expresses the relation between ambient relative humidity (RH) and equilibrium moisture content of a material for a specific temperature. The sorption isotherm can generally be divided into a hygroscopic part covering low, medium and high RH levels, and an over-hygroscopic part close to 100% RH. For wood, the hygroscopic part is dominated by water uptake in cell walls and the over-hygroscopic part by capillary condensed water in cell lumina and other voids within the wood structure. Moisture contents in the over-hygroscopic range are required for fungal degradation, and over-hygroscopic sorption isotherms are thus relevant input data for models describing moisture conditions in outdoor structures, i.e. models needed for service life prediction. The over-hygroscopic range is also relevant when modelling wood drying. Measuring over-hygroscopic absorption and desorption isotherms is however time consuming and challenging and a model enabling prediction of over-hygroscopic sorption isotherms would therefore be valuable. In addition, such a model could give a better understanding of how the wood structure affects the capillary condensation of water. This paper presents an approach for modelling over-hygroscopic sorption isotherms based on quantitative wood anatomy, i.e. based on estimates of dimensions and geometries of voids in the wood structure available for capillary condensation. First results are shown for Norway spruce (Picea abies (L.) Karst.).
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| 6. |
- Fredriksson, Maria, et al.
(författare)
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On sorption hysteresis in wood : Separating hysteresis in cell wall water and capillary water in the full moisture range
- 2019
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 14:11
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Tidskriftsartikel (refereegranskat)abstract
- Moisture influences most physical wood properties and plays an important role in degradation processes. Like most other porous materials, wood exhibits sorption hysteresis. That is, the moisture content is higher if equilibrium is reached by desorption than if it is reached by absorption under the same ambient climate conditions. The mechanism of moisture uptake by wood are different in the hygroscopic and over-hygroscopic moisture ranges and due to methodical issues, most studies of sorption hysteresis have been performed in the hygroscopic range. In the present study, total sorption hysteresis was separated into hysteresis in cell wall water and capillary water respectively in the whole moisture range by a novel combination of experimental techniques. Wood specimens were conditioned to several high moisture contents using a new system based on the pressure plate technique, and the distinction between cell wall water and capillary water was done with differential scanning calorimetry. The results showed that sorption hysteresis in wood cell walls exists in the whole moisture range. The cell walls were not saturated with water until the whole wood specimen was saturated which contradicts the long-held dogma that cell walls are saturated before significant amounts of capillary water are present in wood.
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| 7. |
- Fredriksson, Maria, et al.
(författare)
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Scanning or desorption isotherms? : Characterising sorption hysteresis of wood
- 2018
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 25:8, s. 4477-4485
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
- Fredriksson, Maria, et al.
(författare)
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Water sorption in wood cell walls–data exploration of the influential physicochemical characteristics
- 2023
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 30:3, s. 1857-1871
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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.
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| 10. |
- Johansson, Sanne, et al.
(författare)
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Wood-water interactions in brown-rot decayed wood characterized by Low-Field Nuclear Magnetic Resonance (LFNMR)
- 2017
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It is a trivial fact that water is needed for decay of wood by brown rot fungi, but when this is looked at in more detail, there are several fundamental questions concerning water and decay that are not solved. The purpose of this study is to study how the wood-water interaction is changed during degradation of brown-rot fungi of Norway spruce (Picea abies (L) Karst.) grown at two different parts of Sweden and if it is changed in a way that facilitates further decay. We use Low-Field Nuclear Magnetic Resonance (LFNMR) equipment to measure on water-saturated samples degraded by the brown-rot fungus Postia placenta and exposed to different moisture conditions. With the LFNMR technique, it is possible to distinguish between water in different physical and chemical environments (pore sizes, water-pore wall interactions) and it is therefore possible to study how wood-water interactions changes with different degree of degradation. This conference proceeding concerns part of a larger experiment which is not completely evaluated and only results from the NMR-study will be shown here.
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