| 1. |
- Alakalhunmaa, Suvi, et al.
(författare)
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Softwood-based sponge gels
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:5, s. 3221-3238
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Tidskriftsartikel (refereegranskat)abstract
- Crosslinking-aided gelation was utilized to prepare hydrogels from softwood polysaccharides, with spruce galactoglucomannans (GGM)—a group of largely unexploited hemicelluloses—as the main component, aiming at conversion into sponge-like aerogels. Cellulose nanofibrils were used for the formation of a reinforcing network, which was further crosslinked together with a GGM matrix by ammonium zirconium carbonate, an inorganic salt that is regarded as safe for use in food packaging. The hydrogels were freeze-dried into stiff, low-density aerogels with 98 % of their volume composed of air-filled pores. When immersed in water, the aerogels absorbed water up to 37 times their initial weight, demonstrating elasticity and repeatable and reversible sponge capacity. The developed concept reassembles the wood polysaccharides in a new way, creating interesting possibilities for utilizing the abundant “green gold,†GGM. The obtained biobased materials could find application potential, for example, in the field of food packaging and could contribute in the reduction of the usage of petroleum-based plastics in the future.
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| 2. |
- Ali, Silvia, et al.
(författare)
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From wood shavings to mechanical pulp - a new raw material?
- 2005
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 20:4, s. 418-422
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Tidskriftsartikel (refereegranskat)abstract
- Wood chips used in the thermomechanical pulping (TMP) process were originally designed to suit the chemical pulping process. The production of small wood pieces more suitable for the TMP process could lead to an energy saving in this energy-intensive process. This paper discusses the potential benefits of using wood shavings instead of chips as the raw material for TMP production. In some exploratory trials, wood shavings with a thickness of about 2 mm and wood chips were refined in two steps under normal TMP process conditions in a pilot refiner. The first-stage refining was performed under pressurized conditions at 130°C. The second-stage refining was performed at atmospheric pressure at approximately 100°C at four different energy levels. The quality of the pulp produced from wood shavings was found to be better than that of the pulp produced from wood chips, with respect to both strength properties (except tear index) and optical properties at comparable energy levels. The potential for energy savings at a given tensile index using wood shavings instead of the traditional chips is estimated to be about 25%.
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| 3. |
- Almgren, Karin M., et al.
(författare)
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Effects of Moisture on Dynamic Mechanical Properties of Wood Fiber Composites Studied by Dynamic FT-IR Spectroscopy
- 2008
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Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 27:16-17, s. 1709-1721
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Tidskriftsartikel (refereegranskat)abstract
- Wood fiber reinforced polylactide is a biodegradable composite where both fibers and matrix are from renewable resources. In the development of such new materials, information on mechanical behavior on the macroscopic and the molecular level is useful. In this study, dynamic Fourier transform infrared (FT-IR) spectroscopy is used to measure losses at the molecular level during cyclic tensile loading for bonds that are characteristic of the cellulosic fibers and the polylactid matrix. This molecular behavior is compared with measured macroscopic hysteresis losses for different moisture levels. The results show that moisture ingress will transfer the load from the fibers to the matrix, and that a more efficient fiber-matrix interface would diminish mechanical losses. Although the dynamic FT-IR spectroscopy method is still qualitative, this investigation shows that it can provide information on the stress transfer of the constituents in wood fiber reinforced plastics.
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| 4. |
- Baker, Darren A., et al.
(författare)
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Opportunities in lignin based carbon fibre
- 2015
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Ingår i: NWBC 2015. - Espoo : VTT. - 9789513883539 ; , s. 244-251
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Konferensbidrag (refereegranskat)abstract
- Innventia AB's LignoBoost process enables the extraction of high purity lignin efficiently from the black liquor in kraft mills. A stream of black liquor is taken from the evaporation plant and the lignin is precipitated by acidification and filtered. The filter cake is redispersed and acidified and the resulting slurry is filtered and washed. High purity lignin can be produced at several scales, namely 10g, 1kg, 10kg and over 1,000kg. Innventia has invested significantly to demonstrate the potential of lignin as a viable feedstock for carbon fibre manufacture. Initially, the fibre melt spinning performance of the lignin is assessed using single filament melt extrusion and then melt spinning is performed at the multifilament scale, where fine fibres can be produced for conversion to carbon fibre. Oxidative thermostabilisation of the lignin fibres is carried out so that carbonisation can proceed. The effects of thermal treatment programmes and tensioning have been studied by using either thermomechanical analysis or by using test equipment specially designed to monitor carbonisation profiles with either stress or strain control. In addition, continuous processes for the conversion of lignin fibre to carbon fibre are being developed.
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| 5. |
- Bergström, Elina Mabasa, et al.
(författare)
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Plasticized xyloglucan for improved toughness-Thermal and mechanical behaviour
- 2012
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Ingår i: Carbohydrate Polymers. - : Elsevier. - 0144-8617 .- 1879-1344. ; 87:4, s. 2532-2537
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Tidskriftsartikel (refereegranskat)abstract
- Tamarind seed xyloglucan is an interesting polysaccharide of high molar mass with excellent thermomechanical properties. Several plasticizers were studied in order to facilitate thermal processing and improve toughness (work to fracture) of xyloglucan film materials: sorbitol, urea, glycerol and polyethylene oxide. Films of different compositions were cast and studied by thermogravimetric analysis (TGA), calorimetry (DSC), dynamic mechanical thermal analysis (DMA) and tensile tests. Results are analysed and discussed based on mechanisms and practical considerations. Highly favourable characteristics were found with XG/sorbitol combinations, and the thermomechanical properties motivate further work on this material system, for instance as a matrix in biocomposite materials.
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| 6. |
- Bjurhager, Ingela, et al.
(författare)
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Ultrastructure and Mechanical Properties of Populus Wood with Reduced Lignin Content Caused by Transgenic Down-Regulation of Cinnamate 4-Hydroxylase
- 2010
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 11:9, s. 2359-2365
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Tidskriftsartikel (refereegranskat)abstract
- Several key enzymes in lignin biosynthesis of Populus have been down-regulated by transgenie approaches to investigate their role in wood lignification and to explore their potential for lignin modification. Cinnamate 4-hydroxylase is an enzyme in the early phenylpropanoid pathway that has not yet been functionally analyzed in Populus. This study shows that down-regulation of cinnamate 4-hydroxylase reduced Klason lignin content by 30% with no significant change in syringyl to guaiacyl ratio. The lignin reduction resulted in ultrastructural differences of the wood and a 10% decrease in wood density. Mechanical properties investigated by tensile tests and dynamic mechanical analysis showed a decrease in stiffness, which could be explained by the lower density. The study demonstrates that a large modification in lignin content only has minor influences on tensile properties of wood in its axial direction and highlights the usefulness of wood modified beyond its natural variation by transgene technology in exploring the impact of wood biopolymer composition and ultrastructure on its material properties.
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| 7. |
- Bäckström, Marie, 1964-
(författare)
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The effect of environment on refining efficiency of kraft pulps
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Although the pulp and paper mill processes have been operational for long time there is still a need to understand the unit operations in paper making and how they interact with the ingoing pulp material. This is crucial in order to fully utilize the potential of the wood as well as of the unit operations. In order to do that it is vital to have an understanding about the produced pulp fibres, how they are constructed and how they respond to different conditions of their environment.The aim of this work has been to clarify how the environment influences the refining efficiency of kraft pulps in terms of energy requirement and paper property development. The main hypothesis has been that the swelling of the fibres, due to their inherited polyelectrolytic gel nature, will not only affect the fibre as such but also the strength and properties of the fibre flocs that are mechanically treated between bars in the refiner and in this way affect the refining efficiency.The main focus has been to study how the chemical environment, in particular the initial fibre swelling, affects the refining efficiency. Therefore, the influence of counter-ions to the charged groups, the number of charged groups, electrolyte concentration, pH and rheological behaviour was studied. Additionally, the importance of fibre flocculation for the refining efficiency was investigated by chemical means, i.e. to chemically flocculate and deflocculate a fibre suspension just before entering the refiner and evaluate the refining efficiency. An investigation to clarify the importance of refining homogeneity was also performed. The work was performed both on a laboratory scale and in pilot scale using industrial refiners to ensure the validity of the results.The importance of the counter-ions to the charged groups on refining was demonstrated. When the counter-ions was sodium the refinability, defined as the required energy input to reach a certain WRV or tensile index, was reduced by up to 50%. The more energy-efficient refining of pulps in the Na+-form may be explained as a co-operation between a higher osmotic pressure in the fibre wall and the mechanical stress applied during refining, so called “electrostatic repulsion-assisted refining”. When mechanical forces are applied on the fibre and the fibre wall, the electrostatic repulsion forces due to the ionization act as an additional aid to increase the swelling, and this in turn helps to delaminate the fibre wall. This “electrostatic repulsion-assisted refining” also resulted in another type of external fibrillation of the fibres than that produced for the reference pulp in calcium form. The fibrils were very short and tiny. The improved refining efficiency could not be attributed to any rheological effect such as floc strength or floc size.The number of charges correlated to refinabiliy of the pulp material, but there has to be a balance between the number of charges and ultrastructure of the pulp fibre. If too many charges were introduced, the internal ultrastructure was eventually damaged, and no property development was obtained in the refining.The importance of refining heterogeneity on paper properties was investigated by mixing less refined or unrefined pulps and highly refined pulps in different proportions giving a wide distribution on energy input to individual fibres, as well giving swelling distribution curves. The mechanical properties of the produced paper were surprisingly alike, and the influence of the extreme inhomogeneity was rather small. In a pilot paper machine trial, clear effects due to heterogeneous refining was only observed when 50% of the stock fed to the paper machine was unrefined. This implies that the mills can have large freedom in refining strategies without any significant negative impact on the tensile strength properties at a given density.
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| 8. |
- Chang, Shan-Shan, et al.
(författare)
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Deposition and organisation of cell wall polymers during maturation of poplar tension wood by FTIR microspectroscopy
- 2014
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Ingår i: Planta. - : Springer Science and Business Media LLC. - 0032-0935 .- 1432-2048. ; 239:1, s. 243-254
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Tidskriftsartikel (refereegranskat)abstract
- To advance our understanding of the formation of tension wood, we investigated the macromolecular arrangement in cell walls by Fourier transform infrared microspectroscopy (FTIR) during maturation of tension wood in poplar (Populus tremula x P. alba, clone INRA 717-1B4). The relation between changes in composition and the deposition of the G-layer in tension wood was analysed. Polarised FTIR measurements indicated that in tension wood, already before G-layer formation, a more ordered structure of carbohydrates at an angle more parallel to the fibre axis exists. This was clearly different from the behaviour of opposite wood. With the formation of the S2 layer in opposite wood and the G-layer in tension wood, the orientation signals from the amorphous carbohydrates like hemicelluloses and pectins were different between opposite wood and tension wood. For tension wood, the orientation for these bands remains the same all along the cell wall maturation process, probably reflecting a continued deposition of xyloglucan or xylan, with an orientation different to that in the S2 wall throughout the whole process. In tension wood, the lignin was more highly oriented in the S2 layer than in opposite wood.
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| 9. |
- Dammström, S., et al.
(författare)
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On the interactions between cellulose and xylan, a biomimetic simulation of the hardwood cell wall
- 2009
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Ingår i: BioResources. - 1930-2126. ; 4:1, s. 3-14
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Tidskriftsartikel (refereegranskat)abstract
- The plant cell wall exhibits a hierarchical structure, in which the organization of the constituents on different levels strongly affects the mechanical properties and the performance of the material. In this work, the interactions between cellulose and xylan in a model system consisting of a bacterial cellulose/glucuronoxylan (extracted from aspen, Populus tremula) have been studied and compared to that of a delignified aspen fiber material. The properties of the materials were analyzed using Dynamical Mechanical Analysis (DMA) with moisture scans together with dynamic Infra Red -spectroscopy at dry and humid conditions. The results showed that strong interactions existed between the cellulose and the xylan in the aspen holocellulose. The same kinds of interactions were seen in a water-extracted bacterial cellulose/xylan composite, while unextracted material showed the presence of xylan not interacting with the cellulose. Based on these findings for the model system, it was suggested that there is in hardwood one fraction of xylan that is strongly associated with the cellulose, taking a similar role as glucomannan in softwood.
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| 10. |
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| 11. |
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| 12. |
- De Magistris, Federica, et al.
(författare)
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Combined shear and compression analysis using a modified Iosipescu shear test device : Experimental studies on dry wood
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:5, s. 539-545
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical treatment of wood in a refiner involves a complex combination of shear and compression forces. To obtain more knowledge on this process, the possibility of using an apparatus based on the Iosipescu shear test device to measure the behaviour of wood under a combined shear and compression load was tested. In this new apparatus, different combinations of shear and compression load were achieved by different rotations of the shear test device itself. Numerical simulations of the combined shear and compression test were carried out and compared with experimental data to verify the reliability of the modified device as applied to wood. It was concluded that the new apparatus is suitable for applying different combinations of shear and compression load in testing wood samples. However, finite element analysis showed that with the use of homogeneous material in the model, the level of strain reached would be 10-fold smaller. This fact is probably due to the honeycomb structure of the wood cells, which allows for different local deformation that could not be represented by the continuous material used in the model.
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| 13. |
- De Magistris, Federica, et al.
(författare)
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Combined shear and compression analysis using the Iosipescu device : analytical and experimental studies of medium density fiberboard
- 2004
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 37:6, s. 509-521
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of using the Iosipescu shear test device to study the combined shear and compression behavior of anisotropic materials was examined. Measurements were made using both an original (Wyoming version) and an in-house modified Iosipescu shear and compression fixture. Numerical simulation of the combined shear and compression test was carried out to verify the reliability of the modified device. The numerical results were compared with data from experiments on a medium-density fiberboard. The numerical results show good agreement with the experimental results for the shear test in all the three material directions tested. The shapes as well as the values of the strain fields were similar in the numerical and experimental results. Different rotations of the combined shear and compression device were studied using the finite element method to find the combinations that gave reliable results in shear and compression. It was found that the 45degrees rotation gave the most uniform strain fields in the section between the notches. This rotation was tested on the fiberboard.
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| 14. |
- De Magistris, Federica, et al.
(författare)
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Deformation of wet wood under combined shear and compression
- 2005
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 39:6, s. 460-471
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Tidskriftsartikel (refereegranskat)abstract
- During refining of mechanical pulp, a process occurring at high speed at temperatures of 140-160 degrees C, the flexibility and bonding ability of wood fibres are increased. To understand the mechanical behaviour of the fibres in this operation, deformations at low speed of wet wood specimens at 50 degrees C were studied under two different combinations of shear and compression loadings. The results were compared with the behaviour of wet wood in pure compression. Some features of the deformation that occurred in earlywood were analysed using an image analysis procedure. During pure compression the cell walls bend independently of the shape of the fibre cells and their cell wall thickness. Under combined shear and compression, however, mainly the corners of the fibre cells get deformed. In a second deformation performed in compression, the fibre cells follow the same deformation pattern as given by the first deformation type whether in compression or in combined shear and compression. The interpretation was that permanent defects in the cells themselves were introduced already in the first load cycle of the wood samples. The load combination with lower shear gave the same permanent strain as the case of pure compression but using less energy.
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| 15. |
- De Magistris, Federica, et al.
(författare)
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Finite Element Modelling of wood cell deformation transverse to the fibre axis
- 2008
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 23:2, s. 240-246
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Tidskriftsartikel (refereegranskat)abstract
- Modelling of wet wood under compression and combined shear and compression load was performed to simulate the mechanical pulping of wood chips in refiners. Experiments have shown that the wet fibre network exhibit two different deformation modes; an S-shape mode associated with compression and a brick-shape mode associated with combined shear and compression. To study the factors governing the mechanical behaviour of the fibre network a material model with the characteristics originating from the properties of the wood polymers was developed and was used in a three-dimensional finite element analysis. The effects of material properties were investigated by comparing models with anisotropic one-layer cell walls and orthotropic multi-layer cell walls. The deformation achieved both under compression and under combined shear and compression was found to be similar independent of the material constants used or the number of layers of the cells walls. This implies that the most important factor governing the deformation pattern of the fibre network is the cell structure itself.
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| 16. |
- De Magistris, Federica, et al.
(författare)
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Mechanical behaviour of wet wood in sequences of compression and combined compression and shear
- 2006
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 21:2, s. 231-236
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Tidskriftsartikel (refereegranskat)abstract
- During the refining of mechanical pulp, a process occurring at high speed at temperatures of 140-160°C, the flexibility and bonding ability of the wood fibres increase. To understand the mechanical behaviour of the fibres in this operation, the deformation at low speed of wet wood specimens at 50°C and 90°C were studied under different combinations of shear and compression loading using a modification of the Arcan device. The deformation in earlywood was studied using an image analysis procedure together with measurements of the work done under different loading conditions. The deformation under combined shear and compression load was different from that in pure compression. In the first cycle under compression, the fibre cell walls were bent in a characteristic "S" shape, whereas under the combined load the cells deformed according to a "brick" shape. After a first cycle under combined load, the cells deformed according to the "brick" shape even when subjected to a second load under pure compression. The first deformation cycle required the largest amount of work. Since less energy was needed for the first cycle under a combined load than under a compression load, the application of a combined load as a first cycle may be a way to permanently deform fibres using less work.
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| 17. |
- Dong, F., et al.
(författare)
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Fibre morphological effects on mechano-sorptive creep
- 2010
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 44:3, s. 475-483
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Tidskriftsartikel (refereegranskat)abstract
- The increased creep rate of paper under load during moisture cycling conditions as compared to that at high constant humidity is a problem in the use of packaging materials. In order to investigate the influence of morphological factors of the fibres on the occurrence and magnitude of this phenomenon, i.e. the occurrence of mechano-sorptive creep, studies on wood fibres isolated from different parts of spruce wood were performed. Thus, creep properties were studied on earlywood and latewood fibres from both juvenile wood and mature wood. In general, latewood fibres showed a higher degree of mechano-sorptive creep than earlywood fibres, and mature wood showed a higher degree of mechano-sorptive creep than juvenile fibres. The difference in mechano-sorptive creep rate between different fibres was shown to be correlated to the differences in fibril angle. The smaller the fibril angle the higher was the mechano-sorptive creep ratio. It was suggested that at fibril angles approaching 45° wood fibres do not exhibit mechano-sorptive creep.
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| 18. |
- Eder, Michaela, et al.
(författare)
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Experimental micromechanical characterisation of wood cell walls
- 2013
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Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; :1, s. 163-182
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Tidskriftsartikel (refereegranskat)abstract
- The properties of wood and wood-based materials are strongly dependent on the properties of the fibres, that is, the cell wall properties. It is thus highly important to be able to mechanically characterise cell walls in order to understand structure-property relationships. This article gives a brief overview of the state of the art in experimental techniques to characterise the mechanical properties of wood at both the level of the single cell and that of the cell wall. Challenges, opportunities, drawbacks and limitations of single fibre tensile tests and nanoindentation are discussed with respect to the wood material properties.
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| 19. |
- Engelund, Emil Tang, et al.
(författare)
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Tensile creep and recovery of Norway spruce influenced by temperature and moisture
- 2012
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 66:8, s. 959-965
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Tidskriftsartikel (refereegranskat)abstract
- The time-dependent mechanical behaviour (TDMB) of wood is important when using the material for structural purposes. Recently, a new method for predicting the TDMB by numerical modelling was established based on the assumption that TDMB is caused by the sliding of the microfibrils past each other. In this study, the TDMB is examined via creep experiments on small specimens of Norway spruce latewood. The results of these are compared with results from numerical modelling. The experiments include results at two levels of moisture content and three levels of temperature, enabling an investigation of these two climatic factors on TDMB of wood. It was found that the mechanical response of wood tissue is the sum of responses from both tracheids and middle lamella, with only the previous being reversible. The effect of moisture and temperature differed in that the latter affected the elastic and time-dependent responses equally. Moisture, on the other hand, reduced both the elastic properties and the activation energy barrier for sliding of the microfibrils, but furthermore changed the microfibril angle of the sample as a result of swelling. Hereby, moisture had a larger effect on the time-dependent response than the elastic. All of these effects were predicted by numerical modelling.
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| 20. |
- Fackler, K., et al.
(författare)
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Localisation and characterisation of incipient brown-rot decay within spruce wood cell walls using FT-IR imaging microscopy
- 2010
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Ingår i: Enzyme and microbial technology. - : Elsevier BV. - 0141-0229 .- 1879-0909. ; 47:6, s. 257-267
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Tidskriftsartikel (refereegranskat)abstract
- Spruce wood that had been degraded by brown-rot fungi (Gloeophyllum trabeum or Poria placenta) exhibiting mass losses up to 16% was investigated by transmission Fourier transform infrared (FT-IR) imaging microscopy. Here the first work on the application of FT-IR imaging microscopy and multivariate image analysis of fungal degraded wood is presented and the first report on the spatial distribution of polysaccharide degradation during incipient brown-rot of wood. Brown-rot starts to become significant in the outer cell wall regions (middle lamellae, primary cell walls, and the outer layer of the secondary cell wall S1). This pattern was detected even in a sample with non-detectable mass loss. Most significant during incipient decay was the cleavage of glycosidic bonds, i.e. depolymerisation of wood polysaccharides and the degradation of pectic substances. Accordingly, intramolecular hydrogen bonding within cellulose was reduced, while the presence of phenolic groups increased.
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| 21. |
- Fahlén, Jesper, et al.
(författare)
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Cross-sectional structure of the secondary wall of wood fibers as affected by processing
- 2003
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Ingår i: Journal of Materials Science. - 0022-2461 .- 1573-4803. ; 38:1, s. 119-126
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the arrangement of wood polymers within the fiber wall is important for understanding the mechanical properties of the fibers themselves. Due to their high load bearing ability, the arrangement of cellulose fibrils within the cell wall are of special interest. In this work AFM-Atomic Force Microscopy-in combination with image processing has been used to obtain more information about the arrangement of cellulose aggregates (fibrils) in the secondary cell wall layer of spruce wood. The effects of chemical processing on the arrangement of these cellulose aggregates were also studied. Enlargement of cellulose aggregates was found in the initial phase of the kraft cook. This increase in cellulose aggregate dimensions depended mostly on temperature for treatment temperatures above 140degreesC, regardless of the amount of alkali present. Although hemicelluloses are lost to various degrees under alkaline conditions, the increase in cellulose aggregate size was mainly related to thermally induced rearrangement of the cellulose molecules. The mean side length of cellulose aggregates was found to be around 18 nm in unprocessed wood and 23 nm in processed wood. The cellulose aggregates were assumed to be square shaped in cross section in both cases.
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| 22. |
- Fahlén, Jesper, et al.
(författare)
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On the Lamellar Structure of the Tracheid Cell Wall
- 2002
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Ingår i: Plant Biology. - : Wiley. - 1435-8603 .- 1438-8677. ; 4:3, s. 339-345
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Tidskriftsartikel (refereegranskat)abstract
- It is clear that cross sections of wood cells show a lamellar structure. This paper investigates the orientation of this lamellar structure of spruce (Picea abies) tracheids using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cross sections of spruce wood were produced through fracturing in longitudinal bending and tensile testing. When investigated with SEM, the fracture surfaces show a structure of mostly larger radial lamellae, in the order of 30-100 nm, i.e., agglomerations of a few cellulose aggregates. Thin transverse sections of the fracture zones investigated with atomic force microscopy show concentric lamellae with a width in the order of a single cellulose aggregate, i.e., 15-25 nm. No structural connection to the splinters in the radial direction can be seen. It is suggested that the radial lamellar structure is a consequence of the energy released during fracturing of the wood samples and that the undistorted wood has a concentric lamellar structure on a smaller structural level.
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| 23. |
- Fahlén, Jesper, et al.
(författare)
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Pore and Matrix Distribution in the Fiber Wall Revealed by Atomic Force Microscopy and Image Analysis
- 2005
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 6:1, s. 433-438
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Tidskriftsartikel (refereegranskat)abstract
- A method for the ultrastructural investigation of fiber cross-sections based on atomic force microscopy in combination with image analysis is presented. A uniform distribution of pores across the matrix material within the fiber wall was revealed by impregnation of pulp fibers with poly(ethylene glycol). The effects of chemical and mechanical processing on the pore and matrix structure and on the arrangement of the cellulose fibril aggregates were investigated. During chemical processing, changes in the fiber ultrastructure occur: a broadening of the pore and matrix lamella widths in combination with a reduction in their number and an enlargement of the cellulose fibril aggregates. It was found that pores formed during pulping are evenly distributed across the fiber wall in the transverse direction. In contrast, refining increases the pore and matrix lamella width in the fiber wall closest to the middle lamella an effect which gradually decrease in size toward the lumen side.
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| 24. |
- Fahlén, Jesper, et al.
(författare)
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Ultrastructural changes in a holocellulose pulp revealed by enzymes, thermoporosimetry and atomic force microscopy
- 2005
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Ingår i: Holzforschung. - 0018-3830 .- 1437-434X. ; 59:6, s. 589-597
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Tidskriftsartikel (refereegranskat)abstract
- To increase our knowledge of the ultrastructure within softwood fibres, enzymatic treatment, thermoporosimetry, light microscopy, and atomic force microscopy with image analysis were used to investigate the structure of holocellulose softwood pulp fibres. The size of the average cellulose fibril aggregates and the width of pore and matrix lamellae were found to be uniform across the secondary cell-wall layer in the transverse direction of the wood fibre wall. In holocellulose, these dimensions were very similar to those in the native wood, whereas in kraft pulp the cellulose fibril aggregates were larger and the pore and matrix lamellae broader. These differences between holocellulose and kraft pulp fibres suggest that a high temperature is needed for cellulose fibril aggregation to occur. Neither refining nor drying of the holocellulose pulp changed the cellulose fibril aggregate size. Upon drying and enzymatic treatment, a small decrease in the pore and matrix lamella width was evident throughout the fibre wall. This indicated not only uniform distribution of pores throughout the fibre wall, but also enzymatic accessibility to the entire fibre wall. The holocellulose pulp had a somewhat larger pore volume than the kraft pulp. Refining of the holocellulose pulp led to pore closure, probably due to increased mobility of the fibre wall. The enzymatic treatment revealed that during hydrolysis of one hemicellulose, part of the other was also dissolved, indicating that the two hemicelluloses are to some extent linked to each other in the structure.
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| 25. |
- Fernandes, Susana C. M., et al.
(författare)
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Transparent chitosan films reinforced with a high content of nanofibrillated cellulose
- 2010
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Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 81:2, s. 394-401
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports the preparation and characterization of nanocomposite films based on different chitosan matrices and nanofibrillated cellulose (NFC) for the purpose of improving strength properties. The nanocomposite films were prepared by a simple procedure of casting a water-based suspension of chitosan and NFC, and were characterized by several techniques: namely SEM, X-ray diffraction, visible spectrophotometry, TGA, tensile and dynamic-mechanical analysis. The films obtained were shown to be highly transparent (transmittance varying between 90 and 20% depending on the type of chitosan and NFC content), flexible, displayed better mechanical properties, with a maximum increment on the Young's modulus of 78% and 150% for high molecular weight (HCH) and water-soluble high molecular weight (WSHCH) filled chitosans, respectively; and of 200% and 320% for low molecular weight (LCH) and water-soluble filled (WSLCH) chitosans, respectively. The filled films also showed increased thermal stability, with, for example, an increase in the initial degradation temperature (Td(i)) from 227 degrees C in the unfilled LCH film up to 271 degrees C in filled LCHNFC50% nanocomposite films, and a maximum degradation temperature (Tdi) raising from 304 degrees C to 313 degrees C for the same materials.
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| 26. |
- Gimåker, Magnus, et al.
(författare)
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On The Mechanisms Of Mechano-Sorptive Creep Reduction By Chemical Cross-Linking
- 2009
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Ingår i: Advances in Pulp and Paper Research, Oxford 2009. - Lancashire, UK : The Pulp and Paper Fundamental Research Society. - 9780954527266 ; , s. 1001-1017
-
Konferensbidrag (refereegranskat)abstract
- Despite the technical importance of mechano-sorptive creep in paper, the exact mechanism behind this phenomenon is still not fully understood. In this study it was shown that the mechano-sorptive creep of paper sheets can be significantly reduced by chemical cross-linking through periodate oxidation. The mechanism behind this reduction has been examined through creep measurements of both sheets and individual fibres. For sheets the creep acceleration due to varying humidity was significantly reduced by the chemical cross-linking. For single fibres, however, the creep acceleration was not affected by the chemical crosslinking. In fact the absolute creep rate for the periodate oxidised fibres were higher than that of the reference fibres. This clearly showed that the improvement in mechano-sorptive creep found on a sheet level does not originate from an improved creep resistance for individual fibres but rather from mechanisms operating at the fibre network level. Hygroexpansion and moisture sorption of the sheets during the humidity cycling used for creep testing have also been measured, and the results showed that both was reduced by the periodate oxidation. Reduced moisture sorptivity and hygroexpansion probably minimises stress concentrations at the fibre network level and thereby also the creep acceleration.
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| 27. |
- Giummarella, Nicola, et al.
(författare)
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On the effect of hemicellulose removal on cellulose-lignin interactions
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - : De Gruyter Open Ltd. - 0283-2631 .- 2000-0669. ; 32:4, s. 542-549
-
Tidskriftsartikel (refereegranskat)abstract
- In a recent study, it was suggested that there could be direct associations between cellulose and lignin in mild alkaline cooked pulps. The observation was based on studies showing that the molecular straining of lignin was similar to that of cellulose. This finding has serious ramifications for technical production of pulps as it could expand on what is known about recalcitrant lignin removal during pulping. Herein, we investigate the possible interaction between cellulose and lignin discussing possible mechanisms involved at the nano- and molecular-scales, and present support for that the removal of hemicellulose by hot water extraction or mild kraft pulping causes strong interactions between lignin and cellulose.
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| 28. |
- Guo, Fei, et al.
(författare)
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Hygroscopicity, degradation and thermal stability of isolated bamboo fibers and parenchyma cells upon moderate heat treatment
- 2021
-
Ingår i: Cellulose. - : Springer Science and Business Media B.V.. - 0969-0239 .- 1572-882X. ; 28:13, s. 8867-8876
-
Tidskriftsartikel (refereegranskat)abstract
- Parenchyma cells and fibers are the two dominant types of cells in the bamboo culm. Their mechanical and biological functions in bamboo differ substantially, derived from their cell wall structures and chemical compositions. The objective of this work was to comparatively study the hygroscopicity and the thermal degradation of bamboo fibers and parenchyma cells in order to better understand how to optimize heat treatment of bamboo. FTIR spectroscopy showed that parenchyma cells had a higher hemicellulose content and higher S/G lignin ratio than bamboo fibers based on the spectral changes at 1602 cm−1 with respect to 1505 cm−1. Upon heat treatment, spectral changes related to esterification reactions and loss of hydroxyl groups were observed. The heat treatment reduced hygroscopicity of parenchyma cells more than for bamboo fibers due to their lower thermal stability attributed to the higher hemicellulose content and less compact cell wall structure. Although heat treatment at 180 °C could improve the thermal stability of bamboo, mild heat treatments at 140 °C and 160 °C were found to be adequate to facilitate the degradation of bamboo. © 2021, The Author(s)
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| 29. |
- Guo, Juan, et al.
(författare)
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Changes of wood cell walls in response to hygro-mechanical steam treatment
- 2015
-
Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 115, s. 207-214
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of compression combined with steam treatment (CS-treatment), i.e. a hygro-mechanical steam treatment on Spruce wood were studied on a cell-structure level to understand the chemical and physical changes of the secondary cell wall occurring under such conditions. Specially, imaging FT-IR microscopy, nanoindentation and dynamic vapour absorption were used to track changes in the chemical structure, in micromechanical and hygroscopic properties. It was shown that CS-treatment resulted in different changes in morphological, chemical and physical properties of the cell wall, in comparison with those under pure steam treatment. After CS-treatment, the cellular structure displayed significant deformations, and the biopolymer components, e.g. hemicellulo se and lignin, were degraded, resulting in decreased hygroscopicity and increased mechanical properties of the wood compared to both untreated and steam treated wood. Moreover, CS-treatment resulted in a higher degree of degradation especially in earlywood compared to a more uniform behaviour of wood treated only by steam.
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| 30. |
- Guo, Juan, et al.
(författare)
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Effects of ageing on the cell wall and its hygroscopicity of wood in ancient timber construction
- 2018
-
Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 52:1, s. 131-147
-
Tidskriftsartikel (refereegranskat)abstract
- An important traditional load bearing member in oriental ancient timber structure buildings, i.e. Huagong (flower arm), was selected to explore the alterations in cell wall components and hygroscopic properties of wood during long time ageing. This archaeological poplar (Populus spp.) wood with cal. BP 690: BP 790 was studied from the wood surface and inwards by means of imaging FTIR spectroscopy, X-ray diffraction and dynamic vapour sorption. The deterioration of the archaeological wood mainly displayed a depolymerization of glucomannan and lignin as well as a hydrolysis of the glucuronic acid of xylan and of the aromatic C–O groups in the condensed lignins or lignin–carbohydrate complexes. Furthermore, the degradation promoted the rearrangement of the cellulose molecules in adjacent microfibrils. The cellulose crystallites in the archaeological wood were therefore packed more tightly and had larger diameter. The structural alterations of wood cell wall components and a decrease in crystallinity contributed to an increase in the number of moisture bonding sites and led to an increase in both the equilibrium moisture content of the archaeological wood in the entire RH range as well as an increase in hysteresis.
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| 31. |
- Guo, Juan, et al.
(författare)
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Effects of thermo-hygro-mechanical (THM) treatment on the viscoelasticity of in-situ lignin
- 2017
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 71:6, s. 455-460
-
Tidskriftsartikel (refereegranskat)abstract
- For producing wood products without fractures based on thermo-hygro-mechanical (THM) treatments, it is essential to understand how steaming and compression change the wood softening and cell wall components. In this paper, the effects of compression combined with steam treatment (CS) on the viscoelasticity of the in-situ lignin of Chinese fir has been investigated through dynamic mechanical analysis (DMA) under fully saturated conditions. Several variations were studied, such as the softening temperature (Tg) and apparent activation energy (ΔHa) of the softening process in response to CS treatment conditions (such as steam temperature and compression ratio) under separate consideration of earlywood (EW) and latewood (LW). No difference between EW and LW with respect to the viscoelasticity was noted. Tg and ΔHa of the lignin softening were nearly unaffected by the compression ratio, but were highly influenced by the steam temperature. The Tg decreased significantly with CS treatments at or above 160oC, but showed no appreciable change, compared to the native wood, at the lower steaming temperature of 140oC. ΔHa increased at higher steam temperatures, while ΔHa showed a decreasing tendency with decreasing Tg. This indicates that lignin undergoes a simultaneous depolymerization as well as a condensation during CS treatment.
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| 32. |
- Hammar, Lars-Åke, et al.
(författare)
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The effect of process conditions on pulp quality development at low consistency refining of mechanical pulp - TMP
- 2009
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Ingår i: 2009 International Mechanical Pulping Conference : proceedings. ; , s. 182-185
-
Konferensbidrag (refereegranskat)abstract
- Low consistency refining (LC) as a second refining stage, after a HC-defibration is an energy-efficient process solution. This HC-LC concept has for some time been explored in pilot scale and shown promising results. However it is clear that in order to obtain an optimal development of pulp properties the LC-refining has to be optimized with regard to process conditions. In this study the effects of temperature, pH, and specific edge load in the LC-refining on the pulp quality were investigated. For this purpose a mobile LC refiner rig placed after a primary stage HC mill refiner in the Braviken Paper mill, Holmen Paper was used. The trials show that energy savings are possible with preserved properties in the production of mechanical pulp. High temperature, high pH and low specific edge load were indicated to be preferable for both the tensile index development and for preserving the fibre length of the pulp. An increased degree of refining developed as expected the tensile index but too high specific energy resulted in some fibre shortening.
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| 33. |
- Hammar, Lars-Åke, et al.
(författare)
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The effect of process conditions on pulp quality development in low consistency refining of mechanical pulp - TMP
- 2010
-
Ingår i: Appita journal. - 1038-6807. ; 63:5, s. 377-380
-
Tidskriftsartikel (refereegranskat)abstract
- High consistency (HC) defibration followed by secondary stage low consistency refining (LC) is an energy efficient process in mechanical pulping that has been explored for some time. In this study the effects of temperature, pH, specific edge load and specific energy on pulp quality have been investigated for LC refining using a mobile LC refiner rig placed after a primary stage HC refiner In the Braviken Paper mill. The trials showed that the specific energy consumption in production of mechanical pulp can be reduced with at least 15% with preserved pulp properties. High temperature, pH over 7 and low specific edge load were advantageous both for tensile index development and for preserving the fibre length of the pulp. The development of other pulp properties such as shives content and light scattering coefficient, as a function of freeness, were comparable for the second stage LC- and HC-refining.
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| 34. |
- Jetsu, Petri, et al.
(författare)
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Wood-based thermal insulation materials
- 2016
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Ingår i: Proceedings of the 14th European workshop on lignocellulosics and pulp. - 9791090188020 ; , s. 341-345
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A research project has been undertaken with the aim of developing wood-based cellulosic thermal insulation panel material manufactured by foam forming with high performance and to explore the possibilities of creating a new bio-based cellulosic in-situ spray-on thermal insulation foam to replace traditional spray-on plastics insulation foams. Insulation boards were manufactured from 100% softwood and a mixture of softwood and microfibrillated cellulose (MFC). The foaming surfactant used was sodium dodecyl sulphate (SDS). The materials made of softwood and MFC mixtures were made by layering. The thermal conductivity behaviour of the boards was investigated. It has been demonstrated that by using foam forming technology, nanofibrillated cellulose and softwood kraft pulp, it was possible to create high bulk fibre networks with good thermal insulation properties that simultaneously had outstanding high air flow resistivity in relation to the total density of the material. The results obtained were affected by board density. Air flow decreased with board bulk density, due to higher tortuosity of fibrous structure. Air flow resistance increased with layering strategy, with MFC layer enhancing the performance of boards to limit air going across the board.
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| 35. |
- Kleinhans, Henrik, et al.
(författare)
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Development of lignin carbon fibers : Evaluation of the carbonization process
- 2016
-
Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 133:38
-
Tidskriftsartikel (refereegranskat)abstract
- The use of lignin as a renewable resource for the production of less-expensive carbon fibers has in recent years attracted great interest. In order to develop the strength properties, the stabilization and carbonization processes have to be optimized. For this reason, the process parameters during carbonization have here been studied on stabilized lignin fibers in the temperature interval from 300 to 1300 °C. The effects of temperature, heating rate, and straining of fibers during carbonization on the strength properties of carbon fibers were investigated. The heating rate, in the range from 1 to 40 °C/min, was shown to have no effect on the property development of the fibers. During carbonization with no load applied to the fibers, a shrinkage of 20% was noted. Counteracting the shrinkage by imposing a load on the fibers during the carbonization resulted in fibers with a greater stiffness. The tensile strength was not, however, affected by this loading.
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| 36. |
- Kulasinski, Karol, et al.
(författare)
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Moisture adsorption of glucomannan and xylan hemicelluloses
- 2016
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:3, s. 1629-1637
-
Tidskriftsartikel (refereegranskat)abstract
- Wood and wood materials are highly sensitive to moisture in the environment. To a large extent this relates to the hygroscopicity of wood hemicelluloses. In order to increase our understanding of the effects of moisture sorption of the major wood hemicelluloses, glucomannan and xylan, model experiments using films of amorphous konjak glucomannan and rye arabinoxylan were conducted. Moisture-induced expansion and stiffness softening were characterized using dynamic mechanical testing. Both hemicelluloses showed a threshold around 5Â % of moisture content above which swelling increased whereas the modulus decreased by more than 70Â %. FTIR spectra, using H2O and D2O, indicated that even at high RH about 15Â % of the hydroxyl groups were not accessible to hydrogen exchange by D2O. For xylan both hydroxyl groups were found to exchange in the same manner while for the glucomannan the O(6)H group seemed to be the most accessible.
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| 37. |
- Larsson, Per Tomas, et al.
(författare)
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Influence of cellulose supramolecular structure on strength properties of chemical pulp
- 2014
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 68:8, s. 861-866
-
Tidskriftsartikel (refereegranskat)abstract
- The industrially produced chemical pulps have lower strength properties than those obtained under laboratory conditions, and this difference is referred to as the strength delivery (SD) problem. In this study, the hypothesis was put forward that the SD could, at least in part, be accounted for by the supramolecular structure of the cellulose microfibrils of the fiber wall. To test the hypothesis, two bleached softwood kraft pulps (BSKP) were manufactured from the same starting material with different degrees of cellulose aggregation, but the pulps were otherwise as similar as possible in other controllable respects. The chemical and physical properties, including the pulp strength, were tested. A selective increase of the degree of cellulose microfibril aggregation resulted in a pulp with a decreased tear index (TI) at a specified tensile index, and this decrease was similar in magnitude to what is typically encountered in SD. Accordingly, the current experimental study succeeded in mimicking the SD problem. The lateral fibril aggregate dimensions (LFAD) seem to play a pivotal role and it can be safely concluded in general that the supramolecular structure of cellulose in the fibers may be an important factor contributing to the SD problem.
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| 38. |
- Lecourt, Micheal, et al.
(författare)
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Density profiles of novel kraft pulp and TMP based foam formed thermal insulation materials observed by X-ray tomography and densitometry
- 2018
-
Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 72:5, s. 397-403
-
Tidskriftsartikel (refereegranskat)abstract
- X-ray tomography and densitometry (XRT and XRD) were applied to characterise wood fibre based insulation materials, which were produced by the foam forming technology. XRT is a high resolution approach with long measurement times of around 29 h, while XRD measurement needs only a few minutes. The determination of density distribution of boards in the thickness direction was the focus of this study. Both approaches visualised well the impact of raw materials and manufacturing processes on the structure of the panels. The density profiles were dependent on the pulp applied for panel production, and the processing conditions were also influential. Air flow resistance correlated with the maximum density measured inside the board. Both XRT and XRD revealed similar trends, which are useful for the characterisation of insulation materials.
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| 39. |
- Lindh, Erik L
(författare)
-
Cellulose-water interaction: a spectroscopic study
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The human society of today has a significantly negative impact on the environment and needs to change its way of living towards a more sustainable path if to continue to live on a healthy planet. One path is believed to be an increased usage of naturally degradable and renewable raw materials and, therefore, attention has been focused on the highly abundant biopolymer cellulose. However, a large drawback with cellulose-based materials is the significant change of their mechanical properties when in contact with water. Despite more than a century of research, the extensively investigated interaction between water and cellulose still possesses many unsettled questions, and if the answer to those were known, cellulose-based materials could be more efficiently utilized.It is well understood that one interaction between cellulose and water is through hydrogen bonds, established between water and the hydroxyl groups of the cellulose. Due to the very similar properties of the hydroxyl groups in water and the hydroxyl groups of the cellulose, the specific interaction-induced effect on the hydroxyl groups at a cellulose surface is difficult to investigate. Therefore, a method based on 2H MAS NMR spectroscopy has been developed and validated in this work. Due to the verified ability of the methodology to provide site-selective information regarding the molecular dynamics of the cellulose deuteroxyl groups (i.e. deuterium-exchanged hydroxyl groups), it was shown by investigating 1H-2H exchanged cellulose samples that only two of the three accessible hydroxyl groups (on the surface of cellulose fibrils) exchange with water. This finding was also verified by FT-IR spectroscopy, and together with MD simulations we could establish that it is O(2)H and O(6)H hydroxyl groups (of the constituting glucose units) that exchange with water. From the MD simulations additional conclusion could be drawn regarding the molecular interactions required for hydrogen exchange; an exchanging hydroxyl group needs to donate its hydrogen in a hydrogen bond to water.Exchange kinetics of thin cellulose films were investigated by monitoring two different exchange processes with FT-IR spectroscopy. Specific information about the two exchanging hydroxyl/deuteroxyl groups was then extracted by deconvoluting the changing intensities of the recorded IR spectra. It was recognized that the exchange of the hydroxyl groups were well described by a two-region model, which was assessed to correspond to two fibrillary surfaces differentiated by their respective positions in the fibril aggregate. From the detailed deconvolution it was also possible to estimate the fraction of these two surfaces, which indicated that the average aggregate of cotton cellulose is built up by three to four fibrils. 2H MAS NMR spectroscopy was used to examine different states of water in cellulose samples, hydrated at different relative humidities of heavy water. The results showed that there exist two states of water adsorbed onto the cellulose, differentiated by distinct different mobilities. These two states of water are well separated and had negligible exchange on the time scale of the experiments. It was suggested that they are located at the internal and external surfaces of the fibril aggregates.By letting cellulose nanofibrils undergo an epoxidation reaction with a mono epoxide some indicative results regarding how to protect the cellulose material from the negative impact of water were presented. The protecting effect of the epoxidation were examined by mechanically testing and NMR spectroscopy. It was proposed that by changing the dominant interaction between the fibril aggregates from hydrophilic hydrogen bonds to hydrophobic π-interactions the sensitivity to moisture was much reduced. The results also indicated that the relative reduction in moisture sensitivity was largest for the samples with highest moisture content.
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| 40. |
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| 41. |
- Lindh, Erik L., et al.
(författare)
-
Non-exchanging hydroxyl groups on the surface of cellulose fibrils : The role of interaction with water
- 2016
-
Ingår i: Carbohydrate Research. - : Elsevier BV. - 0008-6215 .- 1873-426X. ; 434, s. 136-142
-
Tidskriftsartikel (refereegranskat)abstract
- The interaction of water with cellulose stages many unresolved questions. Here 2H MAS NMR and IR spectra recorded under carefully selected conditions in 1H-2H exchanged, and re-exchanged, cellulose samples are presented. It is shown here, by a quantitative and robust approach, that only two of the three available hydroxyl groups on the surface of cellulose fibrils are exchanging their hydrogen with the surrounding water molecules. This finding is additionally verified and explained by MD simulations which demonstrate that the 1HO(2) and 1HO(6) hydroxyl groups of the constituting glucose units act as hydrogen-bond donors to water, while the 1HO(3) groups behave exclusively as hydrogen-bond acceptors from water and donate hydrogen to their intra-chain neighbors O(5). We conclude that such a behavior makes the latter hydroxyl group unreactive to hydrogen exchange with water.
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| 42. |
- Lindh, Erik L., et al.
(författare)
-
Surface accessibility of cellulose fibrils studied by hydrogen-deuterium exchange with water
- 2016
-
Ingår i: Cellulose. - : Springer. - 0969-0239 .- 1572-882X. ; 24:1, s. 21-33
-
Tidskriftsartikel (refereegranskat)abstract
- A problem with cellulose-based materials is that they are highly influenced by moisture, leading to reduced strength properties with increasing moisture content. By achieving a more detailed understanding of the water–cellulose interactions, the usage of cellulose-based materials could be better optimized. Two different exchange processes of cellulose hydroxyl/deuteroxyl groups have been monitored by transmission FT-IR spectroscopy. By using line-shape-assisted deconvolution of the changing intensities, we have been able to follow the exchange kinetics in a very detailed and controlled manner. The findings reveal a hydrogen exchange that mainly is located at two different kinds of fibril surfaces, where the differences arise from the water accessibility of that specific surface. The slowly accessible regions are proposed to be located between the fibrils inside of the aggregates, and the readily accessible regions are suggested to be at the surfaces of the fibril aggregates. It was also possible to identify the ratio of slowly and readily accessible surfaces, which indicated that the average aggregate of cotton cellulose is built up by approximately three fibrils with an assumed average size of 12 × 12 cellulose chains. Additionally, the experimental setup enabled visualizing and discussing the implications of some of the deviating spectral features that are pronounced when recording FT-IR spectra of deuterium-exchanging cellulose: the insufficient red shift of the stretching vibrations and the vastly decreasing line widths.
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| 43. |
- Lindh, Erik L., et al.
(författare)
-
Water in cellulose : evidence and identification of immobile and mobile adsorbed phases by 2H MAS NMR
- 2017
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19, s. 4360-4369
-
Tidskriftsartikel (refereegranskat)abstract
- The organization of water molecules adsorbed onto cellulose and the supramolecular hydrated structure of microfibril aggregates represents, still today, one of the open and complex questions in the physical chemistry of natural polymers. Here, we investigate by 2H MAS NMR the mobility of water molecules in carefully 2H-exchanged, and thereafter re-dried, microcrystalline cellulose. By subtracting the spectral contribution of deuteroxyls from the spectrum of hydrated cellulose, we demonstrate the existence of two distinct 2H2O spectral populations associated with mobile and immobile water environments, between which the water molecules do not exchange at the NMR observation time scale. We conclude that those two water phases are located at differently-accessible adsorption sites, here assigned to the cellulose surfaces between and within the microfibril aggregates, respectively. The superior performance of 2H MAS NMR encourages further applications of the same method to other complex systems that expose heterogeneous hygroscopic surfaces, like wood cell walls.
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| 44. |
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| 45. |
- Mikeš, P., et al.
(författare)
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The Mass Production of Lignin Fibres by Means of Needleless Electrospinning
- 2021
-
Ingår i: Journal of Polymers and the Environment. - : Springer. - 1566-2543 .- 1572-8919. ; 29:7, s. 2164-2173
-
Tidskriftsartikel (refereegranskat)abstract
- Abstract: Lignin, a cheap renewable natural polymer, can be used as a precursor for the production of carbon fibres, its conversion into which is significantly faster than that of polyacrylonitrile. Lignin can be fractionated in various solvents via dissolution to decrease its polydispersity. Fractions with a higher molecular weight distribution can then be used in solvent-based spinning technologies such as electrospinning. We selected several solvent systems according to the Hansen solubility theory and subsequently tested them for solubility and electro-spinability. The selected solvent systems were then successfully tested for use in the needleless electrospinning process due to their potential for mass production. The solutions used in the electrospinning process needed high concentrations of lignin, which led to a high degree of viscosity. Therefore, we measured the relaxation times and viskosity for selected solutions, a factor that plays a pivotal role in terms of the production of smooth fibres. Finally, these solutions were tested for electrospinning using alternating current. This technology brings a new possibility in mass production of lignin fibres due to its high productivity and ease of use. Such materials can be used in a number of applications such as batteries, supercapacitors or for the production of composite materials. They provide a cheap and renewable natural polymer source which can easily be transformed into a carbon nanofibrous layer. Graphic Abstract: [Figure not available: see fulltext.].
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| 46. |
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| 47. |
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| 48. |
- Modén, Carl S., 1979-
(författare)
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Transverse anisotropy in softwoods : Modelling and experiments
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transverse anisotropy is an important phenomenon of practical and scientific interest. Although the presence of ray tissue explains the high radial modulus in many hardwoods, experimental data in the literature shows that this is not the case for pine. It is possible that anisotropy in softwoods may be explained by the cellular structure and associated deformation mechanisms. An experimental approach was developed by which local radial modulus in spruce was determined at sub-annual ring scale. Digital speckle photography (DSP) was used, and the density distribution was carefully characterized using x-ray densitometry and the SilviScan apparatus. A unique set of data was generated for radial modulus versus a wide range of densities. This was possible since earlywood density shows large density variations in spruce. Qualitative comparison was made between data and predictions from stretching and bending honeycomb models. The hypothesis for presence of cell wall stretching was supported by data. A model for wood was therefore developed where both cell wall bending and stretching are included. The purpose was a model for predictions of softwood moduli over a wide range of densities. The relative importance of the deformation mechanisms was investigated in a parametric study. A two-phase model was developed and radial and tangential moduli were predicted. Comparison with experimental data showed good agreement considering the nature of the model (density is the only input parameter). Agreement is much better than for a regular honeycomb model. According to the model, cell wall bending dominates at both low and high densities during tangential loading. In radial loading, cell wall stretching dominates at higher densities.
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| 49. |
- Odeberg Glasenapp, Astrid, et al.
(författare)
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Next level of corrugated board research
- 2019
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Ingår i: 29th IAPRI Symposium on packaging, 2019.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For the first time in the Bioeconomy research program at RISE, corrugatedboard has an own research area. Research is building around the main driving forcesin the corrugated board value chain like e-commerce, improved box performance anddigital printing. The main weakness of corrugated board, its moisture sensitivity, isalso addressed.These main driving forces and weaknesses of corrugated board are mirrored in thethemes of this large research program area:Fibre sorption and deformation mechanismsFundamental knowledge on the mechanisms behind moisture sorption and deformation on fibre level is developed to increase moisture and creep resistance throughmodification of paper materials. State of the art methods for characterization ofthe fibre ultra- and nano-structure such as Fourier transform infra-red spectroscopy(FTIR), small angle X-ray scattering (SAXS), and wide angle X-ray scattering (WAXS)give new insights on mechanisms and clarify effects of moisture as well as chemicalmodifications.Papermaking for improved base sheetsConcepts that are explored are fibre-based strength additives produced with novelrefining techniques, and modified ZD-profiles in the sheet for better mechanical properties.Box mechanicsMechanical performance of structures such as corrugated board boxes can be predicted through physically based mathematical modelling by taking the behaviour ofthe constituent materials as well as the geometry into account. Appropriate materialmodels for the corrugated board are identified and finite element models for simulation of corrugated board packaging performance are developed.Tool for inkjet printability on corrugatedThere is a genuine need for improved inkjet printability on corrugated materials thanksto rapid development in e-commerce as well as digitalization along the corrugatedvalue chain. Effective measurement methods and knowledge around ink-substrateinteractions are developed to enable board producers and converters to have effective product development and predictable printability on not only liners but also oncorrugated materials.
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| 50. |
- Olsson, Anne M., et al.
(författare)
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Mechano-sorptive creep in pulp fibres and paper
- 2014
-
Ingår i: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 48:3, s. 569-580
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Tidskriftsartikel (refereegranskat)abstract
- The factors affecting mechano-sorptive creep of wood and paper have been investigated for a long time. It has also been argued that single wood fibres do not exhibit mechano-sorptive creep and that the reasons for the accelerated creep under moisture cycling conditions instead are related to the bonds between the fibres. In order to examine the relevance of this argument, measurements on single pulp fibres of different composition were performed in tension, and the mechano-sorptive creep was compared to that of papers made from the same source of pulp fibres. All fibres tested were found to exhibit an increased creep rate during moisture cycling as compared to constant humidity conditions. Thus, pulp fibres show mechano-sorptive creep and in this sense behave similar to solid wood or paper products made thereof. A linear relation between the creep strain rate during cyclic humidity and the creep strain rate at a constant humidity was also noted for both fibres and paper. This relation was not affected by changes in hemicelluloses content or composition, neither for fibres nor for papers made of these fibres. However, in all cases, papers showed a much higher mechano-sorptive creep than the corresponding fibres they were made of.
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