| 1. |
- Antti, Lena, et al.
(author)
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A microwave applicator for on line wood drying : Temperature and moisture distribution in wood
- 1999
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In: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 33:2, s. 123-138
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Journal article (peer-reviewed)abstract
- An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy, meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the position of each applicator in a larger scale microwave pilot plant.
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| 2. |
- Antti, Lena
(author)
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Heating and drying wood using microwave power
- 1999
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Doctoral thesis (other academic/artistic)abstract
- The potentials for moisture flux in wood during microwave heating have been investigated experimentally and theoretically. The experiments were performed in three different kinds of microwave applicators. A computer model based on the finite difference method was developed to describe and predict the heat and mass transfer. The main conclusions are that microwave energy of 2.45 GHz frequency makes it possible to heat and dry pine and spruce 20 - 30 times faster than with conventional methods without any deterioration in drying quality. Some hardwoods are dried in approximately half the time compared to the softwoods. The drying method evokes unique results either with diminishing colour changes or with possibilities to create such during drying. However, to avoid unevenness in the electromagnetic field distribution and considering the limitation in power penetration depth the drying should be performed on line where wood components continuously are fed through a microwave field.
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| 3. |
- Antti, Lena
(author)
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Microwave drying of pine and spruce
- 1995
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In: European Journal of Wood and Wood Products. - : Springer Science and Business Media LLC. - 0018-3768 .- 1436-736X. ; 53:5, s. 333-338
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Journal article (peer-reviewed)abstract
- Drying rates and power densities are determined for pine-and sprucewood when dried from green to 8% moisture content by microwave power. The process is controlled by measurements of internal wood temperature, internal vapour pressure and rate of moisture evaporation. Microwave power densities ranged from 25 to 78 kW/m3, microwave energy consumption from 365 to 760 kWh/m3. Internal wood temperatures up to 140 °C were used. Internal vapour pressure in the wood could rise to about 20 kPa without checking. Maximal drying rates of 0.20 to 0.45% moisture content per minute are possible to obtain when drying above fiber saturation (fsp). Below fsp the feasible drying rates ranged from 0.10 to 0.20% moisture content per minute. Spruce dried approximately 1.6 times faster than pine. No conditioning of the wood was necessary since the wood was free of stresses. The wood was free of checks but colour changes occured in the interior of some specimens.
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| 4. |
- Antti, Lena, et al.
(author)
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Microwave heating of wood
- 1995
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In: Fifth international conference on microwave and high frequency heating, 17-21 September 1995. - Cambridge : Cambridge University Press. ; , s. E3.1-3.4
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Conference paper (peer-reviewed)
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| 5. |
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| 6. |
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| 7. |
- Karlsson, Olov, et al.
(author)
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Evidence for chemical bonds between lignin and cellulose in kraft pulps
- 1996
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In: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 22:10, s. J397-401
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Journal article (peer-reviewed)abstract
- The cellulose solvent system LiCl-dimethylacetamide has been used to dissolve kraft pulps prepared from pine and birch. The dissolved polymers were analyzed using size-exclusion chromatography combined with both RI- and UV-detection systems in order to monitor simultaneously the major wood polymers (cellulose, hemicellulose and lignin). Kraft pulps from birch were completely soluble in the solvent system and the pine kraft pulp about 80% soluble. Analyses of the kraft pulps strongly suggest that a considerable amount of the residual lignin is chemically linked to the high molecular weight cellulose in pine but not in birch. The presence of stable lignin-cellulose bonds will reduce the possibility of achieving a low kappa number by cooking. For comparison, sulphite and bisulphite pulps were also examined. Both pulps were soluble in the solvent system and analyses indicated that lignin-cellulose bonds also exist in these pulps although to a significantly lesser extent than in the pine kraft pulp
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| 8. |
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| 9. |
- Kifetew, G, et al.
(author)
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Tangential and radial deformation field measurements on wood during drying
- 1997
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In: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 31:1, s. 35-44
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Journal article (peer-reviewed)abstract
- In a previous study, the deformation field measurement method on wood during drying was described. This paper discusses the deformation field measurement results during drying to 8.2% moisture content on the radial and tangential surfaces. It also attempts to explain the observations by an approximate expression based onearlywood-latewood interaction theory. The deformation on the radial surface varied between -0.7% and 7.5%. The actual measurements on the radial surfaces support previous work. Deformation measurements on the tangential surfaces were between -0.5% and 9.0%. Although the investigations were carried out on gross wood specimens, the results provide an insight into the extent to which local density variation within the early- and latewood layers may influence the magnitude of surface deformation.
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| 10. |
- Mathew, Aji P., et al.
(author)
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Transport of styrene monomer through natural rubber
- 1995
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In: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 36:26, s. 4935-4942
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Journal article (peer-reviewed)abstract
- The diffusion and transport of inhibitor-free styrene through crosslinked natural rubber (NR) have been studied at various temperatures. NR has been vulcanized by conventional, efficient, peroxide and mixed vulcanization techniques. The dependence of diffusion coefficient on the crosslinking system has been studied for all the systems. The influence of temperature on the sorption and the activation energies of sorption have been calculated. The interaction parameter, permeability, sorption coefficient and molecular weight between crosslinks have been evaluated using the diffusion data. The effect of degree of crosslinking on the sorption characteristics of styrene through NR has also been investigated for the different crosslinking systems. The peroxide system showed lowest uptake and the conventional system showed highest uptake.
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| 11. |
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| 12. |
- Oksman, Kristiina
(author)
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Improved interaction between wood and synthetic polymers in wood/polymer composites
- 1996
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In: Wood Science and Technology. - 0043-7719 .- 1432-5225. ; 30:3, s. 197-205
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Journal article (peer-reviewed)abstract
- This article describes the properties of wood polymer composites consisting of linear low density polyethylene (LLDPE) and wood flour (WF). In an attempt to improve the interfacial adhesion between the matrix and the filler, different compatibilizers were used. The interaction between polymer and wood were studied by comparing LLDPE/WF composites with composites when compatibilizer was added. The experimental measurements were conducted by impact and tensile strength testing and Scanning Electron Microscopy (SEM). The mechanical properties of the composites were improved with SEBS triblock copolymer modified with maleic anhydride and with the ionomer polymer, Surlyn, as compatibilizers. SEM fractography confirmed better adhesion between wood particles and LLDPE matrix when SEBS was present
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| 13. |
- Oksman, Kristiina
(author)
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Improved properties of thermoplastic wood flour composites
- 1997
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Doctoral thesis (other academic/artistic)abstract
- In this study the properties of composites made of wood flour and thermoplastics have been investigated. In order to improve the interfacial adhesion between hydrophobic and nonpolar thermoplastics and hydrophilic and polar wood flour different additives have been used as compatibilizers in composites systems. The interaction between a wood filler and thermoplastic matrix, with and without compatibilizers, has been studied using conventional mechanical testing, impact testing, dynamic mechanical thermal analysis (DMTA), electron microscopes and infrared spectroscopy. Tests of mechanical properties, such as maximum tensile strength, tensile modulus and impact strength have shown that maleic anhydride grafted styrene-ethylene/butylene-styrene triblock copolymer (SEBS-MA) acts as a compatibilizer in the composite system. The SEBS-MA improves the stress transfer from the matrix to the wood particles and forming an flexible interphase around the wood particle and therefore improves the impact properties. The DMTA measurements indicated that there is an interaction between the wood surfaces and the maleic anhydride part of the SEBS-MA copolymer, and also between PS and wood. Morphological studies with SEM and TEM showed that the addition of SEBS-MA improved the adhesion between the wood particles and polymer matrix and that the compatibilizer is located at the interphase region between them. An infrared spectroscopy study indicated that the MA in the SEBS may react with the wood by forming hydrogen- and esterbonds and also possibly interaction between PS and wood.
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| 14. |
- Oksman, Kristiina, et al.
(author)
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Influence of thermoplastic elastomers on adhesion in polyethylene-wood flour composites
- 1998
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In: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 68:11, s. 1845-1855
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Journal article (peer-reviewed)abstract
- The mechanical properties of recycled low-density polyethylene/wood flour (LDPE/WF) composites are improved when a maleated triblock copolymer styrene-ethylene/butylene-styrene (SEBS-MA) is added as a compatibilizer. The composites' tensile strength reached a maximum level with 4 wt % SEBS-MA content. The compatibilizer had a positive effect on the impact strength and elongation at break but decreased the composites' stiffness. Dynamic mechanical thermal analysis (DMTA), a lap shear adhesion test, and a scanning electron microscope (SEM) were used to investigate the nature of the interfacial adhesion between the WF/SEBS and between the WF/ SEBS-MA. Tan δ peak temperatures for the various combinations showed interaction between the ethylene/butylene (EB) part of the copolymer and the wood flour in the maleated system. The shear lap test showed that adhesion between the wood and SEBS-MA is better than between the wood and SEBS. The electron microscopy study of the fracture surfaces confirmed good adhesion between the wood particles and the LDPE/SEBS-MA matrix. © 1998 John Wiley & Sons, Inc.
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| 15. |
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| 16. |
- Oksman, Kristiina, et al.
(author)
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Interaction between wood and synthetic polymers
- 1995
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In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 49:3, s. 249-254
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Journal article (peer-reviewed)abstract
- The properties of wood composites consisting of low density polyethylene (LDPE) and wood flour (WF) were studied. In an attempt to improve the interfacial adhesion between hydrophobic LDPE matrix and the hydrophilic WF filler, a styrene-butadiene-styrene (SBS) copolymer was added as a compatibilizer. The interaction between LDPE and wood was investigated for PE/WF- and PE/WF/SBS-composites. The experimental measurements were conducted by conventional mechanical testing and Scanning Electron Microscopy (SEM). The interaction between polystyrene and wood in PS/WF composites was also studied by SEM and by Dynamic Mechanical Thermal Analysis (DMTA). PE/WF/SBS composites showed higher maximum tensile stress and strain at failure than the composites without SBS. SEM fractography confirmed better adhesion between the PE matrix and wood particles when SBS was present. DMTA measurements confirmed molecular interaction between PS and wood, the glass transition (Tg) peak of PS moved towards the Tg peak of cellulose
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| 17. |
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| 18. |
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| 19. |
- Oksman, Kristiina
(author)
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Kompositer på naturligt vis
- 1998
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In: Plastforum (1992). - 1104-1501. ; :4, s. 38-41
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Journal article (other academic/artistic)
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| 20. |
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| 21. |
- Oksman, Kristiina, et al.
(author)
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Mechanical properties and morphology of impact modified polypropylene-wood flour composites
- 1998
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In: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 67:9, s. 1503-1513
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Journal article (peer-reviewed)abstract
- The mechanical properties and morphology of polypropylene/wood flour (PP/WF) composites with different impact modifiers and maleated polypropylene (MAPP) as a compatibilizer have been studied. Two different ethylene/propylene/diene terpolymers (EPDM) and one maleated styrene-ethylene/butylene-styrene triblock copolymer (SEBS-MA) have been used as impact modifiers in the PP/WF systems. All three elastomers increased the impact strength of the PP/WF composites but the addition of maleated EPDM and SEBS gave the greatest improvements in impact strength. Addition of MAPP did not affect the impact properties of the composites but had a positive effect on the composite unnotched impact strength when used together with elastomers. Tensile tests showed that MAPP had a negative effect on the elongation at break and a positive effect on tensile strength. The impact modifiers were found to decrease the stiffness of the composites. Scanning electron microscopy showed that maleated EPDM and SEBS had a stronger affinity for the wood surfaces than did the unmodified EPDM. The maleated elastomers are, therefore, expected to form a flexible interphase around the wood particles giving the composites better impact strength. MAPP further enhanced adhesion between WF and impact-modified PP systems. EPDM and EPDM-MA rubber domains were homogeneously dispersed in the PP matrix, the diameter of domains being between 0.1-1 m.
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| 22. |
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| 23. |
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| 24. |
- Oksman, Kristiina, et al.
(author)
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The Influence of a SBS Compatibilizer in Polyethylene-Wood Flour Composites
- 1998
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In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 52:6, s. 661-666
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Journal article (peer-reviewed)abstract
- A styrene-butadiene-styrene (SBS) block copolymer has been used as a compatibilizer in a low density polyethylene/wood flour (LDPE/WF) composite system. Dynamic mechanical thermal analysis (DMTA) and a transmission electron microscopy (TEM) were used to investigate the interfacial properties in the composites. A high resolution study of the composite microstructure, and especially of the interfaces between the wood particles and LDPE matrix, indicated that the SBS compatibilizer was located at the interface region between the wood particles and LDPE matrix and partially covered the wood particle surfaces. The SBS was also found in the LDPE matrix. The unsaturated part of the copolymer was stained with osmium(VIII)tetraoxide (OsO4) to enhance contrast and to allow it to be detectable in TEM. Dynamic mechanical measurements confirmed interaction between polystyrene (PS) and wood in the PE/PS/WF system. The tan d peak of PS was shifted about 10°C to a higher temperature and also broadened when wood flour was added in the LDPE/PS blend.
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| 25. |
- Oksman, Kristiina, et al.
(author)
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The nature and location of SEBS-MA compatibilizer in polyethylene-wood flour composites
- 1998
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In: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 69:1, s. 201-209
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Journal article (peer-reviewed)abstract
- A maleic-anhydride-grafted styrene-ethylene - butylene-styrene (SEBS-MA) triblock copolymer has been used as a compatibilizer in low-density polyethylene-wood flour (LDPE-WF) composite system. The location of compatibilizer was studied using transmission electron microscopy (TEM). The unsaturated parts of the copolymer were stained with osmium tetraoxide (OsO4) to enhance contrast between the different phases. TEM micrographs indicated that part of the compatibilizer was located at the interface between the wood particles and PE matrix and that wood was also stained by the OsO4. The nature of the interface between the wood surface and the SEBS-MA was studied using Fourier transform infrared spectroscopy (FTIR). The results indicated that MA reacts with wood through esterification and hydrogen bonding and also possibly through interaction between the styrene and wood.
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