| 1. |
- Hii, Collin, et al.
(författare)
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The effect of MFC on the pressability and paper properties of TMP and GCC based sheets
- 2012
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:2, s. 388-396
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Tidskriftsartikel (refereegranskat)abstract
- Different qualities of microfibrillated cellulose (MFC) were blended with thermomechanical pulp (TMP) and ground calcium carbonate (GCC) filler. The addition of MFC reduced the drainage of the pulp suspension but improved strength properties. Wet pressing experiments showed that optimal use of MFC and filler could enhance the strength and optical properties without reducing the solids content after wet pressing. Field-emission scanning electron microscopy (FESEM) revealed that MFC adsorbed onto and contributed to the bonding of the filler particles and fibres. The MFC binds the filler-MFC-fines aggregates to the fibre network and partially filled the pore network. As a result, MFC addition increased the air resistance and internal bonding of the sheet.
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| 2. |
- Hii, Collin, et al.
(författare)
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The effect of Newsprint furnish composition and sheet structure on wet pressing efficiency
- 2012
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:4, s. 790-797
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Tidskriftsartikel (refereegranskat)abstract
- The dewatering ability and wet sheet structure after pressing was studied using a dynamic wet pressing simulator in combination with electron microscopy and image analysis. Deinked pulp (DIP) that contains 5% ash dewaters more easily than thermo-mechanical pulp (TMP) when pressed with single roll pulse. The in-plane moisture flow (crushing) in DIP samples started at higher peak pressure and higher solids content compared to TMP samples. The TMP sample showed higher springback after wet pressing compared to DIP samples. When both TMP and DIP samples were designed to have a higher amount of small pores at the dewatering side surface layers, the samples with coarser TMP pulp could achieve similar dryness as DIP samples when pressed with higher nip pressure. In addition, the DIP samples with higher number of small pores in the outermost 10 μm thick surface layer in the dewatering side resulted in lower dryness after pressing with a single roll pulse. The effect of filler distribution in paper z-direction on dryness and sheet structure after wet pressing using an 8 milliseconds roll pulse was also studied. In this study the distribution of filler does not affect the maximum achievable dryness (41%) after wet pressing when the total amount of filler in the sheets remains constant, 13.5%. In addition, the samples with more filler in the dewatering layer dewater more easily and yield the maximum achievable dryness (40%) after wet pressing at lower nip pressure (2.5 MPa) when compared to samples made from TMP (36% at 4.4 MPa) and DIP pulps (40% at 4.9 MPa).
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| 3. |
- Hii, Collin, et al.
(författare)
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The web structure in relation to the furnish composition and shoe press pulse profiles during wet pressing
- 2012
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 27:4, s. 798-805
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that wet-pressing TMP and DIP with a shoe press pulse may yield similar after-press solids, provided that an adequate shoe pulse length with similar pressure profile is applied. A wet web with more porous structure in the sheet dewatering (felt) layer seems to contribute to the increased dewatering during wet pressing. In addition, a shoe press pulse with high peak pressure at the end yields higher solids content after wet-pressing and higher bulk compared to a pulse with a peak pressure in the beginning. The increased dewatering during wet-pressing implies a reduction of steam consumption in the dryer.
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| 4. |
- Rodionova, Galina, et al.
(författare)
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Gas-phase esterification of microfibrillated cellulose (MFC) films
- 2013
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 20:3, s. 1167-1174
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Tidskriftsartikel (refereegranskat)abstract
- The barrier properties of microfibrillated cellulose (MFC) films were improved by heterogeneous gas-phase esterification using various combinations of trifluoroacetic acid anhydride, acetic acid and acetic anhydride. The temperature, reagent ratio and reaction time were varied in the experimental design. The effects of two different purification procedures on the barrier properties of esterified MFC films were investigated. Washing with water did not affect the barrier properties compared to those of the films that were not washed, while the use of diethyl ether led to improved barrier properties as measured by the contact angle (CA) of water. The chemical composition of the modified films was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. Alterations in hydrophobicity and oxygen permeability were evaluated using dynamic CA and oxygen transmission rate measurements, respectively.
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| 5. |
- Rodionova, Galina, et al.
(författare)
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Mechanical and oxygen barrier properties of films prepared from fibrillated dispersions of TEMPO-oxidized Norway spruce and Eucalyptus pulps
- 2012
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19
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Tidskriftsartikel (refereegranskat)abstract
- TEMPO-oxidized cellulose nanofibers (TOCN) were obtained from commercial Norway spruce and mixed Eucalyptus cellulose pulps using TEMPO/sodium bromide (NaBr)/sodium hypochlorite (NaClO) system at pH 10 and 22 °C. After reaction, the fibrillated TEMPO-oxidized celluloses were used for preparation of self-standing films and casting of laminate films on 50 μm thick polyethylene terephthalate. Significant differences between N. spruce and Eucalyptus TOCN were registered. The tensile strength of the films showed a maximum value for spruce samples oxidized with addition of 10 mmol g -1 of NaClO. Oxygen permeability decreased with increasing oxidation levels, being lower for N. spruce TOCN compared to Eucalyptus.
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| 6. |
- Rodionova, Galina, et al.
(författare)
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TEMPO-mediated oxidation of Norway Spruce and Eucalyptus Pulps : Preparation and Characterization of Nanofibres and Nanofiber Dispersions
- 2013
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Ingår i: Journal of Polymers and the Environment. - : Springer Science and Business Media LLC. - 1566-2543 .- 1572-8919 .- 1572-8900. ; 21:1, s. 207-214
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Tidskriftsartikel (refereegranskat)abstract
- This study deals with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. Softwood and hardwood pulp fibers were suspended in water and oxidized to various extents at pH 10 and 22 °C using sodium hypochlorite in the presence of TEMPO radical and sodium bromide. This reaction system is known to be the most efficient one for the introduction of both surface carboxyl and aldehyde groups. Important relationships between formation of these functional groups and the fibrillation yield, light transmittance of the water dispersions and degree of polymerization of the oxidized softwood and hardwood pulps were established in the present study. A birefringence test confirmed the presence of nanofibers which according to atomic force microscopy analyses had diameters in the 1. 6-3. 8 nm range.
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| 7. |
- Rodionova, Galina, et al.
(författare)
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TEMPO-oxidized cellulose nanofiber films: : effect of surface morphology on water resistance
- 2012
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 19:4, s. 1115-1123
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Tidskriftsartikel (refereegranskat)abstract
- 2,2,6,6-Tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers were prepared from two kraft pulps (Norway spruce and mixed eucalyptus) using the TEMPO/NaBr/NaClO system at pH 10 and 22 °C. After reaction and mechanical treatment, the TEMPO-oxidized celluloses were used for preparation of self-standing films and coatings of laminate films on 50-μm-thick polyethylene terephthalate films. Characterization of the films was performed based on water contact angle measurements, laser profilometry, scanning electron microscopy, and field-emission scanning electron microscopy. The purpose of this study is to understand how the measured contact angles are affected by the film's physical properties (morphology, thickness, density, and roughness).
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| 8. |
- Rodionova, Galina, et al.
(författare)
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The formation and characterization of sustainable layered films incorporating microfibrillated cellulose (mfc)
- 2012
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Ingår i: BioResources. - 1930-2126. ; 7:3, s. 3690-3700
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Tidskriftsartikel (refereegranskat)abstract
- Microfibrillated cellulose (MFC), TEMPO-pretreated MFC, and hybrid polymer/MFC mix were used for the production of layered films with interesting properties for application in food packaging. The series of samples were prepared from MFC (base layers) using a dispersion-casting method. The same procedure as well as a bar coating technique was applied to form top layers of different basis weights. The barrier properties and formation of the layered films were investigated in relationship to the preparation procedures, combination of layers, and areal weight (basis weight). Characterization was done with respect to oxygen transmission rates (OTR), water vapor transmission rates (WVTR), tensile properties, and contact angles (CA) with water. The produced layered films yielded OTR values of 4 mL m-2 day-1 and fulfilled oxygen barrier requirements for a modified atmosphere packaging (MAP). Hornification of the MFC films, however, occurred during drying, which may result in a loss of the film's beneficial properties.
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| 9. |
- Brodin, Fredrik Wernersson, et al.
(författare)
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Preparation of individualised lignocellulose microfibrils based on thermomechanical pulp and their effect on paper properties
- 2015
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Ingår i: Nordic Pulp & Paper Research Journal. - : SPCI. - 0283-2631 .- 2000-0669. ; 30:3, s. 443-451
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Tidskriftsartikel (refereegranskat)abstract
- Although mechanical pulp can be considered as a potential raw material for preparation of microfibrils, suitable pre-treatment methods have been missing. Consequently, the objectives of this study were firstly to find a suitable procedure to prepare lignocellulose microfibrils (LCMF) from fractionated thermo-mechanical pulp (TMP) and secondly to evaluate if these TMP-based materials could be used as paper additives to increase paper strength. Carboxymethylation was found to be a suitable pretreatment for both TMP fines and TMP fibres to enable preparation of individualised LCMF after subsequent homogenisation treatment. After air drying, this material formed dense continuous films in conformity with films prepared from cellulose microfibrils (CMF) originating from chemical pulp. Homogenisation only or sulphonation followed by homogenisation did not fibrillate the TMP samples into individualised LCMF. Analysis of paper properties showed that addition of 20% LCMF to a standard TMP furnish improved tensile strength index by 15%. The LCMF-containing papers were also more brittle (less elongation) than the other paper sheets in this study. Similar tensile strength index was also obtained for TMP fines treated by sulphonation followed by homogenisation.
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| 10. |
- Chinga-Carrasco, Gary, et al.
(författare)
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Structural characteristics of pore networks affecting print-through
- 2008
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Ingår i: Journal of Pulp and Paper Science (JPPS). - 0826-6220. ; 34:1, s. 13-22
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Tidskriftsartikel (refereegranskat)abstract
- The pore structure of handsheets and of commercial newsprints is described in detail. The advantages and limitations of scanning electron microscopy and synchrotron radiation X-ray microtomography for pore-structure assessment are discussed. This gives insight into the two-dimensional and three-dimensional characteristics of the pore structure. A major achievement is the effective quantification of the submicron pores by scanning electron microscopy. It is demonstrated that submicron pores contribute positively to light scattering per unit thickness. The relationship between the pore structure, the light scattering and print-through is explored.
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| 11. |
- Enberg, Sofia, et al.
(författare)
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Mapping and modelling of optical properties from pulp to super calendered paper
- 2015
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Ingår i: Appita journal. - 1038-6807. ; 68:2, s. 128-138-
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Forskningsöversikt (refereegranskat)abstract
- During production of mechanical pulp based paper, the pulp darkenswithin the process which represents a significant cost for the mill. Amapping of the optical properties of the pulp was conducted along theprocess, from pulp mill to paper machine, at a mill producing supercalendered (SC) paper on three paper machines. The focus was to evaluateat which positions in the mill the discolouration occurs and also whichfraction of the pulp darkens the most.The fine fraction of the pulp darkened more than the long fibrefraction. Bleached pulp diluted with white water from the paper machinedarkened more during storage than pulp diluted with clear filtrate. Thewhite water contains a considerable amount of suspended solids, i.e.pulp fines and clay. There was a tendency for a shoulder in absorptionspectra of the pulp stored in white water from the paper machine in theregion 550 to 650 nm, both for fibres and for fines. This is in the sameregion where the added dyes have their absorption maxima and also somecomplexes between iron and some of the components among lignin and theextractives. Simulation of retention times of different fractions showedthat, although the main part of the fine material is retained in thepaper within a few hours, a small part might circulate for considerablylonger time.
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| 12. |
- Enberg, Sofia
(författare)
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Storage of Hydrogen Peroxide Bleached Mechanical Pulp : Reduction in Reflectance over the Visible Spectrum
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this thesis is to determine possible causes of the darkening of hydrogen peroxide bleached mechanical pulp over the visible spectrum and their relative contributions. It focuses on both process conditions and the composition of the pulp and the dilution water, including additions or losses of material along the process line from the bleach tower to the paper machine.A mapping of the optical properties of the pulp along the process showed that the fine fraction of the pulp darkened more than the long fibre fraction. Simulation of retention times of different fractions showed that the main part of the fine material is retained in the paper within a few hours, a small part might circulate for considerably longer time and may therefore be strongly coloured.Storage trials were mainly performed using a hydrogen peroxide bleached mechanical pulp intended for SC paper made of Norway spruce (Picea abies), sampled on one occasion and stored in a freezer. Unwashed or well-washed pulp was stored in distilled water or in different process waters. Some complementary trials were included, e.g. unbleached pulp.Time and temperature were the process variables that gave the strongest darkening of the pulp, as expected, both in a clean and a more process-like system, whereas pH only had an effect in the presence of process waters; the highest brightness stability was seen at a pH around 5.5–6.0.The darkening was due to an increase in the light absorption coefficient (k) beginning at short wavelengths, but after longer storage times the increase in kλ also became noticeable at longer wavelengths. The colour (CIE L*, a*, b*) of the pulp changed towards red and yellow, initially more towards red and then more towards yellow. These changes were clearly visible.Washing of the bleached pulp made it less sensitive to storage; possibly due to the removal of extractives, lignin-like substances, metals and pulp fines. This washing had little effect before storage and the amount of material removed was small.The pulp darkened more when stored in process waters compared to distilled water. Apart from fibres, most of the colour was associated with pulp fines or filler but some colour was also found in the dissolved and colloidal fractions. At an increased pulp consistency, the increase in k460 was smaller.Storage in white water from the paper machine gave extensive discolouration with a shoulder in the absorption spectrum around 550–650 nm, which increased with time. The addition of ferric ions increased the light absorption coefficient during storage, but could not explain the increased absorption at 550–650 nm nor could it be the only cause of the darkening in the mill system. A cationic basic violet dye gave a shoulder in the absorption spectrum similar to that of the mill system, but the absorption of the dye did not increase during storage. Model calculations indicate, but do not prove, that ferric ions together with violet and red dyes could have played a major, but not exclusive role in the colour observed in the mill system after storage. The darkening not accounted for, at longer wavelengths and around 550–650 nm, is suggested to be related to fines and fillers including dissolved and colloidal substances associated with these particles.A method to produce representative sheets for determination of optical properties of mechanical pulps was developed. The new method makes it possible to follow changes in light absorption and light scattering coefficients over the visible range of wavelengths. It is approximately six times faster than standard methods, reduces the risk of additional darkening of the sample and can be used with small pulp quantities.The deviation from the expected linear behaviour of the light scattering coefficient, s, at wavelengths corresponding to strong light absorption has been studied using the Kubelka-Munk model and the angular resolved DORT2002 radiative transfer solution method. The decrease in s could not be explained by errors introduced in the Kubelka-Munk modelling by anisotropic scattering.
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| 13. |
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| 14. |
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| 15. |
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