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  • 1. Andersson, Kerstin I.
    et al.
    Pranovich, Andrey V.
    Norgren, Magnus
    Eriksson, Marie
    Holmbom, Bjarne
    Effects of biological treatment on the chemical structure of dissolved lignin-related substances in effluent from thermomechanical pulping2008In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 23, no 2, p. 164-171Article in journal (Refereed)
    Abstract [en]

    Effluent from a TMP-based pulp and paper mill was collected at the inlet and outlet of the mill's biological treatment plant and fractionated by sorption on XAD-8 resin and MTBE precipitation. Fractionation indicated that the refractory dissolved organic material in biologically treated effluent was mainly composed of lignin-related substances. Characterisation of the lignin-related substances by chromatographic and spectrometric methods confirmed the similarities of the isolated material and milled wood lignin. Fractionation and characterisation of alkali-extracted material from solids (biosludge) in biologically treated effluent found evidence of lignin-related material. Results indicated that biological treatment had altered the chemical structure and molar-mass distribution of dissolved lignin-related substances.

  • 2. Engqvist, C.
    et al.
    Forsberg, S.
    Norgren, Magnus
    Edlund, H.
    Andreasson, B.
    Karlsson, O.
    Interactions between single latex particles and silica surfaces studied with AFM2007In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 302, no 03-jan, p. 197-203Article in journal (Refereed)
    Abstract [en]

    The spreading of single styrene-acrylic latex particles on silicon oxide C surfaces was studied using atomic force microscopy (AFM). Three latexes with different glass transition temperature (Tg) were used and the effects of temperature, time and preparation method were investigated. Particle sizes and shape were measured with AFM and the contact angles were calculated. The observed rate for the spreading of latex particles was low and it took several days before the particles reached steady state, even at temperatures well above their T-g. The experimental particle spreading results deviated with two orders of magnitude from predictions Using the WLF equation for polymer diffusion. The deviation could be attributed to polymer-surface interactions that slowed down the particle spreading. The work of adhesion was calculated using two models. The results from using the regular Young-Dupre equation and a modified version of this equation that also included the mechanical properties (E-modulus and Poisson's ratio) of the latexes, were compared. For soft latex particles the results from the two models agreed well and were of the order of 75 J/m(2), but for glassy latexes the Young-Dupre equation underestimated the work of adhesion.

  • 3. Gärdlund, Linda
    et al.
    Norgren, Magnus
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Marklund, Ann
    The use of polyelectrolyte complexes (PEC) as strength additives for different pulps used for production of fine paper2007In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 22, no 2, p. 210-216Article in journal (Refereed)
    Abstract [en]

    In this work the application of polyelectrolyte complexes (PEC) to different pulps, to improve the strength of papers produced from them, is compared with conventional pulp beating. The pulps chosen for the investigation were a fully bleached chemical hardwood pulp (HBK), a fully bleached chemical softwood pulp (SBK), and a peroxide-bleached chemithermomechanical pulp (BCTMP). The polyelectrolytes used were a polyamideamine epichlorohydrine condensate (PAE), traditionally used as a wet-strength additive, and carboxymethylcellulose. Since the prepared complexes had an anionic charge, they could only be used after fibre pre-treatment with the cationic PAE. Results indicate that the addition of 2% PAE and 2% PEC can improve all the measured tensile strength properties of the sheets as much as is commonly achieved by mechanically beating the pulps. In fact, for the chemical pulps, PEC addition at the chosen level produced better results than did traditional beating, since the improved tensile index and tensile energy absorption could be achieved without any significant deterioration in the light scattering coefficient of the papers produced. However, with the BCTMP a significant decrease in light scattering could be detected, especially following the addition of PEC. Adding the chemicals (especially the PEC) increased the sheet density and this together with the increase in the tensile stiffness, following chemical addition, resulted in a constant bending stiffness of the sheets. However, based on the results it can be suggested that a combination of unbeaten HBK and BCTMP treated with PAE and PEC can be used to produce a strong paper with a high bending stiffness.

  • 4. Gärdlund, Linda
    et al.
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Norgren, Magnus
    New insights into the structure of polyelectrolyte complexes2007In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 312, no 2, p. 237-246Article in journal (Refereed)
    Abstract [en]

    The formation of polyelectrolyte complexes (PECs) from oppositely charged linear polyelectrolytes (PELs) was studied using static light scattering at various salt concentrations. The PELs used were poly(allylamine hydro chloride) (PAH) and the two polyanions poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). Physical characteristics such as the radii of gyration, molecular weights, and water contents of the PECs were determined at various molar mixing ratios. Despite relatively small differences in chemical structure between PAA and PMAA, fairly large differences were detected in these physical characteristics. Generally, PECs comprising PMAA were larger and contained more water. Moreover, by using cryogenic transmission electron microscopy, transmission microscopy and atomic force microscopy, shape and structure of the prepared PECs were investigated both in solution and after drying. The PECs were found to be spherical in solution and the shape was retained after freeze-drying. PECs adsorbed on silica surfaces and dried in air at room-temperature still showed a three-dimensional structure. However, the relatively low aspect ratios indicated that the PECs collapsed significantly due to interactions with the silica during adsorption and drying. At intermediate ionic strengths (1-10 mM), stagnation point adsorption reflectometry (SPAR) showed that the adsorption oflow charged cationic PAH-PAA PECs on silica surfaces increased if the pH value was increased from pH 5.5 to 7.5.

  • 5. Halvarsson, Soeren
    et al.
    Edlund, Hakan
    Norgren, Magnus
    Properties of medium-density fibreboard (MDF) based on wheat straw and melamine modified urea formaldehyde (UMF) resin2008In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 28, no 1, p. 37-46Article in journal (Refereed)
    Abstract [en]

    Wheat straw was investigated as a raw material for manufacturing of medium density fibreboard (MDF) in a fully equipped pilot-plant. Commercial urea melamine formaldehyde (UMF) and a mixture of UMF-resin and urea melamine phenol formaldehyde (UMPF) adhesives were used as binders in manufacturing of high performance MDF. The study evaluated the quality of MDF produced of straw (i.e., SMDF). Different qualities of wheat straw and different resin contents (14-17%) were used. Moreover, the SMDF was produced at different thicknesses of 9 and 16 mm and densities of 750-1000 kg/m(3). The properties of the resulting SMDF were evaluated by analysing mechanical and water absorption (anti-swelling) properties as a function of density. internal bond (IB), modulus of rupture (MOR), modulus of elasticity (MOE), thickness swelling (TS), and water absorption (WABS) were the properties analysed. SMDF-panels produced with densities above 780kg/m(3) and resin contents above 14% met the requirements for wood-based MDF standard EN 622-5:1997.

  • 6. Halvarsson, Soren
    et al.
    Edlund, Hakan
    Norgren, Magnus
    Manufacture of High-Performance Rice-Straw Fiberboards2010In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 49, no 3, p. 1428-1435Article in journal (Refereed)
    Abstract [en]

    Rice straw, a waste agriculture material grown and harvested in Willows, CA, was used,is a raw material in the production of thin medium- and high-density fiberboards (MDFs and HDFs). The rice straw was cleaned, size-reduced, and soaked in water before being refined. Defibration was performed in it pressurized pilot-plant single-disk refiner, OHP 20". The fiber production capacity reached a level of 63 kg/h. and the proper fiber quality for MDF/HDF production was established. Analysis of the produced fiber showed an average fiber length of approximately 0.9 mm, in average fiber width of 31 mu m, a shive weight of below 24%, and a dust content of less than 30%. Production of fiberboards was performed by addition of 3%, 4%, and 5% methylene diphenyl diisocyanate (MDI). The flexural properties, internal bond strength, and thickness swelling of the produced fiberboards were evaluated according to ASTM methods. The finished fiberboards based on rice straw and MDI resin showed excellent properties. The internal bond (IB) reached levels of 2.6 MPa, and the modulus of rupture (MOR) and modulus of elasticity (MOE) showed levels comparable to those of wood-based fiberboards and were acceptable according to the requirements or medium-density fiberboard (MDF) for interior applications (American National Standards Institute, ANSI A208.2-2002). The water-repelling properties of the 3-min rice-straw fiberboards were encouraging; the thickness swelling, (TS) was in the range of 15-30%. Two different methods to avoid adhesion between the press plates and the resinated fiber material during hot pressing were investigated: protective paper sheets were placed between the fiber mat and press plates, or a press-release agent was sprayed oil steel plates that were then placed ill the press before pressing Satisfactory results were obtained with both methods, and no adhesion was observed between the fiberboard and the steel plates. The method of using press-release agent during pressing had no notable negative effects oil the fiberboard properties.

  • 7. Halvarsson, Sören
    et al.
    Edlund, Håkan
    Norgren, Magnus
    Manufacture of non-resin wheat straw fibreboards2009In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 29, no 2-3, p. 437-445Article in journal (Refereed)
    Abstract [en]

    Wheat straw was used as raw material in the production of fibreboards. The size-reduced straw was pretreated with steam, hot water and sulphuric acid before the defibration process to loosen its physical structure and reduce the pH. No synthetic binder was added. Adhesive bonding between fibres was initiated by activation of the fibre surfaces by an oxidative treatment during the defibration process. Fenton's reagent (ferrous chloride and hydrogen peroxide) was added. Two different levels of hydrogen peroxide (H2O2), 2.5% or 4.0% were used. The resulting fibres were characterized in terms of fibre length distribution, shive content, pH and pH-buffering capacity. The properties of finished fibreboards were compared with medium-density fibreboard (MDF) with density above 800 kg/m(3) produced from straw and melamine modified UF resin. The modulus of rupture (MOR), modulus of elasticity (MOE) and internal bond (IB) were lower than those of conventional manufactured wheat straw fibreboards but close to the requirements of the MDF standard (EN 622-5: 2006). The water absorption properties for the H2O2 activated straw fibreboards were relatively high, but were reduced by 25% with the addition of CaCl2 into the defibrator system as a water-repelling agent. Increased levels of hydrogen peroxide improved the mechanical and physical properties of the straw fibreboard. Crown

  • 8.
    Holmgren, Anders
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Norgren, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Zhang, Liming
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Henriksson, Gunnar
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    On the role of the monolignol gamma-carbon functionality in lignin biopolymerization2009In: Phytochemistry, ISSN 0031-9422, E-ISSN 1873-3700, Vol. 70, no 1, p. 147-155Article in journal (Refereed)
    Abstract [en]

    In order to investigate the importance of the monomeric gamma-carbon chemistry in lignin biopolymerization and structure, synthetic lignins (dehydrogenation polymers; DHP) were made from monomers with different degrees of oxidation at the gamma-carbon, i.e., carboxylic acid, aldehyde and alcohol. All monomers formed a polymeric material through enzymatic oxidation. The polymers displayed similar sizes by size exclusion chromatography analyses, but also exhibited some physical and chemical differences. The DHP made of coniferaldehyde had poorer solubility properties than the other DHPs, and through contact angle of water measurement on spin-coated surfaces of the polymeric materials, the DHPs made of coniferaldehyde and carboxylic ferulic acid exhibited higher hydrophobicity than the coniferyl alcohol DHP. A structural characterization with C-13 NMR revealed major differences between the coniferyl alcohol-based polymer and the coniferaldehyde/ferulic acid polymers, such as the predominance of aliphatic double bonds and the lack of certain benzylic structures in the latter cases. The biological role of the reduction at the gamma-carbon during monolignol biosynthesis with regard to lignin polymerization is discussed.

  • 9. Norgren, Magnus
    et al.
    Bergfors, E.
    Sorption of kraft lignin from spent liquors on pulp fibres2005In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 39, no 6, p. 512-520Article in journal (Refereed)
    Abstract [en]

    In this investigation, the sorption of kraft lignin (KL) from spent liquors, membrane filtrated and model KL liquors on fully bleached softwood kraft pulp fibres, was studied. The time, temperature and alkalinity during the sorption experiments were chosen to reflect the conditions of black liquor impregnation of chips before the cooking operation. The amount of sorbed KL was estimated by brightness and kappa number measurements. A linear correlation between the k value and the kappa number was found. Among the parameters investigated, the concentration of metal non-process elements was found the most crucial for the sorption of KL on pulp fibres under black liquor impregnation. The influences of KL concentration, metal ion profile and KL molecular weight distribution on the KL sorption behaviour under black liquor impregnation are discussed.

  • 10. Norgren, Magnus
    et al.
    Edlund, H.
    Ion specific differences in salt induced precipitation of kraft lignin2003In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 18, no 4, p. 400-403Article in journal (Refereed)
    Abstract [en]

    Kraft lignin (KL) precipitation, measured as turbidity, in alkaline solutions (pH = 10.5) at 70degreesC in presence of various salts was investigated. Special concern was devoted to study ion specific effects on KL from monovalent cations and anions belonging to the so-called Hofmeister or lyotropic series. Thus, in the study the stability of KL solutions containing different inorganic and organic anions as well as various quaternary ammonium bromides were tested. In the case of inorganic anions, Cl- and Br- induced a higher degree of KL precipitation compared to NO3- and SCN-. The effects of the two tested, sodium uronates were found to diverge and, on a short time-scale, galacturonate showed a better KL stabilizing capacity than C1-. The influence of various tetraalkyl ammonium bromides was compared with the effects of different alkali metal bromides. As the length of the alkyl chain was increased, the KL stability was found to be decreasing. However, at equal concentrations, (CH3)(4)NBr was found to induce a lower degree of KL precipitation than NaBr. From the outcome of the investigation it can be seen that the effects of different cations on KL precipitation follows the mutual order stated by the classical Hofmeister series, whereas the anionic effect has a reversed correspondence.

  • 11. Norgren, Magnus
    et al.
    Edlund, H.
    Stabilisation of kraft lignin solutions by surfactant additions2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 194, no 03-jan, p. 239-248Article in journal (Refereed)
    Abstract [en]

    The colloidal stability of kraft lignin (KL) and some various KL-surfactant mixtures in aqueous alkaline solutions, pH 10.0-11.50, was tuned and investigated at high ionic strengths, 0.5-1.1 M, and elevated temperatures, 70 and 150 degreesC. The main techniques used were Quasi-Elastic Light-Scattering (QELS) and turbidity measurements, together with sample inspection by the naked eye. Samples without surfactant additions and samples containing various alkyl sulfonates showed a comparably low colloidal stability, whereas in mixtures containing sodium salts of bile acids, the stability was found greatly improved. The efficiency of different bile salts was investigated and it was found that the overall best solution stability is obtained in mixtures of KL and sodium taurodeoxycholate (STDC). STDC showed a relatively good stabilising effect also at very high temperatures (150 degreesC). Furthermore, in already aggregated KL solutions, additions of STDC were found to cause 'de-aggregation' and the number of formed aggregates was dramatically decreased. From the outcome of the investigation, it can be concluded that by introducing surfactants, and maybe other designed additives too, new possibilities in controlling the colloidal stability of KL at rough solution conditions are given.

  • 12. Norgren, Magnus
    et al.
    Edlund, H.
    Nilvebrant, N. O.
    Physiochemical differences between dissolved and precipitated Kraft lignin fragments as determined by PFG NMR, CZE and quantitative UV spectrophotometry2001In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 27, no 11, p. 359-363Article in journal (Refereed)
    Abstract [en]

    A combination of analytical techniques, specifically capillary zone electrophoresis, H-1 pulsed-field gradient nuclear magnetic resonance se (diffusion measurements and quantitative UV spectrophotometric measurements, was used to investigate physicochemical differences between dissolved and precipitated kraft lignin (KL)fragments, obtained from the same sample. Precipitation was induced by heating alkaline (pOH4)Indulin AT solutions, containing various concentrations of NaCl (0.20-1.0 mol/L), at 75 degreesC. Depending on the salt concentration in the samples, different amounts of KL were precipitated. The KL precipitated at the lowest NaCl concentrations was found to consist of the largest lignin fragments whereas, at high NaCl concentrations, the KL fragments in the supernatants were found to be of comparably lower mean molecular weights. From the outcome of the investigation, it was found that the combination of analytical techniques used provides the possibility of collecting important information about physicochemical characteristics related to the solution behaviour of industrial lignins.

  • 13. Norgren, Magnus
    et al.
    Edlund, H.
    Wågberg, Lars
    Aggregation of lignin derivatives under alkaline conditions. Kinetics and aggregate structure2002In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 18, no 7, p. 2859-2865Article in journal (Refereed)
    Abstract [en]

    The kinetics of kraft lignin (KL) aggregation at alkaline conditions was studied by quasi-elastic light scattering (QELS) and turbidity measurements. Stability ratios (W) for HL were obtained at 70 degreesC and various concentrations of sodium chloride. By analyzing the early-time evolution data of aggregate growth obtained from QELS, fractal dimensions of flocs formed in both reaction-limited cluster-cluster aggregation regimes and diffusion-limited cluster-cluster aggregation regimes were determined. Correlations between the fractal dimension and the W-ratio were found in accordance to recent studies of a system containing monodisperse polystyrene colloids. By cryogenic transmission electron microscopy, the fractality of KL aggregate structures in the system was also shown. It was seen from stability studies of KL solutions that the effects of specific co- and counterions follow the Hofmeister series. From the outcome of the investigation, different modes of aggregation occurring in a KL system are proposed. Starting from the macromolecular state of KL and evolving through larger aggregates, the KL clusters finally exhibit a supramolecular structure similar to what earlier has been proposed for native softwood lignin.

  • 14. Norgren, Magnus
    et al.
    Edlund, H.
    Wågberg, Lars
    KTH, Superseded Departments, Pulp and Paper Technology.
    Annergren, G.
    Fundamental physical aspects on lignin dissolution2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 4, p. 370-373Article in journal (Refereed)
    Abstract [en]

    The aggregation of diluted kraft lignin (KL) solutions was studied by turbidity measurements at elevated temperatures, various sodium chloride and sodium hydroxide concentrations. Since adsorptive processes usually precede self-aggregation in macromolecular systems as the solution conditions act worse, the interaction between KL and pulp fibres was also investigated. When treating samples of fully bleached softwood pulp fibres in KL solutions under various solution conditions, the light-absorption coefficient increased and the brightness was found to decrease rapidly above pOH 1, as the temperature was elevated. At pOH 2 and 175degreesC, the adsorption of KL was LIP to about 6 mg g(-1). The results are also discussed theoretically in terms of lignin solubility and lignin coagulation.

  • 15. Norgren, Magnus
    et al.
    Edlund, H.
    Wågberg, Lars
    Lindström, B.
    Annergren, G.
    Aggregation of kraft lignin derivatives under conditions relevant to the process, part I: phase behaviour2001In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 194, no 03-jan, p. 85-96Article in journal (Refereed)
    Abstract [en]

    Aggregation of a commercial, polydisperse softwood kraft lignin (Indulin AT) in diluted aqueous alkaline solutions was investigated experimentally, by means of turbidity measurements. The influence of temperature, salt concentration and pOH and the role of a divalent counterion on the aggregation behaviour were studied. When the temperature was increased, an increased tendency of aggregation in samples containing high concentrations of sodium chloride was found. Phase separation could be detected even at pOH = 2 at 175 degreesC and the effect was pronounced when the concentration of hydroxide ions decreased. The phase transition from soluble to precipitated lignin was found to be irreversible concerning temperature change. Small amounts of calcium ions were seen to induce dramatic effects on the system stability, even at relatively high hydroxide concentrations (pOH 1-2). At a given temperature and pOH, the coagulation was found to appear at a certain critical coagulation concentration (CCC) of the added electrolyte. Furthermore, calculations were carried out to compare with the outcome of the experimental observations. A theoretical model, based on the DLVO theory, was found to predict the kraft lignin solution behaviour well.

  • 16. Norgren, Magnus
    et al.
    Gärdlund, Linda
    Notley, Shannon M.
    Htun, Myat
    Wågberg, Lars
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Smooth model surfaces from lignin derivatives. II. Adsorption of polyelectrolytes and PECs monitored by QCM-D2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 7, p. 3737-3743Article in journal (Refereed)
    Abstract [en]

    For the first time to the knowledge of the authors, well-defined and stable lignin model surfaces have been utilized as substrates in polyelectrolyte adsorption studies. The adsorption of polyallylamine (PAH), poly(acrylic acid) (PAA), and polyelectrolyte complexes (PECs) was monitored using quartz crystal microgravimetry with dissipation (QCM-D). The PECs were prepared by mixing PAH and PAA at different ratios and sequences, creating both cationic and anionic PECs with different charge levels. The adsorption experiments were performed in 1 and 10 mM sodium chloride solutions at pH 5 and 7.5. The highest adsorption of PAH and cationic PECs was found at pH 7.5, where the slightly negatively charged nature of the lignin substrate is more pronounced, governing electrostatic attraction of oppositely charged polymeric substances. An increase in the adsorption was further found when the electrolyte concentration was increased. In comparison, both PAA and the anionic PEC showed remarkably high adsorption to the lignin model film. The adsorption of PAA was further studied on silica and was found to be relatively low even at high electrolyte concentrations. This indicated that the high PAA adsorption on the lignin films was not induced by a decreased solubility of the anionic polyelectrolyte. The high levels of adsorption on lignin model surfaces found both for PAA and the anionic PAA-PAH polyelectrolyte complex points to the presence of strong nonionic interactions in these systems.

  • 17. Norgren, Magnus
    et al.
    Lindström, B.
    Dissociation of phenolic groups in kraft lignin at elevated temperatures2000In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, no 5, p. 519-527Article in journal (Refereed)
    Abstract [en]

    The dissociation of the phenolic groups in a polydisperse, low molecular weight kraft lignin (Indulin AT) was studied in alkaline aqueous solutions in the temperature interval 21-70 degrees C, using a UV-spectrophorometric method. It was found that at a constant concentration of hydroxide ions, the degree of dissociation was decreasing when the temperature was elevated. Dissociation curves and apparent pK(0) values were also calculated for the polydisperse sample at the same conditions, using the van't Hoff and the Poisson-Boltzmann equations. At degrees of dissociation exceeding alpha approximate to 0.4, the outcome of the theoretical approach showed to be in good agreement with the experimentally obtained results. Furthermore, calculations were performed for different molecular weights of kraft lignin and from this it was found that the apparent pK(0) is shifted to higher values by increasing molecular weight, due to an increased electrostatic attraction of the hydrogen ions, which is arising from a less curved surface. Predictions of the dissociation behavior at temperatures reached in the kraft process were performed and under these conditions, higher molecular weight lignin fragments seem never to reach the point of complete dissociation. It was also found that an increase in temperature results in phase separation in kraft lignin solutions with high ionic strengths and pH values close to the pK(a) of the phenolic groups.

  • 18. Norgren, Magnus
    et al.
    Lindström, B.
    Physico-chemical characterization of a fractionated kraft lignin2000In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 54, no 5, p. 528-534Article in journal (Refereed)
    Abstract [en]

    A kraft lignin was leached from a softwood pulp and fractionated by ultrafiltration. The fractions were characterized in respect to phenolic group content, molecular weight distributions and self-diffusion coefficients. The H-1-Pulsed Field Gradient (PFG) NMR self-diffusion measurements and the High-Pressure Size Exclusion Chromatography (HPSEC) analysis of the fractions, were seen to correlate fairly well. From the self-diffusion measurements, the mass-weighted median hydrodynamic radii of the diffusants in the fractions, were calculated assuming spherical fragments. Furthermore, the content of phenolic groups in the fractions, was found to decrease by increasing hydrodynamic radius and molecular weight, but the calculated median surface charge densities of the macromolecules, were determined to be constant in the range of oligomers up to at least 65 structural units.

  • 19. Norgren, Magnus
    et al.
    Mackin, Sofia
    Sulfate and Surfactants as Boosters of Kraft Lignin Precipitation2009In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 48, no 10, p. 5098-5104Article in journal (Refereed)
    Abstract [en]

    In the spirit of the biorefinery concept, an increasing interest in further utilization of technical lignins outside the pulp mills has arisen. In this context optimization of the precipitation process to increase the yield of the lignin recovered is of great importance. The objectives of this investigation have been to study how specific salts and surfactants affect kraft lignin yield during precipitation and washing. From the results it was seen that additions of sodium sulfate increased the yield of precipitation at elevated temperatures at much lower concentrations than sodium chloride. Earlier studies of the effect of monovalent salts on kraft lignin stability have shown that specific ions either increase or decrease the fort-nation of precipitates during kraft lignin aggregation. Thus, the presented results in this study further strengthen this dependency concerning divalent anions. Regarding the role of surfactants as precipitation enhancers, cationic surfactants gave rise to fast aggregation and relatively high yields. This was found mainly due to attractive electrostatic interactions between the cationic surfactant headgroup and the oppositely charged groups on the kraft lignin macromolecules, introducing an increased degree of hydrophobicity of the lignin and thus a decreased stability. The nonionic surfactants tested affected the system very differently. In some cases the aggregation was fast and the aggregates became relatively large before settling, whereas some surfactants induced the formation of relatively dense precipitates that settled rapidly. Concerning kraft lignin precipitate washing, calcium chloride at concentrations in the millimolar region decreased the lignin losses dramatically.

  • 20. Norgren, Magnus
    et al.
    Notley, S. M.
    Majtnerova, A.
    Gellerstedt, Göran
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Wood Chemistry and Pulp Technology.
    Smooth model surfaces from lignin derivatives. I. Preparation and characterization2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 3, p. 1209-1214Article in journal (Refereed)
    Abstract [en]

    Lignin model surfaces were prepared from aqueous alkaline solutions by spin-coating on silica wafers. Films of thicknesses between 20 and 140 nm were easily made by variations in the spinning rate or in the lignin concentration. The roughnesses of the lignin surfaces were relatively low, approximately 1.1 nm (rms) on an area of 25 mu m(2), as determined by atomic force microscopy imaging. The stability of the lignin films in aqueous solutions was found to be excellent. No changes in the thickness of model surfaces immersed in slightly alkaline solutions (pH 9.2) could be detected even after 5 It soaking. A 10 percent reduction in the thickness of the lignin film was observed after 5 It of exposure to a solution containing 0.1 M NaCl. This novel preparation method opens great possibilities for further fundamental studies, where interactions between lignin and other substances are of interest to investigate.

  • 21. Notley, S. M.
    et al.
    Norgren, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lignin: Functional Biomaterial with Potential in Surface Chemistry and Nanoscience2009In: The Nanoscience and Technology of Renewable Biomaterials, John Wiley & Sons, 2009, p. 173-205Chapter in book (Refereed)
  • 22. Notley, Shannon M.
    et al.
    Norgren, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Adsorption of a strong polyelectrolyte to model lignin surfaces2008In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 9, no 7, p. 2081-2086Article in journal (Refereed)
    Abstract [en]

    The adsorption of a strong, highly charged cationic polyelectrolyte to a kraft lignin thin film was investigated as a function of the adsorbing solution conditions using the quartz crystal microbalance. The polyelectrolyte, PDADMAC, with a molecular weight of 100 kDa and one cationic charge group per monomer, was adsorbed to the anionically charged lignin film in the pH range 3.5-9.5 in electrolyte solution of 0.1 to 100 mM NaCl. At low pH, the adsorbed amount of PDADMAC was minimal, however, this increased as a function of increasing pH. Indeed, the surface excess increased significantly at about pH 8.5, where ionization of the phenolic groups on the lignin macromolecule may be expected. Furthermore, at this elevated pH, the adsorbed amount of PDADMAC decreased as the ionic strength of the solution increased above I mM. This is due to the competitive adsorption of counterions to the lignin surface and indicates that the adsorption of PDADMAC to lignin is of a pure electrosorption nature.

  • 23. Notley, Shannon M.
    et al.
    Norgren, Magnus
    Measurement of interaction forces between lignin and cellulose as a function of aqueous electrolyte solution conditions2006In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 22, no 26, p. 11199-11204Article in journal (Refereed)
    Abstract [en]

    The interaction between a lignin film and a cellulose sphere has been measured using the colloidal probe force technique as a function of aqueous electrolyte solution conditions. The lignin film was first studied for its roughness and stability using atomic force microscopy imaging and quartz crystal microbalance measurements, respectively. The film was found to be smooth and stable in the pH range of 3.5-9 and in ionic strengths up to and including 0.01 M. This range of ionic strength and pH was hence used to measure the surface force profiles between lignin and cellulose. Under these solution conditions, the measured forces behaved according to DLVO theory. The force-distance curves could be fitted between the limits of constant charge and constant potential, and the surface potential of the lignin films was determined as a function of pH. At a pH greater than 9.5, a short range steric repulsion was observed, indicating that the film was swelling to a large extent but did not dissolve. Thus, lignin films prepared in this manner are suitable for a range of surface force studies.

  • 24. Notley, Shannon M.
    et al.
    Norgren, Magnus
    Surface Energy and Wettability of Spin-Coated Thin Films of Lignin Isolated from Wood2010In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 26, no 8, p. 5484-5490Article in journal (Refereed)
    Abstract [en]

    The surface energy of lignin films spin-coated onto oxidized silicon water has been determined from contact angle measurements of different test liquids with varying polar and dispersive components. Three different lignin raw materials were used, a kraft lignin from softwood, along with milled wood lignin from softwood and hardwood. Infrared and P-31 NMR spectroscopy was used to identify any major functional group differences between the lignin samples. No significant difference in the total solid vapor surface energy or the different lignin films was observed: however, the polar component for the kraft lignin was much greater than for either of the milled wood lignin samples consistent with the presence of carboxyl groups and higher proportion of phenolic hydroxyl groups as shown by quantitative P-31 NMR on the phosphitylated samples. Furthermore, the total surface energy of lignin of 53-56 mJ m(-2) is of a similar magnitude to cellulose, also found in the wood cell wall; however, cellulose has a higher polar component leading to a lower contact angle with water and greater wettability than the milled wood lignin. Although lignin is not hydrophobic according to the strictest definition or a water contact angle greater than 90 degrees, water may only be considered a partially wetting liquid on a lignin surface. This supports the long-held belief that one of the functions of lignin in the wood cell wall is to provide water-proofing to aid in water transport. Furthermore, these results on the solid vapor surface energy of lignin will provide invaluable insight for many natural and industrial applications including in die design and manufacture of many sustainable products such as paper. fiberboard, and polymer composite blends.

  • 25.
    Wågberg, Lars
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Decher, Gero
    Norgren, Magnus
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Lindström, Tom
    Ankerfors, Mikael
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Fibre Technology.
    Axnäs, Karl
    The build-up of polyelectrolyte multilayers of microfibrillated cellulose and cationic polyelectrolytes2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 3, p. 784-795Article in journal (Refereed)
    Abstract [en]

    A new type of nanocellulosic material has been prepared by high-pressure homogenization of carboxymethylated cellulose fibers followed by ultrasonication and centrifugation. This material had a cylindrical cross-section as shown by transmission electron microscopy with a diameter of 5-15 nm and a length of up to 1 mu m. Calculations, using the Poisson-Boltzmann equation, showed that the surface potential was between 200 and 250 mV, depending on the pH, the salt concentration, and the size of the fibrils. They also showed that the carboxyl groups on the surface of the nanofibrils are not fully dissociated until the pH has reached pH = similar to 10 in deionized water. Calculations of the interaction between the fibrils using the Derjaguin-Landau-Verwey-Overbeek theory and assuming a cylindrical geometry indicated that there is a large electrostatic repulsion between these fibrils, provided the carboxyl groups are dissociated. If the pH is too low and/or the salt concentration is too high, there will be a large attraction between the fibrils, leading to a rapid aggregation of the fibrils. It is also possible to form polyelectrolyte multilayers (PEMs) by combining different types of polyelectrolytes and microfibrillated cellulose (MFC). In this study, silicon oxide surfaces were first treated with cationic polyelectrolytes before the surfaces were exposed to MFC. The build-up of the layers was monitored with ellipsometry, and they show that it is possible to form very well-defined layers by combinations of MFC and different types of polyelectrolytes and different ionic strengths of the solutions during the adsorption of the polyelectrolyte. A polyelectrolyte with a three-dimensional structure leads to the build-up of thick layers of MFC, whereas the use of a highly charged linear polyelectrolyte leads to the formation of thinner layers of MFC. An increase in the salt concentration during the adsorption of the polyelectrolyte results in the formation of thicker layers of MFC, indicating that the structure of the adsorbed polyelectrolyte has a large influence on the formation of the MFC layer. The films of polyelectrolytes and MFC were so smooth and well-defined that they showed clearly different interference colors, depending on the film thickness. A comparison between the thickness of the films, as measured with ellipsometry, and the thickness estimated from their colors showed good agreement, assuming that the films consisted mainly of solid cellulose with a refractive index of 1.53. Carboxymethylated MFC is thus a new type of nanomaterial that can be combined with oppositely charged polyelectrolytes to form well-defined layers that may be used to form, for example, new types of sensor materials.

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