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Norrköping, Sweden

Hafren J.,Swedish University of Agricultural Sciences | Muhic D.,Holmen Paper AB | Muhic D.,Metso Paper Inc. | Gerritsen H.C.,University Utrecht | Bader A.N.,University Utrecht
Nordic Pulp and Paper Research Journal | Year: 2011

Norway spruce wood pulps were produced in full industrial scale trials at different thermomechanical pulp refining conditions, such as plate gap, housing pressures and energy consumption levels. To investigate the effects of these refining conditions on the lingocellulosic matrix in fines and fibers, we applied high-resolution spectral imaging in a two-photon fluorescence microscope and compared with conventional pulp and paper analyses (strength, freeness etc.). The fluorescence spectra of lignin in native wood and fibersand fines from pulps showed that spatial- and spectral heterogeneities can be observed using two-photon autofluorescence spectral imaging, and successfully probed on a microscopic level. Moreover, it was shown that wood autofluorescence depends on fiber morphology and becomes red-shifted by increased temperature, but the fluorescence spectrum of TMP long fiber fraction shifted towards blue by increased refining pressure.

Fernando D.,Swedish University of Agricultural Sciences | Muhic D.,Holmen Paper AB | Engstrand P.,Mid Sweden University | Daniel G.,Swedish University of Agricultural Sciences
Holzforschung | Year: 2011

The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons' staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under different process conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP. © 2011 by Walter de Gruyter Berlin Boston.

Winestrand S.,Karlstad University | Winestrand S.,Umea University | Sjode A.,Karlstad University | Cassland P.,Novozymes AS | And 4 more authors.
Industrial Biotechnology | Year: 2014

Precipitation of sparsely soluble calcium oxalate causes scaling problems in the pulp and paper industry. A potential solution is to degrade the oxalic acid using oxalate-degrading enzymes. Four novel fungal oxalate decarboxylases were evaluated in experiments with 16 pH-adjusted bleaching filtrates collected from mills producing mechanical pulp or kraft pulp. The enzymes were also tested in five of the filtrates from mechanical pulping at authentic pH and elevated temperature (55°C). The enzyme that performed best in the screening was selected for a small-scale experiment performed in a mill producing mechanical pulp. The enzyme degraded 70% of the oxalic acid in the fresh filtrate after one hour, without pH adjustment and at the prevailing process temperature (65°C). The new enzyme performed considerably better than the well-studied oxalate decarboxylase from Aspergillus niger, which only degraded 4% of the oxalic acid under the same conditions. © Copyright 2014, Mary Ann Liebert, Inc.

Fernando D.,Swedish University of Agricultural Sciences | Muhic D.,Holmen Paper AB | Engstrand P.,Mid Sweden University | Daniel G.,Swedish University of Agricultural Sciences
Holzforschung | Year: 2012

Refining during mechanical pulping causes delamination and internal fibrillation (D/IF) of the fibre wall and changes the surface ultrastructure. Fundamental knowledge about these phenomena at the fibre cell wall level helps our understanding of the development of pulp and paper properties, which in turn facilitates the optimization of processes, helping to save energy and improve the characteristics of final products. In the present study, pulps were produced by double-disc (DD) refined thermomechanical processes (DD-TMP) and have been characterized at the fibre cell wall micro/ultrastructural level based on Fernando and Daniel's method (2010) of Simons ' staining and scanning electron microscopy (SEM). The pulps studied were never-dried Norway spruce DD-TMP from a full-scale mill trial running under different process conditions; a) varying refining intensity, achieved by using a high-intensity turbine segment (HTS) and a standard (Ref) segment from Metso, and b) varying specific energy consumption (SEC). Improved energy efficiency was obtained with HTS segments, giving adequate or better pulp properties with respect to elongation, light scattering, Canadian Standard Freeness (CSF) at a similar tensile index level and lower energy consumption. Energy efficiency was gained through an elevated degree of D/IF and S2 fibrillation with low energy input. Both the SEC and segment designs had a significant impact on elevating the degree of D/IF. Statistical evaluation of fibre development with respect to D/IF gave evidence for improved energy efficiency in HTS refining. Ultrastructural studies on fibre surfaces showed that HTS refining produced better external fibrillation and leads to exposing the secondary S2 wall as fibre outer layer with different ribbon-type S2 fibrillation. Information obtained at the fibre wall level concerning D/IF and surface ultrastructure contribute to the fundamental knowledge about the pulp and handsheet properties and the energy efficiency of TMP processing. Copyright © by Walter de Gruyter·Berlin·Boston.

Hafren J.,Swedish University of Agricultural Sciences | Nelsson E.,Holmen Paper AB | Gerritsen H.C.,University Utrecht | Bader A.N.,University Utrecht
Holzforschung | Year: 2012

Chips of Norway spruce have been impregnated with Na2SO 3 and refined at two specific energy consumptions levels at full mill scale. The optical properties of thermomechanical pulps (TMPs) obtained were analyzed in terms of brightness, light scattering, opacity, and autofluorescence by spectral imaging. Even at low sulfite dosage (0.24% sulfite by dry weight) light absorption was reduced, and the brightness was elevated, and a clear dose-response effect was observed. Two-photon spectral imaging (TPSI) showed that sulfonation, impregnation, and refining affect the fluorescence properties differently. Compared to native wood, both processed wood chips and pulp fibers revealed blue-shifted fluorescence maxima, a characteristic of shortened conjugated systems. Two subpopulations of fibers with different optical properties were observed, and the fluorescence of one fiber population was red shifted. Copyright © by Walter de Gruyter.

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