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  • 1. Andreasson, B
    et al.
    Forsström, Jennie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Wågberg, Lars
    Determination of fibre pore structure: influence of salt, pH and conventional wet strength resins2005Ingår i: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 12, nr 3, s. 253-265Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However, the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength, measured as zero span-strength of the sheets.

  • 2. Andreasson, Bo
    et al.
    Forsström, Jennie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Wågberg, Lars
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    The porous structure of pulp fibres with different yields and its influence on paper strength2003Ingår i: Cellulose, ISSN 0969-0239, Vol. 10, nr 2, s. 111-123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of 2H in fibres saturated with 2H2O. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.

  • 3.
    Forsström, Jennie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Fundamental Aspects on the Re-use of Wood Based Fibres: Porous Structure of Fibres and Ink Detachment2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this work, different aspects on the re-use of wood based fibres have been studied, focusing on ink detachment of flexographic ink from model cellulose surfaces and changes in porous structure of kraft fibres following different treatments. New model systems for evaluation of ink detachment and ink-cellulose interactions were used. Ink detachment was studied using Impinging jet cell equipment, taking into consideration the influence of storage conditions, surface roughness and surface energy of the cellulose substrate. A micro adhesion measurement apparatus (MAMA) was used to directly study ink-cellulose interactions, from which the adhesive properties between ink and cellulose, having various surface energies, could be derived. UV-light, elevated temperatures, longer storage time, decreased surface energy, i.e. making the cellulose surface more hydrophobic, and high surface roughness all negatively affected ink detachment. Attenuated total reflectance - fourier transform infra red (ATR-FTIR) and atomic force microscopy (AFM) was used to evaluate structural and chemical changes of ink and cellulose upon storage at elevated temperature or under UV-light. After storage at elevated temperatures, ATR-FTIR spectra indicated that a hydrolysis or an oxidative reaction took place as a peak at 1710 cm-1 appeared. AFM revealed that storage at elevated temperatures caused the latex particles present in the ink to form a film, most likely due to annealing. Less ink detached from hydrophobic cellulose surfaces. Ink detachment decreased for rougher cellulose substrates due to an increased molecular contact area.

     

    Fibre pore structure and water retaining ability influenced fibre/fibre joint strength and different paper strength properties. Investigations took into account the effect of pulp yield, counter-ion types, pH, salt, hornification and strength enhancing additives. Nuclear magnetic resonance relaxation (NMR), inverse size exclusion chromatography (ISEC) and water retention value (WRV) measured the changes that occur in the fibre wall upon varying the conditions. Each different measuring technique contained unique information such that a combination of the techniques was necessary to give as complete a picture as possible over the changes that occurred in the fibre wall upon varying the conditions for the fibre. A correlation between fibre pore radius and sheet strength properties was found, suggesting that fibres with larger pores allow for a larger molecular contact area between fibres to be formed during drying and consolidation of the paper. Fibre/fibre joint strength, fibre flexibility, and the number of efficient fibre/fibre contacts also controlled sheet strength. The effect of different strength enhancing additives on fibre pore structure and paper strength was investigated. Larger pores in the fibres allowed for additives to penetrate into the fibre wall. Additives with low molecular mass (Mw) penetrated into the fibre wall to a larger extent than additives with a high Mw, causing an embrittlement of the fibre. However, low Mw additives gave higher sheet tensile strength despite a leveling out in strength at high additions, indicating that the fibre wall can only adsorb a limited amount of chemical. Polyallylamine hydrochloride (PAH) and polyelectrolyte complexes (PEC) of PAH and polyacrylic acid (PAA) were added separately to the pulp. PEC significantly improved both tensile strength and Z-strength, whereas PAH alone did not increase the strength properties to the same extent unless the sheets were heated to 150°C for 10 minutes. The results suggested that the effect of PEC was dominated by an improvement in fibre/fibre joint strength, whereas the effect of PAH was significantly affected by an improvement of the intra-fibre bond strength

     

  • 4.
    Forsström, Jennie
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Eriksson, Malin
    Wågberg, Lars
    A new technique for evaluating ink–cellulose interactions: initial studies of the influence of surface energy and surface roughness2005Ingår i: Journal of Adhesion Science and Technology, ISSN 0169-4243, E-ISSN 1568-5616, Vol. 19, nr 9, s. 783-798Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ink–cellulose interactions were evaluated using a new technique in which the adhesion properties between ink and cellulose were directly measured using a Micro-Adhesion Measurement Apparatus (MAMA). The adhesion properties determined with MAMA were used to estimate the total energy release upon separating ink from cellulose in water. The total energy release was calculated from interfacial energies determined via contact angle measurements and the Lifshitz–van der Waals/acid–base approach. Both methods indicated spontaneous ink release from model cellulose surfaces, although the absolute values differed because of differences in measuring techniques and different ways of evaluation. MAMA measured the dry adhesion between ink and cellulose, whereas the interfacial energies were determined for wet surfaces. The total energy release was linked to ink detachment from model cellulose surfaces, determined using the impinging jet cell. The influences of surface energy and surface roughness were also investigated. Increasing the surface roughness or decreasing the surface energy decreased the ink detachment due to differences in the molecular contact area and differences in the adhesiom properties.

  • 5.
    Forsström, Jennie
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Torgnysdotter, Annsofie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Wågberg, Lars
    Influence of fibre/fibre joint strength and fibre flexibiity on the strentgh of papers from unbleached kraft fibres.2005Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, nr 2, s. 186-191Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The joint strength between single fibres and its influence on strength properties of papers was evaluated, taking into account the effect of pulp yield, ionic form of the carboxyl groups and drying. Fibre/fibre joint strength stayed almost constant for pulps with yield between 45 % and 50 %. Further increasing the pulp yield increased the joint strength until a maximum value was reached at a pulp yield of 57 %, after which the joint strength decreased. Joint strength correlated well to paper tensile strength for never dried fibres, i.e. a lower joint strength resulted in lower sheet tensile index. The decrease in sheet tensile index was not as pronounced as the decrease in joint strength. Changing counter-ion from Na+ to Ca2+ or H+ did not affect fibre flexibility, although it reduced the joint strength as the molecular contact area decreased due to a reduced swelling upon changing the counter-ions. Drying the high yield pulp lowered both the joint strength and the sheet tensile index to the same extent. The sheet tensile index, for the low yield pulp, decreased much more than the fibre/fibre joint strength after drying the fibres. In conclusion, a combination of a lower fibre flexibility, resulting in fewer contact points between fibres in the sheet, and a lower joint strength after drying was responsible for the reduction in sheet tensile index.

  • 6.
    Forsström, Jennie
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Wågberg, Lars
    Influence of different deinking efficiency of waterbased flexographic ink from model cellulose surfaces and sheets2004Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 19, nr 2, s. 250-256Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of UV-light, temperature, atmospheric

    environment and storage time on the ink detachment of

    water-based flexographic ink printed on model cellulose surfaces

    was investigated using an impinging jet cell equipment. The

    printed surfaces were deinked using a NaOH solution (pH = 10)

    and the deinking process was monitored using a microscope

    equipped with a CCD camera. Images were collected at different

    time intervals during the detachment process and image

    analysis was used to quantify the ink detachment from the surface.

    Hand sheets, (the same pulp as used for model surface

    preparation) were also printed and stored under the same conditions,

    after which they were reslushed and deinked. The deinking

    efficiency of the recycled sheets was evaluated using

    brightness and ERIC (Effective Residual Ink Concentration)

    values. It was shown that UV-light had a negative effect on ink

    detachment both from the model cellulose surfaces and from

    the hand sheets. At storage temperatures of 55°C, (dark conditions

    were used) a large negative effect was observed for the

    cellulose surfaces while only a small effect on the ink detachment

    could be seen for the hand sheets. Ink detachment from

    the hand sheets became more difficult when increasing the storage

    temperature above 55°C, as detected as a decrease in

    brightness of the recycled and deinked sheets. A further increase

    in the storage temperature to 105°C gave poorer ink detachment

    efficiency than storage under UV-light for the hand sheets.

    Air had a more negative effect on ink detachment than nitrogen.

  • 7.
    Gärdlund, Linda
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Forsström, Jennie
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Andreasson, Bo
    Wågberg, Lars
    Influence of polyelectrolyte complexes on strength properties of papers made from unbleached kraft pulps with different yields2005Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 20, nr 1, s. 36-42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The properties of the materials combined in corrugated

    board are set to give the board its strength, flexibility

    and protection towards impact and pressure. The raw material is

    of course the single fibre but additives that enhance e.g. the wet

    and dry paper strength are also added. As the strength

    enhancing additives used today are most efficient between pH 4

    and pH 7 there is a need for new types of additives that can be

    used under alkaline conditions. In the present report polyallylamine

    hydrochloride (PAH) and polyelectrolyte complexes

    (PEC) of PAH and polyacrylic acid (PAA) were investigated as

    strength enhancing additives. The components can be used

    under alkaline conditions and results showed that PAH alone or

    incorporated into a PEC gave different effects regarding

    strength properties of sheets from kraft pulps of different yields.

    The results showed that by treating the fibres with PEC´s of

    PAH and PAA it was possible to considerably increase the

    tensile properties, the Z-strength and the compression strength

    of papers made from the treated fibres. The results showed an

    increase of as much as 54 % to 180 % in dry Z-strength and 14

    % to 53 % in compression strength, when using the PEC as an

    additive, indicating an increase in inter-fibre joint strength. It

    was also found that a heat treatment of the non-treated papers

    and of the papers from the PAH treated fibres gave a large

    improvement in tensile properties as well as Z-strength properties

    for the different pulps. For the PEC treated fibres it was not

    necessary to heat-treat the paper to achieve a higher dry

    strength. The molecular mechanism behind the large improvements

    is not identified in the present work but the problem is

    currently being investigated in the lab of the authors.

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