NC State
BioResources
  • 1989
    Cambridge
    pp 471-494T. G. M. van de VenPhysiocochemical and Hydrodynamic Aspects of Fines and Fillers RetentionAbstractPDF

    From the results of model studies on well-characterized systems, valuable conclusions can be drawn regarding several phenomena occurring in papermaking suspensions relevant to fines and fillers retention. We have shown that long range hydrodynamic interactions are operating between small particles (such as fillers) and spheroids (such as fibers) subjected to simple shear, preventing small particles from approaching large ones to within distances where colloidal forces become important. We can expect similar effects in papermaking suspensions, resulting in very low efficiencies for the deposition of fillers or fines on fibers. The efficiency can be improved by high molecular weight polymers which adsorb on the particles and can reduce the minimum distance of approach between a filler and a fiber. From model experiments on the deposition of T102 particles on cellophane, it can be concluded that the electrostatic forces also play an important role in fines and fillers retention. Usually no deposition occurs far below a critical deposition concentration (CDC) of electrolyte, slow deposition occurs just before the CDC and fast deposition above the CDC. Charged polymers, such as cationic polyelectrolytes, are most effective in retention because they can reduce the gap between a filler and a fiber during an encounter, and they ensure that electrostatic repulsion is negligible. Resides increasing the efficiency of deposition, retention aids can also increase the bond strength between a filler and a fiber, thus preventing or minimizing the rupture of fiber-filler bonds.

  • 1989
    Cambridge
    pp 495-508B. AlinceOptimization of Pigment Performance in PaperAbstractPDF

    The apparent light-scattering coefficient of a given pigment in filled papers depends on the state of pigment dispersion and the beating level of fibers. This effect is seen on handsheets containing pigments deliberately introduced either as individual particles or as aggregates; well dispersed T102 is optically superior and its contribution to the total light scattering increases with fiber beating. In order to achieve retention of dispersed pigment particles and to avoid their flocculation caused by polymeric retention aid, the pigment, prior to its addition to the fiber suspension, can be treated with a cationic polyelectrolyte. Since pigment introduction results in tensile strength loss, which is most pronounced with dispersed particles, a plot of optical properties versus tensile strength provides a means for evaluating the pigment effectiveness and for comparing different pigments.

  • 1989
    Cambridge
    pp 413-435L. Wågberg, L. Ödberg, and G. Glad-NordmarkConformation of Adsorbed Polymers and Flocculation of Microcrystalline Cellulose and Pulp SuspensionsAbstractPDF

    This paper consists of three parts. In the first part, the reconformation of polyelectrolytes adsorbed on fiber surfaces has been studied by measuring simultaneously the amount of adsorbed polymer and the number of released counterions. It was found that the time for reconformation from an initial, extended conformation to a more flat conformation was of the order of 60 seconds for a high molecular mass polyacrylamide. In the second and third parts, the flocculation of suspensions of microcrystalline cellulose and pulp fibers has been investigated. The results of these flocculation experiments can be related to the conformation and adsorbed amount of the polyelectrolyte.

  • 1989
    Cambridge
    pp 437-452R. I. S. GillThe Use of Potentiometric Titration and Polyelectrolyte Titration to Measure the Surface Charge of Cellulose FibreAbstractPDF

    The surface charge of cellulosic fibre was determined using two methods . The relative surface charge (PTC) of three bleached pulps was quantified using polyelectrol to titration and compared with the absolute surface charge (So) measured by potentiometric titration. It was established that the polyelectrolyte titration method was a less tedious, but valid method of determining the surface charge of fibre, providing the titration method is standardised and the effect of variables such as suspension, pH, fibre concentration, ionic content and polyelectrolyte molar mass are eliminated. The method was used to construct a charge/pH isotherm of a bleached hardwood fibre similar to those constructed using potentiometric titration. Furthermore, the effect of refining of bleached hardwood and softwood krafts on the PTC was investigated.

  • 1989
    Cambridge
    pp 453-470H. Tanaka and L. ÖdbergExchange of Cationic Polymers Adsorbed on Cellulose Fibers and on Monodisperse Polystyrene LatexAbstractPDF

    Two series of cationic polyacrylamides (C-PAM) were prepared, with and without fluorescent labelling, one with constant charge density (CD:1.4 meq/g) and different molecular weights (MW:2×104, 4×105 and 8×106) and one with constant molecular weight (4×105) and different charge densities (CD:0.65 meq/g, 1.4 meq/g and 2.5 meq/g) .

    The exchange reactions of these C-PAMs on monodisperse polystyrene latex (PSL) and cellulose fibers have been studied using C-PAMs with the same MW and CD except that the pre adsorbed polymers were fluorescently labelled. The first series of experiments was carried out near the saturation level of the pre-adsorbed polymers. For C-PAMs with the highest MW(8×106) no significant exchange could be detected on PSL or on fibers. When C-PAM with the highest. CD (2.5 meq/g) was used a slight exchange occurred on both PSL and fibers . The exchange became more extensive with decreasing MW and CD. The exchange reactions initially proceeded quite rapidly and then slowed down. The initial exchange was more extensive on cellulose fibers than on PSL, probably because of the lower surface CD of the fibers, but it levelled off more rapidly than on PSL. This difference is most probably an effect of the porous structure of the fibers.

  • 1989
    Cambridge
    pp 311-412T. LindströmSome Fundamental Chemical Aspects on Paper FormingAbstractPDF

    The fundamental physico-chemical aspects of retention chemistry are reviewed in the light of basic concepts in colloid chemistry.

    Special emphasis has been paid to the surface chemistry of cellulose and cellulosic materials, their origin of charge, dispersion force interactions as well as the implication of certain aspects of peculiar cellulosic surfaces, e.g. the influence of their porosity on polymer adsorption.

    Charge neutralization, patch flocculation, heterocoagulation, bridging and complex flocculation phenomena are discussed as well as polymer adsorption phenomena at the cellulose/water interface

  • 1989
    Cambridge
    pp 105-120P. Noé and F. HenryHydration of Refined Chemical Pulps Studied by Microwave SpectrometryAbstractPDF

    A bleached sulfate pulp has been refined in a disk refiner to different degrees : from 15 to 75° SR (720 to 70 CSF) . Different water contents ranging from 40 to 90 % by volume (70-90 % by weight) , have been obtained by centrifugation of small samples of ca.30 mg o.d. weight. The samples have been analyzed by microwave spectrometry performed in a cavity at 5 GHz. The theory of small perturbations of a resonant cavity allows the determination of the dielectric losses Es of the hydrated material. The slope of the lines : Es vs. moisture content is an index of the hydration of pulps. At the same water content (in the range 70 to 90 % by weight) , we have shown that refining increases the hydration, which can be defined as the transformation from free water to bound water.

  • 1989
    Cambridge
    pp 39-65L. Tie-Qiang, U. Henriksson, J. C. Eriksson, and L. ÖdbergDeuterium NMR and Water Adsorption Studies of the Effect of Beating on the Water-cellulose InteractionAbstractPDF

    The interaction between water and cellulose has been studied by deuterium NMR and water sorption isotherm measurements for a bleached kraft pulp and an unbleached liner board pulp beaten to various degrees. Measurements of 2H quadrupole splittings, spin lattice relaxation rates and half height line width shave been carried out at different relative humidities. Furthermore, the spin-lattice relaxation rates at 86%relative humidity were measured in the frequency range 2-62 MHz for the bleached kraft pulp, unbleached liner board pulp and for a microfibrillated cellulose sample. The relaxation rates show a strong dependence on the resonance frequency. The reorientation of the water molecules adsorbed on fibers can be described by two corrletion times ofthe order of 10 ns and 50ps respectively. Analysis of the experimental data does not show any effects of beating on the cellulose water interaction strength. All observations made can be explained by morphological changes of the fibers.