1985 Volume 1
Emphasis on the tissue culture propagation of forest tress has increased dramatically. Tissue culture methods available to forestry and the pulp and paper industry are micropropagation, organogenesis, and somatic embryogenesis. Somatic embryogenesis, although more difficult to accomplish, seems to have the most promise for use with forest trees because (1) when appropriately employed it can be a true mass production procedure and (2) the approach can be used efficiently with several genetic engineering techniques. Major genetic gains in growth rate, wood quality, insect and disease resistance, and improved climatic adaptability are anticipated when tissue culture techniques are used in conjunction with genetic engineering. Emphasis in The Institute of Paper Chemistry’s tissue culture research is on the development of a somatic embryogenesis procedure for conifers.
The forming of the web in a paper machine is a highly dynamic process in which the dynamic mechanical properties of the web in the x, y, and z directions are each of central importance for both the process operation and the properties of the final product. The properties in the x and y directions, such as the dynamic tensile stiffness and stress relaxation, affect control of the draw in open draws, web flutter, and stress variation. The dynamic mechanical properties in the z direction affect the behavior of the web in the press section and the post-press dry solids content. All these features are also related to the properties of the final product.
Laboratory research on the dynamic mechanical behavior of wet webs has been carried out with special equipment designed to simulate the paper production process, particularly its dynamic characteristics. The draw and press simulators have been built to monitor and handle properties related to the dynamic mechanical behavior of paper. The draw simulator has been used to study dynamic tensile stiffness and visco-elastic component of the web during drying. The press simulator has been used to monitor the compressibility and pressure in the web as a function of different press impulses and wet pressing temperature.
This paper reviews current knowledge of pulp flocculation over the entire range of consistency found in pulping and papermaking, from dilute suspensions of fibres in water to dry fibres suspended in air. Some of the key factors that govern flocculation in low consistency aqueous suspensions are shown to apply with changing emphasis over the entire consistency range. Several recent findings from our laboratory that fill gaps in current knowledge are also reported.
The z-direction (ZD) elastic properties of paper have received little attention in the past because of measurement difficulties. This paper describes the effects of wet pressing, refining, and yield on three ZD elastic properties, C33, C44, and C55. The elastic parameters were measured using ultrasonic methods on an unbleached kraft oak pulp. The ZD elastic parameters were very sensitive to wet pressing pressure. Increasing the level of refining or decreasing pulp yield produced increases in C33, C44, or C55, which were greater than would be expected by wet pressing alone to the same density. A plausible explanation for this behavior is that the refining and yield changes also significantly change the ZD stiffness and shear stiffness of the fiber cell wall.
Experimental and theoretical measures of flocculation were studied using image analysis. An experimental study of commercial board samples led to the proposal of three descriptive floc features, namely, size, ‘definition’, and contrast. Numerical values were obtained from an ensemble averaged linear auto-correlation function.
In addition a theoretical model of formation was simulated to compare degrees of flocculation. The theoretical structure was created by using a poisson cluster model in conjunction with a coverage model. This led to the superposition of fibrous micro0-flocs whose flock centre radii, R, and fibre content, N, determine the severity of the formation. The variance and p.t.p correlation of the resulting image textures were computed. These measures were found to have a lower limit which is set by the fibrous structure of the flocs.
The findings from the simulation study were then applied in principle to the variance and size information extracted from the board samples to explain their structure. The versatility of programmable image analysis systems was demonstrated for formation measurement.
High resolution ¹³C NMR of crystalline celluloses is both complementary and supplementary to x-ray diffraction analysis because it is effective both for crystalline an non-crystalline materials. Good spectral quality has been achieved for a range of cellulose samples and spectral elements related to lateral order are observed but some interpretational details are still evolving.
The spectrum of a complex material such as wood, shows morphological and conformational features for each chemical component. The resolution achieved is sufficient to allow identification of carbohydrate resonances, methoxyl, and aromatic resonances and methyl and carbonyl resonances of hemicellulose acetyls. The effect of solid state chemical treatments such as acetylation and prehydrolysis are readily detected. The use of interrupted decoupling allows one to separate the lignin and cellulose components of the spectrum.
The potential of the technique for rapid ¹³C NMR analysis of paper debris, coated sheets and insoluble resins is now becoming well-established. More complex biosubstances such as grasses, bark, and plant cell wall are being molecularly examined in their true nascent state for the first time. In this paper, a series of spectra are presented covering the various physical states of Esparto grass: native, holocellulose, alkali extracted, pulp; these spectra are compared to Esparto xylan. The line broadening effect of the latter on the C-1 resonance of cellulose demonstrates the difficulty in interpreting effects of fine structure vs. heterocomposition.
The thermal conductivity of paper was measured using a thermoacoustic method based on the propagation of a periodic temperature wave in the medium. Thermal diffusivity and thermal conductivity can be calculated from the resulting phase shift.
The thermal conductivities of sheets prepared from different pulps were measured under standard conditions and at 70°C and 10% RH.
In paper, heat is conducted through both the solid phase and the gaseous phase. In the case of dense paper and at high moisture contents, heat transfer due to diffusion of water vapour makes a major contribution.
The results were used to construct a qualitative physical model for the conduction of heat in paper. In the normal paper density range of 400 – 900 kg/m³ heat conduction can be explained in terms of layers of air and solid phase connected together in different ways.
At higher densities and higher moisture contents the mechanisms of hear conduction change.
The heat conduction characteristics of paper are better explained using thermal diffusivity calculated in terms of basis weight than by using thermal diffusivity and thermal conductivity.
Oxfordpp 93-131Qualities of Kraft and Thermomechanical Radiata Pine Papermaking FibresAbstractPDF
This review examines the extent to which wood property variation in New Zealand’s radiata pine resource determines pulp quality. The qualities of radiata pine papermaking fibres are very dependent on their original position within a tree (growth rings from pith and/or height in tree), as well as the geographic altitude and latitude of sites on which the trees are grown. Two categories of radiata pine pulpwood are recognised in New Zealand: slabwood of high basic density from the outside of sawlogs; and corewood of relatively low basic density from the smaller logs (non-sawlogs) of the upper part of a tree and from whole-trees less than 20 years old.
The kraft pulp fibres from corewood are shorter and have thinner walls than corresponding fibres from slabwood, but the diameters of these two fibre populations are essentially identical. The handsheet properties (apparent density, and burst, tear, and tensile indices) are strongly correlated with, and can be predicted from, the wall thickness:diameter ratio of pulp fibres or the basic density of the wood sample pulped. These trends hold for whole trees of different age, for parts of trees, and for commercial pulpwood and slabwood material obtained from throughout New Zealand.
Mechanical pulps can be correlated with wood properties to a lesser extent than are kraft pulps. In thermomechanical (TMP) pulp production, slabwood consumes more energy to a given freeness and produces pulps of higher strength than corewood. Pulps from corewood, however, have excellent optical properties whereas those from slabwood are of slightly lower quality. These differences are partly explained by the very different qualities of slabwood and corewood fibres and fines. Slabwood TMP pulps are rich in fibrillar fines, which have a strong consolidating influence on the long and relatively stiff fibres of this furnish. Alternatively, corewood fines are of a more heterogeneous arid coarse quality (and have a lesser consolidating effect on fibres which are shorter and more collapsible than corresponding slabwood fibres) and therefore pack more tightly within handsheets. The handsheets of corewood pulps have excellent optical properties since the fibres and fines of this furnish give more air-to-fibre and air-to-fibre element interfaces than do those of corresponding slabwood fibres and fines.
An analysis of published work, together with new data, has clarified the effect of chemical composition on the strength of wood pulp fibres. Among fibres of low fibril angle, and in nondegrading pulping processes, strength (expressed as breaking stress) is directly proportional to α-cellulose content over a wide yield range. This implies that the cellulose fibrils are the sole tensile-load-bearing elements; hemicellulose and lignin only serve as a matrix that transfers the stress under shear from fibril to fibril. However, pulping to a yield corresponding to an α-cellulose content higher than 80% tends to reduce fibre strength apparently because of the elimination of this stress-equalizing matrix. In cellulose-degrading processes, fibre strength falls below this expectation to an extent dependent upon the degradation. Thus a tool is provided that permits the degradative effect of new pulping or bleaching processes on fibre strength to be assessed. The value of zero-span strength as an index of fibre strength is confirmed.
Our studies of cellulose structure based on X-ray diffractometry, Raman spectroscopy, and Solid State ¹³C-NMR have led us to a model which addresses questions of structure at two levels. The first is that of the organization of individual chains. Two stable ordered states of cellulose chains are postulated, together with a disordered state in which there is less coherence between the orientations of adjacent anhydroglucose rings. The ordered states are identified as kᵢ and kᵢᵢ based on their predominance in celluloses I and II, respectively; both conformations are based on the dimeric anhydrocellobiose as the basic repeat until in the ordered chain. The disordered state is identified as kₒ.
The second level of organization is that of aggregation of chains into three-dimensionally ordered crystalline domains. At this level our model recognizes two crystalline forms within the native state. These are identified as Iα and Iß, the first found to be dominant in bacterial and algal celluloses, the second dominant in celluloses from higher plants. These two forms are found to contain chains possessing the same molecular conformation ᵏI, but the patterns of hydrogen bonding are found to be different. Cellulose II, which is derived from the native state by mercerization or regeneration at low temperatures, is found to consist predominantly of chains in the ᵏII conformation in yet a third distinct crystalline lattice.