1997 Volume 1
The purpose of this paper is to present as complete as possible, a picture of our present knowledge about papermaking fibres and their physico-chemical characteristics. The properties of the papermaking fibres are, in most cases, significantly influenced by the morphology of the wood fibres, but, from one and the same kind of wood fibres, paper can be produced with widely different properties as a result of different pulping and papermaking processes. Dissolution of material from the fibre wall and the middle lamella, structural changes of the polymeric material, and mechanical work on the fibrous material (defibration, refining, and to a certain extent undesired mechanical damage to the fibres in the pulp mill machinery) combine to produce the fibre properties required in the papermaking process.
Starting from the structure of the wood, a survey is given of the pattern of dissolution of different important pulping processes and the resulting bulk composition of the pulps. Characterisation of papermaking properties should include effects of both bulk and surface of the fibres and for that reason they are both discussed. The bulk composition has been studied for many years and we have a fairly good knowledge of the main features, although there is still a need for more detailed knowledge. The properties of the fibre surface are less known, but they have been the subject of several recent studies. They are therefore dealt with in more detail, particularly the problem of making reliable and relevant measurements.
Dissolution of lignin and other components in the pulping process is also important for the chemical composition of the surface. Mechanical removal of the remaining middle lamella and the outer layers of the fibre wall (the primary wall and SI of the secondary wall) substantially change the surface composition and create fines with a large surface area, which may interact with the wet-end chemicals in the paper mill and decrease the over-all effects of these chemicals. Removal of the outer layers will also change the fibre properties as a whole since, for instance, the SI layer restricts outward swelling of the main part of the secondary wall, S2, and preserves fibre rigidity.
Swelling of the fibres influences there fining behaviour of a pulp. For lignin-containing pulps, swelling facilitates refining. For bleached pulps with a very low content of residual lignin, the effect of swelling on refining is rather difficult to as will be briefly discussed.
There are many chemicals, both natural and synthetic, which are used for surface application of paper and board. In this overview shall the use of starch and protein be discussed as representatives of products arriving from renewable resources and the use of latex as there presentative of products arriving from chemical synthesis. Starch is used for coating of paper both in combination of pigments- coating colours, and for surface application in size press, film press or other application units. As the influence of the starch properties -both from the chemical and from viscosity point of view is of great importance for the runnability of the machines and the paper quality, will starch quality be discussed to a great extend. The influence of starch quality on the rheological properties of coating colours of the different types of coating colours will there after be discussed. Protein and latex are mainly used as binders in coating colours. The influence of the chemical and physical properties of these binders on the pigment- binder interaction and the subsequent paper properties will be discussed as far it is possible from a general point of view.
Fundamental aspects on polymer adsorption and flocculation phenomena are reviewed. Special emphasis is placed on recent developments. Examples are the mode of action of microparticle retention aid systems and of retention systems based on polyethylene oxide/phenolic resin.
Fibre flocculation and the strength of fibrous networks are affected by retention aids and this is discussed in,connection with investigations on retention and formation in the laboratory and on pilot-scale paper machines.
Cambridgepp 473-503Transverse Dimensions of Wood Pulp Fibres and Their Implications for End UseAbstractPDF
The transverse dimensions of pulp fibres influence strongly their response to the papermaking process, and most end-use properties of products. However, fibre transverse dimensions are difficult to measure. Confocal microscopy combined with image analysis has been used for rapid and accurate measurement of fibre wall cross-sectional area,perimeter, and thickness. Results on kraft pulp fibres obtained from a variety of wood species are presented. They demonstrate how fibre transverse dimensions are distributed within a species, and can be described analytically. Comparison between different species shows that species with coarse or thick-walled fibres are likely to be more heterogeneous. Implications for pulp quality and fibre selection for end-use requirements are discussed.
Cambridgepp 439-472Genetic Selection of Trees with Designer Fibres for Different Paper and Pulp GradesAbstractPDF
Pinus radiata and eucalypts are fast-grown species, well suited to plantation forestry in New Zealand and elsewhere, and for the manufacture of a wide range of solid wood and reconstituted wood products, including pulp and paper.
This paper examines the variation and end-use potential of the individual-tree kraft fibre and handsheet properties of 25 trees of 13-year-old P. radiata and 29 trees of 15-year-old Eucalyptus nitens. Individual-tree fibre property differences are assessed with reference to the fibre quality requirements of a range of wood-free paper grades. Strategies and procedures are also described which will enable parent trees with desired fibre properties to be identified, propagated and mass produced.
In selecting fibre types for different paper and pulp grades, the apparent density of “unrefined” pulps(500 PFI mill rev) is the base against which other “unrefined” handsheet properties are compared. Apparent density is a direct measure of fibre packing density and arrangements in handsheets, and is determined by fibre length and cross-section dimensions, and the related morphological configurations of collapse and straightness. Although the individual-tree pulps of both species can normally be refined to the same tensile index, apparent density values can be very different depending on their fibre properties. Thus, minimal pulp refining is preferred for comparing individual-tree pulps for trees election.
Apparent density is best predicted by the kraft fibre property combination of the fibre width/thickness ratio and length. The combination of chip basic density and kraft fibre length is also a good predictor of handsheet apparent density but not necessarily of the best fibres for the manufacture of particular products. Wood density is a measure of the ratio of wood substances to void space in each individual-tree chip sample and is not indicative of the numbers of fibers which make up a unit volume.
Kraft handsheet propeties varied widely among trees for both species and were well-predicted by kraft-fibre dimensions. The high broad-sense heritabilities shown for these traits in P. radiata mean that clonal forestry could provide pulpwood of uniform and predictable pulping performance from monoclonal forest blocks. The high narrow-sense heritabilities shown so far for wood properties in P. rafiata (and for some wood properties in E. nitens) indicate that planting control-pollinated families of known characteristics could have a similar though less uniform result.
Cambridgepp 505-519Raman Spectroscopic Analysis of the Microdeformation in Cellulosic FibresAbstractPDF
This paper addresses the application of Raman spectroscopic techniques to analyzing the deformation micromechanics of regenerated cellulosic fibres. In addition to information obtained on the macroscopic deformation, Raman spectroscopy enables the study of changes in internal strain associated with creep and recovery. The analysis of the mechanics of deformation of the fibres begins by following the response of the Raman-sensitive bands to external tensile loading. It is shown that the peak positions of the 895 cm-1 and 1095 cm-1 Raman bands shift to lower vibrational frequency under the action of tensile stress or strain due to the macroscopic deformation leading to direct stretching of the polymer molecules. Moreover, this approach makes possible the modelling of single fibre properties using simple viscoelastic dynamics; thereby relating the macromechanical properties of stress and strain to those obtained at the microscopic level via spectroscopy.
In this review paper, the concept of structural hierarchy is applied to paper in an effort to establish the role of the fibre in the structure of paper . The structure of paper is partitioned according to the size or scale of the features of interest, and the basic nature of a generic paper physics research project is shown to be independent of the scale being considered. The literature dealing with paper structure and properties at each significant scale is briefly introduced, and the similarity of studies at quite different ends of the spectrum is highlighted. The prospects for an integrated model relating a mechanical property such as modulus to structural variables alone are discussed. Throughout the emphasis is on mechanical properties, and the central role of the fibre within the structural hierarchy.
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