Proceeding Articles

Mill-made deinked pulp fibres for news print were compared with virgin single pulps in terms of pulp properties. The results showed that fundamental fibre properties ,which had been proposed by many researchers, were useful for the characterization of deinked pulp, provided their fractions were compared. Possible reason for this is that fractionation sorts the fibres, and in this way helps to characterize the complicated fibre composition of deinked pulp. Notable characteristics of long fibres of deinked pulp seemed to be fibre coarseness , wet fibre flexibility and curl or kink as well as fibre swelling. These results suggested that the characterization of mill-made deinked pulps with these fibre properties should be carried out by taking the fibre types into account. For this reason, a new method for the determination of fibre composition has been proposed. It provides good results within a certain range of pulps, but further studies are required to devise a more sophisticated method

Modern high yield pulps, typified by chemithermomechanical pulp (CTMP), are likely to be used increasingly for printing, writing and publication grades where longevity is a major consideration. This paper reports an investigation of the ageing of papers containing CTMP, and sized both with rosin/alum and alkyl ketene dimer(AKD) systems, using paper made specially for the study on a pilot papermaking machine. Emphasis was placed on mechanical properties, in view of the concern of librarians and archivists with the embrittlement of paper due to acid hydrolysis of the cellulose. The results show that use of CTMP has a negligible effect on rates of loss of strength; in a series of papers containing various proportions of CTMP with a bleached softwood sulphate pulp, sized with AKD, the rate of degradation was very similar, and acceptably low. Naturally, the papers containing CTMP are not initially as strong, and will become yellow on exposure to light; in judging whether or not such papers are acceptable for long term use, all these factors need to be considered with respect to particular applications.

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Three-dimensional topographical maps of paper surfaces under load have been quantified using the confocal laser scanning microscopy. Distributions of the paper surface pores of the same area under different loads were evaluated by the Equivalent Surface Pore (ESP). The ESP roughness of the uncompressed and compressed surfaces of TMP and bleached kraft papers, calendered to the same Print-Surf roughness with different calendering processes, were used to evaluate the local static compressibility of these paper surfaces. Assuming an exponential decay of roughness with pressure, the local static compressibility is defined as the slope of the roughness as a function of the logarithm of the applied pressure. Upon calendering, the local compressibility of the paper surface decreases. The compressibility after calendering depends both on the calendering process and on the furnish. The stiffer TMP fibres present more residual compressibility than the kraft fibres, already pre-collapsed in the uncalendered sheet. The surface compressibility increases with the internal pore volume. The calendered papers were gravure printed at different printing pressures and the number of missing dots counted. A theory is developed which links roughness to ink coverage. It is proposed that roughness is linearly related to the logarithm of the number of missing dots where the slope represents the surface compressibility. Theoretical derivations have been experimentally verified. It was also found that the static roughness is linearly related to the dynamic roughness.

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Fracture toughness is a material’s ability to resist propagation of a preexisting crack. In most end uses where fracture,toughness can be an important performance parameter for paper, stresses are applied in the plane of the sheet. Therefore, like tensile strength and elastic modulus, the fracture toughness of paper should be measured under in ‘ -plane loading. Our current industry practice of measuring the out-of plane tearing resistance by the Elmendor for Brecht-Imset tests seems inappropriate. Several techniques of fracture mechanics have been applied in recent years to characterize the plane stress fracture toughness of paper. An important consideration is whether a material property was measured particularly for tough papers.This contribution provides a background on these techniques.

We study the strength of paper using computer simulations. Our model is a stressed mechanical 2D random fibre network (RFN), the equilibrium of which is computed using a commercial FEM (Finite Element Method) solver Abaqus. The novelty in our approach lies in more detailed introduction of mechanical properties of fibres and bonds into the mechanical model, enabling the study of effects of microscopic (fibre/bond – level) properties.on relations between macroprocessor properties.

The mechanical properties of fibres and bonds are defined by Young’s modulus (or moduli in anisotropic case) and stress displacement curve. In our video presentation, fibres are purely elastic whereas bonds are elastic-plastic. The video shows the behaviour of network being stressed by forcing increasing displacement on one boundary