Proceeding Articles

The paper converting process forms part of that whole area of engineering known as conversion technology, which applies the rules and procedures acquired in converting to the manufacture of finished products from paper and board.

The resulting conversion techniques consist of a sequence of sub processes in which certain changes in the state of the materials are brought about. The sum of these changes leads from the raw materials paper and board up to the final products.

For the reshaping, separating and connecting processes covered by this report, the specific characteristics and physical principles will be described and the main options of technical realisation discussed. In a number of applied examples, details of the real physical mechanisms encountered in the individual processes will be gone into.

The state of knowledge just set out is required for optimised designing of paper and board articles as well as of the necessary procedures and machinery. It is furthermore an absolute necessity with a view to realising the best possible manufacturing processes whilst taking ecological and work hygiene considerations into account and putting the means of production to economical use

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The effect of titanium dioxide, kaolin, calcium carbonate and talc on the properties of foams formed by sodium oleatelsodium stearate solutions and the flotation yield of these pigments in the presence of the same soaps have been investigated. In addition, the flotation of dispersed model coatings prepared from these pigments with styrene-butadiene and polyacrylate latexes was studied. The influence of coating colour composition and flotation chemicals (including silicate) was investigated using factorial experiments. The latexes strongly increase pigment floatability, but the effects are interrelated with the effects of other components in the coatings in a complex way. The flotation yield of the different pigments depend quite differently on the amounts of calcium and silicate added. This indicates that it may be possible to achieve flotation selectivity by proper design of flotation strategies. The factorial experiments also make it possible to draw some tentative conclusions with regard to mechanisms giving rise to the observed effects.

The pulp and paper industry has a fantastic potential to become the first and possibly the only truly “evergreen” industry. Our raw material is renewable, we apply sustainable forest operations, within the next decade our mills will be ecologically balanced, and our products are non-toxic and recyclable.

It is up to ourselves to “do-it-ourselves”, to take charge and to find new solutions which will prepare us for a future full of trend-breaks.

The key is knowledge and competence. Our fundamental task is to build up the knowledge-base that will be necessary if we are to proceed and if we want success.

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.

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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.

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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.

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.