Proceeding Articles

A subjective evaluation of the role of fundamental research in the manufacture of paper over the past 25 – 30 years traces the roots of some important inventions back to fundamental research endeavors. During this time, technical progress in paper manufacture has been both rapid and multifaceted. Fundamental research in relevant areas has resulted in higher productivity, improved process and product control, and better design of the paper-making process and the associated equipment.

These improvements clearly indicate an important role for collective efforts, guided by ‘far-sighted industry leaders, in the area of fundamental research. The assignment of scientists by industry leaders to carry out this research in areas recognised as bottlenecks to technical development appears to have led to many of the important developments. Because improvements to the paper-making process are expected to yield returns to the paper industry, the responsibility for initiating, funding, and guiding fundamental research in appropriate areas must rest with the paper industry.

Symposia of a fundamental nature have been important in reviewing the state of the art, thereby exposing not only knowledge but also the notable lack thereof in essential areas .

Recent trends in structural design theory and material science are reviewed and discussed in relation to research on the mechanical properties of paper and board.

Quality control, statistical quality control, process control, total quality, are some of the phrases used to describe a function that varies considerably from one manufacturer to another and from one author to another. This paper attempts to review the changes in the concept of quality control that have resulted from the application of research programmes.

The historical scenario has three aspects. Just before the war an awareness was arising of the fact that paper was variable and that the variability had two components: along and across the machine. During the war paper had to conform to the same acceptance procedures as a raw material as did other military supplies. Thus the concept of statistical quality control was developed which, whilst recognising the need to relate property levels to the underlying variability, nevertheless used methods more adapted to discrete units of production rather than to a continous product.

It was not until after the war that major studies were undertaken, in the golden era of paper research, into the variability on the macro- and micro-scale of the paper product. This was the period of the awareness of the need for uniformity and freedom from mechanical defects, particularly in paper for high speed letterpress and gravure applications. The results of detailed study into the heterogeneity of the sheet prompted the development of instruments which would enable fundamental properties to be measured.

The result of two decades of fundamental work, not by the paper industry but by the process control industry, is the current situation of integrated measurement and control, which is described in some detail. Finally, the ability to know precisely what is being made has resulted in the concept of total quality.

Such a survey would not be complete without some reference to the development of product quality standards and specialised tests which relate to end user requirements. These, however, whilst constituting a major factor in the industry’s research programme, are, in the authors opinion, of less importance in comparison to the extraordinary developments in process control made by firms specialising in that function.

Acknowledgements are made to very many people throughout the
industry who have helped in this survey.

The need to make the best use of wood supplies, conserve energy, and reduce the costs of pollution abatement has stimulated research to improve the yield, accelerate the rate, and reduce the odoriferous nature of kraft pulping. Because the structure of lignin is imperfectly understood, the quest for reagents which can accelerate delignification has been handicapped. In contrast, because the structure and reactions of cellulose and other wood polysaccharides are known, deductive methods have been applied in the search for reagents which can protect these polymers from alkaline degradation and thus improve pulp yields. The discovery of the dramatic accelerating effect of anthraquinone on alkaline delignification can, in fact, be traced back to a series of investigations which began with a search for reagents capable of inhibiting the alkaline degradation of cellulose. Against this background, research on pulping additives in reviewed, with particular reference to the current status and potential of catalytic accelerators in alkaline pulping.

The basic mechanism for the development of an irreversible swelling hindrance is discussed. It is demonstrated that changes in cell wall structure caused by pulping, chemical modification and straining during drying influence the ability of fibres to reswell after drying.

The results indicate that structural alterations take place during the drying of a cell wall. It is suggested that the basic phenomenon is the irreversible closing of cell wall pores. This essentially leaves a fibre wall which is more resistant to the mechanical treatment which promotes swelling and more prone to fragmentisation and the production of fines.

A study was undertaken to assess the suitability of wheat straw to be pulped by means of the alkali-oxygen cooking process. The effects of some cooking variables, such as oxygen presence, type and amount of alkali, cooking temperature and time, on yield and Kappa number were evaluated.

The alkaline cooking of wheat straw in the presence of oxygen results in increased delignification. This is especially marked when the alkaline agent has a poor delignification capacity (sodium carbonate or bicarbonate). Thus oxygen seems to be very well suited to use in cooking processes with sodium carbonate liquors.

The use of such liquors can bring about a very interesting simplification of the recovery process.

In the second part of the work the influence of oxygen on pulp properties was evaluated as a function of the alkali used and of some cooking variables.

It is shown that the use of oxygen in alkaline cooking results in fibre degradation which affects the strength properties of the unbleached pulps only in the case of caustic soda cooking. The presence of oxygen during carbonate (or bicarbonate) cooking has favourable effects on pulp strength properties. This behaviour can be attributed to the fact that, in the case of carbonate cooking, the increment of delignification due to oxygen is far superior to that obtained in caustic cooking.

At equal delignification levels, the oxygen-carbonate pulps show better strength properties than the oxygen-caustic pulps. Long cooking times usually result in negative effects on strength properties.

The use of magnesium ions as inhibitors of carbohydrate degradation, had no definite effect on yield, viscosity, or strength properties.

The theme of this paper is a comparison of the role, properties, and technology of fibrous paper-making raw materials other than wood, with those of wood. Aspects considered are the economic role in world pulp supplies, the nature and properties of the fibres, technological problems arising in pulping, the properties and economic status of the resulting pulps, and the present and likely future of fundamental research.

To the vast majority of those connected with paper manufacture “cellulose pulp” is instinctively synonymous with wood pulp, especially in North American and Scandinavia. The aim of this paper is to redress this tendency, in particular from the point of view of the title of this Symposium. This is attempted by a comparison from all relevant aspects of the role, properties and technology of fibrous cellulose paper-making raw materials other than wood with those of wood. Thus, non-cellulose fibres (as of asbestos or glass) and modified cellulose fibres (usually derived from wood) are excluded.

This paper presents the results of an experimental and theoretical investigation into the fundamental mechanisms that govern ultrasonic propagation in fibre slurries. An experimental apparatus which measures the attenuation and velocity of ultrasound in slurries is described. Measurements on wood fibre slurries show, in contrast to previous work, that the effect of the fibre on the velocity of ultrasound is negligible. This observation led to the development of an isolated segment model, which can predict attenuation as a function of fibre properties and ultrasonic frequency. The theory assumes the fibres are isolated, isotropic, infinite cylinders. It accounts for scattering, heat conduction, viscous losses in the fluid, and relaxation processes in the fibre. Experiment and theory are shown to be in good agreement for some synthetic fibre slurries. In the more complicated case of wood fibre suspensions, the theory predicts attenuation to the correct order of magnitude and permits speculation about the effects of fibre properties.

The relationship between the torsional and flexural rigidity of single fibres, and the flow resistance of pulp suspensions was investigated from the point of the flocculation process.

The torsional and flexural properties of wetted single pulp fibres were measured by the torsional pendulum method and by the bending method respectively, for chemical pulps. A new experimental apparatus to measure the flow resistance of dilute fibre suspensions to rotary motion was developed in our laboratory.

A good correlation between torsional rigidity and the flexural property of single pulp fibres was observed, and the flexibility of fibres was found to increase intensely during the early stages of beating.

It was found that wall-shear stress, motion decay times, and the shapes of the motion decay curves of fibre suspensions depended on the flexural properties of the fibres, their length, and the concentration and temperature of the suspension.

An apparatus for studying the dynamic compression of saturated paper sheets is described. The apparatus can generate various combinations of haversine and square wave press pulses. The dewatering during a full loading cycle is studied, that is in both the compression and expansion phases. The total applied load, the hydraulic pressure and the thickness of the sheet are simultaneously recorded during the pressing operation. A total pressure of 10 MPa can be applied in pulses of durations as low as 5 ms. The techniques for hydraulic pressure and thickness measurement are examined. The performance of the apparatus is demonstrated and results from press tests with sheets of different grammages and different degrees of beating are given.