Proceeding Articles

The conclusions of many studies on material policy emphasise the need for materials conservation and more efficient utilisation of materials. Recycling of municipal waste is an alternative to solid waste disposal and a means for conserving our natural resources. Although the benefits from recycling are many, there are technological and economic barriers to large scale recycling in the private sector. Unless these uncertainties are removed, increased recycling will occur only when no other alternatives exist.

I believe that the most difficult and complex area in the fibre science of paper-making is precisely the theme of the present conference. This is because the subjects we have addressed owe their existence to the interaction of a trinity of complex entities: (1) water, (2) cellulose, and (3) the structure of fibres and paper.

In closing this symposium I have three things to say. The first is to thank you all for your contributions, both in public and outside this lecture theatre. The stars who were expected to shine have not disappointed us; the others of less renown have either had their say or listened and learned. Everyone has worked hard and I thank you all.

The second is the matter of the subject for the next symposium. It will take place in September 1981, probably in Cambridge. We have not yet agreed upon a form of words for the title, but we are fairly well agreed about what we mean. The idea we have is to discuss how we can use our paper science to decide what properties we require from our raw materials and exactly how they should be processed in order to obtain the specified product. Ladies and Gentlemen. Finally it only remains to wish all of you a safe journey home and to hope to meet you all again at our seventh symposium.

It is wrong to consider that there is anything unique in the conducting of research (and development) in the paper industry. The only difference between this and other industries, is the management attitude which has resulted in the situation described by Ron Allan in his paper (1).

Research demands a combination of the correct organisation, able people, and insight. Insight is a rare characteristic: it is the one that distinguishes “great captains” from mediocre generals.

In managing research for productive ends the rules are the same as for any other management task, but the boundary conditions are different.

My lord, ladies and gentlemen, sixteen years ago, we met in Cambridge on the occasion of the first international symposium organised by the Fundamental Research Committee of the Technical Section of the British Paper and Board Maker’s Association. The subject was The Fundamentals of Papermaking Fibres.

How honoured I am to be asked to address this symposium.

Most administrators are agreed that the decision on the ‘right’ amount of  money to spend on research and development is an art rather than a science. Here, I am quoting from the recent report by Lord Rothschild. Whether or not one agrees with his conclusions-and, from the fur and feathers that flew at the time of the publication of his report, it was obvious that some did not this statement is hardly likely to be challenged, as many of us have found to our cost when faced with making or advising on such decisions. In desperation, one can search for the magic formula, but all too often (when found) it turns out to be a paragram compounded in equivocation.

Not only is one faced with the question of how much to spend, but also the interrelated question of what to spend it on and where.

Three terms that refer to the distribution of local grammage in the plane of a sheet of paper are introduced-the intensity, macroscale and microscale of mass distribution. The measurement of these quantities by an optical method and by beta radiography is discussed. Data are obtained by a specially designed microdensitometer and analysed by a frequency analyser. Results are presented as wavelength spectra of mass distribution.

Experimental spectra for handsheets and machine-made sheets are compared with theoretical spectra for sheets composed of fibres having randomly distributed orientations and positions. It is shown both theoretically and experimentally that it is important to use a small measuring area.

A poor mass distribution is demonstrated to have a negative influence on the scattering coefficient and opacity of paper. It is shown how the mass distribution and other paper properties affect the visual appearance of multi-ply board and the lookthrough and print-through of paper. The concept of mass distribution is extended to the distribution of ink on paper. The connections between the mass distribution of ink and the mottle of the prints are discussed.

Finally, the adverse effect of a poor mass distribution on the strength properties of handsheets and machine-made sheets is demonstrated using recent (partly unpublished) experimental data by Cavlin & Rudström.

In any attempt to predict the durability or runnability of paper in its end uses, a means must be sought that is capable of measuring minimum strengths. Through the use of double exposure interference holography, an analysis is made of the strain variation of newsprint webs under critical tensile loading conditions. The coefficient of variation of strain is compared with formation values, which ideally should be measures of mass distribution. The QNSM, MK Systems and STFI formation testing instruments were used for this purpose and it was found that, in the case of the latter instrument, the index of determination of strain variation could reach 0-81. An assessment of the thermal uniformity of paper webs during tensile straining is facilitated by a liquid crystal thermal analysis and it is found that paper exhibits a particularly uniform distribution of temperature suggesting a constant work field model. While the influence of web defects on strength uniformity is briefly examined in this work, reference is made to a more detailed study to be found in another contribution to this symposium.

Concerning Lyne & Hazell’s paper, Formation testing as a means of monitoring strength uniformity, particularly with reference to the use of holographic interferometry, we wish to make the following comments.

In the theoretical part of this paper, the Tsai-Wu tensor theory is used to determine the equation for the biaxial strength envelope of a material.

One great advantage of using the Tsai-Wu theory for investigating biaxial strength envelopes is that it may be transformed to arbitrary co-ordinate axes by means of tensor transformation laws.

In the experimental part of the paper, the strengths in compression and shear are evaluated using thick-walled tubes consisting of two layers of paper glued together with a non-penetrating glue. In addition, the strength of paper under biaxial stress is determined by subjecting paper tubes to axial tension or compression combined with a radial tension caused by internal pressure.

In the final part of the paper, the application of the Tsai-Wu tensor theory to the prediction of failure of a corrugated container is discussed, as well as practical means of limiting the number of experiments necessary to establish the biaxial failure envelope of paper.