2009 Volume 2

The literature related to the three-dimensional fibre networks is reviewed since 2000. Indeed, a review was presented in these symposia in 2001 [1]. Therefore, the updated articles are only considered here. The previous review concentrated on theory, whereas the focus here is on modern 3D analysis and comparisons of these with theory. Moreover, the focus is on paper structure. However, the general context of 3D structure is considered in the introduction in order to illustrate the main ideas that may be applied to paper. Then, the experimental methods are presented in order to show the potential of such techniques. In a third part, improvements of the description of the 3D structure will be presented. Namely, the quantitative description that completes the visualisation of the structures will be presented. The main 3D morphological properties will be presented and some examples will illustrate the existing developed tools. The Representative Elementary Volume (REV) dedicated to the structure properties will then be introduced. The theoretical models are briefly presented to prove the necessary development of both experimental tools and dedicated theories. Theoretical studies will be exemplified. Indeed, both theoretical and experimental demarches will enrich each other as will be shown. The influence of both deformation and humidity modifications on the 3D structure will illustrate the interest of the knowledge of the 3D structure, to tackle its influence on physical properties. The main perspectives and challenges related to the structure description will end up this presentation.

We use simulation and analytic modelling to probe the structural similarity reported in the literature for fibre networks with manifestly different degrees of uniformity. From simulations of point processes in the plane to represent random, clustered and disperse fibre centres, we show that the distribution of distances between pairs of centres is very insensitive to the extent of clustering. Further, we quantify the correlation between the lengths of adjacent polygon sides arising from a Poisson line process in the plane as being ρ = 0.616 ± 0.001 and show that this is very insensitive to fibre orientation and only weakly influenced by clustering. The relevance of this correlation to pore geometry is discussed.

In the final part we analyze simulated areal density maps and show that their variance relative to that of a random fibre network of the same constituent fibres, as quantified by the formation number, depends at small scales on the flocculation intensity only and depends at large scales on the number of fibres per floc only.

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In this study, a new technique for producing almost fully aligned paper sheets was developed, and the resulting sheets were used to test the validity of the theory most commonly used to relate zero-span tensile strength to individual fibre strength. The standard theory predicts that a zero-span test of a sheet with randomly oriented fibres should yield a breaking load equal to 3/8 of the load that would be observed if all the fibres were aligned in the direction of loading. It is widely used, in spite of the fact that the underlying assumption of affine deformation is questionable under true zero-span conditions. The results obtained here suggest that the fibre strength may be overestimated because inclined fibres in a zero-span grip actually contribute more than the theory predicts. However, the results also suggest that this effect may be confounded because other factors lead to a variable contribution of individual fibres to the zero-span strength of the sheet.

This document reviews degradation phenomenology and life modelling of paper, illustrates different approaches, showing their advantages and applicability limits and raises problems relevant to practical applications of degradation indicators and degradation rate models and evaluation of paper permanence and durability. It deals with the fundamentals of paper degradation rate theory and life modelling, seeks to develop the degradation rate equations of paper that will closely track real degradation experimental results over extended period under practical service conditions, shows a collection of degradation rate and life data of different paper and paper insulation materials under a varied of in-service environmental conditions, develops continuous distribution kinetics theory of cellulose and paper degradation to form a united basis in deriving the traditional Ekenstam degradation rate equation and the alternative percentage DP (and TS) loss rate equations recently proposed by the present author and his coworker, and presents effective methodology for combining time temperature superposition method and paper degradation investigation towards a more reliable prediction of rate and life of paper degradation over a long time period under real in-service conditions.