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Termodynamiczne ujęcie procesu starzenia się papieru: Część III. Dyskusja nowego sposobu oceny odporności papieru bezkwasowego na starzenie

Gonera H., Dąbrowski J.

Przegląd Papierniczy

2010

R. 66, nr 10

589-595

Artykuł stanowi uzupełnienie dwóch poprzednich publikacji (por. 1), a omówiono w nim wyniki analizy szczególnych postaci modelu starzenia się papieru bezkwasowego w odniesieniu do wskaźnika pochłaniania energii (TEA) i oporu przedarcia (FT) papieru.

The article is a supplement of two previous publications (cf. note 1) on the new explanation of the ageing process reasons for acid-free paper, in which the mathematical relationship between the relative change rate of tensile energy absorption (TEA) and of tear resistance (FT) during artificial ageing of the acid-free paper and thermal parameters of that ageing in dry air could be expressed – as it has been shown experimentally – by equations combining both the elements of the theories of Nissan & Sternstein and the equations of Arrhenius and of Eyring. Therefore, it is possible to extrapolate the results of artificial ageing to natural ageing conditions. The general form of the equation derived is the same for both investigated the properties of the acid-free paper. In the published article the results of the analysis of both ageing model forms are discussed which are speciafic for each one of these paper strength characteristics. It has been shown that both models differ in absolute values of coefficients identified on the basis of regression equations. Introducing the numerical values of these coefficients and assuming that the ageing process takes place at the constant temperature 23°C permitted a substantial simplification of the equations, and this made easier to trace the effects of the technological parameters of the acid-free paper manufacture (its composition and the SR pulp slowness) on resistance of the paper to ageing. Using computer graphic analysis of these patterns showed that the decisive influence on the values of the coefficients appearing in the equations, and thus on the resistance to ageing of the acid-free paper, has a beating degree of its pulp. Its effect on the value of the relative reduction in both studied mechanical properties of the acid-free paper manifests itself only after a relatively long time prediction. The lower limit of 95% prediction interval is proposed to adopt for practical applications of the relative value of property changes in the acid-free paper being a result of its natural ageing. Absolute values of the strength of the acid-free paper after a certain time of its ageing depend not only on the relative rate of change but also on the level of its initial value. On the basis of the comparison curves of the minimum of tear resistance values, corresponding to the lower limit of 95% prediction interval, it can be stated that tear resistance values of the acid-free paper will equalise after a relatively long period of its natural ageing, regardless of the initial values of tear resistance. Using the elaborated model, it can be estimated that the studied handsheets of acid-free paper – which technological parameters has deliberately been limited to the area ensuring its high level of resistance to ageing – will retain sufficient strength after a period of at least 1,000 years. It refers to their natural ageing at 23°C and the moisture content in them less than 5%, ensuring the presence of the water in them in the form of monomolecular adsorption layer; as is the case in the so-called normal storage conditions recommended for long-term storage of paper archival media. Therefore, the model omitted the moisture content in paper, because the content being equivalent to the normal storage conditions will have no significant impact on the number of hydrogen bonds in the paper which determines its mechanical properties. Often emphasized the importance of the moisture is related to its effects rather in conjunction with other external and internal factors, especially the microbiological and chemical ones, and those only slightly depend on the matter of acid-free paper deliberately created for archival purposes.