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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.

Termodynamiczne ujęcie starzenia się papieru. Cz. 2. Badania zależności odporności na przedarcie papieru od parametrów jego sztucznego termicznego starzenia

Gonera H., Dąbrowski J.

Przegląd Papierniczy

2008

R. 64, nr 2

97-102

W prezentowanych badaniach wykazano, że względne zmiany odporności papieru na przedarcie wywołane jego przyspieszonym termicznie starzeniem można przedstawić za pomocą takiego samego ogólnego modelu matematycznego jak w przypadku pracy zrywania papieru. Występujące w tym modelu człony znanych praw i teorii upoważniają do zastosowania go do obliczeń wartości analizowanej cechy wytrzymałościowej papieru na drodze ekstrapolacji wyników jej badań w warunkach termicznie przyśpieszonego starzenia do daleko od nich odległych warunków naturalnego starzenia. Wyznaczenie wartości stałych współczynników w podanym modelu wymaga przeprowadzenia badań przyśpieszonego starzenia papieru, w którym parametry podlegają zmianie wg statystycznego planu doświadczeń. Rodzaj i wielkość tego planu mają decydujące znaczenie dla dokładności wyznaczonych wartości stałych współczynników, a przez to także dla dokładności wartości prognozowanych. Przedstawiony model może być wykorzystany do oceny podatności badanego papieru na starzenie. Model nadaje się również do poszukiwania wskazówek odnośnie do doboru parametrów wytwarzania papieru o zakładanej odporności na starzenie.

This general mathematical model, the same as elaborated for TEA, was also useful in describing these relative changes of the tear resistance (Elmendorf) of paper which were induced by artificial thermal ageing of the studied papers. The segments of these well known theories and equations present in the elaborated model, such as developed by Nissan and Sternstein, as well as by Arrhenius and Eyring - confirm usefulness of this model to predict the studied mechanical properties of paper alter its ageing, such as its TEA and tear resistance (FT), by extrapolating the results gained under the conditions of artificial thermal ageing to very unlike conditions of natural ageing. To determine values of these coefficients present in this model, the studies are required on such artificial thermal ageing of paper in which the parameters are altered according to the statistical design of experiments. The kind of this design and its extension are of utmost significance for the precision in determining the values of the coefficients that is decisive for closeness in estimating the predicted values of TEA or FT alter ageing of paper, in thermally accelerated or natural processes. The presented model for TEA and FT may be applied to evaluating the susceptibility of the studied papers to ageing. This model is also suitable for finding the right direction towards selecting the technological parameters that will guarantee the manufacture of paper with the required resistance to ageing.