Physical properties of cellulosic materials related to moisture changes
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Moisture affects the mechanical properties of paper to a high degree. Moreover, the creep properties of paper may be highly affected while the relative humidity is changing, exhibiting mechano-sorptive creep. The reasons for the great sensitivity to moisture changes of papers are not fully explained. In this study, thin papers were examined during sorption processes and the moisture content within the paper, paper length and dynamic elastic modulus during RH changes were measured. It is demonstrated that the dimensional changes of the paper exactly reflected the changes in moisture content within the sample. During both absorption and desorption, the elastic modulus changed so that it was lower than the equilibrium value corresponding to its moisture content. This was especially evident during absorption where the modulus dropped below the equilibrium value at the end RH, i.e. the value was approached from below. The modulus drop was highly related to RH changes made at higher RH and could possibly be related to the softening of carbohydrates.
KeywordsElastic Modulus Moisture Sorption Moisture Change Initial Inability Humidity Change
This work was performed as part of the Paper Mechanics research programme at Innventia AB. The financing companies: Billerud, Eka Chemicals, Mondi Packaging Frantschach, M-real, Peterson & Son, Stora Enso, Södra, Tetra Pak, Voith and International Paper are gratefully acknowledged for their support.
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