The influence of humidity and temperature on the change in elastic properties of single fibres and the corresponding papers are shown to be similar.
Furthermore, expansional changes due to variation in the atmospheric conditions are shown to be related to the elastic properties of the sheet . For thermal expansion in paper, the product of coefficient of linear expansion and the elastic properties is approximately constant in all directions. A similar relationship is also followed in hygroexpansion. In the experiments reported, a slightly higher value in the machine direction was obtained for the product of the dimensional changes and the elastic modulus.
It is also noted that the geometric means of the dimensional instability and elastic properties in machine and cross directions coincide with the same properties of the isotropic sheet.
Hygrodimensional changes for single fibres were measured by means of following the rotational twist of the fibres caused by sorption. It is deemed from these experiments that the fibre swelling is proportional to the moisture regain.
Finally, it is shown that the viscoelastic properties of cellulose material change in an irregular manner during changes of the moisture regain. These effects cause considerable reduction in the creep to failure time (lifetime) of paper in compression or tension under transient atmospheric conditions.