Studies on the Drying Shrinkage of Tobacco Leaves (1)

On the Anisotropic Shrinkage and relationship between Moisture Content and Shrinkage

Abstract

For the sake of improvement of the physical properties of tobacco leaves, the course of dehydration and shrinking of the leaves during curing, especially the directional variation in the shrinkage and the correlations between moisture content and the shrinkage were studied.
1) The leaves were separated into laminae and midribs and the anisotropic shrinkages were measured respectively. No appreciable difference in anisotropic shrinkage was observed between longitudinal and lateral directions of laminae, both showing a value of 0.19-0.24. On the other hand, the value in thickness was remarkable (0.52-0.58).
As for midribs, the value in longitudinal direction was small (0.04-0.06), whereas the shrinkage in diameter was fairly large (0.46-0.53), showing the existence of a distinct directional difference in shrinkage. Microscopic observations revealed that the large shrinkage was mainly due to that of parenchyma cells.
On the whole leaf, it has been reported that the shrinkage in longitudinal direction is smaller than that in lateral direction.
The directiol discrepancy in shrinkage between the whole leaf and the lamina is explainable as due to the presence or absence of the midrib.
2) The apparent volume change, the true volume change and the shrinking strength were measured with laminae in order to see the relationship between the change in moisture content and the shrinkage.
The apparent shrinkage constant was reduced with the decrease of the moisture content ratio, although the curve was slightly convex upwards. It was also shown that the apparent shrinkage ceased near the moisture content ratio of 0.12. The true volume changed proportionally to thechange of moisture content.
The shrinking strength was relatively weak where the moisture content ratio lied in 1 to 0.6-0.7, below which the strength became considerably larger and reached a maximal value at the moisture ratio of 0.1 to 0.2. Any further decrease in the moisture ratio did not affect the value.
The relationships between the change of moisture content and the moisture transport mechanisms were also discussed.