Relationship between morphology and mechanical properties of tobacco leaf lamina

Abstract

To optimize processing parameters, a study was done of the overall mechanical properties of tobacco leaf lamina. Stress-strain tests were performed to determine modulus, yield strength, and toughness (energy to break) of the lamina when deformed under tension and simple shear loads. The cellular morphology of the lamina was obtained by using scanning electron microscopy. Microscopic observation of deformed samples showed an uneven stress distribution and anisotropy. The macroscale phenomenological results indicated a harmony in its mechanical behaviour. Lamina isotropy and homogeneity in the plane of a leaf were determined by testing samples taken from different orientation and locations. Bright and burley tobacco were studied. The relationship between tension and shear properties was also obtained. Both in shear and tension, the lamina became softer with an increase in load. The stress-strain behaviour was characterized by a two-parameter power law equation. Statistically estimated results, obtained from several leaves, did not indicate any significant effect of sample location and orientation. Tobacco lamina appeared softer but tougher in shear than tension. It also showed sensitivity to the rate of deformation, indicating the viscoelastic nature of its behaviour. Material yield during manufacturing related well with mechanical properties. Burley lamina was stiffer and broke at lower strain than bright lamina. Thus, even though at the microlevel, tobacco lamina, is heterogeneous and anisotropic, at the macrolevel it displays homogeneous and uniform mechanical properties.