EVALUATION OF MECHANICAL ANISOTROPY AND ORIENTATION IN UNIAXIALLY STRETCHED POLYVINYL ALCOHOL FILM

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Abstract
The mechanical anisotropies of uniaxially stretched polyvinyl alcohol films were investigated experimentally and theoretically in relation to the orientation of crystallites and noncrystalline chain segments. The theoretical calculations of Young's modulus were carried out on the basis of both the homogeneous stress and the homogeneous strain hypotheses, using two types of structural model. One of them was made up by averaging the aggregation of structural units composed of the orthorhombic crystalline and the isotropic noncrystalline phases under consideration of their orientation distribution and their mechanical constants. On the other hand, the mechanical anisotropy was evaluated for the structural model which is constructed by combinning the averaged crystalline with the averaged noncrystalline phase.The calculation on the basis of the homogeneous stress hypothesis using either structural model gives a considerablly good agreement with both the observed Young's modulus parallel and perpendicular to the stretching direction of the uniaxially stretched film. However, the calculation on the basis of the homogeneous strain hypothesis using the structural model gives results higher than the experimental ones in parallel to and lower than those perpendicular to the stretching direction, respectivelly.

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