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The deformation behavior of a polypropylene (PP) sheet, in which c-axis of b-form PP orients perpendicular to the flow direction in the sheet [transverse direction (TD)], is studied focusing on the mechanical anisotropy. The deformation mechanism of this sample is found to be strongly dependent on the stretching direction. Shear yielding is dominant in TD stretching, indicating that reorganization and phase transformation of crystalline form occur easily with low yield stress. On the contrary, in machine direction (MD) stretching, numerous microvoids appear with the transformation of crystalline form as well as the rotation of c-axis. Moreover, the crazing process, initiated at the orientation defects, occurs locally with remaining undeformed region in which b-form PP orients to TD. The deformation behavior is applicable to a microporous film. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 897-906

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