Anomalous mechanical anisotropy of β form polypropylene sheet with N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide

An extruded polypropylene (PP) sheet in which both the chain-axes of the PP molecules and the crystalline lamellae are oriented perpendicular to the flow direction is obtained via row-nucleation on a specific needle-shaped nucleating agent, N,N′-dicyclohexyl-2,6-naphthalenedicarboxamide. The sheet shows anomalous anisotropy in dynamic tensile modulus, in which, at lower temperatures, the storage modulus in the machine direction (MD) is lower than that in the transverse direction (TD), and this behavior reverses at high temperature. Tensile tests reveal that the Young’s modulus and yield stress in the MD are higher than those in the TD. At high strain rate, the strain at break in the TD is, in contrast, markedly larger than that in the MD.