Influence of nucleating agent self-assembly on structural evolution of isotactic polypropylene during uniaxial stretching

Dotlike, needlelike, and treelike morphologies of N, N'-dicyclohexyl-2,6-naphthalene dicarboxamide (NJS) are induced via self-assembly. Isotactic-polypropylene (iPP)/NJS composite with treelike NJS shows the highest beta-iPP relative crystallinity (K-beta). During uniaxial stretching, a higher K-beta could increase the number of voids. However, the size of voids is similar regardless of the NJS morphology. The beta-alpha phase transition takes place after void formation. During intralamellar and interlamellar slip, no obvious polymer chains orientation can be found for alpha-iPP. In the strain range of 0.1-0.6, the c-axis of the beta-iPP crystal tends to orient perpendicular to the stretching direction. This is caused by lamellae twisting, a unique deformation mode of beta-iPP lamellae. The lamellae twisting is proposed to be responsible for the intense voids formation of the composite with higher K-beta. At a strain larger than 0.6, the drastic increase of orientation is mainly caused by the rotation of the residual fragmented lamellae and the orientation of the newly formed crystals. (c) 2018 Elsevier Ltd. All rights reserved.