β/α Transformation of β-polypropylene during tensile deformation: effect of crystalline morphology
2010
Li, Xiaoxi | Wu, Haiyan | Huang, Ting | Shi, Yunyun | Wang, Yong | Xiang, Fangming | Zhou, Zuowan
In this work, the β/α transformation of β-nucleated iPP at different tensile strains has been analyzed. The crystalline morphology of iPP is controlled by the content of β-phase nucleating agent (β-NA), namely, well-developed β-spherulites induced by critical content of β-NA and bundle-like morphology without distinctly developed spherulites by supercritical content of β-NA. It is interesting to observe that the crystalline morphology of β-iPP exhibits great influence on the β/α transformation process during deformation. For well-developed β-spherulites, the content of β-iPP increases at relatively low tensile strain and then decreases gradually with the further increase of tensile strain. However, for bundle-like morphology, the content of β-iPP decreases monotonically with the increase of tensile strain. More important, well-developed β-spherulites, which have integrated crystalline structures, exhibit much smaller degree of β/α transformation as compared with bundle-like morphology at the same tensile strain, leading to more β-iPP maintaining and participating in the deformation process at high strain and consequently, resulting in better ductility. The results of this study further show the importance of crystalline morphology in determining the ductility of β-nucleated iPP on the one hand. On the other hand, this work provides the illuminating explanation for the reason why the well-developed β-spherulites exhibits more excellent ductility compared with the bundle-like morphology.
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