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Advances in Materials Research
  Volume 2, Number 2, June 2013 , pages 111-118

A study of plastic plateau disappearance in stress-strain curve of annealed polypropylene films during stretching
Caihong Lei, Shuqiu Wu, Ruijie Xu, Yunqi Xu and Xinlong Peng

    The changes of plastic plateau in the stress-strain curves of annealed polypropylene (PP) films during stretching under room temperature were followed and the corresponding melting properties and microstructure were characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that during stretching the plastic plateau disappeared progressively with the increase of drawing ratio. At the same time, the endotherm plateau in DSC curves also disappeared progressively. The presence of the plastic plateau was attributed to the stretching of unstable crystalline part which was formed by tie chains around initial row-nucleated lamellae structure during annealing. During stretching, the unstable part was stretched and converted to bridges connecting separated lamellae. There was direct relationship between the disappearance of plastic plateau and pore formation.
Key Words
    polypropylene; row-nucleated lamellae structure; melt-stretching mechanism; micropores;hard elastomer
Caihong Lei, Shuqiu Wu, Ruijie Xu, Yunqi Xu and Xinlong Peng : School of Materials and Energy, Guangdong University of Technology, Guangzhou 510006, China

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