Investigation of deformation and pore formation in isotactic polypropylene containing active nano‐CaCO3 |
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| Authors: | Lei Ding Tong Wu Qian Ge Guan Xu Feng Yang Ming Xiang |
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| Affiliation: | State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu, People's Republic of China |
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| Abstract: | In order to improve the β‐lamellae distribution and properties of β‐isotactic polypropylene (β‐iPP) membranes, amounts of 5 and 10% active nano‐CaCO3 were added into β‐iPP. Differential scanning calorimetry, X‐ray diffraction and scanning electron microscopy results show that nano‐CaCO3 does not reduce the content of β‐crystals, but the thickness, lamellae thickness distribution and stability of β‐lamellae decrease apparently. Tensile testing was conducted at 25 and 90 °C. The results manifest that the second yield point, which has a strong negative correlation with lamellae thickness distribution, is delayed monotonically with addition of nano‐CaCO3 when stretched at 25 °C, indicating that nano‐CaCO3 could narrow effectively the lamellae thickness distribution of β‐iPP. Furthermore, when stretched at 90 °C, the subdued yield peak, retarded necking‐down phenomenon and enhanced strain‐hardening modulus demonstrate that the deformation stability improves gradually with introduction of nano‐CaCO3, which is completely opposite to the trend for β‐lamellae stability. Through further detailed characterization of morphological evolutions during stretching, we found that interfacial debonding between nano‐CaCO3 and β‐iPP is triggered and abundant microviods can be formed, which can retard the rotation and slip of β‐lamellae and make the β–α transformation slow down in the initial stage of stretching, consequently leading to better isotropic deformation. Moreover, nano‐CaCO3 could efficiently restrain the formation of coarse fibrils, leading to more uniform pore size distribution within the biaxial stretching microporous membrane. However, excessive nano‐CaCO3 (10%) would cause aggregation within the β‐iPP cast film and finally result in larger pores and poor pore distribution in the membrane. © 2017 Society of Chemical Industry |
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| Keywords: | β ‐nucleated polypropylene active nano‐CaCO3 lamellae thickness distribution uniformity of pore size distribution |
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