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Deformation and pore formation mechanism under tensile loading in isotactic polypropylene
Author(s) -
Ding Lei,
Wu Tong,
Yang Feng,
Xiang Ming
Publication year - 2017
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.5364
Subject(s) - materials science , composite material , microporous material , spherulite (polymer physics) , ultimate tensile strength , isothermal process , polypropylene , deformation (meteorology) , tacticity , crystallization , differential scanning calorimetry , polymer , chemical engineering , polymerization , physics , engineering , thermodynamics
Four different polypropylene ( PP ) samples were prepared through isothermally crystallizing at 0 °C ( PP ‐Q), 80 °C ( PP ‐80), 100 °C ( PP ‐100) and 120 °C ( PP ‐120). The results of differential scanning calorimetry, wide‐angle X‐ray diffraction, polarized light microscopy and tensile testing indicate that the spherulite structure gradually improves with increasing isothermal crystallization temperature. Meanwhile, the interface between spherulites becomes more obvious due to the larger dimension and the higher strength of spherulites. Therefore, the trend of interfacial debonding during stretching is enhanced distinctly. In addition, based on the structural characterization of samples at different draw ratios, two completely distinct morphological changes are demonstrated. There are no defects generated after longitudinal stretching within PP ‐Q, because intra‐spherulitic deformation predominates, which is caused by the imperfect spherulites of PP ‐Q. As a result, no microporous structure is produced after sequential biaxial stretching. And the improvement of the crystalline structure makes interfacial debonding more likely to occur. Therefore, fully developed crazes and cracks disperse between microfibril structures after longitudinal stretching. Furthermore, numerous microporous structures are produced through debonding of fully developed crazes and cracks after sequential biaxial stretching. Meanwhile, the quantity, dimension and uniformity of the microporous structures and the porosity are gradually improved. © 2017 Society of Chemical Industry