Abstract
The thermal stability and lifetime of shear-induced precursors under various annealing temperatures, as well as the influence of their relaxation on the crystalline modification in β-nucleated isotactic polypropylene (iPP), are investigated using an ARES rheometer. The wide-angle X-ray diffraction results show that the β-crystal content of sheared β-nucleated iPP samples gradually increases with thermal treatments. The relaxation of shear-induced precursors during annealing which caused the decrease of shear nuclei may restrain the counteraction effect between the shear flow and β-nucleation agent as well as result in the increase of β-crystal content. At the early stage of relaxation, the relaxation degree is closely related to the increase of β-crystals, for which the deeper relaxed shear-induced precursors result in the more restoration of β-crystals. However, when the relaxation degree exceeded a certain limitation, where the β-crystals reached the maximum, the relaxation of shear-induced precursors will no longer influence the crystal structure of β-nucleated iPP.
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