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.

中文翻译：

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剪切诱导前体的热稳定性及其对β-核全同立构聚丙烯晶体结构的影响

使用ARES流变仪研究了剪切诱导的前体在各种退火温度下的热稳定性和寿命，以及它们的弛豫对β型有核全同立构聚丙烯（iPP）中晶体改性的影响。广角X射线衍射结果表明，剪切的β-成核iPP样品的β-晶体含量随热处理而逐渐增加。退火过程中剪切诱导的前驱体的松弛导致剪切核的减少，可能会限制剪切流与β-成核剂之间的抵消作用，并导致β的增加-晶体含量。在弛豫的早期，弛豫程度与β晶体的增加密切相关，为此，较深的弛豫剪切诱导前体导致β晶体的更多还原。但是，当弛豫度超过一定的限制时，β晶体达到最大值，剪切诱导的前体的弛豫将不再影响β形核iPP的晶体结构。