Rheological behaviour of a high-melt-strength polypropylene at elevated pressure and gas loading for foaming purposes
Rheological behaviour of a high-melt-strength polypropylene at elevated pressure and gas loading for foaming purposes
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DOI：
10.1007/s00397-016-0988-6
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发表时间：
2017-02-01
期刊：
影响因子：
2.3
通讯作者：
Altstaedt, Volker
中科院分区：
文献类型：
--
作者：
Raps, Daniel;Koeppl, Thomas;Altstaedt, Volker
研究了长链支化聚丙烯（LCB-PP）在高压、充气、高剪切速率发泡挤出条件下的流变性能以及拉伸变形过程中的流变性能。为了测量PP在中等和高变形速率下的流变性能，使用在线流变仪。结果与标准旋转流变仪的比较显示出良好的一致性。使用温度、压力和气体浓度的转换因子来量化工艺参数的影响。压力对剪切粘度的影响被认为是次要的。相反，剪切粘度明显受CO2浓度的影响，在特定的剪切速率下，在6重量%的浓度下，将其降低至其无气体值的三分之一。与由于溶解的发泡剂引起的变化相比，由温度变化引起的粘度变化在幅度上类似。此外，观察到热流变复杂行为。在发泡过程中，热流变的复杂性可以有助于更好地控制长链支化聚合物相比，线性的形态。使用双曲线模头和膜拉伸工具（UXF）测量拉伸粘度以进行比较。由于熔体的显著应变硬化，它几乎比非线性区域中的剪切粘度高三十倍。
The rheological properties of a long chain branched polypropylene (LCB-PP) were investigated at the processing conditions of foam extrusion, namely high pressure, gas loading and high shear rates, as well as in elongational deformation. For measuring the rheological properties of PP at moderate and high deformation rates, an in-line rheometer was used. Comparison of the results to standard rotational rheometry showed good agreement. The effect of the processing parameters was quantified using shift factors for temperature, pressure and gas concentration. The influence of pressure on the shear viscosity was found to be of minor importance. In contrast, the shear viscosity was distinctly affected by CO2 concentration, reducing it to one third of its gas-free value at a concentration of 6 wt% at a specific shear rate. The change of viscosity by a variation of temperature is similar in magnitude compared to the variation due to dissolved blowing agent. Furthermore, thermo-rheological complex behaviour was observed. In the foaming process, thermo-rheological complexity could contribute to a better morphology control of long chain branched polymers compared to linear ones. The elongational viscosity was measured using both a hyperbolic die and a film stretching tool (UXF) for comparison. It is almost three decades higher than the shear viscosity in the non-linear region, due to pronounced strain hardening of the melt.