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Rheological Properties of Tailor-Made Metallocene and Ziegler-Natta Based Controlled Rheology Polypropylenes

机译：量身定制的茂金属和Ziegler-Natta基控制流变聚丙烯的流变性能

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Controlled rheology polypropylenes (CRPP) have been produced industrially by peroxide induced degradation in post-polymerization reactive extrusion (REX) operations. This has been well developed for commodity Ziegler-Natta based polypropylene (ZN-PP) resins, resulting in materials with controlled rheological properties with accompanying narrower molecular weight distribution (MWD). In this work, this methodology has been tested on both metallocene based polypropylenes (mPP), which have a narrow MWD initially, and ZN-PP resins at various peroxide concentrations. The differences in their degradation process as well as the properties of the resulting CRPPs were compared.A previously developed kinetic model was used to simulate the degradation process at various peroxide concentrations. Modelling results for a mPP and a ZN-PP with similar molecular weight indicated that the MWDs of both materials approached “most probable distribution” (PDI=2) as expected, due to the random nature of the scission reactions involved. However, unlike the ZN-PP resin for which the polydispersity was sharply decreased, the MWDs of CRPPs from mPP was almost unchanged with a PDI of about 2. This indicated that polypropylenes from the two types could be used to produce CRPPs with specified/targeted MW and MWD patterns and therefore special properties.Two groups of tailor-made CRPPs were produced using mPP and ZN-PP. One group had similar MW but different MWDs and another group had similar melt flow rate (MFR). In particular, the zero-shear viscosity and rheological polydispersity, which were obtained through oscillatoryivshear rheometry, were successfully applied to monitor the MW level and the MWD of the products.The two series of materials were also submitted to extrusion tests using a single screw extruder equipped with a capillary die. Based on the extrusion results, with respect to the CRPPs of similar MW, materials of broader MWD, thus stronger shear-thinning at high shear rate, resulted in slower increase of extrusion pressure with apparent shear rate. The shear rate of the onset of extrudate melt-fracture, which coincided with previous studies of polypropylenes extrusion, was higher for broader MWD material. With respect to the CRPPs with similar MFR, a metric commonly used for grade inspection in industry, their extrusion behaviours were nearly identical.
机译：可控流变聚丙烯（CRPP）已在工业上通过后聚合反应挤出（REX）操作中的过氧化物诱导降解而生产。对于商品的基于齐格勒-纳塔的聚丙烯（ZN-PP）树脂，这已经得到了很好的开发，从而使材料具有可控的流变特性，同时具有较窄的分子量分布（MWD）。在这项工作中，此方法已在最初具有较窄MWD的茂金属基聚丙烯（mPP）和各种过氧化物浓度的ZN-PP树脂上进行了测试。比较了它们的降解过程以及所得CRPPs的特性之间的差异。以前开发的动力学模型用于模拟在各种过氧化物浓度下的降解过程。分子量相似的mPP和ZN-PP的建模结果表明，由于所涉及的分裂反应的随机性，两种材料的MWD均达到了预期的“最可能分布”（PDI = 2）。但是，与ZN-PP树脂的多分散性急剧下降不同，mPP的CRPP的MWD几乎没有变化，PDI约为2。这表明两种类型的聚丙烯可用于生产具有指定/目标的CRPP。 MW和MWD模式，因此具有特殊性能。使用mPP和ZN-PP生产了两组定制的CRPP。一组具有相似的MW，但不同的MWD，另一组具有相似的熔体流动速率（MFR）。特别是，通过振荡剪切流变法获得的零剪切粘度和流变多分散性已成功应用于监测产品的MW水平和MWD。这两个系列的材料还通过单螺杆挤出机进行了挤出测试。配有毛细管模具。根据挤出结果，对于类似MW的CRPP，MWD较宽的材料，因此在高剪切速率下更强的剪切稀化性，导致挤出压力在表观剪切速率下的增加较慢。对于较宽的MWD材料，挤出物熔体破裂开始时的剪切速率与以前的聚丙烯挤出研究相吻合。对于具有类似MFR的CRPP（一种通常用于工业品级检查的度量），其挤出行为几乎相同。

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    Nie Shouliang;

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  • 年度 2015
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