Effect of Melt-Memory on the Crystal Polymorphism in Molded Isotactic Polypropylene
Effect of Melt-Memory on the Crystal Polymorphism in Molded Isotactic Polypropylene
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DOI：
10.1002/mame.201800148
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发表时间：
2018-08-01
影响因子：
3.9
通讯作者：
Androsch, Rene
中科院分区：
文献类型：
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作者：
Gohn, Anne M.;Rhoades, Alicyn M.;Androsch, Rene
研究了β-喹吖啶酮作为β-结晶成核剂对注射成型等规聚丙烯（iPP）的影响.将样品注塑成型并通过偏振光光学显微镜和X射线衍射进行表征。充模模拟用于了解样品制备过程中的剪切和冷却过程。使用模拟，与模具壁附近的淬火相关联的冷却速率估计为大于600 K s（-1），证实了先前的研究，即在该冷却速率下不支持晶体生长。非成核的样品在距离皮肤100-300 μ m处和样品的核心中形成-晶体，这是基于静态冷却数据所不期望的。由于模具填充模拟不能预测芯部中的剪切，因此在该区域中形成的晶体的形成归因于成型机的注射单元中的剪切诱导结晶效应，其在流动模拟中未建模，因为它们通常被排除在任何成型模拟分析之外。这种熔体记忆效应已被证明是显着的，它建议，注塑成型的最终性能的预测需要理解和知识的整个剪切历史的材料，包括注射单元。
The influence of -quinacridone as a -crystal nucleating agent in injection molded isotactic polypropylene (iPP) is discussed. Samples are injection molded and characterized via polarized-light optical microscopy and X-ray diffraction. Mold-filling simulation is used to understand the shear and cooling processes during sample preparation. The cooling rate associated with the quench near the mold wall is estimated to be greater than 600 K s(-1) using simulation, confirming previous studies that -crystal growth is not supported at that cooling rate. The non-nucleated samples form -crystals at a distance of 100-300 mu m from the skin and in the core of the sample, which is not expected based on quiescent cooling data. Since the mold-filling simulation does not predict shear in the core, the formation of the -crystals formed in this region is attributed to shear-induced crystallization effects in the injection unit of the molding machine that are not modeled in flow simulation, as they are typically excluded from any molding simulation analysis. This melt-memory effect has shown to be significant, and it is suggested that the prediction of final properties of injection moldings requires understanding and knowledge of the entire shear history of the material including that of the injection unit.