Liparoti Sara, Speranza Vito, Pantani Roberto, Titomanlio Giuseppe
Department of Industrial Engineering, University of Salerno-via Giovanni Paolo II, 132, 84084 Fisciano (SA), Italy.
Materials (Basel). 2019 Feb 7;12(3):505. doi: 10.3390/ma12030505.
It is well known that under high shear rates polymers tend to solidify with formation of morphological elements oriented and aligned along the flow direction. On the other hand, stretched polymer chains may not have sufficient time to undergo the structuring steps, which give rise to fibrillar morphology. In the last decades, several authors have proposed a combined criterion based on both a critical shear rate and a critical mechanical work, which guaranties adequate time for molecular structuring. In this paper, the criterion, reformulated on the basis of critical values of both molecular stretch and mechanical work and adjusted to account for the unsteady character of the polymer processing operations, is applied to the analysis of a set of isotactic polypropylene injection molded samples obtained under very different thermal boundary conditions. The evolutions of molecular stretch and mechanical work are evaluated using process simulation. The results of the model reproduce the main characteristics of the morphology distribution detected on the cross sections of moldings, obtained under very different thermal boundary conditions, assuming that the critical work is a function of temperature.
众所周知，在高剪切速率下，聚合物倾向于固化，并形成沿流动方向取向和排列的形态元素。另一方面，拉伸的聚合物链可能没有足够的时间经历形成纤维状形态的结构化步骤。在过去几十年中，几位作者提出了一种基于临界剪切速率和临界机械功的综合判据，该判据保证了分子结构化有足够的时间。本文将基于分子拉伸和机械功的临界值重新制定并考虑到聚合物加工操作的非稳态特性进行调整后的判据，应用于分析在非常不同的热边界条件下获得的一组全同立构聚丙烯注塑样品。使用过程模拟来评估分子拉伸和机械功的演变。假设临界功是温度的函数，该模型的结果再现了在非常不同的热边界条件下获得的模制品横截面上检测到的形态分布的主要特征。
