Münstedt Helmut
Department of Materials Science and Engineering, Friedrich-Alexander-University Erlangen-Nuremberg, D-91058 Erlangen, Germany.
Polymers (Basel). 2020 Jul 8;12(7):1512. doi: 10.3390/polym12071512.
While the uniaxial elongational viscosity is widely investigated, and its relevance for processing is described in the literature, much less has been published on the recoverable extensional flow of polymer melts. This paper presents a short overview of the dependencies of the recoverable elongation on the molecular structure of a polymer, and on some experimental parameters. Its main focus lies on the discussion of processing operations and applications that are largely affected by the elastic components of elongational flow. The recoverable portions of stretched films are considered, and the exploitation of the shrinkage of films, due to the recovery of frozen recoverable deformations, and its role for applications are addressed. The analysis of measurements of velocity fields in the entry region of a slit die and results on the determination of the recoverable elongation from uniaxial experiments, according to the literature, lead to the conclusion of dominant elastic extensions. Considering these facts, the assumptions for Cogswell's widely used method of determining elongational viscosities under processing conditions from entrance flow are not realistic. As examples of a direct application of extrudate swell from short dies for processing, pelletizing and fused deposition modelling within additive manufacturing are addressed. The special features of extrudate swell from short dies, and uniaxial recoverable elongation for a polymer filled with rigid particles in comparison to an immiscible polymer blend, are presented and discussed.
虽然单轴拉伸粘度已得到广泛研究，且其与加工的相关性在文献中也有描述，但关于聚合物熔体可恢复拉伸流动的报道却少得多。本文简要概述了可恢复伸长率与聚合物分子结构以及一些实验参数之间的依赖关系。其主要重点在于讨论受拉伸流动弹性成分显著影响的加工操作和应用。文中考虑了拉伸薄膜的可恢复部分，并探讨了利用冻结可恢复变形的恢复导致的薄膜收缩及其在应用中的作用。根据文献，对狭缝模头入口区域速度场测量的分析以及单轴实验中可恢复伸长率的测定结果得出了主要弹性伸长的结论。考虑到这些事实，Cogswell广泛使用的从入口流动确定加工条件下拉伸粘度的方法所依据的假设并不现实。作为短模头挤出胀大在加工、造粒和增材制造中的熔融沉积建模方面直接应用的示例进行了探讨。文中展示并讨论了短模头挤出胀大的特点，以及与不相容聚合物共混物相比，填充刚性颗粒的聚合物的单轴可恢复伸长率。
