It has been known for some time that mechanical pretreatments of melts of long-chain branched polymers can increase the melt index and reduce the extrudate swell. This effect is not due to changes of the molar mass, its distribution, or the degree of branching because it may be reversed by long-term annealing or dissolution of the polymeric material and subsequent precipitation. Furthermore, molecular analysis shows a molecular structure unaltered by the treatment. The effect has not been completely understood up to now, and it is still an open question as to whether it is restricted to long-chain branched polymers, which have been preferably studied. This paper gives an overview of results from the literature and presents comparable measurements on a well characterized long-chain branched and a linear polypropylene. A wide range of linear and nonlinear rheological properties were studied, and it became obvious that long-chain branching is a strong structural precondition for the pronounced pretreatment effect occurring in processing. Based on this result, models from the literature are discussed, and it is found that chain alignment may qualitatively explain the rheological measurements.

中文翻译：

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聚合物熔体的机械预处理：线性和长支链聚丙烯的关键方面和新的流变学研究

一段时间以来，人们已经知道对长链支化聚合物熔体进行机械预处理可以提高熔体指数并降低挤出物的溶胀。这种效应不是由于摩尔质量、其分布或支化度的变化，因为它可能会被聚合物材料的长期退火或溶解以及随后的沉淀所逆转。此外，分子分析显示分子结构未因处理而改变。其作用迄今尚未完全了解，是否仅限于长支链聚合物仍是一个悬而未决的问题，已被优选研究。本文概述了文献结果，并提供了对表征良好的长支链和线性聚丙烯的可比较测量。研究了广泛的线性和非线性流变特性，很明显，长链支化是加工过程中出现明显预处理效果的强大结构前提。基于这一结果，讨论了文献中的模型，发现链排列可以定性地解释流变测量。