Polymer crystallization occurs in many plastic manufacturing processes, from injection molding to film blowing. Linear low-density polyethylene (LLDPE) is one of the most commonly processed polymers, wherein the type and extent of short-chain branching (SCB) may be varied to influence crystallization. In this work, we report simultaneous measurements of the rheology and Raman spectra, using a Rheo-Raman microscope, for two industrial-grade LLDPEs undergoing crystallization. These polymers are characterized by broad polydispersity, SCB, and the presence of polymer chain entanglements. The rheological behavior of these entangled LLDPE melts is modeled as a function of crystallinity using a slip-link model. The partially crystallized melt is represented by a blend of linear chains with either free or cross-linked ends, wherein the cross-links represent attachment to growing crystallites, and a modulus shift factor that increases with the degree of crystallinity. In contrast to our previous application of the slip-link model to isotactic polypropylene, in which the introduction of only bridging segments with cross-links at both ends was sufficient to describe the available data, for these LLDPEs, we find it necessary to introduce dangling segments, with cross-links at only one end. The model captures quantitatively the evolution of viscosity and elasticity with crystallization over the whole range of frequencies in the linear regime for the two LLDPE grades.

中文翻译：

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结晶 LLDPE 的流变学


聚合物结晶发生在从注塑到吹膜的许多塑料制造过程中。线性低密度聚乙烯（LLDPE）是最常加工的聚合物之一，其中短链支化（SCB）的类型和程度可以改变以影响结晶。在这项工作中，我们报告了使用流变拉曼显微镜同时测量两种正在结晶的工业级 LLDPE 的流变学和拉曼光谱。这些聚合物的特点是广泛的多分散性、SCB 和聚合物链缠结的存在。使用滑移连接模型将这些缠结的 LLDPE 熔体的流变行为建模为结晶度的函数。部分结晶的熔体由具有自由末端或交联末端的线性链的共混物表示，其中交联表示与生长的微晶的连接，以及随结晶度增加的模量位移因子。与我们之前将滑联模型应用于等规聚丙烯相比，其中仅引入两端具有交联的桥接段就足以描述可用数据，对于这些 LLDPE，我们发现有必要引入悬空片段，仅在一端具有交叉链接。该模型定量地捕获了两种 LLDPE 等级在整个频率范围内线性状态下粘度和弹性随结晶的演变。