An experimental study on the effect of polymer viscoelasticity on layer rearrangement in coextruded structures
An experimental study on the effect of polymer viscoelasticity on layer rearrangement in coextruded structures
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DOI：
10.1002/pen.10274
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发表时间：
1998-07-01
影响因子：
3.2
通讯作者：
Hughes, K
中科院分区：
文献类型：
--
作者：
Dooley, J;Hyun, KS;Hughes, K
以前对共挤结构层厚均匀性的研究主要集中在不同聚合物粘度对各层的影响上。这些粘度的差异导致了一种被称为“粘性封装”的现象，在这种现象中，粘性较低的层倾向于封装较粘性的层，从而产生不均匀的层厚度。本研究通过不同横截面形状的模道共挤多层结构，观察界面位置，研究聚合物粘弹性对多层共挤结构层厚均匀性的影响。为了最大限度地减少粘度效应，在每层中使用相同的材料进行共挤实验，并对其进行着色，以便观察层间界面。实验表明，通过不同几何形状的通道共挤压相同的聚合物可以使层重新排列。由于聚合物的粘弹性特性，这种层重排似乎是由在不同通道几何形状中发生的二次流动引起的。相同聚合物的层重排意味着，即使是粘度与共挤出相匹配的树脂，在通过大型模具共挤出时也可能经历不均匀的层厚度。
Previous work on the layer thickness uniformity of coextruded structures has centered primarily on the effects of differing polymer viscosities in the individual layers. These differences in viscosities result in a phenomenon known as 'viscous encapsulation" in which the less viscous layer tends to encapsulate the more viscous layer producing nonuniform layer thicknesses. In this study, the effect of polymer viscoelasticity on the layer thickness uniformity of multilayer coextruded structures was investigated by coextruding multilayer structures through die channels of different cross-sectional shapes and observing the location of the interface. In order to minimize the viscosity effects, the coextrusion experiments were conducted with identical materials in each layer that were pigmented to allow observation of the layer interface. It was shown experimentally that coextruding identical polymers through channels of various geometries can cause the layers to rearrange. This layer rearrangement appears to be caused by secondary flows that occur in different channel geometries due to the viscoelastic characteristics of the polymer. Layer rearrangement of identical polymers implies that even resins with viscosities well matched for coextrusion may experience nonuniform layer thicknesses when coextruded through large dies.