Coextruded polypropylene/tie/ethylene vinyl alcohol/tie/polypropylene (PP/tie/EVOH/tie/PP) films often exhibit optical defects which appear as randomly distributed scattering objects, in the submillimeter range. These defects may strongly affect the film transparency and prevent their practical use in packaging. Based on an objective optical test aimed at quantifying the film transparency, and on a systematic analysis, through optical microscopy, of transverse cuts of films obtained in various coextrusion conditions, the nature of the defects could be identified as resulting from a modulation of the thickness of the inner ethylene vinyl alcohol (EVOH) layer, with no variation in the overall thickness of the multilayer films. Thanks to a recently developed method to dose the surface density of interfacial copolymers, a clear correlation between the amplitude of the thickness modulation of the inner EVOH layer and the density of copolymer molecules formed in situ at the EVOH/tie layer interface during the coextrusion process was established. These results open the way to a better design of tie layers composition to avoid these kinds of defects.

中文翻译：

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通过界面共聚物的表面密度控制PP / EVOH共挤出多层膜的界面不稳定性

共挤出的聚丙烯/领带/乙烯-乙烯醇/领带/聚丙烯（PP / tie / EVOH / tie / PP）薄膜通常显示出光学缺陷，这些缺陷以随机分布的散射物体出现，在亚毫米范围内。这些缺陷可能会严重影响薄膜的透明度，并妨碍其在包装中的实际使用。基于旨在量化膜透明度的客观光学测试，以及通过光学显微镜对在各种共挤出条件下获得的膜的横向切割进行系统分析的结果，可以确定缺陷的性质是由于厚度调节所致内乙烯乙烯醇（EVOH）层的厚度为100％，而多层膜的总厚度没有变化。多亏了最近开发的界面共聚物表面密度计量方法，在共挤出过程中，内部EVOH层的厚度调制幅度与在EVOH /粘结层界面处原位形成的共聚物分子的密度之间建立了明显的相关性。这些结果为更好地设计粘结层组合物以避免此类缺陷开辟了道路。