ABSTRACT:In an earlier publication we showed that the optical haze properties of blown and cast polyethylene (PE) films were adversely affected (i.e., haze increased) as a result of enhanced surface roughness caused by the formation of distinct optically anisotropic "spherulitic-like" superstructures. In this report we have found that for a very wide variety of PE blown films, the total haze percent exhibited a complex parabolic relationship with the logarithm of the recoverable shear strain parameter, ␥ ϱ . At low values of ␥ ϱ , superstructures were developed (as discussed in our previous report) that increased surface roughness and hence total haze. As ␥ ϱ increased, such superstructures were either significantly diminished in size or altogether absent, giving rise instead to an oriented, row-nucleated, stacked lamella texture that decreased surface roughness and hence total haze. However, at even higher ␥ ϱ values, representing highly melt elastic behavior, fine-scale surface roughness due to high melt elastic instabilities was induced, thereby increasing surface roughness and consequently total haze as well. It was demonstrated in this work that two PE resins could exhibit the same level of total haze as a consequence of two completely different mechanisms or origins. Furthermore, we believe that this is the first time that both very low and very high melt elasticity have been shown as primary causative factors in yielding high haze in PE blown films, albeit for fundamentally very different reasons.
A study utilizing isotactic poly(4-methyl-1-pentene) (PMP) was undertaken to investigate a three-stage process (melt-extrusion/annealing/uniaxial-stretching) (MEAUS) employed to produce microporous films. The results of this study will be reported in the course of two articles. In this first part, three PMP resins were melt-extruded into tubular films (blowup ratio; BUR ϭ 1), where the resins each differ in weight-average molecular weight (M w ). Specific attention was focused upon the morphological and crystal orientation results as a function of the melt-relaxation times as influenced by the resin characteristics and the processing parameters. The results of a number of melt-extrusion conditions are presented. A stacked lamellar morphology was obtained in each case; however, the type of stacked lamellar morphology, planar or twisted, and the orientation state was found to depend upon both the resin characteristics, specifically M w , and the melt-extrusion conditions. Atomic force microscopy and wide-angle X-ray scattering (WAXS) were the main techniques utilized to study the melt-extruded films, while oscillatory shear measurements, in conjunction with a Carreau-Yasuda analysis, aided in differentiating the melt-flow behavior of the three resins.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.