Optical Haze Properties of Polyethylene Blown Films: Part 1 - Surface Versus Bulk Structural Considerations, 2001 Polymers Laminations & Coatings Conference Proceedings

Note: This file can not be downloaded due to file size. To use your free download for this file please call TAPPI’s Member Connection Department.

In this paper we report on some recent findings regarding the factors affecting the optical (haze) properties of polyethylene (PE) blown films. An investigation of blown films made from representative conventional Ziegler- Natta (Z-N) catalyzed linear low density PE (LLDPE) as well as metallocene-catalyzed LLDPE (mLLDPE) resins was conducted. It was found that the large majority of the contribution to the total haze in these blown films was a result of the surface roughness of the films, with the bulk (internal) contribution being relatively minor. Using atomic force microscopy (AFM) and small-angle light scattering (SALS) techniques, we found, quite unexpectedly, that the surface roughness in some of these films was a result of the development of distinct iÔ±spherulitic-likela superstructures formed during the blown film processing. These superstructures were observed only in the mLLDPE blown films, and not in the Z-N LLDPE blown films processed at similar conditions. In addition, we found that the haze of the blown films increased quite systematically with an increase in the degree of surface roughness i.e., an increase in the size of the ihspherulitic-likele superstructures. Analysis of the rheological and molecular characteristics of these various mLLDPE and LLDPE resins revealed that the mLLDPE resins exhibited considerably lower molecular weight, narrower molecular weight distribution and lower melt elasticity compared to the LLDPE resins of similar melt index (MI). We therefore conclude that in blown films of LLDPE-type resins, the optical haze properties are adversely affected due to enhanced surface roughness caused by the formation of iospherulitic-likele superstructures in polymer melts that possess fast relaxing and low melt elasticity rheological characteristics.