Abstracts Engineering

Morphology and optical properties of polyolefin blown films

by Lei Wang

Optical properties of polyethylene blown films are of great commercial and scientific interest. An understanding of the relationship between morphology and optical properties will have a significant impact on product and process optimization. In this work, a number of linear low density polyethylene (LLDPE) resins of different molecular and structural characteristics were studied. Intrinsic properties such as refractive index and absorption coefficient were estimated from resin compositions using group contribution models. The refractive indices of sample films were also measured using the method of Transmission Spectrum. The morphology of polyethylene films was investigated using Atomic Force Microscopy (AFM) and Near-field Scanning Optical Microscopy (NSOM). Both the surface and bulk morphologies were evaluated. The observation shows the dominant spherulitic structure on the surface as well as in the bulk, as the result of nucleation and crystallization during the film blowing process. In addition to qualitative observations and comparisons; quantitative characterization methods were employed to describe the features of the morphology. Based on the morphology characterization, the surface reflection was described by the Beckmann-Davies theory of reflection of electro-magnetic waves by rough surface. The directional distribution of reflected intensity was computed according to the surface roughness information. The gloss values of sample films were computed accordingly and compared with experimental measurements. Furthermore, the problem of light transmission and scattering was investigated. A scattering geometry was proposed from the observations of the morphology of sample films. The light scattering by the surface of polymer films was analyzed using a model that is based on the Mie theory of scattering. The haze values of sample films were computed and compared with experimental measurements.