Processing LLDPE into a blown film by simultaneously stressing the parison along MD (take up direction) and TD (blow up direction), imparts marketable physical properties (esp. puncture and tear resistance) to the film. While the microstructure of several pristine films has been studied, relatively few such analyses have been performed on deformed materials with the intention of elucidating their failure mechanisms. In fact, the pristine “state of crystalline order”, as determined by SAXS, is the only parameter that appears to correlate with puncture and tear properties. Unfortunately, this correlation is of little direct help for understanding the failure mechanisms of these systems and, ultimately, how to improve their performance.<br/>The scarcity of data acquired during and/or subsequent to film deformation reflects the experimental challenges associated with obtaining this information. The SAXS configuration must have the ability to collect data while stretching the films in real-time. In order to make direct comparisons among data, high resolution micrographs that are collected from stretched materials must be viewed perpendicular to the film normal direction, which imparts special challenges to sample preparation.<br/>In this work dynamic SAXS and WAXS patterns and stress-strain curves were collected as the films were drawn along either MD or TD to past their yield points and held. Subsequently, TEM sections of RuO4 stained films were cut in the MD-ND plane and imaged using HAADF. Fourier Transforms of these micrographs were then calculated for direct comparison to the corresponding SAXS pattern.<br/>SAXS measures the average distance between the individual crystallites and, in biaxially oriented films, exhibits noticable variability in the MD-TD plane. Some variability can be associated with variations in orientation among the lamellar components, but most is due to differences in "ordering” among the micelles. We attribute correlations between this microstructure and film physical properties to be related to the number and lengths of the tie chains that bind crystallites together.<br/>In this presentation will we describe our work to compare directly microstructural data sets from deformed PE blown films. We also discuss our subsequent efforts to compare high resolution micrographs with SAXS patterns for a sample deformed along the various points of its stress vs. strain curve: after first yield, after second yield, into the strain hardening regime, etc.

TEM vs. SAXS observations of microstructure in stretched polyethylene blown films

249th National Meeting (2015)

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