Structure Development of Low-Density Polyethylenes During Film Blowing: A Real-Time Wide-Angle X-ray Diffraction Study

Abstract

We studied experimentally the structure development during film blowing for three different low-density polyethylenes at four different processing conditions. For this, we combined blown film extrusion with in situ X-ray diffraction at a synchrotron radiation beam line. The measurements were performed at rheological similar conditions at the die exit, with each grade possessing different molecular properties in terms of molecular weight distribution and branching content. The development of crystallinity and molecular orientation was determined as function of the distance from the die. It is shown that this approach provides a valuable method to study structure evolution during film blowing and can be used to validate results from numerical models and help to improve and/or extend these models.

Designing polymer crystallinity: An industrial perspective

“…The attempt to draw conclusions between two points along this chain without considering intermediates will necessarily limit the validity of the thus established correlations. Similarly, the design of crystallinity in order to achieve specific properties must consider contributions from fundamental science as well as industrial aspects, especially the effects of complex processing operations …”

“…The integration of multiple material characterization methods was necessary to establish relations between composition and properties of LLDEPE/LDPE blends frequently used in practice for combining ease of processing with good film performance . The most advanced example of systematic work involving on‐line studies are the studies of Portale and Peters . Various combinations of LLDPE and LDPE were characterized both regarding basic crystallization properties and on‐line including X‐ray diffraction during film blowing to understand the differences in processing and film performance.…”

Polymer Crystallization Studied by Hyphenated Rheology Techniques: Rheo‐NMR, Rheo‐SAXS, and Rheo‐Microscopy

“…More recently, slit flow experiments on crystallizing polymers based on multipass rheometers were conducted . The structure formation during polymer processing methods such as extrusion, film blowing, and fiber spinning was investigated using the respective hyphenated set‐ups. Despite the insights into the structural buildup during quiescent and flow‐induced crystallization of polymers, these studies lacked information on the evolving rheological behavior of the materials under study.…”

Flow-Induced Crystallization of Polyamide-6

“…To quantify the degree of orientation, the reflection of the Bragg peak closest to the center of the pattern was treated by the 'Full Width at half Maximum' method (FWHM) (Van Drongelen et al, 2014). This method fits a Lorentzian function to the azimuthal intensity profiles according to:…”