Real-timein situ light scattering and X-ray scattering studies of polyethylene blown film deformation

Abstract

A series of linear low-density polyethylene blown films were studied using the techniques of time-resolved, small-angle X-ray scattering (SAXS) using a synchrotron source and a time-resolved, small-angle light scattering. Scattering patterns and the load-extension curve were obtained simultaneously during deformation. It was found that the initial orientation of the film, with respect to the tensile axis, was important in determining the operative elastic deformation modes. Films drawn parallel to the machine direction (MD) showed evidence for lamellar separation, whereas interlamellar shear occurred in films drawn parallel to the transverse direction. In films drawn at 45° to MD, lamellar stack rotation was observed via SAXS. In all cases, the yield point corresponded to the activation of crystallographic deformation and the onset of the disruption of crystalline lamellae. In films drawn parallel to MD, the SAXS showed a distinct 4-point pattern upon macroscopic yield, indicating lamellar corrugation. Regardless of the initial orientation, a fibrillar morphology was achieved at some strain after yield that coexisted with the fragmenting lamellar morphology. Comparison of results from deformed spherulitic bulk samples showed that the study of oriented blown film containing a stacked lamellar morphology may be used, to a first approximation, as a model for the deformation of different regions of spherulites in unoriented spherulitic samples.