Morphological study of HDPE blown films by SAXS, SEM and TEM: a relationship between the melt elasticity parameter and lamellae orientation

Evidence is presented showing how the long relaxation times in the melt aff ect the subsequent morphology of blown films made from medium molecular wei ght (MMW) HDPE homopolymers. The blown film morphology was studied using th e small-angle X-ray scattering (SAXS) technique, scanning electron microsco py (SEM) and transmission electron microscopy (TEM). SAXS data were used to obtain the lamellae orientation functions using the Herman's orientation f unction equation commonly used for wide-angle X-ray diffraction (WAXD). The blown film results showed an increase in orientation function with increas e in E-R, a normalized melt elasticity parameter that reflects an increase in the longest melt relaxation times. In our study, such an increase in the longest relaxation times results from an increase in long-chain branching (LCB). As expected, compression molded samples show random orientation by S AXS. Considerable differences were observed in the lamella organization bet ween the blown films of low and high E-R resins. TEM micrographs show the p resence of fibril nuclei several microns long. Lamellae stack perpendicular to the machine direction (MD) in films made from higher E-R resins. In con trast, stacks of lamellae arranged randomly characterize the micrographs of blown films made from resins of low E-R value. A model is proposed to expl ain the relationship between orientation function and melt relaxation times . (C) 2001 Elsevier Science Ltd. All rights reserved.