Orientation and property correlations for LLDPE blown films

The orientation and property correlations of biaxially oriented polyethylene (PE) blown films have been studied. A linear low density polyethylene (LLDPE) (DOWLEX (TM) 2045A) was used to fabricate films at different conditions with blow up ratio, die gap, and frost line height as the variables. The White-Spruiell orientation factors of crystal unit cells, amorphous chains, and Herman's orientation factors of lamellae were determined from wide-angle X-ray diffraction pole figure, birefringence, and small angle X-ray scattering (SAXS). A general orientation pattern with the crystal unit cell a-axis preferentially oriented to MD, b-axis to TD, lamellae stacking along the MD, and amorphous chains preferentially to the MD has been found for all films in this study. A correlation between the orientation of each element of the morphology hierarchy has been revealed. Key mechanical properties including dart impact and Elmendorf tear strength in both MD and TD have been determined. Good correlation has been found among these properties. Most importantly, these properties have excellent correlation to the orientation. These correlations have been linked to underlying morphology and microdeformation mechanisms. (c) 2006 Wiley Periodicals, Inc.