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The effect of high pressure processing on the morphology of polyethylene films tested by differential scanning calorimetry and X-ray diffraction and its influence on the permeability of the polymer



This study investigated the influence of high-pressure processing on the morphology and permeability of low-density polyethylene (LDPE) films used for food packaging. This was done by monitoring the crystallinity, melting temperature (Tm), and oxygen transmission rate (OTR) of the materials before and after the pressure treatments. A first set of pouches made from the LDPE films were filled with 95% ethanol then pressured at 200, 400, 600, and 800 MPa for 5 and 10 min at 25 and 75°C. The crystallinity and Tm of the films were measured using differential scanning calorimetry (DSC). X-ray diffraction (XRD) was also used to determine the crystallinity. A second set of LDPE pouches were similarly made but a half of them were filled with 95% ethanol and the other half filled with distilled water. These second set of pouches were pressured at 200, 600, and 800 MPa then their OTR tested. Results of the DSC experiments showed that the Tm increased with increasing pressure intensity but the crystallinity changes were not detectible. The XRD method on the other hand, showed significant (P < 0.05) crystallinity increases with increasing pressure treatments. The gas permeability analyses showed decreasing OTR's with increasing high-pressure intensity treatments. The OTR in the pouches filled with the 95% ethanol was slightly lower than that of the pouches filled with water. These findings allowed us to better anticipate the behavior of LDPE films used to package high-pressure processed foods. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009