Gas barrier changes and structural alterations induced by retorting in a high barrier aliphatic polyketone terpolymer

Analysis of the consequences of a typical humid thermal plastic food packaging sterilization (retorting) process over the crystalline morphology and gas barrier properties of a high barrier aliphatic polyketone terpolymer was carried out by in situ simultaneous synchrotron WAXS and SAXS experiments an by DSC, ATR-FTIR spectroscopy, and oxygen transmission rate measurements. From a structural view point, it was observed that the retorting process led to a less crystalline material; however, crystallinity was fully restored by a postdrying process. The humid thermal treatment also favored the sorption of moisture in the amorphous phase to a saturation level, i.e., 2% water uptake. As a result, the oxygen permeability at 21 degrees C was observed to increase by about nine times immediately after the humid treatment, but the barrier character was observed to quickly recover over time. From the results, it is suggested that a simple postdrying process at moderate temperatures can restore morphology and barrier properties. In the overall, it is also suggested that aliphatic polyketones withstand far better the process of retorting in comparison with, for instance, other high barrier polymers such as ethylene-vinyl alcohol copolymers reported earlier and can therefore offer even as a monolayer an alternative in retortable food-packaging applications. (c) 2006 Wiley Periodicals, Inc.