Examine the packaging requirements for high-pressure sterilization processes.

The fundamental behavior of polymers under high pressures has only recently become the subject of systematic study. Most research has sought to determine whether laminate packages remain highly functional after they undergo a high-pressure treatment.

In contrast, we're told that little research has examined the impact of high pressure on the fundamental properties of polymers. However, the interplay of polymer molecules and other permeant molecules under high pressure produces an assortment of often antagonistic actions that may result both in transient or permeation changes to the package.

For example, atmospheric gases and organic vapors condense remarkably faster than packaging polymers, and they ultimately change their state during compression. A compound's solubility in a polymer may either increase or decrease, depending on its compression relative to the compression of the polymer. When solubility is increased, decompression results in the flashing of supersaturated compounds. Eventually, blistering may occur in laminate structures.

Differential compressibility among various laminate layers may also result in delamination. This delamination is facilitated by compression heating, especially when packages with aqueous contents enter the compression cycle at temperatures above 80 C. There is even evidence that a diesel-like ignition may occur inside packages which are heated prior to compression. Selecting compatible polymers for laminated structures can minimize many of the packaging problems that result from high-pressure processing.

Properly controlling temperatures during the compression and decompression cycle may minimize other defects. In order to fully understand and accurately predict the impact of high-pressure processing on laminate packages, the behavior of individual polymers under high pressure must be studied. Further information. George Sadler, National Center for Food Safety and Technology, Illinois Institute of Technology, IIT Moffett Campus, 6502 S. Archer Rd., Summit-Argo, IL 60501; phone: [phone]; email: [e-mail].