Linking morphology changes to barrier properties of polymeric packaging for microwave‐assisted thermal sterilized food

Abstract

It is a priority to develop polymeric packaging that can withstand microwave‐assisted thermal sterilization (MATS) and maintain the quality of low‐acid foods during long‐term storage. In this study, we explored changes in the morphology of pouch films with two multi‐layer structures. The films are based on barrier layers of metal oxide‐coated poly(ethylene terephthalate) (PET) (film A) and ethylene vinyl alcohol (EVOH) (film B). A 8‐oz model food in pouches was processed with MATS (F0 = 9.0 min) and stored at 23, 35 and 45 °C for up to 12 months. Findings reveal that the oxygen barrier of film A was influenced by the coating and crystallinity of PET. The oxygen barrier of film B was primarily affected by the moisture content of the EVOH polymer. Results also show that changes in barrier properties depended on storage temperature. Recrystallization in polymer might be an important morphological change that occurs during storages. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45481.

Development of an Oxygen Sensitive Model Gel System to Detect Defects in Metal Oxide Coated Multilayer Polymeric Films

“…On the other hand, the MOA pouch with no organic coating or overlayer was more susceptible to developing defects after sterilization. Zhang et al., also reported an increase in OTR by 12 times for metal oxide coated films. This was due to processing‐induced defects, in accordance with our results.…”

“…The structural changes in polymers also contribute to reduction in gas barrier properties after thermal treatment. However, morphological changes have less influence on the barrier properties of metal oxide coated films than EVOH‐based multilayer structures (Bhunia et al., ; Dhawan et al., ; Zhang et al., ). Nevertheless, several other factors that may have contributed to changes in film barrier properties include moisture absorption by hygroscopic nylon in the multilayer structure, an increase in free volume and the formation of smaller crystals with increasingly distorted crystal lattices (Bhunia et al., ; Zhang et al., ).…”

“…The change in overall enthalpies of crystallinities in the films may be attributed to changes in chain structures of the polymers caused by the annealing effect induced by sterilization conditions under high moisture environment. In the case of PET and nylon, thermal processing can bring about changes to the molecular structure, resulting in enhanced crystallinity after thermal treatment (Bhunia et al., ; Dhawan et al., ; Zhang et al., ). The PET crystallinity decreased immediately after thermal processing or remained unchanged, while that of nylon increased (Dhawan et al., ; Zhang et al., ).…”

“…In the case of PET and nylon, thermal processing can bring about changes to the molecular structure, resulting in enhanced crystallinity after thermal treatment (Bhunia et al., ; Dhawan et al., ; Zhang et al., ). The PET crystallinity decreased immediately after thermal processing or remained unchanged, while that of nylon increased (Dhawan et al., ; Zhang et al., ). This may have resulted in nylon losing its mechanical strength upon thermal processing, leading to a more brittle structure overall.…”

“…Other factors may include mechanical stresses during storage and handling and absorption of moisture by the polymeric materials such as nylon. Moisture absorption causes plasticization of the chains during thermal processing (Zhang et al., ). During the postprocessing stage, polymers may have released this excess moisture, reducing mechanical strength and increasing defects (Bhunia et al., ; Zhang et al., ).…”