03/27/2026
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a Doctoral Dissertation defense by Sandeep Tripathi on: "Investigation of Foil-Free Metal Oxide Coated Retort Pouches for Military Rations.”

Candidate Name: Sandeep Tripathi
Degree: Doctoral
Defense Date: Friday, April 10, 2026
Time: 1 - 3 p.m.
Location: Ball Hall 302

Committee:

  • Advisor: Amy M. Peterson, Ph.D, Professor, Plastics Engineering, University of Massachusetts Lowell
  • Wan-Ting (Grace) Chen, Ph.D., Associate Professor, Plastics Engineering, University of Massachusetts Lowell
  • Akshay Kokil, Ph.D., Assistant Teaching Professor, Plastics Engineering, University of Massachusetts Lowell
  • Jo Ann Ratto Ross, Ph.D., Adjunct Faculty, Plastics Engineering, University of Massachusetts Lowell

Brief Abstract:
Multilayer flexible retort pouches are widely used to package shelf-stable food items, including Meals, Ready-to-Eat (MREs) rations used by the U.S. military. Currently used military retort pouches rely on aluminum foil as the primary barrier layer; however, foil-based structures have limitations, including poor recyclability, flex cracking, and a lack of microwave compatibility. Inorganic metal oxide-coated, foil-free pouches have emerged as a promising, more sustainable alternative; however, their durability after retorting with different food items and during post-retort storage remains insufficiently understood. This work systematically investigates the effects of retort processing, post-retort storage, and food type on the chemical, morphological, mechanical, and barrier properties of inorganic oxide-coated multilayer retort pouches made from polyethylene terephthalate (PET), Nylon, and polypropylene (PP). Results show that retort processing induces moisture ingress into hygroscopic PET and Nylon layers, leading to plasticization. In addition, hydrolytic degradation of the outer PET layer, thermo-oxidative degradation in the inner PP layer, and microstructural damage in both the inorganic metal oxide coating and the PP layer were observed. These changes collectively result in significant deterioration of barrier and mechanical properties. During storage, recovery in barrier and mechanical properties was observed in pouches retorted without food, primarily due to moisture desorption. However, in food-filled pouches, bidirectional degradation mechanism was observed, in which moisture diffuses inward from the retort environment while lipids and proteins migrate outward from the food. This coupled transport suppresses recovery during storage and leads to further degradation in pouches packed with food items. Overall, this work establishes a comprehensive understanding of degradation mechanisms in inorganic oxide-coated multilayer retort pouches. These findings provide critical insights for designing more durable and sustainable retort pouches and support the development of next-generation foil-free pouches for demanding applications such as military rations.