# Optimizing shape memory polyurethane films for stimuli-responsive food preservation

## TL;DR

Researchers developed smart shape memory polyurethane films that can help preserve fresh food by adjusting gas permeability in response to temperature changes.

## Contribution

The study introduces optimized SMPU films with tailored CO/PEG ratios that enhance shape memory and water vapor permeability for food preservation.

## Key findings

- SMPU films with a 40/60 CO/PEG ratio showed a shape recovery ratio of over 96% and a phase transition temperature range of −18 to 1 °C.
- Films with lower PEG content demonstrated stronger barrier properties, suitable for packaging foods with low respiration rates.
- The optimized films extended cabbage preservation by reducing water loss to 3% and could prolong freshness by up to 10 days.

## Abstract

Shape memory polyurethane (SMPU) films have garnered significant research interest because of their ability to demonstrate reversible shape changes in response to external stimuli. Thus, they are promising candidates in applications such as food preservation. Considering this, the present research explores the optimization of SMPU films that are specifically tailored for stimuli-responsive food preservation, incorporating the effects of various film compositions on the gas permeability and temperature sensitivity of polyurethane films. Using polyethylene glycol (PEG), 1,6-hexamethylene diisocyanate (HDI), 1,4-butanediol (BDO), and castor oil (CO) as essential ingredients, SMPU films were synthesized. This study focused on determining the thermal properties, shape-memory, and water vapor permeability of the synthesized films. Polyurethane films prepared at different CO/PEG ratios revealed phase transition temperatures (switching temperatures) ranging from −18 to 1 °C. The prepared SMPU films containing 40/60 CO/PEG exhibited outstanding shape-memory capabilities. These films had a shape recovery ratio of greater than 96%, which could contribute to an improvement in the preservation of fresh produce in a crisper by up to 10 days. Moreover, the SMPU film with 40/60 CO/PEG demonstrated greater water vapor permeability, with cabbage leaves losing 3% of their water content. The films with lower PEG contents exhibited stronger barrier properties than those with higher PEG contents and may be suitable for packaging foods with lower respiration rates. These new film formulations hold great promise for the development of smart packaging solutions since they provide thermally responsive gas permeability, which can help in preserving fresh foods for longer periods. These findings could pave the way for the development of novel packaging materials that are responsive to changing environmental conditions, thereby enabling more sustainable food preservation.

Shape memory polyurethane (SMPU) films have garnered significant research interest because of their ability to demonstrate reversible shape changes in response to external stimuli.