Demonstration of a novel, flexible, photocatalytic oxygen-scavenging polymer film

Abstract

The preparation of a novel, flexible, photocatalytic, oxygen-scavenging polymer film is described. The film incorporates nanocrystalline titania particles in an ethyl cellulose polymer film, with or without an added sacrificial electron donor of triethanolamine. When coated on the inside of a glass vessel its UV-driven light-scavenging action is demonstrated by platinum octaethyl porphyrin coated glass beads sealed inside, since their luminescence increases with increasing UV-irradiation time. When used as a flexible film, work with an oxygen electrode shows that the film is able to scavenge oxygen at an average rate of 0.017 cm³ O₂ h⁻¹ cm⁻² over a 24 h period, which compares favourably to other, well-established oxygen-scavenger systems. The potential of using such as system for oxygen scavenging in packaging is discussed briefly.

Introduction

Oxygen is responsible for the deterioration of many materials either directly or indirectly [1], [2]. Examples of direct oxidation reactions include the corrosion of metals [2], tainting of beer and the browning of fruit [1], [2]. Examples of indirect oxidation processes include the spoilage of food by micro-organisms that thrive only under an aerobic atmosphere [1]. In order to limit such undesirable processes, oxygen is often excluded, e.g. by applying a layer of paint onto a metal or flushing a food package with an inert gas, such as carbon dioxide or nitrogen [1], [2], [3]. In some cases, e.g. delicate beers, valuable foods, pharmaceuticals or museum pieces, an oxygen scavenger is also incorporated into the package to maintain the oxygen at a very low level, typically <0.1%. Such oxygen scavengers are usually sold in the form of sachets or labels and comprise a mild reducing agent, such as ascorbic acid or finely divided iron or iron(II) oxide [1].

In recent years, there has been a growing interest in the development and application of oxygen scavenging polymers, usually based on ones that simply react with oxygen over time, and several commercial products have been launched successfully. For example, the Oxbar™ and Bind-Ox™, oxygen-scavenging polymer systems based on the oxidation of an aromatic nylon, MXD6, catalysed by a cobalt salt, are used currently in the manufacture of many plastic beer bottles [1], [4]. The identification of new, alternative routes to oxygen scavenging by polymers is of great current interest, and in this communication, we report on a flexible, polymer oxygen-scavenging film that has the novel feature of functioning via a photocatalytic process.