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An O2 smart plastic film for packaging

Mills, Andrew and Lawrie, Katherine and Bardin, Julie and Apedaile, Alistair and Skinner, Graham A. and O'Rourke, Christopher (2012) An O2 smart plastic film for packaging. Analyst, 137 (1). pp. 106-112. ISSN 0003-2654

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Abstract

The preparation and characterisation of a novel, water-proof, irreversible, reusable, UV-activated, O2 sensitive, smart plastic film is described. A pigment, consisting of a redox dye, methylene blue (MB), and a sacrificial electron donor, DL-threitol, coated onto an inorganic support with semiconductor functionality, TiO2, has been extruded in low-density polyethylene (LDPE). The blue-coloured indicator is readily photobleached in <90 s using UVA light (4 mWcm−2), whereby MB is converted to its colourless, leuco form, leuco-methylene blue (LMB). This form persists in the absence of oxygen, but is re-oxidised to MB in 2.5 days in air under ambient conditions (21°C, 65% RH) within the O2 smart plastic film. The rate of recovery is linearly dependent upon the ambient level of O2. At the lower temperature of 5°C, the kinetics of the photobleaching activation step is largely unchanged, whereas that of recovery is markedly reduced to t1/2 = 36 h at 5°C (cf. 9 h at 21°C); the activation energy for the recovery step was calculated as 28 kJmol−1. The O2-sensitive recovery step was found to be moderately dependent upon humidity at 21°C, but not significantly dependent upon humidity at 5°C. The possible application of this type of indicator in food packaging is illustrated and discussed briefly.