An O2 smart plastic film for packaging

• Published in: Analyst (London) Vol. 137; no. 1; pp. 16 - 112
• Main Authors: Mills, Andrew, Lawrie, Katherine, Bardin, Julie, Apedaile, Alistair, Skinner, Graham A, O'Rourke, Christopher
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 07.01.2012
• Subjects: Analytical chemistry; Chemistry; Exact sciences and technology; Water; Polyethylene; Oxygen; Temperature; Support; Activation; Foodstuff; Air; Basic dye; Density; Methylene blue; Thiazine dye; Regulation(control); Preparation; Humidity; Pigments; Kinetics; Application; Activation energy
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/c1an15774d

The preparation and characterisation of a novel, water-proof, irreversible, reusable, UV-activated, O 2 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, TiO 2 , 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 O 2 smart plastic film. The rate of recovery is linearly dependent upon the ambient level of O 2 . 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 t 1/2 = 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 O 2 -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. The preparation and characterisation of a novel, water-proof, irreversible, reusable, UV-activated, O 2 sensitive, smart plastic film is described.