An O₂smart plastic film for packaging

Abstract

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 mW cm(-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 kJ mol(-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.

Self-adhesive graphene oxide-wrapped TiO2 nanoparticles for UV-activated colorimetric oxygen detection

“…As can be seen in Fig. 6C, the initial rate of the color recovery was also dependent on temperature; the more rapidly the film responded to oxygen, the higher the temperature was as expected [10,27]. An activation energy calculated using the Arrhenius equation was 40 kJ/mol, which was not quite different from the value of 54 ± 4 kJ/mol reported in the literature [32].…”

“…6B shows the initial recovery rate of the MB/GO-TiO 2 /glycerol/HEC film as a function of oxygen concentration. The recovery rate was proportional to the oxygen level in the gas phase as reported in the literature [6,9,26,27,32]. The direct relationship between the rate and oxygen concentration is not unexpected recalling the dark color recovery is a reaction of LMB with oxygen (2LMB + O 2 → 2MB + + 2OH − ).…”

“…When plotted against wavelength, this function generates a spectrum similar to the absorbance spectrum [27].…”

“…The recovery reaction was completed within 20 min, and the photobleached MB/GO-TiO 2 /glycerol/HEC film successfully regained its blue color as LMB was reoxidized to blue MB. This color recovery is significantly rapid, considering the other leaching-resistant indicator films based on hydrophobic polymers showed the recovery times of 5 days with SPS [9] and 2.5 days with low-density polyethylene [27].…”

Indicators for optical oxygen sensors

“…Very recently, Mills et al [162] used a redox dye, methylene blue (MB 3b , Fig. 3) in combination with a sacrificial electron donor, DL-threitol, and TiO 2 particles to create an oxygen-sensitive pigment that was then incorporated into a thermoplastic polymer and used as an O 2 smart plastic film.…”