ABSTRACT
In order to match the solid food oxidation during logistics and storage process under severe high temperature, a double-switch temperature-sensitive controlled release antioxidant film embedded with lyophilized nanoliposomes encapsulating rosemary essential oils (REOs) was prepared. The double switch temperature at 35.26 and 56.98 °C was achieved by development of a temperature sensitive polyurethane (TSPU) film. With biaxially oriented polyethylene terephthalate (BOPET) as a barrier layer, the intelligent complex film was prepared via coating the TSPU embedded with lyophilized nanoliposomes encapsulating REOs on BOPET. The results indicate that the REO is well encapsulated in nanoliposomes with encapsulation efficiency (EE) of 67.3%, high stability and lasting antioxidant effect during 60 days. The incorporation of lyophilized nanoliposomes containing REOs into TSPU remains the double-switch temperature-sensitive characteristic of the prepared TSPU. In agreement with porosity and WVTR results, the diffusion coefficient (D) of the antioxidant complex film sharply increases respectively at two switching temperatures, indicating that the intelligent double-switch temperature-sensitive controlled release property is functioning. Furthermore, compared with films directly added with REO, the lower Ds of films added with lyophilized nanoliposomes encapsulating REOs provides a longer-lasting antioxidant activity. Thus, the acquired controlled release antioxidant film sensitive to temperature at 39.56 and 56.00 °C can be potentially applied for protection of solid food during distribution and storage process under severe high temperatures.
ABSTRACT
In the present paper, a novel nanophosphor, Y10W2O21:Eu was synthesized through a simple and low-cost method: co-precipitation. The results of XRD show that resultant samples are Orthorhombic phase and primitive lattice. The average crystallographic sizes could be confirmed to be approximately 80 nm by means of the Scherrer formula, which are in good agreement with the particles sizes exhibited by SEM. In the excitation spectra of Y10W2O21:Eu nanophosphor, by monitoring 610 nm, the charge transfer bands (CTB) of O--Eu and O--W, centering at around 270 and 307 nm, can be observed, respectively. The spectral lines shape and locations of excitation peak corresponding to 4f-->4f transitions are similar in all samples. But the relative intensity ratios between O--Eu and O--W CTB excitation peak increase with the Eu3+ doping concentration increasing. The characteristic red emission at around 610 nm of Eu3+ was also observed, ascribed to the (5)D0--(7)>F2 transition of Eu3+, and the optimal doping concentration is 20 mol%. Finally, the transition intensity parameters omega(lamda = 2,4) and the quantum efficiencies of (5)D0 level of Eu3+ were calculated according to Judd-Ofelt theory. The results indicate that Eu(3+5)D0-->(7)F2 610 nm red luminescence can be effectively excited by 394 nm near-UV light and 464 nm blue light in Y10W2O21 host, which is similar to the familiar Eu3+ doped tungstate (e.g., Gd2(WO4)3, CaWO4). Therefore, the Y10W2O21:Eu red nanophosphors may have a potential application for white LED.
