Abstract:To explore the heating performance changes under high temperature and high humidity storage Mg/Fe flameless food self-heaters were subjected to high temperature and high humidity (55 ℃, 85% RH) conditions SEM-EDS and thermogravimetric analysis to reveal the mechanism performance decline and improve storage method. The results showed that the heating performance of the self-heater decreased over time when stored under high temperature and high humidity condition. When stored for 28 d, the startup time was increased to 68.34 s, and the high temperature maintenance time was reduced to 8.52 min, Disintegrated particles, loose surfaces, and crystallization were observed in Mg powder. The relative content of O element and the pre-reaction loss of Mg powder were increased to 52.82% and 7.71%, respectively. The oxidation and hydration reactions of magnesium powder with water vapor and oxygen led to performance degradation of the self-heaters. Given the same packaging material, adding desiccant delayed performance degradation and resulted in a startup time of 60.84 s and a high-temperature maintenance time of 9 min. High-barrier packaging materials (B2, PET/alumina/PE) effectively delayed the oxidation and hydration rate further in the early storage period; when stored for 42 d, the startup time was 43.83 s, the high-temperature maintenance time was 11.01 min, the O element content was 37.29%. Therefore, the performance degradation of self-heaters is mainly attributed to the decrease of active magnesium content due to oxidation and hydration reactions of Mg powder with water vapor and oxygen. The shelf-life of self-heaters can be improved effectively by using high-barrier packaging materials (B2) and desiccants. The above findings can provide a theoretical basis for developing practical storage methods for self-heaters.
