Self-heating food packaging
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Self-heating food packaging is
Chemistry
The source of the heat for the self-heated can is an exothermic reaction that the user initiates by pressing on the bottom of the can. The can is manufactured as a triple-walled container. A container for the beverage is surrounded by a container of the heating agent separated from a container of water by a thin breakable membrane. When the user pushes on the bottom of the can, a rod pierces the membrane, allowing the water and heating agent to mix. The resulting reaction releases heat and thus warms the beverage which it is surrounding.[1]
The heating agent and responsible reaction vary from product to product. Calcium oxide is used in the following reaction:
- CaO(s)+ H2O(l) → Ca(OH)2(s)
- CuSO4(s) + Zn(s) → ZnSO4(s) + Cu(s)
Anhydrous calcium chloride is often used as well. In this case, no chemical reaction occurs, instead the heat of solution is generated.
Commercial heat sources for self-heating food packaging use an exothermic (heat releasing) reaction, for which there are several common formulations. These include:
- Quicklime aka calcium oxide, and water. Quicklime, inexpensive and readily available, is generally recognized by the FDA as safe.[2]The product of the reaction is calcium hydroxide.
- Finely powdered magnesium metal alloyed with a small amount of iron, and table salt, actuated by adding water, as in an .
Some newer formulations use a Thermite-like reaction between a more reactive metal powder such as aluminum or magnesium, with a less reactive metal oxide such as iron oxide or silicon dioxide [3]
Design
Self-heating
See also
- Beverage can
- Flameless ration heater
References
- ^ US patent 5461867, Scudder, James A. & Berntsen, James L., "Container with integral module for heating or cooling the contents", published 1995-10-31, issued 1998-11-11, assigned to Insta-Heat, Inc.
- ^ "ITG Subject: New Source of Lead and Other Contamination". Food and Drug Administration. 12 August 2007. Archived from the original on 12 August 2007. Retrieved 22 September 2022.
- ^ Lorch, Mark (19 June 2018). "Self-heating drinks cans return – here's how they work". The Conversation. Melbourne, Australia. Archived from the original on 31 May 2022. Retrieved 22 September 2022.
Further reading
- Yam, K.L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6