I am a mechanical engineer by training (degree in Engineering Science, many years ago). I am also an academically trained historian and anthropologist, and nowadays, I do engineering-oriented public policy analysis. My chemical knowledge approximately ends with NAPOM (Nature and Properties of Materials, ie. Introductory Metalurgy). The little I know about organic chemistry is confined to fuels, and the kindred topics of batteries and explosives. What follows is a speculation which arose in the course of buying groceries from Amazon. I became aware that Amazon was inadvertently testing the limits of quality control, and started thinking about what would be required to keep them honest. One obvious requirement is that frozen foods should proveably stay frozen.
The object is to create a product tag for frozen goods, specifically frozen foods, which reveals whether they have remained frozen, or not.
An uninformed suggestion runs as follows: Two chemicals are held apart, in separate frozen layers, sealed up in a plastic package. If the package thaws, the chemicals combine, and go through an irreversible reaction, which produces a change of color, litmus paper fashion. Certain conditions are that the thing would have to be very cheap, on the order of a fraction of a cent, and that it would have to be reasonably nontoxic.
This would be applied to a packet of noodles, costing a dollar or two. So one could not use a micro-controller-based sensor, or anything like that.
I place any conceivable rights I might have in the foregoing into the public domain, and I invite your critique, suggestions, ridicule, etc.
Andrew D. Todd
1249 Pineview Dr., Apt. 1
Morgantown WV 26505
That is a realistic approach. The trick is to manage the phase change, since the application to a package might not be at freezing temperature, nor would the production, shipment and storage be practical at freezing temperatures.
What might work, using 3-D printing technology to keep costs down, is a sheet of very small solution wells with an interface compound that breaks DURING the freezing process - along with the indicator solutions, which could be as simple as a weak acid-base reaction with a colored indicator. The produced indicator sheets could be applied anywhere on a product or package before freezing. When the product is frozen, or packaged for freezing, the cold temperature would freeze both the acid and base solutions, keeping them immobile, and break the separating wall between the two reservoirs.
Then, if the product warms up above freezing (possibly a selectable point, depending on the wall material and the solutions) the liquified solutions would mix, react and change the color. Nothing short of breaking the “sensor” and adding more acid or base would change the color, even if refrozen.