In food packaging, aluminum foil is used as an uncoated metal and in combination with other materials. Bare aluminum foil is mainly used as household foil, packaging materials (such as chocolate) and trays. The vast majority of food packaging relies on aluminum-converted forms of foil, which means that the packaged food does not come into contact with the packaging in the foil itself, but rather with a layer of lacquer and plastic as an intermediate layer of coating. These coatings act as a protective layer to prevent high salt or acid corrosion of food, and as a heat seal layer to achieve a tight seal on the package. Layers of aluminum foil can also be built into packaging consisting of paper or cardboard.
Aluminum is a silver-white metal that belongs to the boron family of chemical elements with an atomic number of 13. It has many important features:
Σ Its density is one-third that of steel, making it a lightweight metal.
Σ The strength in alloy form is very high: whereas the yield strength of pure aluminum is 7–11MPa, the yield strength of aluminum alloys ranges from 200 to 600 MPa.
Σ Corrosion resistance due to "passivation": Aluminum oxide forming a thin layer on the metal surface prevents further oxidation.
Σ It is malleable and malleable at room temperature and easy to form.
Σ It is non-magnetic but a good conductor of heat and electricity. Aluminum is widely used in packaging in the form of aluminum foil, which is just over 6 to about 150 microns thick (a micron is one millionth of a meter). The key properties of aluminum as a packaging material are summarized in Table 9.1. One of the most...
An important property of aluminum as a packaging material is that it is relatively inert to most metals. As mentioned before, when exposed to air, aluminum forms a transparent oxide layer that prevents further oxidation. In addition to being corrosion-resistant, aluminum is non-absorbent, making it an effective barrier to gases and liquids. Heavier foils (larger than 17 mm) completely block gases and liquids. Thinner gauges do allow some transmission: for example, a typical water vapor transmission rate (WTVR) for a 9 mm thick foil is 0.3 g/m2 per 24 hours (at temperature 38°C, relative humidity 90% RH). Aluminum is also stable in cold conditions and can be used for freezing foods. It is resistant to temperatures below 150°C, making it suitable for both refrigeration and reheating of food.
