Biomedical Engineering Reference
In-Depth Information
Metal
The metals used most commonly in the manufacture of food packaging containers
are steel (tin or chromium plated) and aluminum. These metals have a wide range
of mechanical and forming properties, with good strength and low toxicity. Metal
containers are excellent barriers to water vapor, gases, and light, and can tolerate
wide extremes of temperature, such as those found under retort processing condi-
tions. To prevent interactions between products and their containers that could lead
to internal corrosion or staining, internal protective coatings are used frequently in
metal containers; exterior coatings and decorations may also serve to protect the
packaging material against the environment. Disadvantages of metal containers
include the limited shapes available, their considerable weight, and their lack of
suitability for in-container microwave heating of products. Although not generally
reusable, metal containers are nevertheless readily recyclable where collection pro-
grams are in place.
Aluminum foil in the form of thin-rolled sheets of aluminum has additional
applications in laminated flexible packaging and in formed or semi-rigid containers.
However, thinner foils are considered to be somewhat permeable to gases and water
vapor due to the presence of minute pin holes. In other applications, metallized
plastic films are manufactured by condensing aluminum vapor on the surface of
films to improve barrier properties.
Paper and Board
Packaging papers tend to be coarse papers made from unbleached kraft softwood
pulps, and include grease-resistant, glassine papers, and vegetable parchments used
for wrapping foods where resistance to oil, grease, water, and odors is required.
These papers provide structure, light weight, and printability; however, they are
vulnerable to water absorption and puncturing. Paperboard provides a further degree
of strength in packaging applications, such as folding cartons which can also be
laminated or coated to impart specific barrier properties. For example, the laminated
multi-layer brick-shaped structures widely used in aseptic packaging applications
consist of an internal layer of paperboard for rigidity and protection of an aluminum
foil barrier layer, while outer and inner plastic layers provide additional barrier
properties, heat sealability, and food contact surfaces. Transport packaging is gen-
erally made from corrugated paperboard which can be designed to meet the strength
and limited barrier requirements of secondary packaging.
Plastics
Plastic films and containers have many advantages over glass, metal, and paper in
terms of versatility of package shapes, sizes and structural properties, light weight,
toughness, low material cost, microwavability, and generally require less energy for
manufacturing and transportation. The most limiting factor for the use of plastics in
food and beverage packaging is permeability to water vapor, gases, and light. For
example, gas molecules can dissolve and diffuse through plastic materials, and can
thereby enter or leave a closed package. However, knowledge of the gas permeation
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