- May 31, 2004, Dr. Richard M. Podhajny, Ph.D. Contributing Editor
Packaging odors often are a result of residual solvents retained during the printing, coating, and laminating processes. Packaging odors also can result from secondary sources, such as decomposition products from the inks, coatings, adhesives, or packaging substrate itself.
These odors can be a result of resin oxidation, corona discharge-induced oxidation of films or film additives, and the thermal degradation effects on the processed packaging materials. Whereas adhesive lamination can produce higher solvent retention, extrusion lamination can suffer from thermal decomposition of the resin materials, leading to odoriferous by-products.
Removal of undesirable odors in packaging products is a major area of focus in today's packaging development.
Not only is the focus on limiting the usual sources of odor, such as solvent retention, but also on incorporating odor scavenging additives to further reduce the odoriferous products in order to produce packaging products that offer superior “freshness.” Just controlling the retained solvent levels is not going to make the grade in this very competitive arena.
The use of water-based products that contain amines or ultraviolet-curable products potentially can bring additional sources of odor into the package. The presence of acrylic monomers can produce odors that can taint the food products.
Today's packaging development focus is on odor-scavenging. Many different approaches are being taken to extend shelf life of packaged food and reduce objectionable odors, including (1) the use of anti-oxidants in packaging substrates to reduce the level of aldehydes and other odoriferous oxidation by-products; (2) molecular sieves; (3) activated carbon and; (4) oxygen scavenging additives.
The use of antioxidants such as BHA, BHT, and Vitamin E can be an effective packaging strategy in reducing the oxidation of packaging ingredients as well as the packaged food. The lower the level of oxygen, the lower the oxidation and the longer the shelf life. To this end, oxygen scavengers in some applications are used. Films that can absorb oxygen can reduce the oxygen level within the package to near 0% within a few days. Other additives can be used as sachets and can reduce the oxygen within the package.
Aluminum, metallized films, PVDC-coated films, and EVOH film composites provide a high degree of oxygen barrier. However, today's demand for extended shelf life and fresher products are pushing the envelope to reduce the oxygen and oxidation process. The packaging material has to keep oxygen from penetrating the interior of the package, but in addition, the developmental focus is to reduce the oxygen and absorb oxidation by-products.
Additives can be used that are effective as scavengers for odoriferous oxidation by-products, such as aldehydes. Activated carbon and zeolites are some examples of additives that can absorb odoriferous packaging products.
In addition to oxidation decomposition products, packaging odors are generated from the biological degradation process of the packaged food. This degradation process produces odoriferous odors that reduce product freshness. Use of antimicrobial additives can, in some cases, reduce the growth of microbes that contribute to odor generation. For example, emitting ethanol has been shown to reduce the off-odor and extend the shelf life of some packaged foods.
The odor of residual ethylene can be problematic. It can be removed using activated carbon or reactive additives that can oxidize the residual ethylene further.
As new materials are introduced into packaging decoration and barrier properties are added, the source of new odors can be difficult to determine, and new odor standards need to be established and test methods identified.
To be effective against package headspace odors, these additives must target specific chemicals. For example, aldehydes — oxidation by-products — can be targeted to reduce this odoriferous component from the package headspace. Since oxidation can continue to occur, the effectiveness of any aldehyde scavenger will depend on the degree of oxygen reduction that can be incorporated into the package design.
As new substrates, inks, and adhesives become part of the packaging landscape, new challenges arise in the efforts to control sources of packaging odor. To meet these challenges, packaging engineers are focusing their attention not only on meeting demand through increased barrier properties but designing packages to reduce the packaging odors actively.
Dr. Richard M. Podhajny has been in the packaging and printing industry for more than 30 years. Contact him at 267/695-7717; email@example.com