With the breakneck pace of development in nanotechnologies, it is well to update ourselves regarding progress, if any, in the realm of food packaging.
On June 7, 2007, the Project on Emerging Nanotechnologies and the Grocery Manufacturers/Food Products Association (GMA/FPA) held a joint meeting with invited experts to begin discussing possible applications of engineered nanomaterials for use in packaging case studies (see sidebar below). Based on that discussion, three hypothetical applications will be developed to illustrate a range of possible future uses of engineered nanomaterials in packaging.
Possible Uses in Food Packaging
Three basic categories of nanotechnology applications and functionalities appear to be in development for food packaging: enhancement of plastic materials’ barrier; incorporation of active components that can deliver functional attributes beyond those of conventional active packaging; and sensing and signaling of relevant information. The following are illustrative, hypothetical examples of products in these categories that could be addressed in the case studies, though no decisions on the case study examples were made at the meeting.
• Barrier Enhancement. Nanoclays such as montomorillonite are found in nature as platelets arranged in galleries. By dispersing the platelets in a plastic matrix so that they are intercalated (separated into individual platelets) and exfoliated (with a continuous plastic phase between), a tortuous path for the passage of gaseous molecules such as oxygen, water vapor, carbon dioxide, and aromas may be created.
A tortuous path barrier assumes that the clay mineral retards the passage of these gases and that the gas molecules must therefore have a much longer diffusion path to traverse the plastic. A tortuous path also assumes that the clay platelets have an aspect ratio greater than 20:1 and are arranged so that they are all perpendicular to the diffusion path. Furthermore, many platelets must be present to function as a resistance to the diffusion.
With all of these variables (and some more) in place, a relatively small mass oaf nanoclay, less than 5% of the total, can be an effective barrier. Up to 80–90% reduction in oxygen and carbon dioxide permeation have been reported. Whether such a barrier improvement warrants the investment in incorporating the nanoclay into plastic depends on many factors.
Generally, small percentages of nanoclay improve mechanical properties such as temperature resistance; tensile, modulus, and yield strengths; and stiffness. Furthermore, the size of nanoclays permits transmission of visible light, i.e., renders the plastic film, sheet, bottle, or jar transparent (if the plastic is transparent).
Among the concepts advanced for the marriage of nanoclays with plastics for package materials are to be able to enhance the barrier of non-gas-barrier plastics such as polyethylene and polypropylene or of non-barrier package materials such as polylactic acid (PLA). Although the relatively inexpensive polyethylene and polypropylene are excellent water vapor barriers, they are poor gas barriers, and polyethylene is a poor flavor barrier. A prominent biomass-derived plastic, PLA has relatively poor barrier with low glass transition temperature and less strength than many hydrocarbon-origin plastics.
Thus, lower price or lower performance plastics might be improved by the judicious incorporation of nanoclays and subsequently be applicable in situations from which they have been effectively precluded to date: retort pouches, paperboard coatings, aseptic packaging, or packaging for oxygen-sensitive products such as orange juice, beer, and edible oils. It should be noted that nanoclays do not differentiate between gases, so carbon dioxide barrier accompanies oxygen and water vapor barriers, thus attracting attention from packagers of beer and carbonated beverages.
Another projected nanoclay property of interest is obviation of flavor scalping—an elusive objective, since the phenomenon was determined to be of consequence when plastics began their ascent into the universe of long-shelf-life food packaging.
With a few commercial applications of nanocomposite materials, largely in beer bottles in which they are buried in the structure, little public note has been yet made of their presence and impending growth in food (and probably other) packaging. Issues such as technologies for incorporation, costs, and functionalities have been discussed in trade communications. Public policy issues such as labeling, environmental impact, migration, safety, and health are some of the reasons for initiating these case studies.
• Active Packaging. Some materials are known to have antimicrobial properties at nanoscale that could potentially be applied in "active" packaging materials to prevent pathogen growth in fresh produce or meat. For example, it might be possible to formulate a multilayer packaging material could contain an outer layer of traditional film and a trap layer containing a nanoparticle system with a microbial inhibitor such as nisin or silver. A hypothetical engineered nanomaterial product of this kind might be capable of delivering functional chemicals to inhibit pathogen growth in the packaged food, while also protecting the packaged food from soil, moisture loss, and insects and other pests. An active packaging application could also be designed to stop microbial growth once the package is opened by the consumer and rewrapped with an active-film portion of the package.
• Intelligent Packaging. It may be possible to incorporate in clear package film or other packaging materials nanobiosensors engineered to react with and detect specific food spoilage microorganisms. Such sensors might be able to detect and quantify spoilage and indicator organisms in packaged products and convey to those involved in managing supply chains information they can use to ensure the safety and quality of food delivered to commercial purchasers and ultimately to consumers.
Nanotechnologies are innovative and complex, and we—all of us—know very little about them and their potential for good or harm.
Nanomaterials have very large surface areas and singular properties that do not necessarily follow the general physical laws for macro-size materials, e.g., gravity, reactivity, etc. Often, their high surface area leads to greater or faster reactivity. Smaller size can lead to higher probability of movement and entry into sites such as pores that cannot be reached by larger particles. Movement may affect nanoparticle transport within a package material or from a package material to food contents, etc.
Studies on particulates such as carbon black and titanium dioxide suggest that properties of nanoparticles are profoundly different from those of conventionally sized particles of the same molecule. Materials that are "safe" in macro and micro sizes might be more or less hazardous in nano size. Research is steadily accumulating to better understand potential effects of nanoscale materials on biological systems.
The very fact that nanomaterials behave differently from some of our comfortable physical, chemical, and biological laws should alert us to the need to understand much more. That caution might be urged is almost axiomatic to this understanding. The case studies being developed under the auspices of the Project on Emerging Nanotechnologies and GMA/FPA are one step toward ensuring that industry and government alike are asking the right questions and have a clear understanding of how those questions can and should be addressed scientifically. At a minimum, the case studies will surely ignite lively discourse that can enlighten all of us involved in this intriguing new venture.
The Project on Emerging Nanotechnologies was established to help ensure that as nanotechnologies advance, possible risks are minimized, public and consumer engagement remains strong, and the potential benefits of these new technologies are realized. The project’s efforts have focused on analyzing the oversight system for nanotechnology; detailing the needs of environmental, health, and safety risk research; and tracking public perception and consumer product uses of nanotechnology. Recent reports released by the project include "NanoFrontiers: Visions for the Future of Nanotechnology," an investigation of the future of nanotechnology; "Green Nanotechnology: It’s Easier Than You Think," an examination of green nanotechnology; and "EPA and Nanotechnology: Oversight for the 21st Century," an overview of various oversight tools for nanotechnology.
The purposes of the case studies are to build understanding and foster evaluation of industry stewardship practices and the applicable regulatory processes of the Food and Drug Administration and the Environmental Protection Agency so that the roles and responsibilities of the regulatory agencies and the industry are well understood and the system works well to assure the safety of engineered nanomaterials in food and food packaging. The case studies will describe product development pathways and stewardship practices as they relate to product safety, as well as the government regulatory processes, and will identify any scientific, regulatory, or stewardship issues that need clarification or further work to assure the safety of engineered nanomaterials.
The case studies will be developed under the direction of Michael R. Taylor, Research Professor, George Washington University School of Public Health and Health Services, with input from scientific and regulatory experts in the regulatory agencies, the food and packaging industries, and consumer organizations. The case study reports will be made publicly available as they are completed, beginning in 2008. Because the purposes of the case study project are educational and analytical, the reports will not contain policy recommendations, and the project will not engage in advocacy.
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by Aaron L. Brody, Ph.D.,
President and CEO, Packaging/Brody, Inc., Duluth, Ga.