Nano and Food Packaging Technologies Converge

Nanotechnology—actually nanotechnologies—for packaging will grow from a $ 66-million business in 2003 to $360 million by 2008, an astonishing 40% annual increase, if Graham Moore and his colleagues at the Packaging Industries Research Association (PIRA, www.piranet.com) are anywhere near target in their prognostications.

Whether this will occur depends on a host of factors converging successfully in the foreseeable future. Those who have been tracking the science or performing research for food technology applications should welcome the parallel activity that often borders on the interactivity of food product contents and their packaging.

In the realm of “hot topics,” nanotechnology ranks high today, largely on the basis of claimed universal potential but also with some intriguing possibilities in our relatively narrow niche of food packaging. For those who have been sojourning on the far side of the moon during the past five years or so, nanotechnology is the discipline that deals with manipulation of matter at the molecular to the micron level. Many scientists draw the boundary at particles in the size range of 10–9 meters, where they believe that new laws of physics may apply.

Potential Applications
Among the potential applications enumerated for nanotechnology are the following:
• In materials science, quantum dots and quantum-dot lasers; nanocomposites, which are the basis for much of the past and present packaging hyperbole; and self-assembled devices such as wires.

• In electronics and opti-electronics, reflectors to alter the paths of photons for visual displays; semiconductors; plastic electronics, e.g., to modify the electrical properties of plastics; molecular electronics; and memory and storage on sub-chip-size particles.

• In the biomedical area, on-demand controlled drug delivery, which could be applicable to the delivery of antimicrobials or aromas from package structures; targeted wireless-communicating, cancer-killing nanoparticles (shades of Raquel Welch’s “Fantastic Voyage”!); lab on a chip; tissue engineering; self-healing/sealing uniforms (might this concept be applicable to maintaining package hermetic integrity?); cosmetics (although in this arena, some questions have arisen on the possibility of nanomaterials entering the bloodstream); and ultraviolet radiation filters, i.e., sunscreens.

• In industrial applications, chemical catalysts and automotive applications, such as composites for engine compartments (already in commerce) and nanostructured and self-cleaning windshield glass (also applicable for buildings); water and air filtration/purification; and carbon nanotubes as the basis for fuel and solar cells.

• In forest products, in the form of paperboard and corrugated fiberboard (which still constitute the largest single fraction of packaging today), surface modifications of wood and pulp to reinforce the fibers, impart color, and even impart real water vapor and/or gas barrier properties, a perpetual deficiency of the base materials in packaging applications.

In a reversal of application of nanotechnology to forest products, NanoAdd, an Israeli startup company, has developed a nanocellulose, which they call NanoCell. This wood cellulose–based nanomaterial is claimed to be a wood-fiber-replacement filler for plastics and coatings to enhance strength and biodegradability.

• In food packaging, focus on the elementary components of food packaging and the perceived links with nanotechnology offers some intriguing possibilities: silicate nanoparticles (the current major target opportunity); metallic/ceramic nanoparticles (carbon nanofibers) to combine light weight and strength for both equipment and structures; self-assembled monolayers to offer functionality in single layers, thus obviating multilayers and their vagaries; nano bar codes; gas-barrier structures; encoding or decorating individual surfaces; counterfeit protection, especially for high-value consumer products, using nanotaggants; nanocrystalline indicators to sense and signal modified-atmosphere environments within packages; light-activated oxygen-sensing inks; food deterioration sensors; and power for intelligent packaging, such as radiofrequency identification (RFID). Although this list represents only a summary of some packaging potentials, it appears to be formidable in terms of magnitude and possible future significance.

Integration of Nanoclays with Plastics
The challenges of the “relatively simple” alternative of incorporating nanoparticles into plastic matrices are large. Conceptually, the nanoparticles with large aspect ratios should be aligned to produce a multiplicity of layers of fl at platelets that would function to retard the diffusion of gas such as oxygen or water vapor through the plastic by creating tortuous paths. The keys to achieving this structure lie in compatabilizing and exfoliating the nanoclays to uniformly disperse and align them in the plastic matrix.

Although the clays are relatively inexpensive, the additive materials and the processes to ensure their proper alignment are not cheap. If the minerals are to be employed, new methods to incorporate them into the plastic must be developed. Currently, natural clays cost about $3–15/lb, synthetic clays about $10–20/lb, and nano-structured silicons up to $200/lb. Thus,the present cost structure for nanocomposites as barrier materials is not necessarily meeting the commercial hopes, an obstacle that faces many new package materials.

Developers are persistent in their pursuit of clays as nanocomposites because of the notion that natural minerals should be inexpensive as an additive. Other materials are more compatible with the objectives but obviously cost a lot more. I recall the early days of incorporating minerals such as calcium carbonate into polypropylene as a perceived means of reducing the cost of the plastic to that of paper and effecting a universal substitution, an initiative that failed to even approach the expectations. Might today’s initiatives be an analogous adventure fueled by the dazzle of the notion of “molecular manipulation”?

An example of this direction is Nano-PA6, made by Nanocor, Inc., Arlington Heights, Ill. (www.nanocor.com) by applying nanomer in-situ polymerization with high (20%) nanoclay loading. Nanocor and Mitsubishi Gas Chemical, New York, N.Y., have developed a product dubbed Imperm®, a nanocomposite nylon MXD6 with what they claim are outstanding gas and water-vapor barrier properties.

Perhaps the most-publicized probe into nanotechnology for packaging has come from the U.S. Army Natick Soldier Center, the core site of military ration research. Work has been underway for several years searching for alternatives to laminations (particularly aluminum foil) to increase the shelf life of ambient-temperature shelf-stable foods (retort pouches); to reduce solid waste from package materials and facilitate recycling; and to permit rapid reheating in field microwave ovens.

One direction is to incorporate nanoclay platelets into plastic substrates to improve gas and water vapor barrier, increase thermal resistance, and mechanically strengthen the package structure. The Natick staff report that they have formulated plastics containing 1–5% nanoclay platelet weight in twin-screw extruders coupled with blown-film equipment. According to their reports, the clay platelets are properly dispersed to maximize orientation, a key variable in producing the tortuous pathways that resist the diffusion of gas within the plastic matrix.

Natick research has focused on polyethylene, polyester, and ethylene vinyl alcohol (EVOH). Results have demonstrated increases of 80% in thermal resistance and 100% in mechanical strength. Unfortunately, even when combined with nanoclays, EVOH continued to display sensitivity to water vapor.

Nanotubes
Nanotubes are cylinders with nanoscale diameters of 10–150 nm and lengths of 500–15,000 nm, as are found in halloysite clay, i.e., layered aluminosilicate similar to kaolin. Nanotubes appear to be able to enhance the strength of base polymers far more than do conventional bentonite clays, and may obviate the need for exfoliating agents usually required for dispersion of clays in plastics.

Furthermore, the nanotube lumens (hollows) may be filled with materials such as antimicrobials to disperse in the plastic matrix. Developers have postulated that incorporation of nanotubes into compostable plastics such as polylactic acid (PLA) could strengthen the otherwise somewhat marginal physical properties of the material, such as thermal resistance. Some research from Natick indicated that a nanocomposite with PLA exhibited a 200% better water vapor transmission rate than pure PLA, plus increased modulus and toughness.

Nanotubes might also incorporate materials that would improve bioactivity and hence biodegradability of the PLA, still an issue. Thus, by combining two lively contemporary technologies of biomass sourcing plus nanotechnologies, a new family of biodegradable, effective, functional barrier package materials might emerge. In this ultimate scenario, the dissonant attributes of protection and instant return to the Earth after use can be envisioned.

We’re in the Early Stages
The principal commercial applications today are fairly mundane, considering the broad spectrum of interests and study. They include circuit boards for cell telephones; stain-resistant fabrics for outdoor apparel; golf balls and clubs; “bouncier” tennis balls; lightweight automobile parts such as bumpers and no-waxing finishes; and highly electrically conductive films; and others. In other words, the hyperbole has not yet met the reality.

The basic thrust of this food packaging research and development is that nanotechnology is one possible pathway to hydrocarbon (and biomass) plastic enhancement to conjecture much lower mass and thus less cost to achieve the necessary and desirable functionalities. On the other hand, the descriptive term “nano” signals to many scientific heights (or the reverse, to be technical about it) and glamour. Words prefaced with “nano” might appear to be as exciting as radiation, or biodegradable, or laser sterilization of recent vintage.

To paraphrase some of the pioneers in the science, we are in the primeval stages of tinytiny, entering into unexplored universes; we cannot expect to necessarily gain immediate commercial benefits from potential. Most responsible professionals are optimistic, but for the distant future. Let’s meet again tomorrow to contemplate the next generation of learnings and launch our developments from that platform.

by Aaron L. Brody,
Contributing Editor,
President and CEO,
Packaging/Brody, Inc., Duluth, Ga.
[email protected]