A good deal of research work is being carried out on nanoparticles and their contribution in the field of plastics. They are still in the infancy stage, but if the forecasts are right, nanocomposites could turn out to be the biggest little thing to hit plastics in decades. Polymers reinforced with as little as 2% to 5% of these particles via melt compounding or in-situ polymerization exhibit dramatic improvements in thermo-mechanical properties, barrier properties and flame retardancy. They also can outperform standard fillers and fibers in raising heat resistance, dimensional stability and electrical conductivity. Dispersion of nanoscale reinforcements in polymers are already entering the marketplace in automotive and packaging applications, albeit in a low-profile manner and slower than anticipated. But that pace is expected to speed up dramatically.

Three recent conferences on this special product had more than 200 presentations on various aspects of nanotechnology. A report from market research firm Business Communications Co. Inc., estimates the total worldwide market for polymer nanocomposites at about 10,000 MT in 2003, valued at US$90.8 million. It also projects the market to grow at an average annual rate of 18.4% to reach US$211.1 million by 2008. Even if nanodevelopments hit some snags, the rate of growth in a few applications will be faster than 20% pa.

The two types of nanofillers that have been most widely discussed and the first to break into commercial use are nanoclays and carbon nanotubes. Both must be chemically modified with surface treatments in order to achieve the fine dispersion and resin coupling required to derive maximum benefit. Both of these nano-fillers have demonstrated improvements in structural, thermal, barrier and flame-retardant properties of plastics. Carbon nanotubes also enhance electrical conductivity.

So far, nanoclays have shown the broadest commercial viability due to their lower cost of US$5-7/kg, and their utility in common thermoplastics like PP, TPO, PET, PE, PS and nylon.

The leading nanoclay is montmorillonite, a layered alumino-silicate whose individual platelets measure around 1 micron diam., giving them an aspect ratio of 1000:1. The two major producers are Nanocor with its Nanomer line, and Southern Clay Products with its Cloisite line. Both companies have formed alliances with suppliers of resins and surfactants, compounders and automotive OEMs and packaging firms. While much of their work is proprietary, they have disclosed several commercial successes.

Carbon nanotubes include both single and multi-walled structures. The former have a typical outside diameter of 1 to 2 nm while the latter have an OD of 8 to 12 nm. They can range in length from the typical 10 microns to as much as 100 microns and have at least a 1000:1 aspect ratio. Carbon nanotubes have 50 times the tensile strength of stainless steel (100 GPa vs. 2 GPa) and 5 times the thermal conductivity of copper. When incorporated into a polymer matrix, they have the potential to boost electrical or thermal conductivity by orders of magnitude over the performance possible with traditional fillers such as carbon black or metal powder.

The suppliers of nanotubes include Hyperion Catalysis with its Fibril multi-walled nanotubes and a newcomer Zyvex Corp. with its NanoSolve single or multi walled tubes. Both suppliers now offer their products in masterbatches that typically contain 15% to 20% nanotubes.

Polymer barrier technology is also getting a boost from nanoclays. Mitshubishi and Honeywell both are using Nanocor's nanoclays in nylons as barrier layers in multi-layer PET bottles and films for food packaging. MGC's MXD6 nylon nanocomposite, called Imperm N, is used commercially in Europe in multi-layer PET bottles for beer and other alcoholic beverages. It is also being evaluated for small carbonated soft-drink bottles. Other Imperm applications that will debut in the next 6 months are multi-layer thermoformed containers for deli meats and cheeses and flexible multi-layer films for potato chips and ketchup.

Honeywell has aimed its Aegis nylon 6 nanocomposites initially at PET beer bottles. In late 2003, a version containing an oxygen scavenger made a commercial splash with the introduction of the 1.6 litre Hite Pitcher beer bottle from Hite Brewery Co. in South Korea. Aegis is the barrier layer in this three-layer structure, which is said to provide a 26 week shelf life.

The U.S. military and NASA, in conjunction with Triton Systems Inc., are looking into nanoclay as a barrier enhancer for EVOH in long-shelf-life packaging. An experimental thermoformed food tray was made from EVOH plus 3% of Southern Clay's Cloisite in a layer sandwiched between two PP layers. It reportedly imparts a 3- 5 year shelf life without refrigeration, plus good clarity, processability and recyclability.

Alcoa CSI is seeking a patent on coextruded barrier liners for plastic bottle caps for beer, juice or carbonated soft drinks. The liners include a layer of nylon 6/nanoclay composite plus 1-2 EVA layers with oxygen scavengers. This liner is said to outperform other barrier materials at very high humidity (95% to 96% RH).

Extensive research at NIST has established the effectiveness of nanoclays as flame-retardant synergists. Nanoclay levels of 2% and 5% in nylon 6 reduces the rate of heat release by 32% and 63%, respectively.

Specialty compounder Foster Corp. recently demonstrated that higher levels (13.9%) of nanoclay can be added to nylon 12 elastomers to achieve UL 94V-0 rating at 1/8-in. thickness. Used as a char former, the nanoclay allows the typical 50% loading of halogen/antimony oxide flame-retardant system to be cut in half, which significantly reduces detrimental effects on physical properties. The company first introduced nylon 12/nanoclay compounds for tubing and film in 2001.

Germany's Sud-Chemie (U.S. office in Louisville) offers modified nanoclays called Nanofil as flame retardants. It recently developed halogen-free EVA/PE wire and cable compounds containing 3% to 5% of new Nanofil SE 3000, plus 52% to 55% alumina trihydrate or magnesium hydroxide (typically used at 65% levels). The result is said to be improved mechanical properties, smoother cable and higher extrusion speeds.

Two recent studies by Hyperion Catalysis show that multi walled carbon nanotubes may act as a flame retardant without use of halogen. In both EVA and maleic-anhydride-modified PP, 2.4% to 4.8% loadings of nanotubes show heat-release rates comparable to or better than those obtained with nanoclays.

Among its many virtues, nanoclay can work as a nucleating agent to control foam cell structure and enhance properties of polymeric foams for applications from insulation to packaging. The University of Toronto's Dept. of Mechanical and Industrial Engineering studied extrusion of chemically foamed LDPE/wood-fiber compounds. Addition of 5% nanoclay to the mix decreased the cell size, increased the cell density and facilitated foam expansion. When burned, the foam showed good char formation. Similar results were obtained in LDPE/nanoclay foam blown with CO2 gas.

Researchers at Ohio State University's Dept. of Chemical Engineering (Columbus) found that small amounts of nanoclay surface-grafted with PMMA can reduce cell size and increase cell density in microcellular PS foamed with CO2. Another OSU study showed that smaller cell size and higher density can be achieved with 5% nanoclay in polyurethane foams blown with pentane or water.

Louisiana State University's Mechanical Engineering Dept. (Baton Rouge) reports that 4% to 5% nanoclay increases the flexural strength and elongation of epoxy syntactic foams used as core materials for sandwich composites in structural applications.

(based on papers from: Nanocomposites 2004 in San Francisco, SPE Antec 2004 in Chicago, Nanocomposites 2004 in Brussels, Belgium)