More muscular TPOs
Papers presented by General Motors and Southern Clay Products discussed numerous enhancements to automotive TPOs obtained with nanoclays. Those advances did not come easily: Early processing problems caused by clay agglomeration were ultimately resolved by optimizing the clay infeed position at the extruder, the screw design, screw speed, temperature, and pressure. Once processing issues were resolved, nanocomposite TPOs outperformed conventional talc-filled TPOs in consistency of properties, retention of low-temperature ductility, elimination of “tiger striping,” reduced paint delamination, and improved knit-line appearance, colorability, grain patterns, scratch and mar resistance, and recyclability. What's more, the lower filler level means 3% to 21% lower density (0.92 vs. 0.96 to 1.13 g/cc). Lighter weight requires less adhesive for attachment, which cuts cost.
Among the many auto exterior, interior, and under-hood applications for which nanocomposites appear suited are fascias, rocker covers, side trim, grilles, hood louvers, instrument panels, seat/IP foams, door inners, pillar covers, vertical and horizontal body and closure panels, engine shrouds, fan shrouds, air intakes, fuel tanks, and fuel lines.
In addition to TPO/nanoclay composites, GM has explored using carbon nanotubes to replace current thermoset structural composites. GM is interested in reducing reinforcement levels in Class A applications by replacing continuous carbon fibers with nanotubes or short nano-fibers. Nanotubes also have the potential to reduce plastics' coefficient of thermal expansion more effectively.
Better barriers
Polymer barrier technology is also getting a boost from nanoclays. Mitsubishi Gas Chemical (MGC) and Honeywell Specialty Polymers 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 six 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-liter 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.
Honeywell is aiming other Aegis nanocomposite grades (without oxygen scavenger) as replacements for EVOH in films and pouches. Such grades reportedly are lower in cost than EVOH, provide a better barrier that allows for light weighting, and also have better puncture resistance and good clarity. (Because of their size, nano-particles do not interfere with light transmission.)
The U.S. military and NASA, in conjunction with Triton Systems, Inc., Chelmsford, Mass., 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 three- to five-year shelf life without refrigeration, plus good clarity, processability, and recyclability.
Alcoa CSI, Crawfordsville, Ind., 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 one or two EVA layers with oxygen scavengers. This liner is said to outperform other barrier materials at very high humidity (95% to 96% RH).
LG Chem. Ltd. of South Korea has developed high-barrier, monolayer blow molded containers of HDPE with 3% to 5% nanoclay for handling toluene and light hydrocarbon fluids. LG reports that permeation of the hydrocarbon solvents is cut by a factor of 40 to 200 compared with neat HDPE.