By Jan H. Schut
Imagine nonmetallic wires for airplanes that could save thousands of pounds of weight and not start electrical fires. House paint that converts heat to electricity to run your lights. Highly conductive organic plastic films that can replace today’s films made of costly rare metals like tellurium. Or charging your cell phone using body heat.
When the Lehigh Valley Section of the Society of Plastics Engineers hosts this year’s Polymer Nanocomposites 2011 conference March 7-9 at Lehigh University in Bethlehem, Pa. (www.4spe.org/sites/default/files/polynanon11-techpgm.pdf), much of the excitement will be generated by new nanocomposite technologies targeting futuristic uses like these. “The energy storage theme runs through the whole conference,” says technical program chairman Raymond Pearson, a professor at Lehigh, “but not by design.” That’s just where the leading edge seems to be.
The two days of presentations are divided into silicate-based and carbon-based nanocomposites with new energy storage technologies emerging with both nano materials. I regrouped the technologies instead by their polymeric component: thermoplastic, emulsion, or thermoset. Here are some of the exciting new technologies that will be presented either for the first time or for the first time to a plastics audience.
New Thermoplastic Nanocomposites
Emmanuel Giannelis, professor at Cornell University, Ithaca, N.Y. (www.cornell.edu), in his “Polymer Nanocomposites: Status Report” will present solvent-less liquid nanomaterials for the first time (www.ip.cctec.cornell.edu). The patent-applied-for nanoliquid technology (U.S. Pat. Applic. # 2007/0254994) can be based on silica, carbon and a variety of metal nanoparticles. The nanoparticle core is functionalized by a charged corona, so the nanoparticles flow like liquids. But because they contain no solvent or diluent, they give off no vapor. They can also be dispersed into thermoplastics at high loadings. In early testing Cornell researchers have made composites of PP with up to 30 wt % nanoliquid silica. Adding the nanoparticle fluid had little affect on polymer properties, Cornell’s Giannelis says, except to impart thermal conductivity. Still in the early stage, these materials could potentially be used to create thermoplastics with tunable levels of electrical or thermal conductivity.
Changzai Chi, a senior scientist at DuPont Co. in Wilmington, DE (www.dupont.com), will describe the “Effect of Particle Shape and Surface Chemistry on Dispersion of Nanofiller and Properties of Polymer Composites,” analyzing and comparing several surface treatments for nanosilica and their effects on dispersion in a thermoplastic. This will also be the first presentation of DuPont’s patent-pending technology for in situ polymerization of nanosilica-filled polymers, including PPT (Sorona) and other polyesters. The reported test results show that by dispersing colloidal silica first into PDO monomer before polymerizing the PPT composite, nanosilica is much more evenly dispersed. DuPont treated the silica nanoparticle surface with proprietary patent-pending silane in PDO. Dispersion improved so much that the composite material is reportedly as clear as the neat resin–only 20.8% haze–where dispersing untreated nanosilica makes a composite with 88% haze. Testing is still early, but the expected benefit from the treated nanomaterial is improved mechanical properties without loss of clarity.
Joseph Golba, Jr., lead scientist, reactive extrusion at PolyOne Corp., Avon Lake, Ohio, will give an update on PolyOne’s ongoing work to produce scalable “CNT-Based Nanocomposites: Full Formulations and Masterbatches.” For two years PolyOne has had a team of six scientists, engineers, and chemists working on scalable production methods to make electrically conductive carbon-nanotube composites with thermoplastics. Other partners supporting the research include Columbus, Ohio-based Ohio Third Frontier (www.ohiothirdfrontier.com), a state board that awards grants for new technology development, and Zyvex Technologies (www.zyvexpro.com), which makes functionalized carbon nanotubes. PolyOne’s initial research focused on melt compounding, and established that there was no difference in dispersion of carbon nanotubes between using fully formulated polymer or masterbatch. The group’s next R&D focus will be reactive polymerization of CNT into caprolactam to make nylon 6 composites.
New Nanoparticle Emulsions
Jaime C. Grunlan, associate professor at Texas A&M University, College Station, Texas, (www.tamu.edu) will describe the “High Electrical Conductivity and Thermoelectric Performance in a Segregated Network Polymer” for the first time to a plastics audience. His “segregated-network polymer nanocomposites,” introduced two years ago to chemists and composites engineers, are formed by suspending carbon nanotubes and latex particles in water and then coating this emulsion onto a substrate. When the emulsion dries, it leaves a closely interconnected grid of carbon nanotubes packed around spherical molecules of latex, which is highly thermoelectrically conductive. Additionally, applying negatively stabilized nanotubes and positively-charged polymers in very thin alternating layers creates a highly electrically conductive film. This clear film approaches the electrical conductivity of Indium-Tin Oxide coatings for potential applications like touch screens and solar panels, Texas A&M’s Grunlan says, but at much lower cost.
Harris Goldberg, president and CEO of InMat Inc., Hillsborough, N.J. (www.inmat.com) is introducing new nanocomposite barrier coatings that are here and now in “Aqueous Nanocomposite Barrier Coatings – A more sustainable option for reducing permeation.” The 10-year-old company makes a range of Nanolok composite barrier coatings less than a micron thick for flexible packaging. The clear coatings, which contain a variety of exfoliated clay nanoparticles, including vermiculite and montmorillonite, can significantly improve the oxygen barrier of thermoplastic packaging films. For example, 1-mil PP film with a 1-micron coating of Nanolok has its oxygen barrier improved more than 1000 times, while its moisture barrier is improved two to three times. InMat will present a new line of more water-resistant formulations (Nanolok WR), which provide good oxygen barrier in up to 85% humidity, where previous formulations provided good barrier only up to 80% humidity. InMat is also testing a new flexible barrier coating formulation, which could potentially allow barrier coated films to be thermoformed.
New Thermosetting Nanocomposites
Erik Thostenson, assistant professor at the Univ. of Delaware in Newark (www.udel.edu) in his presentation on “Carbon Nanotube-Based Multifunctional Composites” describes using carbon nanotubes as a non-destructive real time way to test for continuous fiber composite failure. The University of Delaware’s R&D over the past three years on this subject has been presented frequently to structural composite audiences, but this is the first presentation to a plastics audience. Adding less than 0.1 wt % carbon nanotubes into a nonconductive plastic material or adhesive in a composite with continuous glass or carbon fiber or prepreg creates a conductive nerve-like network. The carbon nanotubes act like nanoscale wires, capable of sensing the start of delamination, crack formation or fiber failure.
Douglas Goetz, a lead research specialist at 3M Corp. in St. Paul, Minn. (www.mmm.com) will present “The Effect of Epoxy Matrix Modification with Nanosilica on the Processing and Mechanical Properties of Carbon Fiber Composites,” showing the effect of very high loadings of nanosilica on compressive failure of epoxy/carbon fiber composites. The study compares compression strength of carbon fiber epoxy composites with 15, 25, 35, and 45 wt % loadings of nanosilica in the epoxy matrix. Nanoparticles improve the modulus of the resin better to support the carbon fibers, keeping them from micro-buckling. 3M began introducing its highly nanosilica-filled epoxies last year as 3M Matrix Resins and now offers seven products. The new one is Matrix Resin 4831, which actually has a nominal fill level of 49 wt % nanosilica for filament wound pressure tanks. The very high loading of nanosilica reportedly increases after-impact burst strength for tanks by 30% vs unfilled epoxy.
Raymond Pearson, director of the Center for Polymer Science and Engineering at Lehigh (fp2.cc.lehigh.edu/inpolctr/cpse_home_page.htm) also reports on “Improving the Mechanical Properties of Epoxies Using Nanosilica” by adding micron-sized silica along with nano-sized. The idea was to improve fracture toughness by increasing the debonding of nanosilica particles at the crack tip. Debonding around nanoparticles causes holes in the matrix similar to cavitation in rubber-reinforced epoxies. Typically, however, only about 15% of nanosilica particles debond at the crack tip. The addition of micron-sized silica improved debonding dramatically–virtually all the nanosilica particles debonded at the crack tip. Fracture toughness and modulus did improve, but not as much as expected.
Donghai Wang, assistant professor at Penn State University, University Park, Pa. (www.psu.edu) will give test results for new “Polymer-Graphene Nanocomposites for Electrochemical Energy Storage.” The graphene polymer composites were made with 5 wt % graphene polymerized in solution with an electrochemically active anthraquinone-based polymer and showed better conductivity than carbon nanotube composites, Wang says. The capacity of the polymer-graphene cathode reportedly can reach 150 mAh/g at 10C charge/discharge rate (in battery language). Graphene polymer composites are already being tested for applications like electrodes for energy storage and improved performance of cathodes in lithium-ion batteries because of their high electrical conductivity. Graphene, or molecule-sized particles of graphite, is of interest because it could potentially be available on a large scale. Graphene has only been known as a material since 2004, when two Russian-born scientists in the U.K. published their work creating it, for which they won a Nobel prize in physics in October last year.
And the Poster Session Winner Is….
In addition eight students from around the country will present nanocomposite posters, which will be judged by attendees at the conference. (My personal favorite, based purely on its title, is from the University of Maine on “Functionalized Carrier Systems for Cellulose Nanofibrils Designed for Polypropylene Composites.”) Once the vote is in, we’ll post the winner.