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College Park, Maryland      June 6 - 10 , 2004

MP14: Experimental Studies and Modeling of Clay/PolyDicyclopentadiene Resin and Carbon Nanofiber/Phenolic Resin Composites Mitra Yoonessi, Hossein Toghiani (Dave C. Swalm School of Chemical Engineering, Mississippi State University), Charles Pittman, Jr. (Department of Chemistry, Mississippi State University)

Hybrid organic-inorganic nanocomposites have received much attention by the researchers during the last five years due to their unexpected properties. A large number of different inorganic materials have been used to enhance matrix properties.

This work incorporated two types of nanophases, Montmorillonite clay and Carbon nanofibers (CNF) into polyDicyclopentadiene and phenolic resin matrices. Montmorillonite has a 2:1 structure consisting of an alumina octahedral layer sandwiched between two silica tetrahedral layers. The crystalline structure is continuous in the a and b directions, but stacked in the c direction. Carbon nanofibers are relatively inexpensive reinforcing agents composed of an inner filament made of highly graphitic carbon sheets packed as concentric cones which are aligned at a highly oblique angle along the fiber axis. The inner filament is covered with a turbostratic CVD carbon outer layer.

Clay nanocomposites were synthesized by stirring and sonication of organically modified clay into Dicyclopentadiene monomer, which caused expansion and further delamination of clay nanolayers (In-situ polymerization). Highly delaminated composites were examined using x-ray diffraction, x-ray scattering and high resolution TEM. Composites with 0.5-1 weight percentage of clay showed improvements in Tg and flexural modulus. These composites were also studied using small angle neutron scattering (SANS) and ultra small angle neutron scattering (USANS). The slopes of scattering intensities, I(q), versus wave vector, q, were in the range of 2.5 to 2.7. The scattering intensities were fitted to the stacked disk model. The resulting data were compared with HR-TEM analysis.

Carbon nanofibers (PR-19-HT) were dispersed within a resole phenolic resin, Hitco 134A to prepare CNF/phenolic nanocomposites. A solvent processing method was used to disperse 1-4wt% CNF/phenolic resin composites. The viscoelastic properties of these composite were studied by DMTA. These showed improved glass transition temperatures with increases in CNF weight percent up to 4wt%. The bending storage modulus below Tg was improved for all composites (1-4wt%) relative to pure resin control samples. A major improvement in E was observed at temperatures above the Tg, where the storage bending modulus stayed high up to ~ 300oC. Improvements in the CNF dispersion were studied by TEM. Better dispersions and surface wetting of the fibers were observed. TEM studies showed that fibers had diameters in the range of 50-100 nm and length in the range of 1-2 microns. Nanocomposites containing low weight percentages of CNFs (0.1-1wt%) were further studied using SANS and USANS. When plotted on a logarithmic scale, the slope of the scattering intensities from particles as a function of wave vector, q, was in the range of 2.9 to -3 for the low q range. In the high q range, 0.015-0.07 -1, the slopes were increased with increasing CNF concentrations.

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