Browsing by Author "Lozano, Karen"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Development and characterization of a nanofiber-reinforced thermoplastic composite
    (1999) Lozano, Karen; Barrera, Enrique V.
    Polypropylene composites with vapor-grown carbon nanofibers (VGCF's) as reinforcement were prepared. The fibers used have an rage diameter of 200 nm with interesting thermal, electrical and mechanical properties which make them very promising for engineering applications. Fiber purification and activation of functional groups were conducted, where amorphous carbon particles were successfully removed, achieving, high purity fibers. Sample preparation was performed using conventional plastic processing technologies. Interactions between the fibers and the matrix were analyzed by physical, mechanical and electrical properties of the composite. Thermal physical analysis on the samples showed that the presence of the fibers influenced the morphology and crystallinity of the matrix. The decomposition temperature, as well as the crystallization rate increased with increasing fiber content. The electrical resistivity of the prepared composites decreased 12 orders of magnitude providing a potential composite for ESD applications. The addition of VGCF's showed an increase in stiffness of 350. Melt viscosity values were also increased by the VGCF reinforcement. Dispersion, porosity, and bonding aspects were also analyzed.
  • Thumbnail Image
    Item
    Oriented nanofibers embedded in a polymer matrix
    (2011-03-01) Barrera, Enrique V.; Rodriguez-Macias, Fernando J.; Lozano, Karen; Chibante, Luis Paulo Felipe; Stewart, David Harris; Rice University; United States Patent and Trademark Office
    A method of forming a composite of embedded nanofibers in a polymer matrix is disclosed. The method includes incorporating nanofibers in a plastic matrix forming agglomerates, and uniformly distributing the nanofibers by exposing the agglomerates to hydrodynamic stresses. The hydrodynamic said stresses force the agglomerates to break apart. In combination or additionally elongational flow is used to achieve small diameters and alignment. A nanofiber reinforced polymer composite system is disclosed. The system includes a plurality of nanofibers that are embedded in polymer matrices in micron size fibers. A method for producing nanotube continuous fibers is disclosed. Nanofibers are fibrils with diameters of 100 nm, multiwall nanotubes, single wall nanotubes and their various functionalized and derivatized forms. The method includes mixing a nanofiber in a polymer; and inducing an orientation of the nanofibers that enables the nanofibers to be used to enhance mechanical, thermal and electrical properties. Orientation is induced by high shear mixing and elongational flow, singly or in combination. The polymer may be removed from said nanofibers, leaving micron size fibers of aligned nanofibers.
  • Thumbnail Image
    ItemUnknown
    Solubility and rheological examination of buckminsterfullerene in decalin and PSVS
    (1996) Lozano, Karen; Barrera, Enrique V.
    The structure-property relationships of C$\sb{60}$ dissolved in decahydronaphtalene (decalin) and a petroleum solvent viscous standard (PSVS) were studied. This work was motivated mainly by the interest to improve fullerene dispersion in powder processing and the development of a viscoelastic standard for commercial use. Decalin was selected based on the amount of fullerene it can hold, the toxicity grade, rate of evaporation, and inability to interfere with the test method. The PSVS is a standard for viscous calibration of rheological instruments. Measurements of solubility, density, viscosity and elasticity values were conducted. The results are for samples classified as 0, 25, 50, 75 and 100% of C$\sb{60}$ saturation level. Decalin can dissolve 1.9 mg/ml of C$\sb{60}$ while the PSVS only dissolves 0.15 mg/ml. The viscosity behavior shown by both solvents was Newtonian, with a small increase in viscosity as a function of fullerene concentration. The elastic portion of the solvents did not change with fullerene concentration.