NASA Scientific and Technical Aerospace Reports

The structural development of a nanocomposite, containing 95 wt% isotactic polypropylene (iPP) and 5 wt% modified
carbon nanofiber (MCNF), during fiber spinning was investigated by in-situ synchrotron small-angle X-ray scattering (SAXS)
and wide-angle X-ray diffraction (WAXD) techniques. The modification of carbon nanofibers (CNFs) was accomplished by
a chemical surface treatment using in-situ polymerization of olefin segments to enhance its compatibility with iPP. The
iPP/MCNF nanocomposite was prepared by a two- step blending process in order to ensure the exfoliation of MCNF. X-ray
results showed that at low spin-draw ratios, the iPP!MCNF nanocomposite fiber exhibited much higher iPP crystalline
orientation than the control’ pure iPP fiber. At higher spin-draw ratios, the crystalline orientation of the nanocomposite fiber
and that of the pure iPP fiber was about the same. The crystallinity of the composite fiber was higher than that of the control
iPP fiber, indicating the nucleating effect of the modified carbon nanofibers. The nanocomposite fiber also showed larger long
periods at low spin-draw ratios. Measurements of mechanical properties indicated that the nanocomposite fiber with 5 wt%
MCNF had much higher tensile strength, modulus and longer elongation to break. The mechanical enhancement can be
attributed to the exfoliation of MCNF in the matrix, which was confirmed by SEM results.
DTIC
Nanocomposites; Nanofabrication; Carbon Fibers; Polypropylene; Crystal Structure
20040073725 California Univ., Davis, CA
Densification of nanocrystalline powders. Field Activated Sintering of Tantalum nanopowders
Groza, J. R.; Nov. 7, 2003; 12 pp.; In English; Original contains color illustrations
Contract(s)/Grant(s): DAAD19-00-1-0182
Report No.(s): AD-A422641; ARO-40112.3-MS; No Copyright; Avail: CASI; A03, Hardcopy
This work focused on the specifics of densification of nanocrystalline powders using an externally applied pulsed
electrical current. Studies were performed to characterize the surface structure of select metal nanopowders (Ni, Al and Ta)
and understand differences due to handling and storage conditions. For the oxygen sensitive Ta, methods were designed to
clean previously coated nanoparticle surfaces. Grain growth behavior of nanocrystalline materials was characterized by in-situ
TEM with and without an externally applied electrical current. An integrated heating/electrical biasing holder was designed
and built for in-situ TEM coarsening studies. For field sintering of nanomaterials, a more detailed characterization of the
commercial SPS machine was required, and temperature evolution and distribution, and heating rate effects were evaluated.
Based on the experience in SPS sintering of conventional parts (19 mm in diameter and 5 mm thick) from Ni nanoparticles,
large specimens (thickness up to 19 mm) were sintered for mechanical testing. Ta nanopowders (40 nm) were sintered to a
final density of 12.9 g/cm3 at 1200 C. The grain/crystallite size very small (2. 5 nm). This was also attributed to a phase
transformation from tetragonal to cubic in Ta. Mechanical property characterization is being performed on large Ni specimens
and sintered Ta at ARL, Aberdeen Proving Ground, Maryland.
DTIC
Densification; Mechanical Properties; Powder (Particles); Sintering; Tantalum; Tantalum Compounds
20040073726 Colorado Univ., Boulder, CO
Pentachlorophenol Hydroxylase: Analysis of Catalytic Abilities and Evolution of a Better Enzyme
Cople, Shelley D.; Jan. 19, 2004; 4 pp.; In English
Contract(s)/Grant(s): DAAD19-99-1-0301
Report No.(s): AD-A422642; ARO-40132.1-LS; No Copyright; Avail: CASI; A01, Hardcopy
Sphingobium chlorophenolicum is a Gram-negative soil bacterium that can mineralize pentachlorophenol (PCP), although
degradation is slow and the bacterium cannot tolerate high levels of PCP. The rate of degradation is limited by the first enzyme
in the pathway, PCP hydroxylase, which is a very poor catalyst. We have used DNA shuffling to produce mutant enzymes with
modestly improved catalytic activities. We discovered that the reason for our limited success was that our selection was based
upon publications claiming that the product formed by PCP hydroxylase is tetrachlorohydroquinone (TCHQ). Since TCHQ
is less toxic than PCP, cells expressing better enzymes should be able to grow in the presence of higher levels of PCP.
However, we found that the product formed from PCP is actually tetrachlorobenzoquinone (TCBQ), which is more toxic than
PCP. We also discovered a previously unrecognized enzyme that converts TCBQ to TCHQ. Our new knowledge about the
pathway will allow us to design a more effective selection for improved PCP hydroxylase enzymes. Finally, we have used
genome shuffling to generate strains of S. chlorophenolicum that have greatly increased tolerance to the toxicity of PCP and
have significantly improved rates of degradation.
DTIC
Catalysts; Deoxyribonucleic Acid; Enzymes
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