This article continues our study published earlier on the application of the oxidative induction test to a wide variety of
In a series of thermoplastic olefin elastomers (TPO), the extrapolated induction time on the Arrhenius plot was found to coincide
with published results based on oven aging mechanical studies extending to much lower temperatures and times as long as nearly
a year. This agreement indicates the potential of the OIT for long term durability prediction.
For medical flexible PVC compounds, the traditional measure of extent of degradation by color formation was found to correlate
to measured oxidative induction times. Furthermore, three distinct regimes were also detected, where in the first phase, little
color changes can be detected.
In a longer time, lower temperature study, effect of room temperature fluctuations was clearly detected, emphasizing the need
for good environmental control for sensitive detections. These and other recent results will be presented to illustrate the
utility of this versatile test.
A field experiment was carried out to study the effect of K nutrition and genotypic variation on the dry matter (DM) accumulation, and the K concentration, accumulation, uptake and utilization efficiency in barley (Hordeum vulgare L.). Successive increases in potassium nutrition had a significant effect on the dry matter and K accumulation either in the total or in various plant parts of barley at the tillering, stem elongation, heading and maturity growth stages. K nutrition also led to significantly higher grain yield with each unit K application than without K application. The yield increase due to K application was mainly due to the improvement in spike development from tillers. Dry matter and K accumulation in various plant parts varied significantly between genotypes at the main growth stages. Among the various plant parts, the stem contained the highest K concentration, had the highest K accumulation at maturity and changed considerably with the K level, while other plant parts remained relatively unchanged. Among the eleven genotypes, genotype 98-6 had the highest grain yield and the K use efficiency of this genotype was 10.4 kg grain per kg K applied. It could thus be used as a breeding line to breed barley varieties for higher productivity under rainfed conditions with low available soil potassium.
Authors:L. Woo, A. Khare, C. Sandford, M. Ling, and S. Ding
In polymer degradation and durability studies, as well as predicting shelf-life for medical devices, one is confronted with
the need for accurate prediction and difficulties of long term real-time evaluation. Various ways to accelerate the degradation
process have met with mixed success. However, recently, in our own studies, a ‘master curve’ like behavior was found to be
valid for polypropylene samples studied. Evidently, for samples obeying the master curve, very few data points at high temperatures
can be scaled to obtain reasonably accurate estimates on long term durability.
Nevertheless, in a reference medium density polyethylene (MDPE) film material, the high temperature oxidative induction time
data appear to diverge when run under air atmosphere compared with oxygen environments. In this article, we will present data
on many of the polymer systems studied with an emphasis on extrapolation schemes for high temperature accelerated data to
lower temperature very long-term durability. In this context, polymer and antioxidant reactivity toward oxygen, morphology,
and mechanical property dependence on extent of degradation all need to be considered. And the potential and limitations of
this approach will be discussed.
For the enhancement of thermal stability of poly(p-dioxanone) (PPDO), the isocyanate end-capping reagent was prepared by treatment of toluene-2,4-diisocyanate with an equivalent
of 1-hexyl alcohol. The end-capping reagent and the end-capping PPDO with an inherent viscosity of 0.26 dL g−1 were characterized by FTIR and 1H-NMR. Thermal stability of the end-capping PPDO with an inherent viscosity of 0.92 dL g−1 was investigated isothermally and non-isothermally under air atmosphere using thermogravimetry. It has been shown that the
addition of the prepared isocyanate can enhance significantly the thermal stability of PPDO. The activation energies for non-isothermal
degradation estimated by Kissinger method and Friedman method are 91, 81 kJ mol−1 for as-prepared PPDO, and 160, 149 kJ mol−1 for the end-capping PPDO, respectively. The activation energy increases by about 70 kJ mol−1 through the end-capping.
AP/HTPB based composite
propellants with additives such as ammonium oxalate (AO), mixture of ammonium
oxalate and strontium carbonate (SC) was investigated by burning rate, TG-DTG
and FTIR experiments. The results show that the burning rates of these propellants
are decreased significantly. TG-DTG experiments indicate that decomposition
temperatures of AP with these additives are increased. Furthermore, the activation
energy of the decomposition reaction of AP is also increased in the presence
of AO or AO/SC. These results show that AO or AO/SC restrains the decomposition
of AP. The burning rates of these propellants are decreased. The burning rate
temperature sensitivity of AP/HTPB based propellants is reduced significantly
by the addition of AO or AO/SC. But the effect of AO is less than that of
AO/SC. AO/SC is better effect to reduce temperature sensitivity and at the
same time, to reduce pressure exponent. The reduced heat release at the burning
surface of AP/HTPB/AO is responsible for the reduced temperature sensitivity.
Synergetic action is probably produced between AO and SC within AP/HTPB based
propellants in the pressure range tested. This synergetic effect causes the
heat release to reduce and the burning surface temperature to increase. Moreover,
it makes the net exothermal reaction of condensed phase become little dependent
on T0. Thus, the
burning rate temperature sensitivity is reduced.
Retention indexes (RI's) on SE-30 and Carbowax 20M columns are characteristic and can be used for identification purposes. A method for predicting RI on the basis of the number of atoms and contributions from substituents and functional groups is discussed. This method establishes a structure retention index relationship (SRIR), capable of relating structure to RI and is useful for suggesting structure to match with radioactive peaks. Examples of labeled side products tentatively identified in this manner are given.
Authors:Y. Xu, S. Zhang, H. Ding, X. Lu, W. Yang, S. Yuan, Y. Xiao, and Y. Niu
The neutron-rich target-like isotope 236Th has been produced in the 238U-2p multinucleon transfer reaction between a 60 MeV/u 18O beam and natural 238U targets. The activities of thorium were determined after radiochemical separation of Th from the mixture of uranium and
reaction products. The 236Th isotope was identified by the characteristic γ-rays of 642.2, 687.6 and 229.6 keV. The production cross section of 236Th was determined to be 250±50 μb.
Authors:W. Ehmann, X. Ding, S. Khare, M. Lovell, B. Ni, L. Tandon, D. Vance, and D. Wenstrup
It has been suggested that several age-related neurological diseases such as Alzheimer's disease and amyotrophic lateral sclerosis may be related to environmental toxins. Bulk sample multielement analyses by INAA alone are not adequate to define the role of trace elements in these diseases. A multitechnique approach has been developed that incorporates 14 MeV, instrumental reactor, radiochemical, and pre-irradiation chemical neutron activation analysis, together with laser microprobe mass spectrometry. The analytical scheme is able to provide bulk or protein normalized elemental concentrations, as well as microstructural, cellular, and subcellular localization information.
Authors:S. -P. Ding, J. Fan, J. L. Green, Q. Lu, E. Sanchez, and C. A. Angell
Trehalose dihydrate, on careful dehydration below its fusion point, retains its original crystal facets but becomes X-ray amorphous, an unusual example of direct crystal-to-glass transformation. From DSC studies, the glass obtained by this route seems to be of abnormally low enthalpy, but after an initial scan, the normal form of glass transition is exhibited, withTg=115‡C, a higher value than previously reported. We give a preliminary thermal and mechanical characterization of this material and find it to be a very fragile liquid. The highTg is shown to rationalize the exceptionally high water content of the trehalose+water solution that vitrifies at ambient temperature (i.e.Tg=298 K), and hence helps explain its use by Nature as a desiccation protectant. The spontaneous vitrification of crystalline materials during desolvation is related to the phenomenology of pressure-induced or decompression-induced vitrification of crystals via the concept of limiting metastability.
Authors:H. Ding, Y. Niu, Y. Xu, W. Yang, S. Yuan, Z. Qin, and X. Wu
Solvent extraction of protactinium with tri-iso-octyl-amine (TIOA) in xylene, benzene, carbon tetrachloride and chloroform
from HCl, HF, HNO3, HClO4 and H2SO4 media was studied using 233Pa as a radiotracer. The extraction efficiencies of protactinium were determined as a function of shaking time, concentrations
of mineral acids in aqueous phase, extractant concentrations and diluents in organic phase. The extraction mechanism was discussed.
The results show that the extracted species in the organic phase is [(R3N−H)nPa(OH)xCl