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71.
Correlation of antioxidant depletion and mechanical performance during thermal degradation of an HTPB elastomer 总被引:1,自引:0,他引:1
M. Celina J.M. Skutnik Elliott S.T. Winters R.A. Assink L.M. Minier 《Polymer Degradation and Stability》2006,91(8):1870-1879
Thermal degradation studies of a stabilized HTPB based elastomer were conducted at temperatures from 50 °C to 110 °C. The concentration of extractable antioxidant (AO2246) in the polymer was quantified via AO extraction and a gas chromatography-based method using internal standards. The decrease in extractable AO levels as a function of time and temperature was evaluated and correlated with mechanical property changes. Most importantly, AO depletion features were found to be temperature dependent. At elevated temperatures (>80 °C) extractable AO levels decreased rapidly and faster than the concurrent loss in mechanical properties. While extractable AO concentrations decrease quickly, the material is able to maintain some useful mechanical properties, perhaps via non-extractable or grafted AO species formed during degradation providing additional protection. At lower aging temperatures extractable or free AO levels decreased more slowly than the mechanical properties. Therefore, for condition monitoring purposes a universal correlation between AO levels and aging state or material condition could not be established. Most importantly, however, loss of mechanical properties and oxidative degradation is observed at lower temperatures despite significant levels of free antioxidant in the material. The antioxidant appears to be limited in its effectiveness to completely prevent degradation reactions, or only fractions of the total AO available are actually involved in the inhibition process. 相似文献
72.
Summary A method is described for the determination of shortchain aliphatic amines in ambient air based on impinger sampling in dilute H2SO4, selective enrichment across a PTFE gas membrane and quantification by gas chromatography. The enrichment step is carried out in a flow system directly connected to the chromatograph. The separation is performed on a packed column with nitrogen selective detection. The enrichment per sample volume was in the range 7.3 to 8.2 mL–1 for C1–C6 amines. Detection limits were ca 3–10 nM with enrichment of a 2.9 mL liquid sample. After impinger sampling of 5 m3 air in 10 mL absorption solution, this corresponds, to 0.4–0.8 ng/m3 (ca 0.2–0.5 ppt by volume) in air. 相似文献
73.
The capillary gas chromatography of the C2-C5 lower aliphatic aldehydes (e.g.,acetaldehyde, propionaldehyde, n- and i-butyraldehydes, n- and i-valeraldehydes) which, in the free form in air, have unpleasant odors and low threshold odor values, has been studied using cold-trap preconcentration with liquid oxygen. The capillary column outlet was connected to enable simultaneous detection by FID, ECD, FPD AND FTD (SID). 相似文献
74.
Qing-Shan Li Juan-Juan Xu Jian-Jiang Zhong 《Applied biochemistry and biotechnology》1997,62(2-3):243-250
Effects of water content and carbon and nitrogen sources on the production ofL-glutamate oxidase (GOD) by solid state fermentation (SSF) ofStreptomyces sp. N1 were investigated in a 250-mL shake flask. The results show that in the solid medium containing wheat bran 98% (w/w), KCl
0.2% (w/w), and MgCl2 0.2% (w/w), addition of 2.0-mL water per gram solid medium and 0.4% (w/w) (NH4)2SO4 was the best for GOD production. In this work, we also developed a simple technique forin situ measuring oxygen uptake rate (OUR) and carbon dioxide evolution rate (CER) in SSF in a shake flask based on the principle
of Warburg manometer. The method was successfully applied to determine OUR and CER values in SSF ofStreptomyces sp. N1. The results indicate that the largest OUR value was detected about one or two days ahead of the highest GOD activity reached
depending on the fermentation conditions, and the OUR may be used as anin situ indicator of GOD production in the SSF process. 相似文献
75.
Sampling and sample-preparation strategies based on solid-phase microextraction for analysis of indoor air 总被引:3,自引:0,他引:3
Applications of solid-phase microextraction (SPME) to the sampling and analysis of volatile organic compounds in indoor air are reviewed, including a summary of quantification methods, coatings, compounds, concentrations, sampling locations and times, and detection limits. Strategies for on-site and off-site sampling and analysis, advantages and challenges associated with SPME for air sampling are discussed. 相似文献
76.
Adam Sokoowski Jan Chlebicki Kazimiera A. Wilk 《Colloids and surfaces. A, Physicochemical and engineering aspects》1993,80(2-3):243-249
The surface tension isotherms for pure oligooxypropylenated piperidine and morpholine at the aqueous solution—air interface were determined and interpreted. The surface excess concentration, Γ, the surface area per molecule, A, and the standard free energy of adsorption, ΔG°, were calculated according to a new empirical adsorption equation. The standard free energy contribution for the oxypropylene group (PO) in morpholine derivatives,ΔG° (PO) = −3.34 kJ mol−1, is substantially lower than that for the PO group located in the piperidine derivatives, i.e. ΔG° (PO)= −3.12 kJ mol−1. 相似文献
77.
78.
Decomposition of Toluene and Acetone in Packed Dielectric Barrier Discharge Reactors 总被引:2,自引:0,他引:2
Chung-Liang?ChangEmail author Tser-Sheng?Lin 《Plasma Chemistry and Plasma Processing》2005,25(3):227-243
The influences of TiO2 catalytic material and glass pellet packing on the decomposition efficiency of toluene and acetone in air by dielectric barrier discharge (DBD) reactors were experimentally investigated in this study. The effects of both packing materials on the formation of byproducts such as CO and CO2 were also evaluated. Experimental results indicate that the introduction of glass materials into the plasma zone of a wire-tube reactor would improve the decomposition efficiency of toluene and acetone compared to a nonpacked reactor. The apparent decomposition rate constant of a glass packed-bed reactor was 4.5–4.8 times greater than that of a nonpacked reactor. The results also indicate that the decomposition rate constant of toluene was approximately 2.6 times higher than that of acetone no matter which type reactor was utilized. The application of TiO2 coated pellets in DBD reactors will enforce the hydrocarbon byproducts to further be oxidized to CO2, notwithstanding, it will not significantly improve the performance of the reactors in the decomposition of toluene and acetone, and in the formation of CO. The results show that the best selectivity of CO2 for acetone decomposition in a TiO2 coated pellets packed-bed reactor was approximately 40% higher than that in a glass packed-bed reactor. 相似文献
79.
P. C. Schulz M. A. Morini M. E. Gschaider de Ferreira 《Colloid and polymer science》1998,276(3):232-238
The system dodecyltrimethylammonium hydroxide (DTAOH)–water was studied by surface tension, ion-selective electrodes and
evaporation in an electrobalance. Results confirmed earlier conclusions about a stepwise aggregation mechanism in DTAOH solutions.
The aggregation process started at a total concentration C
T=(2.51±0.10)×10-4 mol dm-3) which probably corresponds to the formation of dimers. At C
T= (1.300±0.041)×10-3 mol dm-3 there was a change in the surface and evaporation behavior, corresponding to the formation of small, fully ionized aggregates
which grew with increasing concentration. At C
T= (1.108±0.010)×10-2 mol dm-3 the formation of true micelles with hydroxide counterions in the Stern layer did not change significantly the evaporation
and adsorption behavior. This means that between this concentration and C
T=(3.02±0.28)× M28.8n10-2 mol dm-3, the changes in structure were gradual. At the latter concentration there was a sudden change in the monolayer state at the
air/water interface, with a strong surfactant desorption, and a major change in evaporation behavior. The changes are compatible
with the formation of few, large aggregates reducing the total concentration of kinetically independent solute units, which
in turn increased the activity of the solvent. This phenomenon is in agreement with literature information. The reduction
in the evaporation rate of water was mainly due to the reduction of the water activity, caused by colligative effects. The
reduction of the effective area available for evaporation had only a slight effect in water evaporation.
Received: 9 January 1997 Accepted: 19 October 1997 相似文献
80.
Long-term study of an intermittent air sparged MBR for synthetic wastewater treatment 总被引:6,自引:0,他引:6
Membrane bioreactors (MBR) combine biological processes with membrane filtration. Advantages of MBR in municipal wastewater treatment include high effluent quality and reduced space requirements. Steady operation of membrane plants requires careful management of membrane fouling. Even though it might be impossible to prevent, fouling can be limited by techniques such as gas sparging. The injection of gas bubbles increases the shear stress and removes fouling material from the membrane surface. Most cited literature on air sparging refers to short-term experiments, often times in bench scale. The aim of this study was therefore long-term investigations in pilot plant scale of a 70 L reactor fed with glucose-based synthetic wastewater. The main focus was on enhancing permeate flux by air sparging. The results showed that using air sparging significantly increased the permeate flux was doubled even over several weeks. The findings were interpreted using the dimensionless fouling and shear stress number. The fouling resistance was found to decrease significantly with air injection ratios between 0.4 and 0.5. When air sparging was applied after a period without air sparging, the shear stress number doubled. This increase in shear led to a reduction of the fouling number by approximately 30%. During several weeks air sparging only a slow fouling number increase was. In contrast to that after air sparging was ceased, an exponential increase of the fouling number was observed. 相似文献