Oxidative stability measurement

Li-peroxo transition metal complexes, 1060 Conductivity, oxidation stability measurement, 664... 

Kodali, D.R. Oxidative stability measurement of high-stability oils by pressure differential scanning calorimeter (PDSC). J. Agric. Food Chem. 2005, 53, 7649-7653. Kris-Etherton, P.M. Harris, W.S. Appel, L.J. Fish consumption, fish oil, omega-3 fatty acids and cardiovascular disease. Circulation 2002, 106, 2747-2757. 

Oxidation stability (distillate fuel oil) NF M 07-047 ISO/DlS 12205 ASTM D 2274 Measurement of precipitate after 16 h of oxygen sparging at 95°C... 

The absence of both secondary and tertiary C—H bonds leads to a high measure of oxidative stability. Oxidation does take place when thin films are heated in air to temperatures above 300°C and causes cross-linking but this is of little practical significance. The absence of double bonds gives a very good but not absolute resistance to ozone. 

A study was done measuring the thermal oxidative stability of polyurethanes made from PPG polyols, varying the isocyanate curative. Oxygen absorption was... 

DSC helps in determining the glass-transition temperature, vulcanization, and oxidative stability. TG mainly is applied for the quantitative determination of major components of a polymer sample. TMA or DLTMA (dynamic load thermomechanical analysis) measures the elastic properties viz. modulus. 

For PPV-imine and PPV-ether the oxidation potential, measured by cyclic voltammetry using Ag/AgCl as a reference are ,M.=0.8 eV and 0.92 eV, respectively. By adopting the values 4.6 eV and 4.8 eV for the work functions of a Ag/AgCl and an 1TO electrode, respectively, one arrives at zero field injection barriers of 0.4 and 0.55 eV. These values represent lower bounds because cyclic voltammetry is carried out in polar solvents in which the stabilization cncigy of radical ions exceeds that in a polymer film, where only electronic polarization takes place. E x values for LPPP and PPPV are not available but in theory they should exceed those of PPV-imine and PPV-ether. 

IV, CCR and oxidation stability are three strictly co-related parameters. As a general rale, the reduction of IV (on the same feedstock) dramatically improves the oxidation stability. On the contrary the distillation step removes the main part of naturally occurring antioxidants. For this reason, even after hydrogenation the Rancimat induction time (as measured according to the EN 14112 standard) of the hydrogenated sample does not fulfill the EN 14214 requirement for oxidation stabihty (6 hours at 110°C), 4 hours being the measured induction period. 

Si(Pc)0] (S04)o.09)n> i-s limited by the oxidative stability of the sulfate anion. Thermoelectric power, optical reflectivity, magnetic susceptibility, and four-probe electrical conductivity measurements evidence behavior typical of an [Si(PcP+)0]n compound where p 0.20. That is, there is no evidence that the more concentrated counterion charge has induced significant localization of the band structure. 

Measuring the relative oxidative stability of polymers is important. Measurements can be used to determine dependencies on structural and molecular weight/weight distribution or the effectiveness of an antioxidant, or to perhaps assess the amount present in a polymer sample, etc. The preferred and commonest method consists in raising the sample temperature to a predetermined level, while in an inert atmosphere, then switching the atmosphere to air or oxygen. The time to the onset of exothermic reaction is measured. 

Rancimat is an accelerated method to assess oxidative stability of fats and oils. In this test, the sample is subjected to an accelerated oxidative process (by heat in presence of oxygen), where short-chain volatile acids are produced. The acids formed are measured by conductivity. 

Oxidation kinetics of oriented PP was measured under conditions of external priming. The parameter specifying the oxidability of a polymer is slightly dependent on deformation. For instance, at 200°C it only decreases by 1.5 times with X changing from 0 to 10. This unambiguously clarifies that the main reason for increase in thermal-oxidative stability of deformed PP is a sharp drop in the escape of a branching agent (hydroperoxide), i.e. a decrease in hydroperoxide escape. 

The laboratory-to-laboratory reproducibility of the isothermal oxidative stability procedure for measuring the oxidative stability of polyolefin insulation used in telecommunications applications has been improved from approximately 45% to approximately 85%. The improved protocol is described in some detail. 12 refs. 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

This test method is commonly utilized throughout the world to rapidly determine the oxidative stability of distillate fuel. Although not as effective at predicting the long-term stability of distillate fuel as ASTM D-4625, this method is useful for measuring the resistance of fuel to rapid degradation by oxidation. Metal catalysts such as copper and iron are sometimes added to the fuel to further accelerate... 

Improved heat-resistant UV compositions for optical fiber applications These compositions are nonurethane UV cure compositions that have neither carbamate moieties nor long-chain poly(alkylene oxide) soft segments and exhibit inherently better thermal stability measured by thermogravimetric analysis (TGA) than typical coatings for optical fibers based on urethane acrylate oligomers. 

A further modification of the PMR-12F-71 resin comprises changing from the nadic endgroups to vinylphenyl endgroups, simply by using p-aminostyrene in the synthesis. This resin was called V-cap-12F-71 (see Fig. 37). The V-cap versions of PMR-II-50 (V-cap 11-50) and PMR-12F-71 (V-cap-12F-71) underwent a comparative long term thermal oxidative stability testing (112). Neat resin weight loss was measured at 343 °C in air over a period of 750 hours (Fig. 38). The data clearly indicate that the 12F-PMR resins exhibit excellent thermal oxidative stability and it also shows that the NE endcap is thermally less stable than the V-cap in the PMR-II series. 

The major concern was the thermal oxidative stability performance of the new resin. Weight loss measurements at 250,285 and 300 °C provided comparable low values at 250 and 285 °C. However, at 300 °C, the B1 composite exhibited a marketly lower weight loss than PMR-15. The temperature capability of B1 composite is obvious from Fig. 41, where the flexural properties of resins are plotted as a function of the ageing time at 285 °C. PMR-15 seems to be a superior resin in this test. 

Another ASTM test method, Potential Gum (D873), combines the existent gum and the oxidation stability tests to measure potential gum. A sample of gasoline is subjected to the oxidation stability test for 960 min, filtered to remove particulates, and then subjected to an existent gum test. The potential gum is expressed as the total (unwashed) gum in this test. 

NOTE This method relies on either of two commercially available instruments that consist of a means of controlling sample temperature (maintained at 0.1 °C), an air distribution system, conductivity tubes, stoppers and probes, and electronics or software for measuring conductivity and determining induction period. The following steps are generally applicable to both the Rancimat and the Oxidative Stability Instrument however, some variations exist due to differences in hardware and models available. Consult the manufacturer s instructions for additional detail. 

The oil stability index (OSI) method provides results in a matter of hours instead of months (required for studies done at ambient temperatures). These OSI results are useful as comparative measures of oxidative stability, i.e., to determine the effect of a treatment or antioxidant compared to a control sample. Meaningful predictions of the actual shelf lives of specific commodities require that such shelf life studies be performed at ambient conditions. If only accelerated tests are to be performed, two or more tests based on different principles of lipid oxidation measurement should be conducted the effect of accelerated storage temperature should also be investigated. 

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