Oxidation stability peroxides

In addition to the oxides MO, peroxides MO2 are known for the heavier alkaline earth metals and there is some evidence for yellow superoxides M(02)2 of Ca, Sr and Ba impure ozonides Ca(03)2 and Ba(03)2 have also been reported. As with the alkali metals, stability... 

Peroxide decomposers—These function by reacting with the initiating peroxides to form nonradical products. Presumably mercaptans, thiophenols, and other organic sulfin compounds function in this way [19]. It has been suggested that zinc dialkyldithiocarbamates function as peroxide decomposers, thus giving mbber compounds good initial oxidative stability. 

The phenyl modified polymers possess the optimum combination of high temperature and elastomeric properties and were used in the study of formulation parameters These variables can have an important effect on the thermal stability and property profile of vulcanized systems For example, the use of reinforcing silicas, peroxide content, and oxidative stabilizers have been shown to be important ( 3, 10, in However, polymer-silica interactions had the most pronounced effect on retaining properties during high temperature aging studies ... 

Why do some of the alkali metals form oxides, while others form peroxides when they burn in the air How does the stability of the alkali metal oxides and peroxides change (from lithium to cesium) when heated Why is the formation of peroxides and also of ozonides the most characteristic of the alkali metals ... 

The time to reach a certain PV may be used as an index of oxidative stability for food lipids. The effects of antioxidants and food processing on fats are often monitored in this way. Thus, a longer time period to reach a certain PV is generally indicative of a better antioxidant activity for the additive under examination. However, a low PV represents either early or advanced oxidation the breakdown of peroxides to secondary oxidation products will result in a decrease in PVs during the storage period. For determination in foodstuff, a major disadvantage to the classical iodometric PV assay is that a 5-g test portion is required it is sometimes difficult to obtain sufficient quantities of lipid from foods low in fat. Despite its drawbacks, PV determination is one of the most common tests employed to monitor lipid oxidation. 

The maximum shelf-life of bulk packaged WMP containing 3% moisture is about 6 months at 30°C (Kjaergaard Jensen, 1988). The oxidation of WMP, as measured by peroxide value, is dependent on the moisture content of the powder, van Mil and Jans (1991) reported that under similar storage conditions, the peroxide value of WMP increases more rapidly for powder containing 3% moisture than in powder containing 2.4% moisture. The water activity (aw) range for WMP is usually 0.13 0.20, with a typical value from 0.16 to 0.18 (Wewala, 1990). Stapelfeldt et al. (1997) found that the quality of WMP is maintained best at aw between 0.11 and 0.23, whereas the quality of the powder decreases when stored at aw of 0.31 at 45°C. However, the critical aw for improved oxidative stability of WMP stored at 40°C for one year is 0.21 0.24 at a moisture level of 3.4% (Wewala, 1990). 

To our knowledge, the first Raman investigations of the states of the barium phase during ongoing NOv decomposition were reported by Lunsford and coworkers (Haller et al., 1996 Mestl et al., 1997a,b, 1998 Xie et al., 1997). They used a MgO-supported barium oxide model catalyst for their investigation of NO decomposition. It was found that the supported barium oxide phase stabilized peroxide species in the presence of molecular 02 in the feed, which in turn reacted with gas-phase NO to... 

Active Oxygen Method for Fat Stability (AOM) (Cd 12-57) determines the time (in hours) for a sample of fat or oil to attain a predetermined peroxide value (PV) under the conditions of the test. The method is used to estimate the comparative oxidative stability of fats and oils. The method has been placed in surplus, in favor of Cd 12b-92 (Oil Stability Index), but retains official status and is still used in domestic industry. p-Anisidine Value (AV) (Cd 18-90) determines the amount of aldehydes (principally 2-alkenals and 2,4-dienals) in animal and vegetable fats and oils. These are degradation products of peroxides, which are not removed by bleaching. Some fats and oils chemists propose increased use of this method in purchase specifications. Bleaching Test for Soybean Oil (Cc 8e-s63) determines the color of a sample of soybean oil after treatment with a specified bleaching earth. Specific methods exist for other oil species. 

Properly end-capped acetal resins, substantially free of ionic impurities, are relatively thermally stable. However, the methylene groups in the polymer backbone are sites for peroxidation or hydroperoxidation reactions which ultimately lead to scission and depolymerization. Thus antioxidants (qv), especially hindered phenols, are included in most commercially available acetal resins for optimal thermal oxidative stability. 

Another example is Dias Analytics styrenic membrane based on the well-known block copolymer styrene-ethylene/butylene-styrene family.This membrane has good conductivity 0.07 to 1.0 S/cm when fully hydrated. It showed reasonable performance but had poor oxidative stability due to the susceptibility of its aliphatic backbone to peroxide attack. 

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