Degradation oxygen uptake

Polypropylene differs from polyethylene in its chemical reactivity because of the presence of tertiary carbon atoms occurring alternately on the chain backbone. Of particular significance is the susceptibility of the polymer to oxidation at elevated temperatures. Some estimate of the difference between the two polymers can be obtained from Figure 1J.7, which compares- the rates of oxygen uptake of eaeh polymer at 93°C. Substantial improvements can be made by the inclusion of antioxidants and such additives are used in all commercial compounds. Whereas polyethylene cross-links on oxidation, polypropylene degrades to form lower molecular weight products. Similar effects are noted... 

Whole-cell studies using oxygen uptake by Burkholderia (Pseudomonas) sp. strain LB400 had clearly shown the versatility of this organism in the degradation of PCB congeners containing up... 

Figure 6 (a) Oxygen uptake vs degradation (b) UV absorbance at 400 nm vs degradation... 

These COD fractions can be determined by an OUR experiment typically performed during 0.5-2 days. The slowly hydrolyzable fraction of the COD, Xs slow, cannot be determined from the oxygen uptake because the degradation of this fraction takes considerable time and also interferes with the degradation of already produced biomass. A determination based on a COD mass balance is, however, possible ... 

Flask tests involve the testing of native soil and groundwater without additives, in which the oxygen uptake (or carbon dioxide produced) is continually monitored. After about 1 to 5 days, the concentration of contaminant is analyzed and compared with the initial concentration. Results indicate the rate of degradation with only oxygen addition, and the quantity of oxygen required per unit of contaminant. 

A combination of ZDDP and hard-core RMs leads to a synergistic effect of metallic detergents on the degradation of ZDDP. These phenomena are observed in many tests and can be explained in terms of (a) the acid neutralization property of hard-core RMs that leads to the prevention of decomposition of ZDDP (in the valve train wear test and the thin film oxygen uptake test), (b) the competitive adsorption of detergents that reduce the effective concentration of ZDDP on the metal surface (in the four-ball test), (c) the formation of mixed films on the metal surface, formed through the decomposition of ZDDP in the presence of hard-core RM s (the coefficient of friction in the Falex wear test). 

Although the yellowness index, oxygen uptake, and percent weight loss were not valid indicators for evaluating the extent of degradation at... 

From the oxygen uptake and CO/CO2 formation in nitrogen, it can be concluded that the main degradation mechanism of both PECOs is photooxidation, which is initiated by the photolysis of the PBT phase. 

In another technique, the densities of pieces of degraded samples are profiled using a salt gradient column (7 ). This technique provides a profile on oxygen uptake in the sample—information which is complementary to that provided by the techniques based on changes in mechanical properties. Oxidation of samples normally leads to increases in sample density. 

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