Oxygen REACTION INDEX

Chemical Antioxidant Systems. The antioxidant activity of tea extracts and tea polyphenols have been determined using in vitro model systems which are based on hydroxyl-, peroxyl-, superoxide-, hydrogen peroxide-, and oxygen-induced oxidation reactions (109—113). The effectiveness of purified tea polyphenols and cmde tea extracts as antioxidants against the autoxidation of fats has been studied using the standard Rancimat system, an assay based on air oxidation of fats or oils. A direct correlation between the antioxidant index of a tea extract and the concentration of epigallocatechin gallate in the extract was found (107). 

Except as an index of respiration, carbon dioxide is seldom considered in fermentations but plays important roles. Its participation in carbonate equilibria affects pH removal of carbon dioxide by photosynthesis can force the pH above 10 in dense, well-illuminated algal cultures. Several biochemical reactions involve carbon dioxide, so their kinetics and equilibrium concentrations are dependent on gas concentrations, and metabolic rates of associated reactions may also change. Attempts to increase oxygen transfer rates by elevating pressure to get more driving force sometimes encounter poor process performance that might oe attributed to excessive dissolved carbon dioxide. 

The properties and applications are very variable according to the nature and the ratio of the substituents, the crosslinking reaction and the formulation but one always finds a good fire resistance resulting in a high oxygen index, a ... 

One very efficient system which may work this way was reported by Chien and Kiang (32) who found that 1.5% chromium, introduced by the tard reaction, raised the oxygen index of polypropylene to 27 (Fig. 4) and char formation was promoted. The hypotheses as to mode of action included the idea that dehydrogenation catalysis might be involved. 

An increase of char yield is generally reflected as an improvement in oxygen index. In the styrylpyridine based polyesters and polycarbonate an intermolecular thermally induced Diels-Alder reaction has occurred through the double bond, this increased the char yield and decreased the flammability. The Fries rearrangement, as well as dimerization and isomerization, occurred simultaneously during the UV irradiation of p-VPPB, but no dimerization or isomerization occurred for p,p -BVPDPC, probably due to steric effects. 

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