Mechanism of degradation

These mechanisms describe how degradation occurs, but do not adequately account for the fact that, theoretically, the polymer should be stable at temperatures of up to 300 C, based 

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A related mechanism of degradation involves the direct interaction of the radioactive emission with other tracer molecules in the preparation. This phenomenon is likely to occur in high specific activity compounds stored at high radiochemical concentrations in the absence of free-radical scavengers. 

The mechanisms of degradation and the mode of action of the various PVC stabilisers have both been widely studied. Often at least one aspect of their operation is some sort of reaction with the first trace of hydrogen chloride evolved. This removes what would otherwise act as the catalyst for further dehydrochlorination, and hence significantly retards the degradation process. In addition, many stabilisers are themselves capable of reacting across any double bonds formed, thereby reversing the process that causes discoloration and embrittlement. 

Degradation. Although the actual mechanisms of degradation are many and complex, HSPF uses a simple first-order relationship to approximate this process. 

Similarly to polymer synthesis, there are essentially two main mechanisms of degradation of synthetic polymers involving main chain links and leading to... 

TGA indicated that the initiation mechanism of degradation of POM was by random scission of the main chain. (Formaldehyde observed in the TGA-MS measurements is a direct consequence of random scission.)... 

Although the exact mechanism of degradation at metabolic level for each compound or group of compounds is not well known, the involvement of extracellular oxidative enzymes such as LAC, MnP, LiP, and versatile peroxidase (VP) (see Tables 1 and 2 of Chap. 6) and intracellular monooxygenases as cytochrome P-450 is well documented for pollutants such as hydrocarbons, dyes, and halogenated solvents [25]. To determine the actual role of the extracellular enzymes, many studies are performed in vitro experiments with purified enzymes. In the case of cytochrome P-450, usually inhibitors are used. 

In recent years, numerous papers have been published about one of the most important groups of phytochemicals, the polyphenols (Manach and others 2004). These compounds, which possess an array of healthy properties, but also some disadvantages that will be discussed in this chapter, are present in a variety of plants used in both human and animal diets. However, the structure of this type of compound means that they can be oxidized by several pro-oxidant agents. The objective of this chapter is to describe the main enzymatic agents responsible for the degradation of polyphenols. In order to understand the mechanisms of degradation that will be described in the following sections, a brief summary of the main properties of the polyphenols is required. 

A thorough study of the mechanism of degradation of several fire retardant melamine salts is carried out using thermogravimetry, evolved gas analysis and spectroscopic characterisation of the products of degradation. 

The introduction of ionol in oxidized PIB decreases the peroxyl radical concentration by 94 times and rate of degradation via the reaction P02 + P02 by 942 = 8836 times, but the observed rate of macromolecules degradation decreases by seven times only. This means the appearance of another mechanism of degradation in the presence of the antioxidant. The kinetic study of PIB degradation in the process of initiated oxidation confirmed this hypothesis. The PIB degradation via the reaction P02 + P02 leads to the proportionality vs [InH]-2 v2. Experiments on PIB oxidation with different antioxidants (phenols, amines, and aminophenols) and variation of concentrations of an initiator, as well as inhibitor, proved the following equation ... 

The degradative mechanisms in plastics have been described in detail [1, 2]. This section will outline the agents and basic mechanisms of degradation and identify those which are most significant for life prediction. 

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