Agents and Mechanisms of Degradation

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. 

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. 

The book by Prof. Yanko [1] discusses a mechanism of degradation of the flue walls, stating that the main corrosion agents are aluminium fluoride and sodium fluoride. The temperature of evaporation of aluminium fluoride is - 950 °C, while the temperature of evaporation of sodium fluoride is - 1,050 °C. Volatile sodium and aluminium fluoride penetrate the permeable pores of refractory [1] and interact with silica, giving volatile silicon tetrafluoride, while sodium oxide is released in the pores ... 

Corrosion is generally taken to be the waste of a metal by the action of corrosive agents. However, a wider definition is the degradation of a material through contact with its environment. Thus, corrosion can include non-metallic materials such as concrete and plastics and mechanisms such as cracking in addition to wastage (i.e. loss of material). This chapter is primarily concerned with metallic corrosion, through a variety of mechanisms. 

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