Basic Principles of Stabilization

In the stabilization of plastics, we generally distinguish between stabilization against thermal-oxidative and photo-oxidative or light-induced degradation. Various 

Among these stabilization procedures, addition of stabilizers is most commonly used and has a wide range of applications [531]. The requirements for stabilizers can be summarized as follows  

A simplified and frequently used schematic explanation for the oxidizing process of a wide variety of plastics is radical autoxidation. Fig. 3.1 (and Fig. 1.13, s. Section 1.4.2). 

Left thermai-oxidative degradation Right iight-induoed degradation 

All stabilizers have in common that their effect is limited to their close molecular neighborhood. Consequently, peroxide decomposers and radical interceptors have to be distributed as homogeneously as possible in the polymer, whereas UV absorbers and UV stabilizers are most effective near the surface. The reactivity of stabilizers varies with temperature. This fact is explained by the activation steps that are often necessary, varying mobility below and above glass transition, and degradation occurring at high temperatures. 

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An ionic charge on the particles in the presence of alkali is the chief mechanism of stabilization in commercial sols. However, a completely satisfactory theory of stabilization has apparently not yet been developed. The basic principles of stabilization by the ionic double layer around particles were developed by Derjaguin and Landau (44) and Vcrwey and Overbeek (45), hence the DLVO theory it has been specifically applied to spherical particles (46a). An excellent summary of the forces affecting the stability of disperse systems was presented by Ottewill (46b). 

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