Metal ion deactivators

Metal Ion Deactivators. These generally chelate ions of copper and the transition metals which might otherwise catalyze the decomposition of hydroperoxides to free radicals,... 

Metal compounds reach the lubricating oil by surface abrasion or the corrosive action of acidic oxidation products. The combustion fuel products with metal ions can be combined in a complex form and thus "masked" by so-called deactivators. Materials previously referred to as corrosion and rust inhibitors also function as metal ion deactivators, due to their ability to form a coating on the metal surface. 

Metal ion deactivators. Certain chemicals prevent the initiation reactions catalysed by transition metal ions, e.g. Ca, Fe, Zri and Mri. Unless the activity of these ions is restricted they can provide a source of free radicals for the oxidation chain reactions described by Equations 11.4 to 11.6. The activity of these metal ions in generating free radicals may be generalised by the following equations [Crawford and Miller 1963]... 

Chelating the metal ions is a recognised way of preventing their entering into these undesirable chemical reactions. Some examples of metal ion deactivators are ... 

Metal ion deactivators (MD) act, primarily, by retarding metal-catalyzed oxidation of polymers (see Scheme 1, reaction 4c). They are used in polymers that are in contact with metals such as copper in wires and power cables. Metal deactivators are normally polyfunctional metal chelating compoimds (eg, AOs 33,... 

The basic objective in the selection of antioxidants is to obtain the best stabilization with no effect on optimum values of technical properties of polymers. The stabilizing effect on oxidative degradation is based on protection against the formation of active free radicals and on nonradical decomposition of hydroperoxides. Optimum stabilization is obtained by the combination of different compounds that function with different mechanisms as metallic ion deactivating agents, UV absorbers, and so on. 

Plastigone, developed by Oilead of Plastopil Hazorea, Israel, contains a minimum of two metal (especially iron) complex additives known as antioxi-dant-photoactivators, for example an iron complex used together with at least one Ni or Co complex to act as a metal ion deactivating compound and also as a photosensitizer. The effect of such additives is exemplified in Fig. 3. 

Efficient metal (ion) deactivators are based on their ability to form stable complexes with the metal, especially with copper ions. Mainly polyolefins and mbbers need to be stabilized by those metal (ion) deactivators that must resist extraction in aqueous surroundings. An important commercial product is 2, 3-bis[[3-[3,5-di- ert-butyl-4-hydroxyphenyl]propionyl]] pro-pionohydrazide (Irganox MD-1024, BASF). 

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