Metal deactivators

In polymers, oxidative degradation is catalyzed strongly by traces of metals that can undergo redox reaction. Most prominent is copper, but also solubilized iron, cobalt, nickel, chromium and manganese may contribute to degradation of the polymers. Apart from polymers, metal deactivators are used widely in lubricating oils. 

Many organic materials that are used in electrical technology for insulation purposes, for example, polymers such as (1)  

Very often, thermoplastics contain minute amounts of metallic compounds which originate from polymerization catalysts, contaminated fillers, polymerization or processing equipment, or metal contact (wire and cable insulators) during the use of the polymer. The interactions between the polymer and metallic substances are complex, but generally result in the accelerated aging of the material. Most metal deactivators are bifunctional stabilizers with phenolic and nitrogen, or phenohc sulfide and phosphite, moieties in their structure, and act by a chelating action which reduces the harmful effects of the metal ions. 

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Metal composites Metal conditioners Metal containers Metal deactivators... 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

Metal Deactivation. Compounds capable of forming coordination complexes with metal ions are needed for this purpose. A chelating agent such as ethylene-diaminetetraacetic acid (EDTA) is a good example. 

Metal Deactivators. The abiUty of metal ions to catalyse oxidation can be inhibited by metal deactivators (19). These additives chelate metal ions and increase the potential difference between the oxidised and reduced states of the metal ions. This decreases the abiUty of the metal to produce radicals from hydroperoxides by oxidation and reduction (eqs. 15 and 16). Complexation of the metal by the metal deactivator also blocks its abiUty to associate with a hydroperoxide, a requirement for catalysis (20). 

Examples of commercial metal deactivators used in polymers, gasoline, and foods are oxalyl bis(bensyhdene)hydraside [6629-10-3] (28). 

The stabili2ation of polyolefins used to insulate copper conductors requires the use of a long-term antioxidant plus a copper deactivator. Both A[,Ar-bis(3,5-di-/ A-butyl-4-hydroxycinnamoyl)hydra2ine (29) and 2,2 -oxamidobisethyl(3,5-di-/ A-butyl-4-hydroxycinnamate) (30) are bifimctional. They are persistent antioxidants that have built-in metal deactivators. Oxalyl bis(ben2yhdenehydra2ide) (28) is an effective copper deactivator when part of an additive package that includes an antioxidant. 

The catalytic activity of copper as an oxidant can be inhibited by the use of a metal deactivator such as N,1S7-disahcyhdene-l,2-diaminopropane (31) at a concentration of 5—10 ppm. 

It is possible to deactivate a metal ioa by adding a compouad such as disahcyhdeae alkyl diamiae, which readily forms a chelate with most metal atoms to reader them iaeffective. Metal deactivator has beea showa to reduce oxidatioa deposits dramatically ia the JFTOT test and ia single tube heat exchanger rigs. The role of metal deactivator ia improving fuel stabiUty is complex, siace quantities beyond those needed to chelate metal atoms act as passivators of metal surfaces and as antioxidants (13). 

The precious metals possess much higher specific catalytic activity than do the base metals. In addition, base metal catalysts sinter upon exposure to the exhaust gas temperatures found in engine exhaust, thereby losing the catalytic performance needed for low temperature operation. Also, the base metals deactivate because of reactions with sulfur compounds at the low temperature end of auto exhaust. As a result, a base metal automobile exhaust... 

The peroxide decomposer will drastically reduce the number of radicals, which can then be more effectively mopped up by the chain-breaking materials. A widely used combination is 4-methyl-2,6,di-t-butylphenol and dilauryl thiodipropionate. It is possible to envisage most powerful combinations where a chain-breaking antioxidant, a regenerating agent, a peroxide decomposer, a metal deactivator and an ultraviolet absorber are all employed together. 

Metal deactivators (MD) act, primarily, by retarding metal-catalyzed oxidation of polymers they are, therefore, important under conditions where polymers are in contact with metals, e.g., wires and power cables. Metal deactivators are normally polyfunctional metal chelating compounds (e.g.. Table la, AO 19-22) that can chelate with metals and decrease their catalytic activity [21]. 

Another additive used is a metal deactivator to chemically deactivate any catalytic metals such as copper accidentally dissolved in the fuel from metal surfaces. Uless they are chemically deactivated, dissolved metals cause the loss of good stability quality. 

Metal deactivator To form inactive protective films on metal surfaces which otherwise might catalyse oxidation and corrosion reactions Trialkyl and triaryl phosphites, organic dihydroxyphosphines, some active sulphur compounds, diamines in lubricating greases, mercaptobenzothiazole and phosphites... 

Metal deactivators—Organic compounds capable of forming coordination complexes with metals are known to be useful in inhibiting metal-activated oxidation. These compounds have multiple coordination sites and are capable of forming cyclic strucmres, which cage the pro-oxidant metal ions. EDTA and its various salts are examples of this type of metal chelating compounds. 

In TLC the choice of mobile phase depends primarily on the additive in question. Gedeon el al. [394] have listed mobile phases for the separation of AOs and plasticisers. Bataillard et al. [351] have reported R values for various solvents and visualisation modes for a great variety of primary and secondary AOs, UVAs, HALS and metal deactivators. 

There have been some examples of the use of LDMS applied to the analysis of compounds separated via TLC, although not specifically dealing with polymer additives [852]. Dewey and Finney [838] have described direct TLC-spectroscopy and TLC-LMMS as applied to the analysis of lubricating oil additives (phenolic and amine antioxidants, detergents, dispersants, viscosity index improvers, corrosion inhibitors and metal deactivators). Also a series of general organics and ionic surfactants were analysed by means of direct normal-phase HPTLC-LMMS [837]. Novak and Hercules [858] have... 

Retard efficiently oxidation of polymers catalysed by metal impurities. Function by chelation. Effective metal deactivators are complexing agents which have the ability to co-ordinate the vacant orbitals of transition metal ions to their maximum co-ordination number and thus inhibit co-ordination of hydroperoxides to metal ions. Main use of stabilisation against metal-catalysed oxidation is in wire and cable applications where hydrocarbon materials are in contact with metallic compounds, e.g. copper. 

Contact of aqueous ethylene glycol solutions with d.c.-energised silvered copper wires causes ignition of the latter. Bare copper or nickel- or tin-plated wires were inert and silver-plated wire can be made so by adding benzotriazole as a metal deactivator to the coolant solution [1], This problem of electrical connector fires in aircraft has been studied in detail to identify the significant factors [2],... 

Metal deactivators N,N -bis(3-(3,5-di-tert-butyI-4-hydroxyphenyl)propionyl) hydrazide... 

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