Metal oxides vulcanization activator

Activators. Activators are chemicals that increase the rate of vulcanization by reacting first with the accelerators to form mbber soluble complexes. These complexes then react with the sulfur to achieve vulcanization. The most common activators are combinations of zinc oxide and stearic acid. Other metal oxides have been used for specific purposes, ie, lead, cadmium, etc, and other fatty acids used include lauric, oleic, and propionic acids. Soluble zinc salts of fatty acid such as zinc 2-ethyIhexanoate are also used, and these mbber-soluble activators are effective in natural mbber to produce low set, low creep compounds used in load-bearing appHcations. Weak amines and amino alcohols have also been used as activators in combination with the metal oxides. 

Based on an analysis of references, it was found that organic vulcanization accelerators are especially active in the presence of several oxides and hydroxides of metals (vulcanization activators) like zinc, lead, magnesium, calcium, cadmium, bismuth, and their combinations. 

In the vulcanization of elastomers, metal oxides in combination with fatty acids activate the sulfur accelerator systems. 

The accelerators that are most commonly used are derivatives of 2-meicaptobenzothiazole. They are very effective when used in combinations of metal oxides with fatty acids (referred to as activators). The favorite activators are zinc oxide combined with stearic acid. The combinations permit rapid vulcanizations that take minutes compared to hours when sulfiir is used alone. In the process of vulcanization 2,2 -dithiobisbenzthiazole forms initially and then reacts with sulfur to form polysulfides ... 

It was also discovered that small amounts of ZnO (in combination with stearic acid) decrease the duration of vulcanization and improve the properties of the vuleanized products, even in case of non-accelerated vulcanization. Fat acids (stearic acid in particular) are used as an additive for a better dispersion of the ZnO within the system and help in forming a complex of free Zn ions with the accelerators [46], Nowadays, it is known that a lot of metal oxides such as ZnO, MgO, CdO, CaO, PbO etc. have an activator effect. The essential representative from this group is the ZnO. Almost all the formulations for rubber articles contain this metal oxide. It has been known that the stearic acid is in dosage up to 3 phr. In the last few years the results which were received from researehing the effect of the stearic acid on some properties of the eompounds and the vuleanizates in amounts over 3 phr were published [47, 48]. 

Most rubber is based on polymers of isoprene or butadiene and contains many reactive C=C double bonds available for cross-linking. It is cross-linked by sulfur, aided by metal oxides and organic catalysts, producing sulfide cross-links between the polymer chains. Ethylene-propylene rubber is mostly made with several percent of diene ter-monomer to inttoduce C=C double bonds, which can then be vulcanized in the same way. Similarly, butyl rubber is made with a few percent of isoprene comonomer to introduce C=C double bonds and permit sulfur vulcanization. Even saturated elastomers are sometimes cured by sulfur, using peroxides and catalysts to activate C-H bonds, and metal oxides to attack C-Cl bonds. 

Zinc oxide is essential in rubber technology because it is the most commonly used activator for sulfur cure systems. Just about every rubber compound that uses sulfur as the vulcanizing agent will most likely contain a small amount of zinc oxide to activate the cure. Also zinc is alloyed with copper to form brass. Special brass-plated steel tire cord is a primary reinforcing material for producing steel-belted radial tires. The brass coating of the steel tire cord enables very good rubber-to-metal adhesion. Therefore, zinc metal and zinc oxide are very important to the rubber industry. 

The rate at which sulfur will react with the unsaturated polymer chains can be increased by the addition of activators a metal oxide plus fatty acid. The most common combination is zinc oxide and stearic acid, with the primary fimction of the fatty acid being to solubilize the zinc in the elastomer. In the presence of the metal, it is believed that the sulfur reacts as a cation at the double bond which results in charged and uncharged polysulfides, the latter of which could in turn form free radicals. Metal activated sulfur vulcanization will proceed more rapidly than crosslinking by sulfur alone, but still too slow for most production purposes. The metal oxide/fatty acid is, in practice, used not to activate the sulfur itself, but to activate the organic compounds used as vulcanization accelerators. 

Mesoporous carbon materials were prepared using ordered silica templates. The Pt catalysts supported on mesoporous carbons were prepared by an impregnation method for use in the methanol electro-oxidation. The Pt/MC catalysts retained highly dispersed Pt particles on the supports. In the methanol electro-oxidation, the Pt/MC catalysts exhibited better catalytic performance than the Pt/Vulcan catalyst. The enhanced catalytic performance of Pt/MC catalysts resulted from large active metal surface areas. The catalytic performance was in the following order Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It was also revealed that CMK-1 with 3-dimensional pore structure was more favorable for metal dispersion than CMK-3 with 2-dimensional pore arrangement. It is eoncluded that the metal dispersion was a critical factor determining the catalytic performance in the methanol electro-oxidation. 

Phenanthroline in the presence of heavy metals acts as an activator of the polymerization of vinyl compounds558,559 and other olefins.560-564 It also assists the dimerization of olefins in the presence of titanium catalysts.565,566 It enhances the metal catalyzed oxidation of ascorbic acid567 and dimethyl sulfoxide.568 On the other hand, on its own it can inhibit several polymerization processes.545,569 It also stabilizes butadiene and isoprene and prevents their dimerization.570 It prevents peroxide formation in ether,571 inhibits the vinylation of alcohol572 and stabilizes cumyl chloride.573 It accelerates the vulcanization of diene rubbers574 and copolymers.575 1,10-Phenanthroline catalyzes the autooxidation of linoleic and ascorbic acids in the absence of metals.567... 

Zinc oxide is a very old technological material. Already in the Bronze Age it was produced as a byproduct of copper ore smelting and used for healing of wounds. Early in history it was also used for the production of brass (Cu-Zn alloy). This was the major application of ZnO for many centuries before metallic zinc replaced the oxide [149]. With the start of the industrial age in the middle of the nineteenth century, ZnO was used in white paints (chinese white), in rubber for the activation of the vulcanization process and in porcelain enamels. In the following a number of existing and emerging electronic applications of ZnO are briefly described. 

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