Vulcanization metal-accelerated

Dithiophosphates. These compounds (13) are made by reaction of an alcohol with phosphoms pentasulfide, then neutralization of the dithiophosphoric acid with a metal oxide. Like xanthates, dithiophosphates contain no nitrogen and do not generate nitrosamines during vulcanization. Dithiophosphates find use as high temperature accelerators for the sulfur vulcanization of ethylene—propylene—diene (EPDM) terpolymers. 

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. 

Rubber. The mbber industry consumes finely ground metallic selenium and Selenac (selenium diethyl dithiocarbamate, R. T. Vanderbilt). Both are used with natural mbber and styrene—butadiene mbber (SBR) to increase the rate of vulcanization and improve the aging and mechanical properties of sulfudess and low sulfur stocks. Selenac is also used as an accelerator in butyl mbber and as an activator for other types of accelerators, eg, thiazoles (see Rubber chemicals). Selenium compounds are useflil as antioxidants (qv), uv stabilizers, (qv), bonding agents, carbon black activators, and polymerization additives. Selenac improves the adhesion of polyester fibers to mbber. 

Cross-linking reactions for the polyisobutylene-type polymers depend on adding a reactive site, usually an aHyUc hydrogen or halogen. These reactive sites allow vulcanization with sulfur and accelerators or metal oxides (76,77). 

The product is a random polymer that is vulcanized with sulfur or with metal oxides (zinc oxide, magnesium oxide etc.). Vulcanization with sulfur is very slow, and an accelerator is usually required. 

Most accelerators used in the accelerated sulfur vulcanization of other high diene rubbers are not applicable to the metal oxide vulcanization of CR. An exception is the use of so-called mixed-curing system for CR, in which metal oxide and accelerated sulfur vulcanization are combined. Along with the metal oxides, TMTD, DOTG, and sulfur are used. This is a good method to obtain high resilience and dimensional stability. 

The accelerator that has been widely used with metal oxide cures is ethylene thiurea (ETU) or 2-mercaptoimidazoline. Further extensive use of ETU in vulcanization of CR is restricted because of suspected carcinogen. The related compound, thiocarbanahde, used formerly as an accelerator for sulfur vulcanization, has been revived for CR vulcanization other substitute for ETU has been proposed [29,30]. 

The silver white, shiny, metal-like semiconductor is considered a semimetal. The atomic weight is greater than that of the following neighbor (iodine), because tellurium isotopes are neutron-rich (compare Ar/K). Its main use is in alloys, as the addition of small amounts considerably improves properties such as hardness and corrosion resistance. New applications of tellurium include optoelectronics (lasers), electrical resistors, thermoelectric elements (a current gives rise to a temperature gradient), photocopier drums, infrared cameras, and solar cells. Tellurium accelerates the vulcanization of rubber. 

Uses. Vulcanization accelerator for type of rubber usually used in the production of household rubber gloves rather than medical rubber gloves corrosion inhibitor in metal-working fluids, detergents, antifreeze, and photographic emulsions. 

Uses. Rapid vulcanization accelerators in the rubber industry as preservatives in paints, oils, metal-working fluids... 

The vulcanization of polychloroprene (Neoprene) is carried out in different ways. Vulcanization by sulfur, even with an accelerator, is not practiced to a large extent. Vulcanizations by metal oxides (without diamine), either alone or in combination with sulfur (sometimes together with an accelerator), give the best physical properties for the crosslinked product. Halogenated butyl rubber is crosslinked in a similar manner. The mechanism for crosslinking by metal oxide alone is not established [Stewart et al., 1985 Vukov, 1984]. 

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... 

It is often difficult to obtain satisfactory adhesion of rubbers of different compositions and types with metal. The amounts of sulphur and accelerators of various types influence adhesion. These must be chosen so that there is no under or over vulcanization. 

Pipendine. the hydrogenation product of pyridine, is used as an intermediate for drugs and for making rubber-vulcanization accelerators, e.g., piperidinium pentamechylenedithiocarbamate (also known as Accelerator 552 ). On a commercial scale, piperidine (hexahydropyridine) is prepared by the catalytic hydrogenation of pyridine, e.g., with nickel catalysts at from 68 to 136 atmospheres pressure and at l50-20C,c,C. or under milder conditions with noble-metal catalysts. Pyridine derivatives can be similarly reduced to substitute piperidines. See formulas below. 

Ostromyslensky [90] observed that rubber could be vulcanized in the absence of sulphur or its compounds if small quantities of aromatic nitro compounds, e.g. nitrobenzene, dinitro- or sym- trinitro-benzene, tetranitronaphthalene plus certain oxidizing compounds, such as benzoyl peroxide, were added to it. The resultant vulcanized rubber had mechanical properties not inferior to those of a product vulcanized by sulphur alone, and when free from accelerators it exhibited a greater resistance to ageing. Some metal oxides, such as PbO, CaO, BaO, promoted vulcanization by nitro compounds. Urea played the role of an accelerator of vulcanization. These observations have been confirmed in more recent studies by other workers. 

Dithiocarbamates are normally prepared as alkali metal salts by the action of primary or secondary amines on CS2 in the presence of, say, NaOH. The zinc, manganese, and iron dithiocarbamates are extensively used as agricultural fungicides, and zinc salts as accelerators in the vulcanization of rubber. Alkali metal dithiocarbamates are usually hydrated and are dissociated in aqueous solution. When anhydrous, they are soluble in organic solvents in which they are associated. 

The metal (zinc, nickel, etc.) dithiophosphonates are attractive antioxidants in lubricants and plastics,124,125 and vulcanization accelerators (more active than analogous dithiophosphates).126 Many metal dithiophosphonates can be extracted with organic solvents and this property can be exploited for analytical applications, e.g., for copper(II) and bismuth(III) (O-hexyl)butyldithio-phosphonates,127 nickel(II), cobalt(II), and palladium(II) (0-ethyl)methyldithiophosphonates,128 platinum(IV), palladium(II), and gold(III) (O-ethyl)methyldithiophosphonates,129 and noble and rare metal (O-methyl)methyldithiophosphonates.130... 

Metal dithiocarbamates have been investigated as single-source precursors for MOCVD nanosized particles of metal sulfides, such as PtS and PdS,43 PbS,437,4 8 and Bi2S3,439 and tin sulfide thin films.440 In this respect the termochemistry of dithiocarbamates (periodically reviewed441 144) is important. Molybdenum dialkyldithiocarbamates are highly effective antiwear, antiseize, and antifriction additives for lubricating oils,445 and are used as vulcanization accelerators.446... 

Azocine derivatives have been employed as antiparasitics,201 herbicides,202-209 insecticides,210 211 pesticides,212 marine antifoulants,213 214 corrosion inhibitors,215 217 vulcanization accelerators,218-220 dyes,221,222 polymer stabilizers and inhibitors,223-225 bacteriocides,226 and as com-plexing agents in the determination of metals.227-229... 

Inorganic accelerators and metallic oxides (usually zinc) are essential for satisfactory cure. Organic accelerators, introduced in the early 1920s, notably shortened vulcanization time. 

Complexes with SCN throw light on the relative affinities of the two metals for N-and 5-donors. In [Zn(NCS)4] the ligand is A-bonded whereas in [Cd(SCN)4] it is 5-bonded. SCN can also act as a bridging group, as in [Cd S=C(NHCH2)2 2(SCN)2] when linear chains of octahedrally coordinated Cd are formed (Fig. 29.3c). A number of zinc-sulfur compounds are used as accelerators in the vulcanization of rubber. Among these are the dithio-carbamates, of which [Zn(S2CNEt2)2]2, and the isostructural Cd and Hg compounds achieve... 

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. 

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