Amine vulcanization accelerators

Amines are important industrial chemicals which are involved in everyday life [3, 4]. Apart from the usual classification into primary, secondary, and tertiary amines, the distinction is often made between lighf amines (less than six-carbon substituents) and fatty amines. light amines are intermediates for the synthesis of drugs, herbicides, cosmetics, etc. [3]. They also find use as vulcanization accelerators and extraction agents. Fatty amines are involved in the synthesis of corrosion inhibitors and cationic surfactants, which are used in ore flotation processes and are good fabric softeners and antistatic agents [4—6],... 

Over half of the remaining market for products used in the processing of rubber is made up of antioxidants, antiozonants and stabilizers, either amino compounds or phenols. Aniline is used to manufacture vulcanization accelerators, antioxidants and antidegradants. Of the latter, several are A-substituted derivatives of p-phenylenediamine and octyl dipheny-lamine. Diphenylamines terminate free-radical reactions by donating the amino hydrogen, and are used to protect a wide range of polymers and elastomers. Many synthetic rubbers incorporate alkylated diphenylamine antioxidants. Other antioxidants include aryl amine resinous products from, e.g. condensation of aniline and acetone in the presence of... 

Kawaoka, Y. Studies of rubber vulcanization accelerators. VII. Dimethyl-amine salt of mercaptobenzothiazol. J. Soc. Chem. Ind. Japan 43, Suppl. 223 (1940) Chem. Abstracts 35, 2368 (1941). 

EINECS 205-138-7 Fast Garnet B Base Fast Garnet Base B HSDB 1080 a-Naftalamin 1-Nafti(amina a-Nafty/amin 1-Naftylamin 1-Naftylamine 1-Naphthalamine 1-Naphthalenamine Naphthalidam Naphthalidine 1-Naphthylamin a-Naphthylamine 1-Naphthylamine RCRA waste number U167 UN2077. Used in manufacture of dyestuffs, as a rubber vulcanization accelerator and as a chemical feedstock, mp = 49.2° bp = 300.8° d = 1.0228 Xm = 243,318, 328 nm (cyclohexane) soluble in H2O (1.7 mg/l), soluble in CHCI3 LDso (rat orl) = 779 mg/kg. 

Rate of vulcanization Ultra-accelerators include dithiocarbamates and xanthates. Semiultra-accelerators include thiurams and amines. Fast accelerators are thiazoles and sulfonamides. A medium-rate system is diphenylguanidine. A slow accelerator is thiocarbanilide. 

In the rubber industry, chemicals containing amines are used as vulcanization accelerating agents, which may be transformed during the production process (vulcanization) into nitrosamines. Such substances are added to condoms to give the rubber the needed degree of elasticity. 

Uses Emulsifier for creams/lotions, oils, fats, waxes, cosmetics, min. oil and paraffin wax emulsions, leather dressings, textile specialties, polishes, cleaners absorbent for acidic gases medicine buffer in cosmetics solubilizer, stabilizer, buffer in pharmaceuticals formaldehyde scavenger in curing U-F resins, phenolics amine soaps (metalworking fluids) synthesis of surfactants, vulcanization accelerators, pharmaceuticals chemical intermediate for paints, etc. 

Properties Colorless to It. yel. oily liq. ammonialike odor sol. in alcohol, ether, oxygenated soivs. insol. in water m.w. 197.28 dens. 1.017 m.p. -26 C b.p. 300 C ref. index 1.5740 Toxicology Irritant TSCA listed Uses Rubber activator vulcanization accelerator corrosion inhibitor bacteriostat intermediate amination reagent reagent for metals detection of cobalt, cyanate, and iron Manuf./Distrib. ABCR http //www.abcr.de, Acros Org. http //www.acros.be, Aldrich http //www.sigma-aldrich.com, Alfa Aesar http //www.aifa.com, Bayer http //WWW. bayerus. com Cambrex http //www.cambrex.com, Fluka http //www.sigma-aidrich.com, ICN Biomed. Research Prods, http //www.icnbiomed.com, Interchem http //www.interchem.com, Koei Chem. http //www.koeichem.com Lancaster Synthesis Noveon Kalama Pfaltz Bauer http //www.pfaitzandbauer.com, Robinson Bros. Ltd http //www.robac.co.uk, Sithean... 

In addition, many of the organosulfur compounds and organometallic compounds used in rubber compounds as vulcanization accelerators are known to have antioxidant activity. Mercaptobenzimidazole and its zinc salt have been shown to have antioxidant activity. In addition, mercaptobenzimidazole, when combined with other known antioxidants, has been shown to have a synergistic effect in oxidation prevention when metal ion catalyzed oxidation is prevalent. Also, metal and amine salts of dialkyldithio-carbarnates have been shown to have antioxidant action. 

The aliphatic amines are valuable intermediates for chemical synthesis applications, Reaction of ethylamine with cyanuric chloride yields triazine-type herbicides, Diethylamine is used in the preparation of vulcanization accelerators where reaction with carbon disulfide yields a dithiocarbamate. Triethyl-amine is used as an acid acceptor in chemical syntheses and as a salt former in various purification processes. The amine is used as a corrosion inhibitor in aqueous systems, as a catalyst in polyurethane applications, in textile and photographic applications, and in anodic electrocoating. 

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

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. 

Sulfenamide accelerators generally requite less fatty acid because they release an amine during the vulcanization process which acts to solubilize the zinc. Guanidines and similar amine accelerators also serve to both activate and accelerate vulcanization. 

The thiophthalimide (CTP) and sulfenamide classes of retarders differ from the organic acid types by thek abiUty to retard scorch (onset of vulcanization) without significantly affecting cure rate or performance properties. Much has been pubUshed on the mechanism of CTP retardation. It functions particularly well with sulfenamide-accelerated diene polymers, typically those used in the the industry. During the initial stages of vulcanization, sulfenamides decompose to form mercaptobenzothiazole (MBT) and an amine. The MBT formed reacts with additional sulfenamide to complete the vulcanization process. If the MBT initially formed is removed as soon as it forms, vulcanization does not occur. It is the role of CTP to remove MBT as it forms. The retardation effect is linear with CTP concentration and allows for excellent control of scorch behavior. 

The Goodyear vulcanization process takes hours or even days to be produced. Accelerators can be added to reduce the vulcanization time. Accelerators are derived from aniline and other amines, and the most efficient are the mercaptoben-zothiazoles, guanidines, dithiocarbamates, and thiurams (Fig. 32). Sulphenamides can also be used as accelerators for rubber vulcanization. A major change in the sulphur vulcanization was the substitution of lead oxide by zinc oxide. Zinc oxide is an activator of the accelerator system, and the amount generally added in rubber formulations is 3 to 5 phr. Fatty acids (mainly stearic acid) are also added to avoid low curing rates. Today, the cross-linking of any unsaturated rubber can be accomplished in minutes by heating rubber with sulphur, zinc oxide, a fatty acid and the appropriate accelerator. 

In a preliminary study we have recently reported (1) that the air in three rubber and tire industry plants was contaminated with several N-nitroso compounds. The compounds included N-nitrosomorpholine (NMOR), N-nitrosodimethylaminne (NDMA), and N-nitrosodiphenylamine (NDPhA). The latter compound is used as a vulcanization retarder, so its presence near processes employing it was not surprising. Bismorpholine-carbamylsulfonamide, a cross-linking accelerator used in rubber tires was found in tire factories and may be contaminated with NMOR. The source of the NDMA was not identified, but it could arise from nitrosation of amines which may be decomposition products of diamine based accelerators, as pointed out by Yeager, et al (2). 

These were first investigated and used in rubber as accelerators. Their effect in improving the vulcanizing and ageing properties of rubber was utilized for several years. Primary diamines, primary secondary amines and aminophenols are much more active than simple primary amines. Aminophenol and phenolamine salts are effective antidegradents. 

Hydrogen peroxide used over a wide pH range has been employed to oxidize sulfur compounds. The scope of the oxidation using hydrogen peroxide includes coupling of thiols to disulfides355 and thiols coupled with amines,356 which are used to produce industrially important compounds. For example, sulfenamides are accelerators for rubber vulcanization (Figure 3.91).357... 

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. 

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