Thiuram rubber accelerators

Oral medications taken by athletes may also be allergenic, particularly the non-steroidal agents (especially piroxicam) and antibiotics (ciprofloxacin, nalidixic acid, sulfonamides, tetracyclines), which are photosensitizers (Wainwright et al. 1993). Prior sensitization to thiuram rubber accelerators makes athletes susceptible to systemic eczematous dermatitis if Antabuse (disulfiram - a thiuram derivative) is given orally (Pirila 1957 Shelley 1961). 

TMTM and TMTD are both classified as thiuram rubber accelerators that are very fast curing. Unfortunately, they both generate nitrosamine gases during the curing process, which can pose a health risk to workers. Therefore, thiuram accelerators have decreased in use because of the nitrosamine issue. 

FD-MS is also an effective analytical method for direct analysis of many rubber and plastic additives. Lattimer and Welch [113,114] showed that FD-MS gives excellent molecular ion spectra for a variety of polymer additives, including rubber accelerators (dithiocar-bamates, guanidines, benzothiazyl, and thiuram derivatives), antioxidants (hindered phenols, aromatic amines), p-phcnylenediamine-based antiozonants, processing oils and phthalate plasticisers. Alkylphenol ethoxylate surfactants have been characterised by FD-MS [115]. Jack-son et al. [116] analysed some plastic additives (hindered phenol AOs and benzotriazole UVA) by FD-MS. Reaction products of a p-phenylenediaminc antiozonant and d.v-9-lricoscnc (a model olefin) were assessed by FD-MS [117],... 

MONO-THIURAD MONOTHIURAM PENNAC MS TETRAMETHYLTHIURAMMONIUM SULHDE TETRAMETHYLTHIURAMMONOSULHDE TETRAMETHYLTHIURAM SULFIDE TETRAMETHYD TRITHIO CARBAMIC ANHYDRIDE l,l -THIOBIS(N3 -DIMETHYLTHIO)FORMAMIDE THIONEX THIONEX RUBBER ACCELERATOR TMTM TMTMS LTSIADS USAF B-32 USAF EK-P-6255 VULKACIT THIURAM MS/C... 

Use The metal salts of the acid are important as strong (ultra) rubber accelerators, as are the thiuram disulfide derivatives. Seed disinfectant. 

The rising of the rate of chemical reactions between sulfur and rubber, acceleration of the vulcanization, and reduction of its temperature are accomplished using special accelerators. The use of a few accelerators may improve the vulcanization process because of their mutual activation. Two accelerators were used tetramethyl-thiuram-disulhde (thiuram-D) and CAPTAX . They act mutually and thus improve the vulcanization process and the resulting properties of RubCon. 

Sulfads . [R.T. Vanderbilt] Dqienta-methylene thiuram tetrasulfide accelerator, vulcanizing r entfiornatural and synthetic rubbers. 

TM/ETD. [Akrochem] 60% Tetramethyl thiuram disulfide/40% tetraethyl thiu-ram disulfide rubber accelerator. 

The oxidation of thiols to disulphides is facile, and can be carried out in either acid [225] or alkaline conditions. Alkaline aqueous conditions are usually chosen, where the thiol dissolves as its anion but the product disulphide separates as liquid or solid. By far the largest application of this chemistry is in production of rubber accelerators (Figure 9.14), including thiuram disulphides [226] and benzothiazole disulphides [227]. 

The principal thiurams used industrially are tetramethylthiuram monosulfide (TMTM), tetrame-thylthiuram disulfide (TMTD), tetraethylthiuram disulfide (TETD) and dipentamethylenethiuram disulfide (PTD). These thiurams are frequently used as mixes, whose exact composition varies with the particular rubber product, as well as with the country of origin. Worldwide, TMTM and TMTD are most used. Thiurams are among the more frequently used rubber accelerators, especially in the manufacturing of gloves. Numerous other consumer products also contain thiurams (Table 6). 

Tetraethylthiuram disulfide is a rubber accelerator of the thiuram group, contained in the " thiuram mix . It can cross react with other thiurams, especially thiu-rame (TMTD). When being administered as an adjunctive treatment for alcoholism, it caused occupational contact dermatitis in the treating nurse. 

Tetramethylthiuram monosulfide is a rubber accelerator, contained in the thiuram mix . The most frequent occupational categories are metal industry, homemakers, health services and laboratories, and building industries. 

In sulphur cured rubbers, accelerators are generally used to reduce the dependency on sulphur in order to achieve more efficient vulcanisation, to improve heat and flex resistance due to the presence of more monosulphidic crosslinks, and to increase the cure rate of the rubber and improve production capacity. Two accelerators which have been shown to enhance bondability of rubbers are 2-mercaptobenzothiazole (MBT) and mercaptobenzothiazole disulphide (MBTS). An accelerator which is known to negatively impact on adhesion is tetramethyl thiuram disulphide (TMTD). 

ZnDBC is commonly referred to as an ultra-accelerator because the dithiocarba-mate class of rubber accelerators is known for imparting a very fast cure rate (just like the thiuram accelerator class). 

DPG is the most commonly used member of the guanidine class of rubber accelerators. DPG is commonly used as a secondary accelerator (or kicker ) with primary sulfenamide accelerators and sometimes with thiazole accelerators as well. DPG is also a silanization accelerator. It can interact with the silica surface, which then reacts with organosilanes in tread stocks to help reduce rolling resistance. DPG is not as chemically active as the thiuram or dithiocarbamate accelerators. 

Piperidines. A significant use of piperidine (18) has been ia the manufacture of vulcanization accelerators, eg, thiuram disulfide [120-54-7] (115) (see Rubber chemicals). Mepiquat dichloride [24307-26-4] the dimethyl quaternary salt of (18), is used as a plant growth regulator for cotton (qv). Piperidine is used to make vasodilators such as dipyridamole [58-32-2] (116) and minoxidil [38304-91-5] (117), and diuretics such as etozoline [73-09-6] (118). 

Rubber Chemicals. Sodium nitrite is an important raw material in the manufacture of mbber processing chemicals. Accelerators, retarders, antioxidants (qv), and antiozonants (qv) are the types of compounds made using sodium nitrite. Accelerators, eg, thiuram [137-26-8J, greatly increase the rate of vulcaniza tion and lead to marked improvement in mbber quaUty. Retarders, on the other hand (eg, /V-nitrosodiphenylamine [156-10-5]) delay the onset of vulcanization but do not inhibit the subsequent process rate. Antioxidants and antiozonants, sometimes referred to as antidegradants, serve to slow the rate of oxidation by acting as chain stoppers, transfer agents, and peroxide decomposers. A commonly used antioxidant is A/,AT-disubstituted Nphenylenediamine which can employ sodium nitrite in its manufacture (see Rubber chemicals). 

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 general, the reaction mechanism of elastomeric polymers with vulcanisation reagents is slow. Therefore, it is natural to add special accelerators to rubber compounds to speed the reaction. Accelerators are usually organic compounds such as amines, aldehyde-amines, thiazoles, thiurams or dithio-carbamates, either on their own or in various combinations. 

For the purpose of polymer/additive analysis most applications refer to vulcanisate analysis. Weber [370] has determined various vulcanisation accelerators (Vulkazit Thiuram/Pextra N/Merkapto/AZ/DM) in rubbers using PC. Similarly, Zijp [371] has described application of PC for identification of various vulcanisation accelerator classes (guanidines, dithiocarbaminates, thiuramsulfides, mercapto-substituted heterocyclic compounds, thioureas, etc.). The same author has also... 

Phenolic antioxidants in rubber extracts were determined indirectly photometrically after reaction with Fe(III) salts which form a red Fe(II)-dipyridyl compound. The method was applicable to Vulkanox BKF and Vulkanox KB [52]. Similarly, aromatic amines (Vulkanox PBN, 4020, DDA, 4010 NA) were determined photometrically after coupling with Echtrotsalz GG (4-nitrobenzdiazonium fluoroborate). For qualitative analysis of vulcanisation accelerators in extracts of rubbers and elastomers colour reactions with dithio-carbamates (for Vulkacit P, ZP, L, LDA, LDB, WL), thiuram derivatives (for Vulkacit I), zinc 2-mercaptobenzthiazol (for Vulkacit ZM, DM, F, AZ, CZ, MOZ, DZ) and hexamethylene tetramine (for Vulkacit H30), were mentioned as well as PC and TLC analyses (according to DIN 53622) followed by IR identification [52]. 8-Hydroquinoline extraction of interference ions and alizarin-La3+ complexation were utilised for the spectrophotometric determination of fluorine in silica used as an antistatic agent in PE [74], Also Polygard (trisnonylphenylphosphite) in styrene-butadienes has been determined by colorimetric methods [75,76], Most procedures are fairly dated for more detailed descriptions see references [25,42,44],... 

FAB has been used to analyse additives in (un) vulcanised elastomer systems [92,94] and FAB matrices have been developed which permit the direct analysis of mixtures of elastomer additives without chromatographic separation. The T-156 triblend vulcanised elastomer additives poly-TMDQ (AO), CTP (retarder), HPPD (antiozonant), and TMTD, OBTS, MBT and A,lV-diisopropyl-2-benzothiazylsulfenamide (accelerators) were studied in three matrix solutions (glycerol, oleic acid, and NPOE) [94]. The thiuram class of accelerators were least successful. Mixture analysis of complex rubber vulcanisates without chromatographic separation was demonstrated. The differentiation of matrix ions from sample ions was enhanced by use of high-resolution acquisition. 

Ostromow [328] has described the use of conductometry for the analysis of extracts from elastomers and rubbers, such as the determination of various vulcanisation accelerations dithiocarbamates, thiurams (tetramethylthiuramdisulfide, tetramethylthiurammono-sulfide), 2-mercaptobenzothiazole, diphenylguanidine... 

If accelerators which leave amine residues in the rubber compound are used, then the above mentioned deterioration of a polyester fabric will occur. Thiurams and dithiocarbamates can also damage fabrics. These accelerator residues cause deterioration of both fabric and adhesion levels which usually occur under service conditions after long periods of exposure to high temperatures. 

Captax (Structure 15.21) is used to the extent of 1% with hevea rubber and accounts for the major part of the over 30,000 t of accelerators used annually in the United States. Other accelerators widely used include 2-mercaptobenzothiazole sulfenamide (Santocure Structure 15.22), used for the vulcanization of SBR dithiocarbamates and thiuram disulfides. Thiuram disulfide (Structure 15.23) is a member of a group called ultra-accelerators, which allow the curing of rubber at moderate temperatures and may be used in the absence of sulfur. 

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