Vulcanisation accelerator

The production of hexamethylenetetramine consumes about 6% of the U.S. formaldehyde supply (115). Its principal use is as a thermosetting catalyst for phenoHc resins. Other significant uses are for the manufacture of RDX (cyclonite) high explosives, in mol ding compounds, and for mbber vulcanisation accelerators. Some hexamethylenetetramine is made as an unisolated intermediate in the manufacture of nitfilotriacetic acid. 

Peroxides decompose when heated to produce active free radicals which ia turn react with the mbber to produce cross-links. The rate of peroxide cure is coatroUed by temperature and selection of the specific peroxide, based on half-hfe considerations (see Initiators, free-RADICAL Peroxy compounds, organic). Although some chemicals, such as bismaleimides, triaHyl isocyanurate, and diaHyl phthalate, act as coagents ia peroxide cures, they are aot vulcanisation accelerators. lastead they act to improve cross-link efftcieacy (cross-linking vs scissioa), but aot rate of cross-link formatioa. 

It is now common practice to use sulphur in conjunction with several other additives. First amongst them are vulcanisation accelerators, of which there are many types. In the absence of an accelerator about 10 parts of sulphur is required, the vulcanisation time may be a matter of hours and much of the sulphur is... 

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

Much of this work does not represent current practice particularly with regard to the stationary phases. The analysis of AOs and vulcanisation accelerators in rubber materials by GC, HPLC and TLC was reviewed... 

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],... 

Scheme 5.4 Structural formulae of some vulcanisation accelerators (I) FDMPTD, (II) FDMPTM, (III) FZMPC and (IV) OFPBG. After Kelm and Gross [252]. Reprinted with permission from Rubber Chemistry and Technology. Copyright (1985), Rubber Division, American Chemical Society, Inc.

Salmona et al. [66] used El and CIMS to identify benzothiazole derivatives leached into injections by rubber plunger seals from disposable syringes. One of the compounds was used as a rubber vulcanisation accelerator, and four others were formed during syringe sterilisation with ethylene oxide. Applications of hyphenated chemical impact mass-spectrometric techniques are described elsewhere GC-MS (Section 7.3.1.2), for polar and nonpolar volatile organics, SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

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... 

It is accepted that many widely used latex vulcanisation accelerators - dithiocaibamates, thiurams and thiazoles - are capable of producing Type IV allergic response in certain individuals within the population and may also possess increasingly unacceptable eco-toxic and acute toxicity profiles. Thiurams and dithiocaibamates (derived from secondary amines) can also produce potentially harmful N-nitrosamines. Four safer accelerators developed and commercialised by Robinson Brothers are described. They are designed to reduce or eliminate the impact of the above problems using sustainable technology. At the same time these accelerators produce equivalent technological performances to those conventionally used. 10 refs. 

Xanthates are used commercially as flotation agents in froth flotation processes for the separation of crushed materials, and their use as vulcanisation accelerators for rubber has already been mentioned (p. 264). 

Kodama and co-workers [58] have reported TG-DSC curves for the analysis of the interaction between vulcanisation accelerators (tetramethylthiuram disulphide, dibenzothiazolyl disulphide, diphenylguanidine and N-cyclohexyl-2-benzothiazolyl-sulphenamide) and fillers (carbon black, white carbon, hard clay and CaC03). The initial melting point (MP) of the accelerators was largely influenced by the fillers. The higher the surface activity of the filler is, the lower and wider the melting range becomes. 

Whereas Redfern [57] has pointed out the advantages of simultaneous thermal analysis techniques (particularly TG-DSC and TG-DTA) over techniques conducted singly, an even more complete thermal profile is provided when a thermal analyser is coupled to some form of gas analyser (MS or FTIR). Mohler and co-workers [51] have reported TG-DSC-MS of the thermal decomposition of the vulcanisation accelerator tetramethyl thiuram disulphide (TMTD) in rubber degradation of TMTD starts at about 155 °C, as evidenced by m/z 76 (CS2) and 44 (radical of the secondary dimethylamine). 

Dimethylomine and Derivatives Dimethylomine, (H3C)2NH, mw 45.08, N 31.07%, col gas at RT and liq at below 7° sp gr 0.680 at 0°/4, fr p —92.2° extremely flammable and hazardous causes bums sol in w, ale eth. Can be prepd by passing a mixture of ammonia with vapors of methanol over a catalyst, such as silica gel. Has been used in agricultural herbicides and fungicides, synthetic textiles, fiber solvents, rubber vulcanising accelerators and in missile fuels (Refs 1, 2. 4)... 

Carbon disulfide (1) reacts with aniline and potassium hydroxide in boiling ethanol to yield syw-diphenylthiourea (8) (Scheme 5), which is used as a rubber vulcanisation accelerator (see Chapter 11, p. 219). 

These are easily prepared by the reaction of amines with carbon disulfide (1) in the presence of alkali (Scheme 17).2 The synthesis of dithiocarba mates (4) was first reported by Debus in 1850. Dithiocarba mates (4) form metal chelates, and sodium dimethyl dithiocarbamate is used in quantitative inorganic analysis for the estimation of metals, e.g. copper and zinc. Dithiocarba mates are also employed as vulcanisation accelerators and antioxidants in the rubber industry, and as agricultural fungicides.3 The parent dithiocarbamic acids are unstable, decomposing to thiocyanic acid and hydrogen sulfide however, the salts and esters are stable compounds. Dithiocarba mates (4) are oxidised by mild oxidants to the thiuram disulfides (38) (Scheme 17). 

Many organosulfur compounds have major industrial uses. For instance, carbon disulfide and DMSO are important commercial solvents and dithiocarbamates are used in the rubber industry as vulcanisation accelerators long chain alkanesulfonic or arenesulfonic acids are important synthetic detergents. Xanthates are used in the manufacture of rayon (see Chapter 8, p. 135) and cellophane, and many commercial dyes contain sulfonic acid groups (see Introduction, p. 5). Sulfamic acid derivatives such as saccharin (see Chapter 9, p. 162) acesulfame potassium (see Introduction, p. 5) and cydamates (see Chapter 9, p. 162) are valuable artificial sweeteners. 

ISO 188 1998 Rubber, vulcanised—Accelerated ageing or heat resistance tests. 

Details A crystalline solid, and a vulcanisation accelerator of rubber. 

Amino acids find use in cosmetics, in plant protection agents [60] e.g. Roundup , Basta - cf. section 8.1), as dispersion aids, stabilisers for PVC, vulcanisation accelerators, corrosion inhibitors, and as additives in electroplating and photography. 

Free acid unstable and has not been isolated. Na and K salts sol HgO Ox. (I, ferncyanide, etc.) — tetraethylthiuram disulphide, Zn salt and organic amine salts (particularly the diethylamine salt) used as rubber vulcanisation accelerators. 

Free acid very unstable. Rapidly oxidised to tetramethylthiuram disulphide. The salts are employed as rubber vulcanisation accelerators. Na salt, 2 HaO anhydrous at 130°. 

Important applications of P-S compounds are in matches, as insecticides, as lubricating oil additives, flotation agents and vulcanisation accelerators (Chapter 12). Some P-S compounds exhibit interesting electrical and magnetic properties and several P/S glass systems have been studied in recent years. 

Constit. of Eichhornia crassipes and Narcissus tazetta. Rubber vulcanisation accelerator. Indicator used in the anal, of organometallic reagents. Fluorescent probe for detn. of detergent critical micelle concentrations. Prisms or needles (EtOH), leaflets (petrol). Mp 62°. 

Constit. of Aconitum karakolicum, Acroptilon repens, Daucus carota and Eichhornia crassipes. Formerly used as a rubber vulcanisation accelerator. Inhibits polymerisation of conjugated dienes. Needles (MeOH). Mod. sol. EtOH, ECO, AcOH, C.H. Mp 108° (103-104°). Bp 395-399.5°, Bp, 237°. Solns. show blue fluor. Natural occurrence appears doubtful. Probable contaminant. 

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