Rubber compounding accelerators

MAJOR USES Used in the production of dyes photographic developing agent vulcanization accelerator antioxidant in rubber compounds accelerator for synthetic fibers laboratory reagent photochemical measurements. 

Studies on the vulcanisation of a black and oil filled styrene-butadiene rubber compound accelerated by a number of different sulphenamide and sulphenimide compounds were made using a conventional curemeter operated to normal ASTM standards. The vulcanisation reactions were also studied using different modelling software, CODESSA software for deriving quantitative structure-property relationships and MOPAC software for semiempirical molecular orbital calculations which together yielded excellent correlation to onset of cure and maximum cure... 

Cyclohexylamine condensed with mercaptobenzothiazole produces the large volume moderated mbber accelerator JV-cyclohexyl-2-henzothiazolesulfenamide (41) [95-33-0] (see Rubber compounding). DCHA similady is used in piepaiing... 

Positive SIMS spectra obtained from plasma polymerized acetylene films on polished steel substrates after reaction with the model rubber compound for times between zero and 65 min are shown in Fig. 44. The positive spectrum obtained after zero reaction time was characteristic of an as-deposited film of plasma polymerized acetylene. However, as reaction time increased, new peaks appeared in the positive SIMS spectrum, including m/z = 59, 64, and 182. The peaks at 59 and 64 were attributed to Co+ and Zn, respectively, while the peak at 182 was assigned to NH,J(C6Hn)2, a fragment from the DCBS accelerator. The peak at 59 was much stronger than that at 64 for a reaction time of 15 min. However,... 

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. 

Deformulation of vulcanised rubbers and rubber compounds at Dunlop (1988) is given in Scheme 2.3. Schnecko and Angerer [72] have reviewed the effectiveness of NMR, MS, TG and DSC for the analysis of rubber and rubber compounds containing curing agents, fillers, accelerators and other additives. PyGC has been widely used for the analysis of elastomers, e.g. in the determination of the vulcanisation mode (peroxide or sulfur) of natural rubbers. 

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). 

An accelerator which permits processing of rubber compounds to be carried out with less risk of scorching but which does not slow down the rate of cure at normal vulcanisation temperatures. Demoulding... 

Hydrated or slaked lime Ca(OH)2 is an inorganic accelerator used in the curing of fluoroelastomers. In conventional sulphur cured polymers it counteracts the retardation of cure due to the presence of acidic substances in a rubber compound. Quicklime (CaO) dispersed in mineral oil or in wax/oil is used as a dessicant to reduce porosity in vulcanisates, particularly in fluid bed curing. 

C17H35COOH, one of the fatty acids found in animal fats. Commercial stearic acid is a mixture of stearic and palmitic acids. It is used in rubber compounding as an organic activator of accelerators. 

An ultra accelerator too scorchy for use as the sole accelerator in dry rubber compounding, but popular in latex work. In dry rubber compounding it is a useful booster for thiazole type accelerators. In some low ammonia latices it is used as a preservative. 

An activator in rubber compounds containing organic accelerators. In polychloroprene, zinc oxide is considered to be the accelerator rather than the activator. The use of zinc oxide as a reinforcing agent and as a white colouring agent is obsolescent. Zinc oxide is manufactured by either the French (or indirect) process or by the American (or direct) process. It can be used as a filler to impart high thermal conductivity. 

The rate of vulcanisation of a rubber compound is controllable by the choice of accelerator. The range of products offered to the rubber industry has been categorised historically into recognised classes. New developments have resulted in products that improve compound performance and which overcome dermatological problems, and do not generate nitrosamines and other extractable or volatile decomposition products. 

Classed as ultra accelerators, xanthates are among the fastest of accelerators available to the rubber compounder. Their speed is such that they find only limited application in solid rubber product manufacture but they are used in low temperature curing of latex articles. 

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. 

A further complicating factor with rubber compounds is that some compounding ingredients, e g., 2-mercaptobenzothiazole, will accelerate and increase the sulphur blooming. 

Types of Latex Compounds. For comparison with dry-rubber compounds, some examples of various latex compounds and the physical properties of their vulcanizates are given in Table 23. Recipes of natural rubber latex compounds, including one without antioxidant, and data on tensile strength and elongation of sheets made from those, both before and after accelerated aging, are also listed. The effects of curing ingredients, accelerator, and antioxidant are also listed. Table 24 also includes similar data for an SBR latex compound. A phenolic antioxidant was used in all cases. 

This acid is very corrosive towards most of the common metals and alloys. The corrosivity is increased where aeration or contamination by oxidising agents is present. Copper is particularly prone to this problem. Also many failures occur due to the presence of minor impurities such as ferric chloride. Rubber-lined steel is widely used for pipelines and large or small vessels. The rubber compound should be free from copper bearing antioxidants or accelerators. 

---