Accelerated vulcanization delayed-action

Delayed-Action Accelerated Vulcanization. If cross-link formation is by a free radical mechanism, delayed action could be the result of a quenching action by the monomeric polysulfldes formed by reactions between accelerator and sulfur. If the polymeric poly-thiyl radicals (cross-link precursors) are rapidly quenched by an exchange reaction before they are able to form cross-links, cross-link formation would be impeded until substantial depletion of the monomeric polysulfldes. This is illustrated in Scheme 4. 

Organic chemical accelerators were not used until 1906 (65 years after the Goodyear-Hancock development of unaccelerated vulcanization [Fig. 8]), when the effect of aniline on sulfur vulcanization was discovered by Oenslager [11]. This could have been, at least partially, in response to the development of pneumatic tires and automobiles near the turn of the century. Aniline, however, is too toxic for use in rubber products. Its less toxic reaction product with carbon disulfide, thiocarbanilide, was introduced as an accelerator in 1907. Further developments lead to guanidine accelerators [12]. Reaction products formed between carbon disulfide and aliphatic amines (dithiocarba-mates) were first used as accelerators in 1919 [13]. These were and are still the most active accelerators with respect to both crosslinking rate and extent of crosslink formation. However, most of the dithiocarbamate accelerators give little or no scorch resistance and their use is impossible in many factoryprocessing situations. The first delayed-action accelerators were introduced in 1925 with the development of 2-mercaptobenzothiazole (MET) and 2-... 

Reviews on the subject of brass-plated steel cord-natural rubber adhesion have been written by van Ooij who has done much of the work in the field. Van Ooij [46] has given a model for rubber-brass adhesion, in which a copper sulfide layer forms on the brass before the onset of crosslink formation. The thin film of copper sulfide has good adhesion and cohesion. In addition, the film is so porous that rubber molecules can become entangled with it. It is not required that the film forms simultaneously with the formation of crosslinks during vulcanization but, rather, it is required that the copper sulfide film be completely formed before crosshnking starts. Indeed, adhesion between brass-plated steel and natural rubber can frequently be improved by the use of the retarder, CTP [4] or by using a more delayed action accelerator such as N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS) [47]. 

The first application of pyrazino[2,3-6]pyrazines as vulcanization accelerators for rubber copolymerization has been reported in CHEC-I. Some new pyrazino[2,3-A]pyrazine derivatives are in use as electrophotographic developers <90JAP(K)2135365) and light-resistant fluorescent polymers <89JAP(K)0l 153750). Some alkylsubstituted decahydropyrazino[2,3-6]pyrazines are suitable as delayed-action catalysts for the preparation of urethanes <83USP452839l>. Other pyrazinopyrazine derivatives are reported to have inhibitory effects on tomato spotted wilt virus <83MI 719-01). 

Uses Delayed-action vulcanization accelerator for rubbers accelerator for food-contact rubber articles for repeated use... 

Accelerated-sulfur vulcanization is the most widely used method. For many applications, it is the only rapid crossUnking technique that can, in a practical manner, give the delayed action required for processing, shaping, and forming before the formation of the intractable vulcanized network. It is used to vulcanize natural rubber (NR), synthetic isoprene rubber (IR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), butyl rubber (HR), chlorobutyl rubber (ClIR), bromobutyl rubber (BUR), and ethylene-propylene-diene-monomer rubber (EPDM). The reactive moiety for all of these elastomers can be represented by... 

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