Rubber blends sulphur

Whilst the blend has a good green strength it is usual to vulcanise the rubber by an accelerated sulphur system using a higher than usual accelerator sulphur ratio. 

The percentage sulphur (determined in the un-vulcanized reclaim) and the available rubber hydrocarbon are taken into consideration while evolving the compound formulation. It should be noted that reclaimed rubber is not all rubber. In arriving at the total rubber content in the rubber formulation containing reclaim, allowance must be made for its rubber content. For example in the following blend of smoked sheet and whole tyre reclaim, the total rubber content is to be considered as 100 parts instead of 125 parts as below and the proportion of other ingredients should be worked out accordingly on "parts per hundred rubber" (phr) basis. 

In this chapter the word elastomer is used to describe the base polymer and rubber to describe the fully compounded finished component. A rubber formulation is a complex blend of ingredients, and a typical high extract sulphur cured natural rubber formulation is given in Table 12.4. 

Stephen, R., Jose, S., Joseph, K., Thomas, S., Ommen, Z. Thermal stability and ageing properties of sulphur and gamma radiation vulcanized natural rubber (NR) and carboxylated st3 rene butadiene mbber (XSBR) latices and their blends. J. Polym. Degrad. Stab. 91, 1717-1725 (2006)... 

The thermal stability of NR and carboxylated styrene butadiene rubber (XSBR) lattices and their blends were studied by thermogravimetric methods by Stephen et The thermal degradation and ageing properties of these individual lattices and their blends were investigated with special reference to blend ratio and vulcanization techniques. As already described, as the XSBR content in the blends increased, their thermal stability was also found to increase. Among sulphur and radiation-vulcanized samples, radiation cured possessed higher thermal stability due to the higher thermal stability of carbon carbon crosslinks. 

Figures 1 and 2 show the degree of polymer crosslinking and free sulphur content as a function of vulcanization time for the films prepared from latex Polysar lY. In the case where the initial sulphur content in the films was 2.5 pph or more (blends 6-9), the rate of addition of sulphur to rubber does not change during the vulcanization process, (i.e., it can be described by a straigjit line).

As long as sulphur content in the blends is considerably less than that of rubber (for example, in the blend 6 sulphur rubber ratio is 1 40), independence of the reaction rate on the sulphur concentration can be explained only by concluding that the vulcanization reaction affects only a small part of the rubber -the surface layers of latex globules - while the main part of rubber, the inner volume of latex globules, remains unvulcanized. 

In this study, the degree of autohesion between two layers deposited on the surface of a glass mold was investigated. The Latex blend consisted of (in weight parts) rubber of natural centrifugated latex - 100 sulphur - 2 zinc dimethyldithiocar-bamate - 1 zinc mercaptobenzothiazole - 1 2,2 -methylenebis (6-tert-butyl-4-methylphenol) - 0.5. 

Blends with nitrile rubbers will give improved oil resistance but a poorer level of vulcanisate physical properties. They are normally limited to sulphur modified types using a cure system based on TETD (0-2-0-5 phr). 

Most passenger car tyre tread compounds are based on SBR or SBR/BR blends and crosslinked with a cure system containing sulphur and various accelerators. Synthetic rubber vulcanisates are not as sensitive to reversion as NR vulcanisates but nevertheless they are subject to alterations due to changes in the crosslink... 

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