Insoluble sulphur

A form of sulphur mainly of the rhombic variety but containing a proportion (up to 30%) of insoluble sulphur. 

An amorphous form of sulphur which is insoluble in rubber. It is used in rubber compounds which have to be stored for some considerable time in the uncured state without loss of tack, e.g., repair materials for tyres and belting. Since this form of sulphur is insoluble in the rubber it cannot bloom to the surface. The use of insoluble sulphur also gives some degree of scorch control since it is inactive until it reverts to the soluble form. Insulation... 

The degree to which one substance will dissolve in another. In rubber compounding it should be noted that many compounding ingredients are soluble in rubber and may also be soluble in each other. See Blooming, Insoluble Sulphur, Staining. Solution... 

Sulphur in its amorphous form is known in the rubber industry as insoluble sulphur . Insoluble sulphur is used by the rubber industry as, if not converted to the rhombic form by excessive processing heat, it will remain undissolved in the rubber and thus cannot bloom to the surface of the unvulcanised rubber compound. This is a factor which is very important for products which require a number of processing assembly steps in their manufacture. 

Dispersion of soluble rhombic sulphur does not usually create problems in most polymers, but addition of the insoluble form can create problems of incorporation into the rubber compound due to insolubility in the rubber. The insoluble sulphur particles tend to agglomerate into small lumps, which cannot then be dispersed effectively. Various treated insoluble sulphur products are available which aid incorporation. 

Insoluble sulphur, if handled incorrectly, can generate a high degree of static charge on its particles and has been the cause of a number of explosions whilst being discharged into storage hoppers and silos. 

Exposure to bright light, for example to a concentrated beam of the sun s rays or to the electric arc, produces an increase in the proportion of the. -modification in liquid sulphur. A similar effect is observable even in solution if a solution of sulphur in carbon disulphide is similarly illuminated, insoluble sulphur gradually separates the reverse change occurs in the dark.7 The conclusion can therefore be drawn that in solution also there is an equilibrium between the A- and p-forms at the ordinary temperature, but that except under the influence of light the concentration of p-sulphur is not sufficient to cause separation of Llic corresponding solid. 

Insoluble Amorphous Sulphur is produced, usually together with some sulphur soluble in carbon disulphide, by many reactions in which sulphur is set free. The slow decomposition of sulphur chloride or bromide by water, which may require several days for completion, gives a very stable form of insoluble sulphur.8 The action of mineral acids on... 

Flowers of sulphur (see p. 12), when freshly prepared, commonly contains about. 80 per cent, of insoluble sulphur, but this percentage may vary considerably.7 However, if sulphur vapour is condensed on the surface of cold water or especially on the surface of a cold aqueous solution of a mineral acid such as sulphuric acid, the proportion of the insoluble amorphous modification in the deposit may be so high as to render it the main constituent,8... 

That under suitable conditions y-sulphur can retain its individuality for a considerable period is clearly demonstrated by the fact that insoluble sulphur has been found in a specimen of llowers of sulphur prepared more than fifty years previously. Indeed, the presence of insoluble sulphur serves as a trustworthy characteristic of genuine flowers of sulphur by which the fraudulent substitution of powdered sulphur may easily be detected. 

The latent heat of fusion of solid sulphur varies with the different allotropic forms and with the temperature it is lowest for octahedral sulphur it is also influenced by the proportion of insoluble sulphur (y- or fjt,-) in the original solid and in the liquid formed.8 By electrical heating at the melting-point, the latent heat of fusion of monoclinie sulphur has been found to be 4 8-85 gm.-cals. per gm. 

To get proper rubber to fabric adhesion the fabric must be quite dry and evenly coated with the adhesive and adequately dried up. Defective adhesion occurs due to contamination by surface blooming of ingredients. Sulphur blooms can be eliminated by the use of insoluble sulphur. Waxy softeners which bloom at the surface should be avoided in compounding formulations. 

Arsenic Pentasulphide, As2S5.—When arsenic is fused with an excess of sulphur the product contains arsenic, sulphur and arsenic pentasulphide the last-named may be extracted with liquid ammonia 8 or, by careful fractionation, the arsenic and sulphur may be removed, leaving the sulphide. If the elements are fused together in stoichiometric proportions, a greenish-yellow plastic mass is obtained which gradually hardens and becomes lemon-yellow if this product is powdered and digested with aqueous ammonia, a yellow solution results and insoluble sulphur remains. After filtering, the addition of an acid to the yellow solution precipitates the pentasulphide. 

According to A. F. de Fourcroy,4 if the vapour of sulphur and ammonia be led through a red-hot tube, hydrogen, nitrogen, and a crystalline mixture of ammonium mono- and poly-sulphides are formed. F. Jones said that dry sulphur absorbs ammonia, and when the product is heated, ammonium sulphide is formed. A. Smith and W. B. Holmes found that if ammonia gas be passed over molten sulphur no insoluble sulphur is formed during the cooling. C. A. Seely found that liquid... 

A coarse sulphur sol can be prepared by pouring a saturated solution of sulphur in alcohol or acetone into water just below boiling point. The alcohol or acetone vaporises, leaving the water-insoluble sulphur colloidally dispersed. This technique is convenient for dispersing wax-like material in an aqueous medium. 

The thiols, containing the SH groups, are readily oxidized in the fibre to the original insoluble sulphur dye, giving a colour with very good wetfastness. 

One example of such reduced metabolic products that readily react with electrodes is Fl2S, which is produced by sulphate reducers in MFCs [19]. The primary oxidation product in this process is insoluble sulphur (S°). Reduction of sulphate to sulphide requires eight electrons, but oxidation of sulphide to S° releases only two of fhese eight electrons at the electrode surface. For example, when pyruvafe was used as the substrate, the above electrochemical reactions might be expressed as... 

Bead wire coat compounds are also generally tough and highly reinforced. Here the problem is excessive temperature build-up during processing which is sufficient to cause reversion of insoluble sulphur to its normal form which is then capable of blooming to the surface of the compound... 

An examination is made of the range of mbber chemicals produced by Flexsys, including accelerators, anti-reversion agents and antidegradants. Particular attention is paid to Perkalink 900, an anti-reversion agent based on biscitraconimidomethylbenzene. Reference is made to investments by the Company in environmental protection, the constmction of a plant in Antwerp for the production of intermediates for antiozonants, and the acquisition of Kali Chemie s activities in the production of insoluble sulphur. FLEXSYS KALI CHEMIE AG... 

Helsinki, Finland, 13th-15th June 2000, paper 73 IMPROVED FORM OF INSOLUBLE SULPHUR... 

Insoluble sulphur is a high molecular weight polymeric form of sulphur and is insoluble in rubber. This feature provides the rubber compounder with the freedom to formulate compounds containing high levels of sulphur but with no detrimental effect on green compound tack. The use of ordinary rubber makers sulphur (RMS) in such... 

POLSESEX - AN INSOLUBLE SULPHUR WITH HIGH THERMAL STABILITY... 

This comprehensive article supplies detailed results of a study evaluating a new insoluble sulphur, Polsinex, compared to conventional currently available insoluble sulphur. Information is included on the procedures of the study and focuses on the findings, which show that Polsinex exhibits high thermal stability and very good dispersibility. 7 refs. 

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