The knowledge of Insoluble sulfur

- Oct 16, 2018-

Insoluble sulfur is a long-chain polymer of sulfur. The number of sulfur atoms in the long chain is more than 106. It is called μ-sulfur in the early crystallography. It is now called ω-sulfur. It belongs to a homomorphic form of sulfur and is insoluble. The nature of carbon disulfide and rubber. Due to the easy breaking of the sulfur-carbon bond and the instability of the electronic structure of the long-chain molecular double-end radical, the insoluble sulfur has a metastable nature and has a tendency to convert to soluble sulfur, ie, orthorhombic sulfur, which is the instability of insoluble sulfur. Sex. Based on this property, the insoluble sulfur commodity is a mixture of insoluble and soluble sulfur, and its insoluble sulfur content can reach 98% or more. Insoluble sulfur is subject to heat loss, contact with alkaline materials or long-term storage. Since insoluble sulfur is produced by a free radical polymerization method under high heat, the product usually has a static charge, which tends to cause agglomeration of the product, uneven dispersion in the rubber compound or cause a processing accident. For this reason, most of the commercially available products are oil-filled and non-flying products, and the naphthenic oil filled can reduce the static charge and improve the dispersibility in the rubber compound.

Physical properties: Ordinary soluble sulfur is an orthorhombic crystal of S8 ring structure, which can be added to rubber. The solubility in rubber at room temperature is about 1%, and it increases with the increase of rubber temperature. When the rubber mixture is cooled to room temperature, the compound becomes a supersaturated solution of soluble sulfur, and more than 1% of the added sulfur will crystallize and migrate to the surface of the rubber to form a frost. If this kind of blooming occurs on the semi-finished rubber parts, it not only plays a role of not requiring a release agent, but also seriously affects the adhesion and molding between the rubber parts or between the rubber parts and the skeleton material, and produces sulfur in the rubber compound. The heterogeneous distribution in the veneer will result in uneven density of vulcanized rubber crosslinks, ultimately reducing the bond strength and mechanical properties of the rubber product. In contrast to soluble sulfur, the insoluble sulfur is a serrated long-chain structure, also known as μ-sulfur, which has the viscoelastic properties of ordinary polymers. As long as the mixing temperature reaches its glass transition temperature, the μ-sulfur is converted from solid to plastic. It is easy to blend with plasticized rubber. This kind of μ-sulfur-containing rubber compound, even if it is cooled to room temperature, cannot crystallize, migrate, and form a frosting in the rubber compound due to its long-chain structure, so that the surface of the rubber member can be kept fresh and the semi-finished product can be improved. The adhesion between the rubber parts or the rubber parts and the skeleton material, and ensures the uniform distribution of sulfur in the rubber compound, and improves the vulcanization quality and mechanical properties of the rubber products, especially the tires.

Use characteristics: Insoluble sulfur is used as a vulcanizing agent for natural rubber and synthetic rubber, and can be directly added to the compound during kneading. Usually added in the final stage of mixing. If feeding on the internal mixer, it is best to reduce the temperature of the rubber to 90 ° C before discharge. For IS-HS products, it can be added at no higher than 105 °C. Generally, the amount is 0.2-5.0 parts in the soft rubber product, and the amount is not less than 3.5 parts in the rubber-bonded compound. With the development of radial tires, tire companies generally require insoluble sulfur to maintain a rate of 40% or more at 120 ° C for 15 min. That is, high thermal stability insoluble sulfur.

Note: Alkaline strong compounding agents or thiazole accelerators may pose a risk of blooming when combined with insoluble sulfur. This product is flammable and should be protected from fire when stored and used.