It does not dissolve in rubber and does not migrate, so it does not cause blooming.
Insoluble sulfur is primarily used for rubber. Its advantage is that it does not dissolve in rubber and does not migrate, thus preventing the so-called blooming. At room temperature, the S8 cyclic molecules present in normal soluble sulfur open up when the temperature exceeds 158°C, causing sulfur chains to bond together and polymerize. By rapidly cooling this molten polymer chain, sulfur is transformed into an insoluble sulfur state that does not revert back to S8 cyclic molecules, resulting in a metastable polymer structure. This polymer chain is insoluble in organic solvents and rubber, and in rubber compounds, it remains suspended like an inactive filler. It softens to some extent with temperature and exhibits thermoplastic behavior. Most standard grades of insoluble sulfur consist of over 90% sulfur polymer and less than 10% soluble sulfur. However, due to its very fine particle size, it tends to clump together due to static electricity, making it difficult to disperse in rubber. Insoluble sulfur often clings around the nip during roll processing, which is believed to be due to its higher tendency to become charged with static electricity compared to normal soluble sulfur.
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basic information
Structol SU50 - Insoluble sulfur compound - Yellow, non-dusting powder ■ Ensures optimal dispersion ■ Suitable for formulations where dispersion is an important factor Structol SU109 - Insoluble sulfur compound - Yellow, non-dusting powder ■ Suitable for replacing polymer or oil medium types; higher dispersibility Structol SU135/SU135 GR75 - Soluble sulfur compound - Yellow, non-dusting powder ■ Mixture of insoluble and soluble sulfur; optimal mixing ratio ■ Outperforms conventional oil medium types ■ Suitable for formulations that can contain soluble sulfur ■ GR 75 type: EPDM medium; granule form; easy handling and mixing
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Applications/Examples of results
Improvement of rubber processability
Line up（4）
| Model number | overview |
|---|---|
| Stractol SU 50 | Insoluble sulfur compound, non-dusting powder |
| Stractol SU 109 | Insoluble sulfur compound, non-dusting powder |
| Stractol SU 135 | Soluble sulfur compound, non-dusting powder |
| Stractol SU 135 GR 75 | Soluble sulfur compound, non-dusting powder |
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Company information
We offer a wide range of German-made processing aids for rubber under the "Structol" brand, starting with lubricants. For many years, we have been favored by numerous rubber manufacturers in Japan, including the four major tire manufacturers, as well as many large, medium, and small companies. In recent times, with rising electricity costs and increasing raw material prices putting pressure on cost reduction, "Structol" contributes to reducing production costs for rubber product manufacturers by improving productivity, enhancing quality, and reducing defects.