What it does
Polymeric sulfur that is insoluble in rubber. Does not bloom in the compound and preserves cord adhesion. Standard vulcanizing agent for tire carcass and tread compounds. Oil-treated (OT) grades reduce dust formation.
Compatible rubbers
NRSBRBRNBRCR
Typical properties
Appearance
Yellow powderInsoluble sulfur
≥ 90% (IS-90) · ≥ 60% (IS-60)Thermal stability
105 °C / 15 min ≥ 80%Oil content (OT20)
~20%Heat loss
≤ 0.5%Melting pointP
95.3 °CDensityP
2.07 g/cm³P marked values are PubChem literature data (pure substance). Others are typical commercial specifications and vary by producer and grade [TO BE VERIFIED].
Typical dosage
1.0–4.0 phr (sulfur equivalent) [TO BE VERIFIED]
FAQ
What is the difference between insoluble sulfur and ordinary sulfur?Ordinary (rhombic) sulfur has limited solubility in rubber; the excess blooms to the surface on cooling and impairs ply-to-ply adhesion. Insoluble (polymeric) sulfur does not dissolve in rubber and stays dispersed. At vulcanization temperature it converts to ordinary sulfur and reacts.
At what temperature is insoluble sulfur added to the compound?Its thermal stability is limited; at high temperature it reverts to ordinary sulfur and the advantage is lost. It is usually added in the final mixing stage at low temperature (below about 100 °C).
What does OT20 mean?It means the grade is coated with 20% oil (oil treated). It reduces dust and caking and improves dispersion. When calculating the sulfur equivalent, 80% of the product is taken as sulfur.
Related guides
Insoluble sulfur: why, how, how much?Conventional, semi-EV and EV sulfur systems
Looking to source IS in Türkiye? Let's talk about producer selection and samples.rubberchem.com.tr →
Sources: PubChem CID 5362487 · General rubber chemistry literature · PubChem page