Insoluble Sulphur (IS 60 / IS 90 / HD Grades)

Polymeric sulphur for tyre vulcanisation, bought on insoluble content and thermal stability

Insoluble sulphur is not a mined or recovered sulphur in the sense of the rest of this family; it is elemental sulphur heated above its polymerisation point, quenched and extracted so that the chain form (polymeric, µ-sulphur) is left behind and the crystalline rhombic form that dissolves in rubber is stripped out. That is the entire point of the product. Ordinary rhombic sulphur dissolves in a rubber compound and migrates to the surface as it cools — bloom — which destroys the tack between the plies of a radial tyre before the cure and gives an uneven crosslink density afterwards; the polymeric form stays put until the cure temperature converts it, so steel-cord skim, belt and carcass compounds are built on it. The grade sheet has four lines that matter. Insoluble content is the fraction of the sulphur that does not dissolve in carbon disulphide, 60% or better for IS 60 and 90% or better for IS 90, tested after a fixed heat-ageing; thermal stability is the insoluble content retained after holding at 105°C for 15 minutes (or a similar producer method), the number that separates a grade that survives a hot mixing cycle from one that reverts to rhombic in the Banbury; oil content is the naphthenic or aromatic process oil the powder is treated with to suppress dust and static, 10% for the standard IS 60 and IS 90 oil-treated grades and 20% for the higher-treated grades; and dispersion, for the HD grades, is a mixing-test rating that predicts whether the powder distributes through a high-viscosity skim compound without agglomerates. Behind those sit acidity (≤ 0.05% as H₂SO₄), ash (≤ 0.3%), heating loss, and a particle size expressed as residue on a 100 or 150 mesh sieve. Classification follows the grade: untreated and oil-treated insoluble sulphur is declared under HS 2802.00 as sublimed or precipitated sulphur, while some producers and customs authorities put the oil-treated and pre-dispersed rubber grades under HS 3812.39, the prepared rubber-compounding heading; check which your importer's tariff line expects before the shipment is documented.

The producers are a short list: China (the volume supplier and the source of most Asian and Middle Eastern tonnage), India, Japan, Germany and the USA, with the Western producers holding the high-dispersion and high-thermal-stability end where the passenger-radial and truck-tyre plants specify by producer name. The buyer is a tyre plant in India, Turkiye, Egypt, Thailand or Vietnam, a conveyor-belt or hose maker, or a rubber-chemicals distributor supplying all of them, and the desk holds two rubber-chemicals enquiries at present. CBIL is a commodity brokerage company and brokers insoluble sulphur from Chinese, Indian, Japanese, German and US producers and distributor positions against SGS or Intertek certification of insoluble content, thermal stability, oil content, acidity, ash and sieve residue at load, with the producer's certificate of analysis and, where the plant requires it, a pre-shipment sample for a mixing trial. The product moves in 25 kg polyethylene-lined paper or PP bags on pallets, 18–20 MT to a 20-foot container, on FOB, CFR and CIF terms; it is a container cargo and the chartering desk is not the point here. Send your grade, the thermal-stability method you test against and the plant it is going into and we will work the producer to it.

Need the ship as well? Our chartering desk prices Gulf to India sulphur and fertilizer freight on LaycanDesk.