| HS Code | 246832 |
| Chemical Name | 2,2'-Dibenzothiazyl Disulfide (Dibenzothiazole Disulfide) |
| Synonyms | MBTS, Accelerator MBTS, 2,2'-Dithiobis(benzothiazole) |
| Cas Number | 120-78-5 |
| Molecular Formula | C14H8N2S4 |
| Molecular Weight | 332.48 g/mol |
| Appearance | Off-white to pale yellow crystalline powder or granules |
| Melting Point | 178-182 °C |
| Density | 1.50 g/cm³ at 20 °C |
| Solubility | Insoluble in water; soluble in carbon disulfide, chloroform, benzene, and acetone; sparingly soluble in ethanol |
| Flash Point | Above 200 °C |
| Stability | Stable under normal conditions; incompatible with strong oxidizing agents |
| Toxicity | Harmful if swallowed; may cause skin and eye irritation; avoid inhaling dust |
| Applications | Used as a vulcanization accelerator for natural and synthetic rubber |
| Storage | Store in a cool, dry, well-ventilated area away from heat, flame, and oxidizing agents |
| Purity | Typically ≥ 95% for industrial grade |
As an accredited Dibenzothiazole Disulfide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Dibenzothiazole Disulfide is packaged in 25 kg polyethylene-lined kraft bags, ensuring dry, stable storage and safe handling. |
| Container Loading (20′ FCL) | Load 20′ FCL with packaged Dibenzothiazole Disulfide, distribute weight evenly, secure firmly, keep dry, ventilated, and labeled. |
| Shipping | Dibenzothiazole Disulfide ships as a stable, non-hazardous powder in sealed bags or fiber drums, palletized and protected from moisture. It should be transported in dry, ventilated vehicles, stored away from heat, sparks, and incompatible materials. Ensure proper labeling and handling precautions to prevent dust exposure during loading and unloading. |
| Storage | Store Dibenzothiazole Disulfide in a cool, dry, well-ventilated area away from direct sunlight, heat, and open flames. Keep the container tightly sealed to prevent moisture absorption and contamination. Avoid storage near strong oxidizers, acids, or combustible materials. Maintain appropriate ventilation to prevent dust accumulation and follow all local regulations. |
| Shelf Life | Dibenzothiazole Disulfide has a typical shelf life of two years when stored in a cool, dry place. |
In sulfur-vulcanized tire tread and carcass compounds, dibenzothiazole disulfide (MBTS, CAS 120-78-5) operates as a moderately fast primary thiazole accelerator with a delayed action relative to mercaptobenzothiazole. In truck tire tread formulations based on natural rubber and solution-polymerized styrene-butadiene rubber, the accelerator is added at 0.8 phr to 1.4 phr alongside 2.2 phr to 2.8 phr soluble sulfur, 3.0 phr zinc oxide, 2.0 phr stearic acid, and 1.5 phr to 2.5 phr antidegradant package. The cure curve generated on a moving die rheometer at 160°C according to ASTM D5289 shows a distinct induction period that provides sufficient processing safety during tread extrusion and tire building. Scorch safety is monitored as Mooney t5 at 121°C under ASTM D1646 because the uncured tread slab must survive multiple heating histories before the final press cure. On a 270 L intermeshing internal mixer with a four-wing rotor and a dump temperature held below 150°C, MBTS is introduced during the final masterbatch stage after carbon black and plasticizer have been dispersed. When the dump temperature exceeds 155°C, the surface of the MBTS pellets can soften and form persistent agglomerates that appear as pale specks in the calendered tread panel. The cured tread compound is routinely tested for tensile strength per ISO 37, tear strength per ISO 34-1 Method B, and abrasion resistance per ISO 4649 Method A. The addition of MBTS increases reversion resistance in natural rubber-rich treads relative to unaccelerated sulfur systems because it shifts the crosslink distribution toward shorter and more thermally stable sulfur bridges. When the MBTS dosage is pushed beyond the level required for full cure, the mono- and disulfidic crosslink fraction increases and the fatigue crack growth resistance measured under ASTM D813 can deteriorate; the exact threshold is polymer-specific. In breaker skim compounds, MBTS is used at 0.5 phr to 0.9 phr with a sulfenamide primary accelerator to adjust the onset of vulcanization without destabilizing the cord adhesion system. The cured products include regional truck tire treads, sidewall veneers, and textile carcass skim compounds.
Because MBTS has a melting point above 170°C and is insoluble in water, dispersion in the polymer matrix depends on shear rather than solubility. In the 270 L internal mixer, the second-stage mixing procedure adds MBTS at a ram pressure of 0.4 MPa to 0.6 MPa after the first-stage stock has cooled below 60°C. When the second-stage dump temperature is kept between 95°C and 110°C, the dispersion rating measured by reflected light microscopy remains below 2% undispersed area on a polished cut surface. The mixed tread stock is released when Mooney viscosity ML(1+4) at 100°C under ASTM D1646 falls between 60 MU and 80 MU and Mooney scorch t5 at 121°C exceeds the plant-specific minimum, commonly above 20 min. Storage of MBTS requires closed, dry packaging below 40°C because exposure to moisture and elevated temperature promotes caking; caked material causes weigh-up errors and localized over-acceleration. The accelerator should not be blended directly with strong acids or strong oxidizing agents because decomposition can generate sulfur oxides and nitrogen oxides.
In fabric-reinforced conveyor belt cover compounds, the limiting process variable is not the accelerator activity alone but the residence time of the mixed stock in the calender bank at cover-skimming temperature. A typical cover formulation combines styrene-butadiene rubber and high-cis polybutadiene in a 70/30 ratio with 40 phr to 55 phr carbon black N220 or N234, paraffinic or aromatic process oil, 1.0 phr to 1.5 phr MBTS, and 2.0 phr to 2.6 phr sulfur. The stock is mixed in a 160 L tangential internal mixer in two stages; MBTS is charged at the start of the second stage with sulfur and vulcanization retarder when required. After dumping, the batch is sheeted on a two-roll mill with roll temperature held below 70°C and then cooled to below 40°C before storage. During calendering, the cover compound is applied to the carcass at bank temperatures not exceeding 95°C, because a calender bank with excessive friction can raise the local temperature above the incipient cure point. The Mooney t5 at 121°C under ASTM D1646 is used as the release criterion for the calendering step; stocks with t5 below the plant-specific minimum are held back and re-cooled before processing.
The vulcanized belt cover must meet abrasion loss requirements under ISO 4649 Method A, tear resistance under ISO 34-1, ozone resistance under ISO 1431-1, and ply adhesion after aging under ISO 252. MBTS contributes to a flat cure plateau in thick covers, which reduces the risk of overcuring at the surface while the center reaches cure temperature in a rotocure press. In compounds where MBTS is partially replaced by a delayed-action sulfenamide, the scorch time is extended but the modulus development at 150°C can become slower; the choice between MBTS and sulfenamide is set by the required press cure time and belt thickness. The terminal products are textile or steel cord conveyor belts used in mining, port handling, cement plants, and bulk material transfer.
Dense and sponge weatherstrip profiles based on ethylene-propylene-diene monomer rubber cannot be cured by MBTS alone because the low unsaturation in a standard 4–8% ethylidene norbornene EPDM grade requires a stronger accelerator combination. The practical function of MBTS in this system is to moderate the initial cure rate and to reduce the tendency of thiuram and dithiocarbamate accelerators to produce porosity during continuous hot-air vulcanization. A representative dense weatherstrip compound contains 0.8 phr to 1.5 phr MBTS, 0.6 phr to 1.0 phr tetramethylthiuram disulfide, 0.3 phr to 0.6 phr zinc dibutyldithiocarbamate, 0.5 phr to 1.2 phr soluble sulfur, and a high-purity calcium oxide desiccant to prevent moisture-induced porosity. The compound is extruded on a 70:1 L/D pin-barrel vacuum extruder with a die temperature from 70°C to 90°C and then passed through a microwave/hot-air curing tunnel at 180°C to 220°C. The MDR torque curve at 180°C under ASTM D5289 is used to set the line speed so that the profile exits the tunnel after reaching at least 90% of maximum torque. Compression set is tested on cured profile sections according to ASTM D395 Method B at 70°C or 100°C, and ozone resistance is tested under ISO 1431-1 at 50 pphm ozone, 40°C, and 20% elongation.
Because MBTS has limited solubility in EPDM, uncured masterbatch that is stored below 15°C for more than 72 h can develop surface bloom; the exact threshold varies with ethylene content, oil loading, and anticaking processing aids. Published data for specific low-ENB EPDM grades under factory storage conditions is limited, so extrusion trials with a 24 h cold-storage cycle are commonly used to set the maximum MBTS addition. The finish products are automotive door seals, glass run channels, trunk seals, and cowl weatherstrips.
Molded acrylonitrile-butadiene rubber sealing elements for fuel and oil service use MBTS at 1.0 phr to 1.8 phr with tetramethylthiuram disulfide or a sulfur-donor curative to balance compression set against elongation and tear strength. A common 33–34% acrylonitrile NBR compound contains 70 phr to 90 phr fast extrusion furnace carbon black, plasticizer, antioxidant, 0.5 phr to 1.5 phr soluble sulfur, and MBTS as the primary thiazole accelerator. The compound is prepared in an internal mixer and then injection molded on a 200-ton screw-ram machine with barrel zones from 70°C to 90°C and a mold temperature from 175°C to 190°C. Cure time is set at the rheometer t90 at mold temperature plus 1.0 min per millimetre of maximum part cross-section; typical small O-ring cavities cure in 3 min to 6 min. The cured parts are then post-cured for 4 h to 8 h at 120°C to stabilize compression set and reduce residual volatile by-products. The tensile strength and ultimate elongation are measured per ISO 37, tear resistance per ISO 34-1, and compression set per ASTM D395 Method B after 22 h at 100°C. Oil resistance is tested in IRM 901 oil according to ISO 1817 for 70 h at 100°C.
MBTS is generally compatible with NBR compounds containing plasticizers such as dioctyl phthalate or polyester adipate, but high-acid-number plasticizers can interfere with the thiazole acceleration mechanism by consuming zinc oxide. For repeated-use rubber articles intended for food-contact service, the accelerator status must be verified against FDA 21 CFR 177.2600 and the applicable jurisdiction-specific positive list; supplier compliance documentation is required because batch-to-batch residual accelerator content can vary. The terminal products include hydraulic O-rings, fuel line gaskets, valve cover seals, and oil filter gaskets.
| Property | Test method | Reference condition |
|---|---|---|
| Hardness | ISO 48-4 / ASTM D2240 | Shore A at 23°C |
| Tensile and elongation | ISO 37 / ASTM D412 | Type 2 dumbbell, 500 mm/min |
| Tear strength | ISO 34-1 Method B / ASTM D624 | Unnicked angle test piece |
| Compression set | ASTM D395 Method B | 22 h/100°C, 25% compression |
| Heat aging | ISO 188 / ASTM D573 | 70 h/100°C |
| Fluid resistance | ISO 1817 | IRM 901 oil, 70 h/100°C |
In natural latex prevulcanization, MBTS is selected when the latex compound must remain stable during transport and dipping but still cure to a high tensile strength film after post-vulcanization. The accelerator is first converted into a 50% aqueous dispersion by ball milling with dispersing agents and colloidal stabilizers; the dispersion is then added to 60% centrifuged natural rubber latex at 0.5 phr to 1.5 phr dry rubber. A typical latex formulation includes 1.0 phr to 2.0 phr sulfur, 0.5 phr to 1.0 phr zinc oxide, 0.3 phr to 0.8 phr zinc diethyldithiocarbamate, and a phenolic antioxidant dispersion. The mixture is heated to 60°C to 70°C under slow agitation for 2 h to 4 h; the degree of prevulcanization is monitored by the chloroform coagulation number, with a grade of 2 to 3 indicating sufficient crosslink formation for subsequent dipping. After dipping, the wet gel is dried and vulcanized in hot air at 100°C to 120°C. Tensile properties of the finished film are determined on die-cut dumbbells according to ASTM D412, while examination glove products are evaluated under ASTM D3578 and the applicable regional glove standards.
Because MBTS does not contain secondary amine groups, it does not add to the nitrosatable accelerator fraction in the latex compound; nitrosamine content is still monitored where required by rubber latex product specifications. The primary processing limit is the sedimentation of MBTS in the latex tank if the dispersion particle size exceeds 5 µm; slow stirring alone is insufficient to redisperse settled accelerator. The end products include examination and household gloves, balloons, and latex foam articles.
Unit sole compounds based on styrene-butadiene rubber and high-cis polybutadiene are mixed on a two-roll mill or internal mixer with 1.0 phr to 1.8 phr MBTS, 2.0 phr to 2.5 phr sulfur, 3.0 phr zinc oxide, 2.0 phr stearic acid, precipitated silica, silane coupling agent, and a light-coloured reinforcing filler. The use of MBTS rather than a sulfenamide in footwear compounds is justified by the need to cure thick unit soles in a short compression-molding cycle without excessive mold staining. The mixed slab is placed in a multi-cavity compression mold at 150°C to 170°C; a 10 mm sole section is cured for 6 min to 10 min. The cured sole must meet flex crack resistance according to ISO 4643 or ASTM D1052, abrasion resistance according to ISO 20871 or DIN 53516, and slip resistance according to ISO 13287. Hardness is measured with a Shore A durometer under ISO 48-4 or ASTM D2240. In light-coloured soles, MBTS can contribute to yellowing during prolonged UV exposure; 2.0 phr to 4.0 phr rutile titanium dioxide and a non-staining phenolic antioxidant are used to mask the discoloration. The terminal products are casual footwear, work boot soles, school shoe soles, and vulcanized sheet stock for die-cut shoe components.
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Dibenzothiazole disulfide, commonly abbreviated MBTS and assigned CAS number 120-78-5 with EC number 204-424-9, is a symmetrical thiazole accelerator based on the dimer of 2-mercaptobenzothiazole. The empirical formula C14H8N2S4 corresponds to a relative molecular mass of 332.49 g/mol. The product is supplied as an off-white to pale yellow powder, free-flowing granules, oil-coated dust-suppressed granules, and polymer-bound 80% active predispersions. In sulfur vulcanization of diene rubbers it provides intermediate scorch safety and moderate cure activity relative to the monomeric thiazole mercaptobenzothiazole and the sulfenamide accelerators. Typical use levels are 0.5–2.5 phr as a primary accelerator and 0.1–0.5 phr as a secondary accelerator in thiuram- or dithiocarbamate-activated cure systems. Sulfur-curable rubbers include natural rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, and ethylene-propylene-diene terpolymer; the material is not suitable for peroxide-cure or sulfur-free systems.
Commercial acceptance for technical powder and granule grades is typically defined by the following control window. Because no single ISO monograph covers all properties, supplier certificates may combine HPLC assay with general compounding-material methods.
| Parameter | Commercial acceptance window | Reference method or instrument |
|---|---|---|
| Appearance | Off-white to pale yellow powder or granules | Visual, supplier quality plan |
| Assay, dry basis | ≥ 98.0% | HPLC, external calibration |
| Initial melting point | ≥ 165.0°C | ISO 10398 |
| Ash content | ≤ 0.30% | ASTM D4574 |
| Loss on drying | ≤ 0.30% at 70°C for 2 h | ASTM D4571 |
| Residue on 150 µm sieve, powder | ≤ 0.10% | ISO 3310-1 test sieve |
| Free MBT | ≤ 1.0% | HPLC |
| Specific gravity | 1.50 at 25°C | Pycnometer |
The disulfide bridge is the critical structural feature controlling accelerator activity. MBTS does not act as a full accelerator until the sulfur-sulfur bond is cleaved in the presence of zinc oxide and a fatty acid activator to generate zinc-accelerator complexes that carry sulfur into the polymer chain.
Processing safety for MBTS is not inferred from a visual stock surface temperature. The accelerator must first undergo cleavage of the disulfide bridge in the presence of zinc oxide and a fatty acid activator. This cleavage is temperature- and dispersion-dependent. Mooney scorch testing per ASTM D1646 at 121°C accelerates the early stage of cure so that a t5 value can be obtained in a practical laboratory time scale while still ranking compounds in the same order as production behavior. A compound containing MBTS at 1.2 phr in a natural rubber/carbon black system typically exhibits a longer t5 than the same formulation based on MBT, but a shorter t5 than a CBS or TBBS sulfenamide formulation. Exact t5 values are compound-specific; material substitution without re-generating scorch data under ISO 289-1 or ASTM D1646 can result in unexpected pressure spikes on extrusion.
On a 45 L intermeshing internal mixer, MBTS is generally introduced with sulfur in the final productive stage at a dump temperature of 95–105°C. When dump temperature exceeds 110°C, re-milling can produce hard, partially scorched stock. In a single-screw extruder with 20:1 L/D, inadequately dispersed MBTS clusters have been observed to produce localized cure heterogeneity and head-pressure fluctuations even though bulk stock temperature remains below the die setpoint. The corrective action is to reduce rotor speed, improve pellet pre-blending, or use a granular MBTS with controlled sieve residue rather than a fines-rich powder.
In an accelerator selection matrix, MBTS occupies the middle position between the faster mercaptobenzothiazole chemistry and the delayed-action sulfenamide chemistry. MBT, the monomeric thiol, presents a reactive thiol proton and can form zinc mercaptide rapidly. MBTS contains a covalent disulfide bridge that must be reduced before the active benzothiazole thiolate is available, which lengthens induction time. Dimethyl thiuram disulfide and zinc dithiocarbamate accelerators are substantially faster and are used at low loading with MBTS as secondary accelerators to raise cure state without excessive scorch. N-cyclohexyl-2-benzothiazole sulfenamide and N-tert-butyl-2-benzothiazole sulfenamide provide longer scorch delay and higher modulus development than MBTS in sulfur-rich systems; MBTS is selected where a simpler release of active thiazole is required or where sulfenamide-derived amine residues are undesirable.
Stoichiometric comparison can be made on the benzothiazole ring content. Because one mole of MBTS carries two benzothiazole units, a replacement of 1.0 phr MBT with MBTS requires 0.994 phr MBTS for the same thiazole functionality. Replacing 1.0 phr CBS with MBTS requires approximately 0.63 phr MBTS on the same benzothiazole-group basis, but the loss of the cyclohexylamine release changes cure kinetics so directly that equal thiazole content is not a sufficient formulation rule. The benzothiazole disulfide structure contains no secondary amine nitrogen; therefore MBTS cannot produce N-nitrosamines during vulcanization, unlike morpholine-derived sulfenamides. Bloom control in MBTS compounds is achieved by limiting dosage and using granule forms; bloom is generally less severe than with MBT because no free thiol is present in the raw accelerator.
The difference from sulfenamide accelerators is most visible in curemeter curves per ISO 3417. CBS and TBBS exhibit a characteristic induction period followed by a fast torque rise; MBTS shows a milder transition after the initial torque rise. The maximum torque at equivalent molar thiazole content is generally lower for MBTS, which can be compensated with a secondary accelerator such as DPG or a small amount of thiuram or dithiocarbamate. MBTS and DPG are often used together in semi-EV formulations because DPG activates the thiazole while MBTS provides sulfur-bearing crosslink intermediates; the DPG level is typically 0.2–0.5 phr. For light-colored goods, dithiocarbamate accelerators are added only where low bloom can be confirmed because MBTS may not scavenge the dithiocarbamate decomposition products.
Direct weight-for-weight replacement of MBT by MBTS in a conventional sulfur cure package is not automatically equivalent in cured properties. The equal-weight replacement is nearly equal on a thiazole-group basis, but the disulfide linkage delays the formation of the active zinc complex, so the cure curve shifts to longer scorch time and may show slightly lower maximum torque at the same curing time. Formulators adjusting from MBT to MBTS should compare rheometer curves per ISO 3417 or ASTM D5289 at the intended press temperature. The usual adjustment is to raise MBTS loading by 5–15% over the original MBT phr, or to raise sulfur slightly within the range 2.0–2.5 phr, while holding zinc oxide at 5.0 phr and stearic acid at 2.0 phr.
In a standard natural rubber truck-tread model compound cured at 150°C, MBTS-based stocks typically show a more gradual march to MH and a lower reversion rate during extended cure than the MBT reference, but tensile modulus measured per ISO 37 may be lower unless the sulfur/accelerator ratio is optimized. For applications where tensile strength per ASTM D412 is the primary specification, MBTS can be paired with 0.1–0.5 phr of a dithiocarbamate or thiuram accelerator to increase cure state. In such binary systems MBTS acts as the delayed-action primary accelerator, while the second accelerator lowers onset temperature; scorch safety should be rechecked by ASTM D1646 because the addition of dithiocarbamates can reduce t5 substantially.
In highly filled silica tread compounds, MBTS activity is sensitive to mixing sequence because unreacted silanol groups can adsorb thiazole accelerators and reduce the concentration available for sulfur crosslinking. If MBTS is added before the silanization reaction between silica and mercaptosilane or sulfidosilane is complete, a slower cure and lower state of cure are observed in rotorless curemeter traces per ASTM D5289. The standard control is to add MBTS after the silanization stage, typically following the discharge and cooling of the masterbatch. In an intermeshing internal mixer with a 55–60°C second-stage start temperature, MBTS is added with sulfur and any second accelerator only after silane coupling agent dispersion has been verified by a drop in compound viscosity and a stable mixing torque.
Published data for a single universal replacement factor in silica compounds is limited. In practice, MBTS demand is influenced by filler surface area, silane type, residual ethanol from silane condensation, and the presence of zinc oxide. A lab-scale mixing study using a 70 phr silica/NR/BR blend may require an increase of 0.2–0.5 phr MBTS relative to a carbon black reference to obtain the same MH; this is an operational starting range and must be confirmed by ISO 3417 rheography. Attention should also be paid to the zinc oxide level: lower zinc oxide retards the formation of the zinc benzothiazole mercaptide intermediate, so reductions below 3.0 phr in silica compounds can create cure-rate variability.
Regulatory classification of MBTS under the EU CLP mechanism includes skin sensitisation category 1, hazard statement H317. The compound is registered under REACH with EC number 204-424-9. When the cured rubber article is intended for repeated food-contact use, formulation compliance may be evaluated under 21 CFR 177.2600(e)(4), which lists benzothiazyl disulfide among permitted accelerators and limits total accelerator content to 1.5% by weight of the rubber product. These regulatory provisions apply to the finished article in its intended service condition, not to the raw accelerator alone.
Incoming material should be stored in a dry area below 30°C and protected from moisture. At relative humidity above 60%, powder MBTS should be pre-dried at 40–50°C for 2 h in a vacuum dryer or dry-air oven before use, because surface moisture changes feed uniformity and can lead to assay drift in precision weighing systems. MBTS is incompatible with peroxide-cure systems because sulfur and thiazole species consume free radicals generated by peroxide decomposition. It is also incompatible with strong oxidizers and should not be stored in contact with amines or strong bases that can promote premature decomposition of the disulfide bridge.
