2,2'-Dithiobisbenzothiazole
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HS Code |
932869 |
| Chemical Formula | C14H8N2S4 |
| Molecular Weight | 332.49 g/mol |
| Appearance | yellowish - brown powder |
| Odor | characteristic odor |
| Melting Point | 175 - 181 °C |
| Solubility In Water | insoluble |
| Solubility In Organic Solvents | soluble in chloroform, benzene, carbon tetrachloride |
| Density | 1.52 - 1.54 g/cm³ |
| Stability | stable under normal conditions |
| Flash Point | 218 °C |
| Hazard Class | irritant |
As an accredited 2,2'-Dithiobisbenzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25 - kg bags for 2,2'-Dithiobisbenzothiazole, well - sealed for chemical protection. |
| Shipping | 2,2'-Dithiobisbenzothiazole is shipped in well - sealed containers to prevent contact with air and moisture. Special handling precautions are taken due to its chemical nature, and it's transported in compliance with relevant hazardous material shipping regulations. |
| Storage | 2,2'-Dithiobisbenzothiazole should be stored in a cool, dry, well - ventilated area. Keep it away from heat sources, ignition sources, and oxidizing agents. Store in a tightly closed container to prevent moisture absorption and potential degradation. Avoid storing near incompatible substances to ensure safety and maintain chemical integrity. |
When compounded into a styrene-butadiene rubber (SBR) masterbatch via a two-roll mill set at a nip gap of 0.5–0.8 mm and a front roll temperature of 45 °C, 2,2′-dithiobisbenzothiazole demonstrates a solubility threshold that becomes the dominant processing constraint before any other performance limitation manifests. The crystalline powder, with a melting point of approximately 180 °C, dissolves only partially in most general-purpose elastomers under standard mixing conditions, and bloom-free addition levels rarely exceed 2.0 phr in natural rubber (NR) or 2.5 phr in SBR matrices compounded with aromatic process oils. At addition levels above 2.5 phr in a sidewall-typical formulation containing 50 phr NR / 50 phr polybutadiene (BR), visual inspection after 72 h of ambient storage under 60 % relative humidity reveals a greyish surface film that is analytically confirmed as unreacted MBTS by FT-IR microscopy, correlating with a 15–20 % reduction in self-adhesion tack as measured by a modified probe-tack test adapted from ASTM D2979-16. Pre-dispersion of MBTS in a binder wax or predispersion masterbatch containing 70 wt% active ingredient in EPDM carrier resin substantially mitigates this bloom tendency, but only when the compound is allowed a maturing period of 24 h at 23 ± 2 °C after final mixing before calendering or extrusion operations commence. In injection-molded automotive body plugs produced from an EPDM compound containing 1.5 phr MBTS as secondary accelerator alongside 0.8 phr zinc dibenzyldithiocarbamate and 0.5 phr tetramethylthiuram disulfide, the flash-free sealing surfaces exhibit no visible exudation after 500 h of heat aging at 100 °C, provided the compound is vulcanized to a torque rise state of at least 90 % of maximum modulus on an MDR moving-die rheometer operated under ISO 6502-2:2018 conditions.What Limits the Critical Cure Plateau Width When MBTS Is the Sole Accelerator in Large-Diameter Conveyor Drum Covers?Steel-cord conveyor belt cover compounds that require press-cure cycles exceeding 35 min at 151 °C in platens larger than 10 m in length impose a unique demand on the accelerator system: the onset of reversion must be delayed long after the thickest section of the rubber mass has reached a uniform state of crosslinking. In a natural rubber cover formulation filled with 50 phr carbon black N330 and plasticized with 6 phr naphthenic oil, MBTS used as the primary accelerator at 2.2 phr in combination with 2.5 phr insoluble sulfur produces a torque plateau that extends for approximately 12 min beyond the time to reach 90 % cure (t90) when measured on a rotorless curemeter at 151 °C. This plateau is a direct consequence of the disulfide bridge in the molecule acting as a sulfur donor, gradually releasing active sulfur for crosslink formation while the thiazole moieties form zinc-accelerator complexes that retard the approach to equilibrium overcure. Production-scale data from a 3.6 m × 10 m multi-daylight hydraulic press operating at 16 MPa specific pressure reveals that the modulus gradient across a 28 mm-thick cover slab remains within ±0.5 dNm as long as the MBTS-to-sulfur weight ratio is maintained between 0.7:1 and 1.1:1. Outside this window, the surface layer, which reaches cure temperature within 3 min, undergoes irreversible network degradation before the core reaches t90, manifesting as a sticky surface with a 30 % loss in tensile strength when tested according to ISO 37:2017. The limitation of MBTS as a sole accelerator in such compounds becomes evident when the cure temperature is raised to 165 °C to shorten press occupancy: the plateau width collapses to less than 3 min, making the process window too narrow for manufacturing consistency. In such thermal regimes, MBTS is partially replaced by a sulfenamide accelerator, typically N-cyclohexyl-2-benzothiazolesulfenamide (CBS) at 0.4 phr, which shifts the vulcanization onset to a later time while preserving a flattened torque curve through the MBTS-dominated later stages of the cure.Latex Dipping Line Compound Maturation and the Control of Film Tack-Time DriftIn natural rubber latex compound maturation for surgical glove and balloon dipping operations, the pre-vulcanization behavior of MBTS-dispersed systems departs significantly from its behavior in dry rubber mixing, primarily because the thiazole disulfide structure hydrolyzes slowly in the aqueous alkaline phase stabilized with 0.3 phr potassium hydroxide and 0.5 phr potassium laurate. A typical prevulcanization formulation contains 1.0 phr sulfur, 0.8 phr zinc oxide, 0.7 phr MBTS dispersion (50 % active content, milled in a ball mill to a particle size d50 < 5 µm), and 0.3 phr zinc diethyldithiocarbamate as secondary accelerator, all expressed on dry rubber content. The maturation process, carried out under continuous gentle stirring at 55–60 °C for 2.5–3.5 h, must be terminated at a chloroform number corresponding to a lightly crosslinked gel state (grade 2–3 on the modified chloroform test), which correlates with a residual MBTS concentration of 0.3–0.5 phr remaining as active, unreacted accelerator. Dipping line operators record that the tack-time of the deposited film on porcelain formers—defined as the interval between withdrawal from the latex tank and the point at which the film no longer picks up lint or particles from ambient air—drifts by as much as 4–6 s over an 8 h shift if the maturation temperature exceeds 62 °C, because excessive consumption of MBTS shifts the residual cure rate such that the film surface skins over faster but with a lower crosslink density gradient. This drift is monitored inline by sampling the latex tank every 30 min and measuring the dynamic viscosity at 23 °C using a Brookfield RV viscometer with Spindle 2 at 20 rpm; a sustained rise above 35 mPa·s triggers immediate cooling and partial replacement of the latex batch. Compliance with medical glove quality standards is verified against ASTM D3578-19 for tensile properties and ASTM D5151-19 for pinhole defects, with the MBTS-derived accelerator system needing to achieve a residual nitrosatable amine content below the detection limit of 0.1 µg/dm² per EN 12868:2017, a requirement MBTS fulfills by its molecular architecture lacking secondary amine functional groups.Production-scale twin-screw extruders with a length-to-diameter ratio of 24:1 used for continuous vulcanization of EPDM-based automotive weatherstrip profiles highlight an interaction between MBTS and high-hardness filler systems that is rarely documented in laboratory-grade studies. When a profile compound containing 100 phr EPDM (ethylene content 55 %, ENB termonomer 4.5 %), 120 phr calcium carbonate with a particle top cut of 10 µm, and 70 phr paraffinic process oil is accelerated with 1.8 phr MBTS and 0.6 phr of a 1:1 blend of tetramethylthiuram monosulfide and mercaptobenzothiazole, the extrudate surface quality at a screw speed of 45 rpm and a head pressure of 8.5 MPa degrades progressively within the first 90 min of a production run. The appearance of sharkskin roughness, with a characteristic wavelength of 0.3–0.5 mm visible under oblique light, coincides with a measured rise in melt temperature from 72 °C to 84 °C at the breaker plate, despite barrel temperature setpoints remaining unchanged. The mechanistic root is traced to the MBTS undergoing thermally induced scission of its disulfide bond inside the extruder metering zone, generating 2-mercaptobenzothiazole radicals that recombine or react with the zinc oxide present to form zinc mercaptobenzothiazole salts; these salts act as internal lubricants, lowering the apparent melt viscosity by 8–12 % but simultaneously reducing the critical shear stress for melt fracture onset from approximately 0.35 MPa to 0.28 MPa. The corrective action applied on the manufacturing floor involves a forced reduction of the screw temperature in the final barrel zone by 12 °C and the incorporation of 2.0 phr of a high-structure fumed silica (BET surface area 200 m²/g) to compensate for the lubricating effect without affecting the final Shore A hardness target of 75 ± 3 (ISO 48-4:2018).
When Brass-Coated Steel Adhesion Demands a Delayed-Action Scorch Profile in Tire Belt SkimAdhesion between brass-coated steel cord (copper content 63 ± 2 %, coating thickness 0.20 ± 0.05 µm) and a typical belt skim compound based on 100 phr NR containing 60 phr carbon black N326 and an adhesion-promoting cobalt-boron complex at 0.8 phr elemental cobalt equivalent is highly sensitive to the timing of sulfur consumption during the initial stages of vulcanization. If crosslinking proceeds too rapidly, the sulfur needed for interfacial copper sulfide layer formation is depleted from the rubber phase before the adhesive bond can mature, resulting in pull-out forces below 350 N per cord when tested per ASTM D2229-12 after humidity aging at 65 °C and 95 % RH for 7 days. MBTS, at an addition level of 0.7 phr in combination with 0.9 phr N,N-dicyclohexyl-2-benzothiazolesulfenamide (DCBS), extends the scorch time (ts5 at 140 °C) from 18 min to 27 min relative to a DCBS-only reference, allowing the cobalt carboxylate to migrate to the brass surface and initiate the formation of a non-stoichiometric CuxS layer at a measured thickness of 80–120 nm as characterized by SEM-EDS on ultramicrotomed cross-sections. The ratio of MBTS to sulfenamide is limited to a maximum of 1:1, because beyond this proportion the release of 2-mercaptobenzothiazole during the reaction with zinc oxide can partially dissolve the nascent copper sulfide film, leading to a drop in aged pull-out adhesion by 15–20 %. This chemical boundary condition is monitored on the factory floor by subjecting a compound sample to an MDR test at 155 °C and accepting only batches where the viscosity rise between 10 % and 90 % of full cure occurs over at least 5.5 min. Calendering of the skim compound onto brass cord at a line speed of 30 m/min in a 4-roll calender with roll temperatures maintained at 80–85 °C is interrupted if the Mooney viscosity at 100 °C (ML 1+4) exceeds 45 MU, a sign that MBTS-induced prevulcanization during warm-up has consumed the scorch safety margin required to preserve wire adhesion integrity through the belt building and vulcanization steps.Footwear expansion-molding compounds based on a ternary blend of 70 phr ethylene-vinyl acetate copolymer (EVA, vinyl acetate content 18 %), 20 phr NR, and 10 phr solution-polymerized SBR demand an accelerator recipe that synchronizes the decomposition of the blowing agent with the earliest stages of crosslink network development to prevent cell coalescence. The blowing agent azodicarbonamide, added at 4.5 phr and activated with 1.2 phr zinc oxide and 0.5 phr urea-type kicker, begins to evolve gas at approximately 160 °C under the constraint of a mold cavity pressure of 6 MPa. MBTS, dosed at 1.0 phr alongside 0.6 phr diphenylguanidine (DPG) as a basic accelerator pair, initiates the EVA crosslinking reaction at a temperature 5–8 °C higher than the onset of gas evolution, providing a narrow processing window wherein the polymer melt gains enough melt strength to trap expanding cells without restricting their growth prematurely. Measurement of the decomposition-conversion curve of MBTS by dynamic DSC at a ramp rate of 10 °C/min under nitrogen shows an exothermic peak onset at 167 °C, which aligns with the temperature at which the blowing agent has already released 60–70 % of its theoretical gas volume, as determined by thermogravimetric analysis. Plant trials with a 3-zone injection-expansion molding machine (clamp force 800 kN) demonstrate that when MBTS is pre-combined with DPG in a 1:1 melt-blended masterbatch before addition, the standard deviation of final foam density within a single shot of 12 cavities drops from ±0.028 g/cm³ to ±0.012 g/cm³, because localized accelerator concentration variants that cause uneven crosslinking and cell rupture are eliminated. The finished midsole component, with a target density of 0.25 g/cm³ and Shore Asker C hardness of 58 ± 2, is required to pass the repeated compression test of SATRA TM64 at 60 % compression for 150,000 cycles without cracking, a performance benchmark that is only achievable if the crosslink density, indirectly read as the torque difference (MH−ML) on the curemeter, stays within 7.5–8.5 dNm—a narrow corridor controlled by the MBTS-DPG stoichiometry.
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2,2′-Dithiobisbenzothiazole (CAS 120-78-5; IUPAC: 2,2′-dibenzothiazyl disulfide), routinely abbreviated as MBTS or DM, is supplied as a cream-colored to pale yellow free-flowing powder or compacted granular solid with a characteristic faint amine odor. Industrial grades exhibit a purity window of 96.0–99.5 % (HPLC), typically used as a medium-speed primary or secondary accelerator in sulfur-based vulcanization of natural rubber (NR), polyisoprene (IR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), and ethylene-propylene-diene terpolymer (EPDM). The molecule functions through thermal cleavage of the disulfide bond to generate 2-mercaptobenzothiazole (MBT) radicals that activate elemental sulfur, forming active sulfurating agents in the presence of zinc oxide and stearic acid. Its scorch safety, defined under ASTM D1646 at 121 °C, exceeds that of MBT by a factor of approximately 1.8–2.5× while being lower than the sulfenamide class, positioning MBTS as a cost-effective intermediate in processing safety–cure rate trade-offs.
Commercial MBTS is manufactured in multiple physical forms to address plant-specific material handling and dispersion requirements. Powder grades, with a typical mean particle size (d50) of 15–25 µm, present high surface area that facilitates rapid solubility in the polymer matrix during warm-up cycles, but exhibit increased hygroscopicity and dusting propensity in open-hopper feeding systems. Granular and pastille forms, with a d50 range of 0.5–1.2 mm, reduce airborne dust below 0.1 mg/m³ (eight-hour time-weighted average, ISO 12103-1 reference conditions), an important occupational hygiene consideration. In tangential rotor internal mixers (Banbury-type, rotor speed 40–60 rpm, fill factor 0.70–0.75), granular MBTS subjected to dump temperatures of 135–155 °C achieves full dispersion in NR masterbatch within 2.5–3.0 min post peak power draw; insufficient incorporation manifests as pale yellow specks on extruder die lips, a defect quantified by microscopic surface inspection per ISO 2393 batch control procedures. On open two-roll mills with a nip gap of 2.0–3.5 mm, mill roll temperature held at 50–70 °C, powder grades cut banding time by 15–25 % relative to granules but demand precise cross-blade folding practices to avoid local scorch nuclei. Plants blending at ambient humidity above 65 % RH without climate-controlled raw material storage report batch-to-batch variation in Mooney scorch time (Δt5) of up to ±3.5 min, arising from moisture-accelerated partial disulfide cleavage before curatives reach the rubber phase.
| Property | Method | Typical Specification Range |
|---|---|---|
| Assay (HPLC, area%) | ASTM D4936 | 96.0–99.5 % |
| Free MBT content | Potentiometric titration | ≤ 1.5 % |
| Moisture (Karl Fischer) | ISO 760 | ≤ 0.50 % |
| Ash residue (800 °C, 2 h) | ASTM D4574 | ≤ 0.30 % |
| Melting range | Capillary tube | 177–186 °C |
| Sieving residue (>150 µm) | ASTM D4572 | ≤ 0.10 % |
| Bulk density (tapped) | ISO 3953 | 0.50–0.70 g/cm³ |
Substituting an equimolar sulfur contribution of MBT with MBTS in an efficient vulcanization (EV) recipe for NBR containing 0.8 phr sulfur and 2.5 phr ZnO retards the onset of crosslinking without proportionally decreasing the maximum torque. Oscillating disc rheometer traces (ASTM D5289, 160 °C, 1° arc) indicate an increase in ts2 from a baseline of 2.1 min to 3.6–4.2 min, while t90 shifts from 5.8 min to 7.2–8.0 min. The induction period extension emerges because the disulfide must undergo homolytic scission (activation energy ~140–160 kJ/mol in a rubber melt) before releasing the MBT moiety capable of forming zinc-accelerator complexes. This kinetic barrier translates to superior flow properties in injection molding operations: at a nozzle temperature of 95–105 °C and injection pressure 90–110 MPa, spiral flow length increases by 18–22 % relative to the MBT-accelerated compound, documented on a 50-mm reciprocating screw machine with a clamp force of 1,500 kN. However, crosslink density as measured by equilibrium swelling in toluene (ISO 1817) remains within 5 % of the MBT control, and tensile strength (ASTM D412, die C) values of 19–22 MPa are statistically indistinguishable. The key operational boundary: when cure temperatures exceed 180 °C, the MBTS activation sequence enters a runaway regime, and ts2 collapses below 1.5 min, eliminating the processing safety window and risking premature scorch in large-part compression molds.
Continuous vulcanization in a salt-bath LCM line (salt temperature 250 °C, residence time 45 s) relies on the steep positive temperature coefficient of MBTS activation to achieve rapid through-cure of EPDM automotive weatherstrip profiles while maintaining dimensional stability during the heating ramp. Here, the accelerator is combined with a small fraction (0.2–0.3 phr) of a thiuram co-accelerator; the thiuram contributes fast dithiocarbamate radicals that bypass the disulfide scission step at the outermost skin layer, resolving the surface tackiness defect associated with under-curing at these short dwell times. Published production-line audits report a reduction in scrap rate from 6.2 % to 1.8 % after adjusting the MBTS:thiuram ratio from 4:1 to 6:1, maintaining a shore A hardness (ASTM D2240) of 68–72.
Truck tire tread stocks based on a NR/BR (70/30 phr) blend conventionally utilize N-cyclohexyl-2-benzothiazole sulfenamide (CBS) as the sole accelerator at loadings of 0.6–1.0 phr. Partial substitution of CBS with MBTS at a 1:1 weight ratio cuts compound cost while modifying the vulcanization profile. The mixed accelerator system yields a bimodal crosslink distribution: the sulfenamide decomposes rapidly above 140 °C to release MBT and cyclohexylamine, delivering a fast-crosslinking front, whereas the free MBTS enters the zinc-activation cycle more gradually, continuing network maturation in the post-torque-rise plateau. Rotorless curemeter data (ISO 6502) at 150 °C show a t10 of 4.8–5.3 min for the 0.5/0.5 CBS/MBTS split, compared to 3.0–3.5 min for 1.0 phr CBS alone, affording an additional 1.3–2.0 min of safe flow in the tread extrusion and tire-building stages. Peak rate of vulcanization increases by 8–12 %, while the 300 % modulus (ASTM D412) gains 1.5–2.0 MPa without embrittlement; elongation at break remains above 500 %, a critical indicator for resistance to chunking in on/off-road service. The DSC oxidation induction time (ASTM D3895) at 180 °C drops by only 4 %, confirming no significant pro-oxidative behavior of the residual MBT by-products. Process engineers report that the compound requires tighter control of dump temperature during finish mixing: excursions above 120 °C cause MBTS pre-scission, evidenced by a Mooney viscosity rise (ML 1+4, 100 °C) of 8–12 units in subsequent processing steps, mandating a thermocouple-monitored two-pass mixing protocol with a discharge temperature cap of 115 °C.
In silica-filled tread formulations requiring a silane coupling reaction, MBTS’s sulfur donation capacity interferes with the silanization equilibrium if added before the silane-silica condensation is complete. Field data collected on a 320-L intermeshing mixer indicate that MBTS addition during the initial masterbatch stage (before silane addition) reduces coupling efficiency, measured via the Payne effect (G′ at 0.56 strain / G′ at 100 % strain, ISO 13145), by 28–32 %. The corrective procedure separates silanization and accelerators into a second, lower-temperature stage (100–105 °C).
Unlike tetramethylthiuram disulfide (TMTD) and zinc dimethyldithiocarbamate (ZDMC), 2,2′-dithiobisbenzothiazole contains no secondary amine functionality; consequently, it does not serve as a nitrosamine precursor during vulcanization or subsequent service life. Gas chromatography–thermal energy analysis (GC-TEA) headspace testing of cured NR sheet compounds accelerated with 2.0 phr MBTS (160 °C, 12 min) detected <0.1 µg/kg of total N-nitrosamines, below the limit of quantification for ISO 29941. This characteristic renders MBTS an essential building block for rubber goods subject to German TRGS 552 and the EU Nitrosamines Directive (93/11/EEC), specifically baby bottle teats, pharmaceutical closures, and potable water pipeline gaskets covered by EN 681-1. In potable water sealing applications, migration limits from Regulation (EC) No. 1935/2004 and its specific elastomer guidance (EN 12873-1) are met at typical cure levels of 1.0–1.5 phr MBTS, provided the cured article undergoes a post-cure leach cycle of 2 h in boiling deionized water. The replacement of TMTD by MBTS in a commercial low-hardness EPDM gasket formulation resulted in a 15 % reduction in compression set (ASTM D395, method B, 70 h at 125 °C), attributed to the elimination of zinc sulfide by-products that catalyze oxidative network scission. The trade-off is a 20–25 % increase in t90, requiring cycle time adjustment on the injection molding line.
Nevertheless, MBTS displays limited efficacy in low-sulfur or sulfurless systems where a thiol-terminated accelerator is kinetically essential. Formulations employing a thiuram-only cure for steam-resistant EPDM cannot directly substitute MBTS without a donor sulfur compound; attempts to use MBTS at 3.0 phr without elemental sulfur yield t90 values exceeding 30 min at 160 °C, a condition commercially obsolete for high-volume production.
Long-term storage trials conducted in a non-climatized Southeast Asian warehouse (ambient temperature 28–35 °C, relative humidity 75–90 %) revealed that the free MBT content of unpackaged MBTS powder rose from 0.8 % to 4.2 % over 12 weeks, while HPLC assay declined by 6.5 percentage points. The hydrolysis pathway involves nucleophilic attack of water at the disulfide linkage, releasing MBT and oxidized sulfur species. In an NR matrix, the hydrolyzed product depresses delta torque by 10–15 % at identical loading compared to fresh MBTS, an effect reversible only by increasing dosage by 0.2–0.3 phr with corresponding adjustment of sulfur. Warehouses operating under ISO 9001 ensure that MBTS remains sealed in multi-layer kraft bags with an internal moisture-impervious aluminum film until point of use; under such condition, shelf life extends to 24 months from date of manufacture with assay loss limited to <1.0 %. Plant personnel monitoring moisture content via Karl Fischer titration (ISO 760) before weighing reject any batch exceeding 0.50 % water, and pre-drying in a vacuum oven at 40 °C and –80 kPa gauge pressure for 4–6 h can restore material with moisture up to 0.90 % to specification without thermal decomposition, provided the oven temperature remains below the melting onset of 177 °C.
Direct contact with alkaline materials—such as un-neutralized sodium hydroxide or amine-containing anti-degradants—causes rapid catalyst decomposition even at ambient temperatures. In one documented plant incident, a mixing operator inadvertently charged MBTS into a Banbury batch already containing hexamethylenetetramine as a resin curative; subsequent violent exothermic decomposition generated a temperature spike to 230 °C within 40 s, slagging the batch into an unprocessable char. Process hazard analysis for rubber compounding facilities therefore mandates separate storage and dedicated addition sequence protocols for acidic curatives.
In aqueous dip-coating operations for fabric-reinforced rubber goods, MBTS is pre-dispersed as a 50 % aqueous paste with critical control of pH between 6.5–7.5 to prevent agglomeration. The paste, stabilized with lignosulfonate surfactant at 1.5–2.0 wt%, is continuously agitated at 30–50 rpm in baffled tanks to maintain homogeneity before metering into the latex compound. Viscosity of the paste, measured by Brookfield viscometer (ISO 2555, spindle 4, 20 rpm), must remain within 800–1,200 mPa·s for reliable pumping; batches falling outside this range lead to accelerator concentration drift in the dip tank, detected by a ±8 % variation in grab tensile strength of the dipped cord after curing.
