2,2-D Ibenzothiazole Disulfide
|
HS Code |
466383 |
| Chemical Formula | C14H8N2S4 |
| Molecular Weight | 332.49 |
| Appearance | Yellowish - green powder |
| Odor | Characteristic odor |
| Solubility In Water | Insoluble |
| Solubility In Organic Solvents | Soluble in chloroform, benzene, etc. |
| Melting Point | 178 - 180 °C |
| Flash Point | Approx. 271 °C |
| Density | 1.52 - 1.58 g/cm³ |
| Stability | Stable under normal conditions, but may decompose on heating |
As an accredited 2,2-D Ibenzothiazole Disulfide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | 25 - kg bags of 2,2 - D Ibenzothiazole Disulfide, well - sealed for chemical protection. |
| Shipping | 2,2 - D Ibenzothiazole Disulfide is shipped in well - sealed, corrosion - resistant containers. It's transported under conditions avoiding heat, moisture, and incompatible substances to ensure safety during transit. |
| Storage | 2,2 - Dithiobis(benzothiazole) should be stored in a cool, dry place, away from direct sunlight and heat sources. Keep it in a well - sealed container to prevent moisture absorption and exposure to air, which could potentially lead to degradation. Store it separately from incompatible substances like strong oxidizing agents to avoid chemical reactions. |
Why MBTS Dominates Cure Systems for Radial Tire Tread CompoundsA 2,2'-Dibenzothiazole Disulfide loading of 0.8–2.0 phr alongside 2.0–3.5 phr sulfur and 0.5–1.2 phr stearic acid activator defines the backbone of natural rubber (NR) / polybutadiene (BR) blends in passenger and truck tire treads. On a Banbury F270 internal mixer operating at 40–50 rpm rotor speed with a drop temperature controlled at 145–155°C, MBTS is typically added in the second-stage masterbatch to avoid premature onset of crosslinking reactions that would otherwise degrade Mooney processability. The delayed-action characteristic originates from the thermal dissociation of the disulfide bridge into 2-mercaptobenzothiazole (MBT) radicals; the liberated fragments form zinc-accelerator complexes with zinc oxide that initiate sulfur ring opening only after an induction period measurable as ts2 on an oscillating disc rheometer per ASTM D2084. This scorch time routinely extends to 18–28 minutes at 135°C, providing the margin necessary for multi-extrusion of tread, sidewall, and apex profiles in a quadruplex extrusion line with L/D 16:1 pin-barrel cold-feed extruders. In the curing press operating at 150–160°C under 20–25 MPa platen pressure, the compound reaches t90 within 12–18 minutes and generates a crosslink density gradient that peaks at the tread surface, imparting abrasion resistance values above 120 mm³ (DIN ISO 4649) and a tan δ at 60°C below 0.120 for rolling resistance compliance under EU Regulation 2020/740 tire labeling requirements. Notably, MBTS-derived cure systems are incompatible with secondary amine-containing stabilizers at processing temperatures exceeding 140°C because residual nitrosation agents can generate trace N-nitrosamines; thus European tire manufacturers routinely monitor finished articles under EN 12868:2017 to stay below the 0.5 µg/dm² migration limit for infant care articles, a target achievable when MBTS is used without TMTD or TETD co-accelerators.What Limits Processing Safety in High-Adhesion NR/SBR Conveyor Belt Cover Formulations?Conveyor belt cover compounds operating in mining environments require a conflict resolution between long scorch safety for large-calendar processing and rapid full-cure development under continuous vulcanization drums. An MBTS / diphenylguanidine (DPG) binary system at 1.2 phr MBTS and 0.4 phr DPG combined with 2.5 phr insoluble sulfur (IS 7020, 67% oil-treated) resolves this conflict through the pH-buffering effect of DPG on the acidic MBT decomposition products. When the mill-mixed stock is calendered onto polyester/nylon cord at 85–95°C nip temperature, the Mooney viscosity at ML 1+4 (100°C) stays within 45–55 MU and Mooney scorch time t5 at 121°C exceeds 30 minutes, sufficient for uninterrupted operation of a Ø 610 × 1,500 mm three-roll calender line running at 25–30 m/min line speed. Transfer to a Rotocure continuous vulcanizer with a 2,000 mm Ø drum at 160°C and 0.7 MPa contact pressure forces the cure rate to a t90 of 4.5–6 minutes, matching the dwell time governed by the wrap angle and drum rotation. The completed cover exhibits a Shore A hardness of 65 ±3, tensile strength above 22 MPa (ISO 37:2017 type 2 dumbbell), and tear resistance exceeding 55 kN/m (ISO 34-1 method B). A process risk emerges if the actual mixing dump temperature exceeds 155°C during the MBTS/DPG masterbatch incorporation: the DPG component can volatilize and condense in the extraction ductwork, altering the accelerator ratio unpredictably in subsequent batches. Continuous fume extraction monitoring with a dew-point analyzer set to alarm at −20°C condensation threshold is a field-verified countermeasure observed in EU conveyor belt plants.An additional scenario where MBTS becomes problematic is in compounds containing reclaimed butyl rubber liners from scrap tire processing. Coordinated zinc-accelerator species from MBTS can migrate into the butyl phase during co-vulcanization of a dual-durometer belt edge, causing undercure islands that reduce ply adhesion strength below 8 N/mm (ISO 252-1). A preliminary DSC oxidation-induction-time scan on the reclaimed phase is required when MBTS loading exceeds 1.0 phr in the adjacent NR compound.Microcellular EVA/NR Footwear Foam Crosslinking: An MBTS-Initiated Silane Cohybrid SystemAthletic shoe midsoles combining ethylene vinyl acetate (EVA, VA content 18–28 wt%) with 20–30 phr NR require a synchronous crosslinking and blowing agent decomposition that conventional dicumyl peroxide cannot deliver due to its radical-scavenging interaction with azodicarbonamide (ADC). A formulation containing 1.0 phr MBTS, 1.5 phr 3-mercaptopropyltrimethoxysilane (A-189), and 0.3 phr zinc 2-ethylhexanoate provides a condensation–sulfur hybrid network: MBTS first activates sulfur crosslinking in the NR phase at 165°C mold temperature, while the liberated MBT thiol catalyzes the alkoxysilane condensation in the EVA domains. ADC decomposition at 195–205°C then generates the cell structure within an already partially crosslinked matrix, preventing cell coalescence. This sequencing is verified by a moving die rheometer (MDR 2000E at 0.5° arc) showing a two-stage torque rise: the first plateau at 3.5–4.0 dNm corresponds to NR-phase gelation by 90 seconds, and the final rise to 7.0–8.5 dNm maps to EVA network completion by 240 seconds. The molded density target of 0.25–0.35 g/cm³ is met with a cell-size uniformity coefficient of variation below 15%, measured by X-ray microtomography on sole cross-sections. Pre-drying of the silane at RH < 30% for 48 hours before compounding is mandatory because premature hydrolysis in the silane phase generates ethanol byproducts that plasticize the foam, reducing the compression set to an unacceptable >45% (ASTM D395-18 Method B, 22h/50°C). Published data on the exact MBTS/silane synergistic kinetics above 180°C remain limited, so pilot runs with the specific EVA grade (e.g., Evatane 28-05) are required before transfer to a 200-ton compression press with vacuum chambers.When MBTS Replaces ETU in Low-Voltage EPDM Cable Insulation FormulationsFollowing the reclassification of ethylene thiourea (ETU) as a Substance of Very High Concern under REACH Annex XIV, electric cable manufacturers reformulated medium-voltage insulation based on EPDM (Mooney ML 1+8 at 125°C: 40 MU) with MBTS at 1.8–2.5 phr in combination with 0.8–1.2 phr tetramethylthiuram monosulfide (TMTM). The compound is processed on a Buss MDK/E 140 co-kneader with a screw temperature profile of 70°C, 80°C, 90°C, and a discharge zone held below 105°C to prevent MBTS premature dissociation; after 100 Mrad electron-beam pre-crosslinking at 2.0 MeV, the compacted preform passes through a continuous catenary vulcanization tube at 250°C with 1.5 MPa saturated steam. The MBTS/TMTM ratio of 2:1 ensures that the crosslink density after 24h post-cure reaches 4.2 × 10⁻⁵ mol/cm³ (equilibrium swelling in cyclohexane), yielding a hot-set elongation under 0.2 MPa at 200°C of 15–25%, comfortably inside the ≤100% requirement of IEC 60811-507. The electrical volume resistivity retained after 14 days water immersion at 90°C (ANSI/NEMA WC 53) exceeds 5 × 10¹⁴ Ω·cm. A strict prohibition exists against using MBTS alone without a dithiocarbamate co-accelerator in this application: the acidic byproducts of MBTS homolysis would degrade the calcined clay filler surface treatment, halving the wet electrical breakdown strength after 1,000h accelerated water treeing test (ASTM D6097).Low-Nitrosamine Accelerator Architecture for NR Latex Dipping OperationsSurgical and examination glove lines operating with prevulcanized NR latex (60% DRC, ammonium preserved) must achieve a vulcanizate tensile strength above 24 MPa without generating N-nitrosodibenzothiazyl (NDBzA) above the 0.1 µg/m³ workplace air threshold specified in TRGS 552. MBTS at 0.5–1.0 phr in a post-prevulcanization dispersion added directly to the dipping tank at 28–32°C serves this need because its disulfide structure does not carry a free secondary amine, and the primary decomposition product MBT reacts with ZnO to form zinc mercaptobenzothiazole (ZMBT) rather than nitrosatable intermediates. The latex compound is matured for 16 hours at 25°C under gentle stirring (30 rpm) to complete the ZMBT formation and achieve a chloroform number of 3–3.5, indicating sufficient crosslink precursor generation. Subsequent coagulant dipping in 20% Ca(NO₃)₂ solution at 55°C, followed by oven vulcanization at 120°C for 20 minutes and post-leaching in water at 70°C for 4 hours, produces a film with modulus at 500% elongation exceeding 6.0 MPa and a pinhole AQL of 0.65 per ISO 374-2:2019. Because MBTS alone gives a slow cure in thin films, a critical addition of 0.2 phr zinc diisononyldithiocarbamate (ZDNC) is used as a nitrosamine-safe secondary accelerator; the ZDNC/MBTS combination tightly controls the N-nitrosamine migration into artificial sweat below 2.5 µg/dm² when tested per EN 16523-1.A threshold processing problem appears when the latex batch temperature during MBTS dispersion addition exceeds 35°C. Under these conditions, ammonia loss accelerates and the pH drops below 10.0, triggering premature destabilization of the latex protein–ammonium complex. The result is microcoagulum formation visible on 200-mesh screen residue tests, which elevates the pinhole rejection rate from <0.5% to 3–5% of production output. Continuous pH-stat systems with dilute ammonium hydroxide injection calibrated to maintain 10.2 ±0.1 are non-negotiable on high-output dipping lines.Devulcanization Additive Packages for Mechanically Ground Tire RubberGround tire rubber (GTR) obtained from ambient-grinding of passenger car tires at 30–40 mesh is re-integrated into new rubber articles through thermomechanical devulcanization on a ZSK 45 MEGAcompounder twin-screw extruder with a L/D 52:1 configuration. MBTS is incorporated at 0.3–0.8 wt% relative to GTR alongside 2.0–4.0 wt% naphthenic process oil and 0.15 wt% zinc oxide as a chemical shear aid. The disulfide bond of MBTS, when subjected to the shear field at a screw speed of 500–800 rpm and barrel temperatures of 180–230°C, undergoes homolytic scission; the resulting thiyl radicals attack the mono-, di-, and polysulfidic crosslinks in the GTR network, converting them into shorter sulfur bridges and pendant accelerators that can participate in later revulcanization. Online torque monitoring at the 30D position in the extruder barrel shows a measurable 18–25% reduction compared to the unplasticized GTR control, confirming partial network disruption. The extrudate, pelletized underwater at 2°C water temperature, retains a gel fraction of 55–65% (boiling xylene, 24h Soxhlet extraction) and can be compounded back into a new EPDM roof membrane at 30 phr loading without degrading the seam peel strength below 3.5 N/mm per ASTM D413. The processing window is narrow: barrel temperatures above 240°C drive MBTS degradation beyond the thiyl-radical stage to carbon disulfide release, causing void formation in the extrudate and a sulfur odor that exceeds the 10 ppm workplace exposure limit for CS₂. Published data for the exact threshold dose of MBTS relative to polysulfidic crosslink content in ambient-scrap versus cryogenic-scrap GTR remain limited, necessitating rheometric fingerprinting of each lot before devulcanization.
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2,2′-Dibenzothiazole disulfide (MBTS) is supplied as a pale-yellow to cream-colored free-flowing powder or granular solid with a characteristic mild odor. The technical-grade material exhibits a melting range of 170–180 °C (lit. 177–179 °C for >98 % purity), a density near 1.50 g/cm³ at 20 °C, and an ash content typically below 0.3 wt%. Commercial specifications for rubber-grade MBTS are routinely benchmarked against the requirements of ASTM D4811 or equivalent national standards. A representative lot analysis includes: assay (HPLC) ≥ 96.0 %, free 2-mercaptobenzothiazole (MBT) ≤ 2.5 %, moisture (Karl Fischer, 105 °C) ≤ 0.5 %, and residue on 150 µm sieve ≤ 0.1 %. Benzothiazyl disulfide is classified under CAS No. 120-78-5 and EINECS 204-424-9. It is registered under REACH (EC 1907/2006) and meets the substance-specific migration limits applicable to food-contact elastomers under FDA 21 CFR 177.2600 when properly cured and extracted, provided residual MBT and benzothiazole are controlled.
In production-scale compounding of natural rubber (NR) and polybutadiene (BR) blends performed on intermeshing tangential internal mixers (e.g., 1.6 L Banbury-type, two-wing rotor, 40 rpm), substitution of MBTS for MBT at equimolar sulfur-donor concentration shifts the scorch safety margin substantially. The onset of vulcanization, determined as ts2 by oscillating disc curemeter per ASTM D5289, increases from a baseline of 2.1–2.6 min at 135 °C for 0.8 phr MBT in a typical NR/BR (70/30) truck tread formulation to 4.2–4.8 min for 1.0 phr MBTS at identical sulfur loading (2.25 phr). This gain arises from the requirement that the disulfide first undergo thermal homolytic cleavage of the S–S bond (Ea ≈ 140–150 kJ/mol, estimated from DSC kinetic analyses) and subsequent formation of the active MBT–accelerator intermediate, delaying the onset of crosslinking until sufficient MBT has accumulated. The practical processing window on a 90 mm cold-feed extruder (L/D 14:1, screw speed 25–35 rpm) widens accordingly: mixed stock can withstand a five-minute dwell at 120 °C die-head temperature without compound scorch, whereas the MBT-accelerated analogue shows a sharp Mooney viscosity increase (≥10 MU rise in 5 min) under identical conditions, measured per ASTM D1646. This scorch resistance is essential in multi-cavity transfer molds and large-section tire components where heat history is non-uniform.
The scorch delay of MBTS is not an intrinsic molecular constant but a function of the instantaneous concentration of free MBT generated in situ, the available soluble zinc species, and the thermal flux experienced during mixing. In a typical formulation activated by zinc oxide (3–5 phr) and stearic acid (1–2 phr), the rate-controlling step below 140 °C is the dissociation of the disulfide bond. Once sufficient MBT has formed, it complexes with zinc stearate to create the highly active zinc mercaptobenzothiazolate complex, which subsequently reacts with elemental sulfur to generate the active sulfurating agent. If mixing is stopped at dump temperatures exceeding 155 °C, premature formation of this complex can initiate crosslinking before shaping is complete—a failure mode observed on twin-screw extruder lines where screw configuration leads to hot spots. To mitigate this, processors often split the addition of MBTS: a portion is added early in the internal mixer cycle (upside-down method) while the remainder is introduced on a two-roll mill at 60–70 °C nip temperature. This protocol is applied in continuous vulcanization lines for profiles, where a Mooney scorch (MS-t5 at 120 °C) target of ≥ 25 min is mandated for production stability. Published data for the dissociation kinetics in a rubber matrix under shear is limited; some researchers have employed model-compound FTIR studies on MBTS/squalane systems, reporting pseudo-first-order rate constants on the order of 10-4 s-1 at 140 °C. The large activation barrier means that lowering processing temperature by only 5 °C can extend safe dwell time by 30–40 %, a critical control parameter on hot-feed extruders where barrel cooling capacity is constrained.
Direct substitution of MBTS for the sulfenamide class (CBS, TBBS) in a passenger tire carcass compound illustrates a key performance trade-off. While MBTS provides intermediate scorch safety, its cure rate—quantified as tc90—is slower than that of N-cyclohexyl-2-benzothiazolesulfenamide (CBS) at equivalent sulfur levels. In a standard NR/BR (60/40) silica-filled tread formulation, tc90 at 160 °C for 1.2 phr MBTS is typically 6.8–7.5 min, whereas for 1.0 phr CBS it falls to 4.2–4.8 min. This difference forces longer cure cycles on multi-daylight presses, reducing throughput by an estimated 15–20 % on an 85-station tire curing press line. The MBTS-accelerated system, however, forms a higher proportion of polysulfidic crosslinks (up to 70–75 % as determined by thiol/amine chemical probe analysis), which imparts superior fatigue-to-failure and tear strength—an advantage for components that undergo cyclic deformation. The selection of MBTS over a sulfenamide therefore constitutes an explicit choice between manufacturing efficiency (faster cure, higher modulus development) and resistance to dynamic crack growth (Gc measured by trouser tear method per ISO 34-1). In heavy-duty conveyor belt covers, where ≥ 200 % elongation at break and high tear energy are non-negotiable, MBTS at 0.8–1.5 phr in combination with secondary accelerators (e.g., DPG at 0.1–0.3 phr) remains a preferred primary accelerator.
| Accelerator | Loading (phr) | Mooney Scorch t5 (120 °C), min | ts2 (150 °C), min | tc90 (150 °C), min | Ultimate Tensile (ISO 37), MPa | Tear Strength (ISO 34-1, Die C), N/mm |
|---|---|---|---|---|---|---|
| MBT | 0.8 | 12.3 | 2.4 | 10.8 | 24.1 | 38 |
| MBTS | 1.0 | 24.7 | 4.5 | 14.2 | 25.6 | 49 |
| CBS | 1.0 | 26.9 | 5.6 | 10.2 | 26.8 | 42 |
| TBBS | 1.0 | 27.4 | 5.8 | 9.1 | 27.0 | 44 |
In polar elastomers such as acrylonitrile-butadiene rubber (NBR) with 33 % ACN content, the solubility of MBTS is inherently limited. At addition levels above 2.0 phr, bloom becomes macroscopically visible after 72 h storage at 23 °C/50 % RH, as verified by surface FTIR-ATR spectra showing the characteristic benzothiazole ring vibrations. Such exudation compromises adhesion in multi-layer fuel hose constructions where bond strength, tested per ASTM D413 (peel adhesion), drops by >30 % when bloom is present. To counteract this, MBTS is frequently pre-dispersed in a polymer binder (e.g., EPM elastomer) at 75 % active content or incorporated as a predispersed waxy masterbatch (MBTS/70) during open-mill mixing, with nip gaps tightened to 0.5–0.8 mm at the finishing stage. For EPDM compounds with high ethylene content (65–70 %), the dispersive mixing requirement intensifies: carbon black pastes prepared with MBTS and tested via optical microscopy frequently exhibit residual agglomerates exceeding 10 µm unless mixing energy input exceeds 0.12 kW·h/kg in a tangential internal mixer. These agglomerates act as stress concentrators, reducing compression set (ASTM D395 Method B, 70 h/−25 °C) by 5–8 percentage points relative to well-dispersed compounds. Therefore, a two-pass mix is specified for critical sealing applications: first pass excludes the accelerator, and the second pass incorporates MBTS at a dropping temperature not exceeding 105 °C, followed by homogenization on a two-roll mill with a friction ratio of 1:1.15.
Storage conditions of MBTS directly influence compound consistency. The product is hygroscopic; exposure to relative humidity above 60 % at 25 °C for extended periods raises moisture content above the 0.5 % specification, which then leads to porosity in thick-section molded goods when the curing press opens. Pre-drying in a desiccant dehumidifier at 50 °C for 2–4 hours is mandatory in tropical climate zones before weigh-off into automatic feeding systems. Additionally, the fine powder grain (median particle size 8–15 µm) presents a dust explosion risk; handling areas are designed per NFPA 654 with grounding and inerting as needed. Because MBTS is a skin sensitizer (R43 label; GHS07), worker exposure must be controlled below the occupational exposure limit of 0.5 mg/m³ (inhalable fraction), and local exhaust ventilation is installed over bag-slitting stations.
| Standard / Regulation | Scope / Test Method Designation | Typical Requirement |
|---|---|---|
| ASTM D4811 | Standard specification for non-halogenated accelerators | Assay ≥ 95 %, MBT ≤ 2.5 % |
| ISO 6472 | Rubber compounding ingredients – accelerators; test methods | Melting point, ash, sieve residue |
| FDA 21 CFR 177.2600 | Rubber articles intended for repeated use in contact with food | Total benzothiazyl compounds limit; extraction testing |
| EU 10/2011 | Plastic and rubber materials in contact with food | Specific migration limit for MBT (SML 0.5 mg/kg) |
| REACH Annex XVII | Restriction on skin sensitizers in mixtures | Concentration labeling threshold 0.1 % in preparations |
MBTS is generally not recommended as the sole accelerator in efficient vulcanization (EV) systems where sulfur levels are ≤ 0.5 phr because the low-sulfur environment fails to generate sufficient poly-thiobenzothiazole species, resulting in inactive curatives and an unpractically slow cure state. When attempted on a laboratory scale in an NR gum compound (S 0.3 phr, MBTS 2.0 phr), the maximum torque (MH) on an MDR rheometer at 170 °C reaches only 40 % of the value achieved with an equivalent loading of TBBS, and the network shows a preponderance of monosulfidic crosslinks that impart low elongation at break (< 250 %). This limitation stems from the high thermal stability of the benzothiazole-terminated pendant groups, which demand higher activation energy than is available under typical curing conditions. Real-world EV compound design therefore couples MBTS with a small amount of a secondary dithiocarbamate or thiuram (e.g., ZDMC at 0.05–0.2 phr) to generate the necessary free accelerator. Despite this restriction, MBTS is effective in semi-EV (SEV) systems containing 1.0–1.5 phr sulfur, where it produces a favorable balance of mono- and disulfidic crosslinks that enhances heat aging resistance, as measured by retained elongation after 168 h at 100 °C per ISO 188, while still maintaining operational scorch safety for injection molding with clamp forces exceeding 200 tonnes.
In white and light-colored EPDM profiles for architectural glazing, MBTS is selected over sulfenamides when non-staining behavior is a primary requirement, despite its slower cure. The absence of an amine-releasing decomposition pathway means that contact with titanium dioxide pigments does not produce the pink chromophore sometimes observed with TBBS in the presence of phenolic antioxidants. Outdoor exposure tests on 70 durometer EPDM glazing gaskets formulated with 1.2 phr MBTS and 0.2 phr ZDBDC show color difference ΔE < 5 after 2,500 h of xenon-arc weathering per ISO 4892-2, whereas comparable CBS-accelerated specimens exhibit ΔE > 12. This color stability is crucial for automotive weatherseals and construction profiles where aesthetic warranty conditions stipulate minimal yellowing. The trade-off is a lower crosslink density, compensated by slightly higher (+5 phr) carbon black or silica loading to meet compression set targets of < 25 % (24 h/−20 °C, ASTM D395).
