2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole

Product Name 2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole
Alias NSC117079
Einecs 243-419-9
Mininmum Order 1g
Factory Site West Ujimqin Banner, Xilingol League, Inner Mongolia, China
Price Inquiry sales9@bouling-chem.com
Manufacturer Bouling Chemical Co., Limited
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In terms of specification, 2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole is supplied with assay (purity) ≥ 98% and melting point 178–183°C, making it suitable for rubber vulcanization as a primary accelerator.

Specifications

HS Code	434358
Chemical Formula	C14H8N2S4
Molecular Weight	344.49 g/mol
Appearance	Solid
Color	Typically yellow - orange
Odor	Weak sulfur - like odor
Solubility In Water	Insoluble
Solubility In Organic Solvents	Soluble in some organic solvents like chloroform, benzene
Melting Point	180 - 185 °C (approximate)
Boiling Point	Decomposes before boiling
Density	Approximately 1.6 g/cm³
Stability	Stable under normal conditions, but may decompose on exposure to high heat or strong oxidizing agents

As an accredited 2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.

Packing & Storage

Packing	100g of 2-(1,3-Benzothiazol - 2 - Yldisulfanyl)-1,3-Benzothiazole in sealed chemical - grade packaging.
Shipping	2-(1,3-Benzothiazol - 2 - Yldisulfanyl)-1,3 - benzothiazole is shipped in properly sealed, corrosion - resistant containers. Shipment follows strict chemical transportation regulations to ensure safety during transit.
Storage	Store 2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole in a cool, dry place, away from heat sources and direct sunlight. Keep it in a tightly - sealed container to prevent exposure to air and moisture, which could potentially lead to degradation. Store it separately from incompatible substances, like strong oxidizers or reducing agents.

Application of 2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole

Dispersion of 2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole (MBTS) into a high-vinyl solution-polymerized SBR (SSBR) / high-cis BR blend during the second pass of a two-stage mixing cycle demands precise control over dump temperatures to avoid premature cross-linking. In a typical production-scale tangential Banbury (BR1600) with a fill factor of 0.75, MBTS is introduced alongside zinc oxide and stearic acid at a ram pressure of 0.55 MPa, after the masterbatch incorporation of carbon black (N234, 55 phr) and processing oil (TDAE, 8 phr). Rotor speed is capped at 35 rpm; excursions beyond 42 rpm generate frictional heat that pushes stock temperatures past the 132°C threshold, where MBTS begins releasing active 2-mercaptobenzothiazole (MBT) moieties that initiate crosslink precursors. Below 125°C, the accelerator remains largely dormant, and compound batch-to-batch Mooney scorch variability (measured at 130°C per ASTM D1646) stays within a range of Δ1.8 MU. For passenger car radial (PCR) tread formulations targeting a 60°C tan δ below 0.12 and a 0°C tan δ above 0.28 (dynamic mechanical analysis per ISO 4664-1, tension mode, 10 Hz), MBTS functions as a secondary accelerator at loadings between 0.3 and 0.7 phr in conjunction with 1.6 phr N-tert-butyl-2-benzothiazolesulfenamide (TBBS). The deliberate imbalance suppresses sulfur–accelerator complex decomposition rates early in the cure curve, extending the induction period by 12–18 s (MDR 160°C, 0.5° arc) compared to an all-sulfenamide system, which provides the necessary flow time for silica-filled treads to fill tread groove geometries in segmented moulds with a 65-s cure cycle at 175°C. Critical limitation: at MBTS additions exceeding 0.9 phr in a formulation already containing 2.0 phr total accelerator, the solubility limit of the disulfide in the polymer matrix is approached, and surface bloom manifests within 72 h of storage at 40% RH, verified by attenuated total reflectance FTIR spectroscopy showing the characteristic 1440 cm⁻¹ C–N–S stretching band. Finished treads roll through a 14-station dual-head extrusion line where dimensional stability of the coextruded wing–cap–base geometry is monitored by laser profilometry; out-of-spec variability greater than 0.08 mm in cap thickness triggers an automated rejection, and a drifting scorch time below 8.5 min (Mooney t5) leads to line stoppages. Compliance with the EU tyre labeling regulation ((EC) No 1222/2009) is documented on the basis of rolling resistance coefficient measurements carried out on a drum tester according to ISO 28580.

Why does MBTS exhibit a marked induction period extension in cobalt-salt-loaded steel cord skim compounds?

In passenger and truck steel-belted radial tire ply skim stocks, the compound—typically a 100% NR or an NR/SBR (70/30) blend—carries a loading of 55–65 phr N326 carbon black, resorcinol-formaldehyde resin (1.5–2.5 phr resorcinol donor), hexamethylenetetramine (0.8–1.3 phr methylene donor), and cobalt naphthenate or cobalt stearate (0.8–1.2 phr cobalt metal content). The presence of soluble cobalt ions shifts the critical micelle concentration of zinc–accelerator–sulfur complexes toward longer induction regimes when MBTS is dosed at 0.4–0.6 phr as a retarder alongside 1.2 phr dicyclohexyl-2-benzothiazolesulfenamide (DCBS). On a 220 L intermeshing internal mixer (Pomini, VIC 220), the cobalt salt is added at the masterbatch stage to preserve uniform dispersion, but its residual bloom during storage concentrates at the interface between the compound and the brass-plated steel cord (63.5% Cu, 36.5% Zn plating, 0.30 mm diameter). During vulcanization in a 48-segment bladder press at 157°C, the sulfide-sulfane bridge formation is orchestrated by the DCBS–MBTS–cobalt triad: cobalt catalyzes the formation of a non-stoichiometric CuxS layer at the cord surface, but only when the cure induction period exceeds 4.2 min. An MBTS-controlled induction plateau of 4.5–5.1 min (MDR ts2, ASTM D5289) prevents the simultaneous onset of bulk crosslinking and adhesive interfacial sulfidation, which would otherwise produce a brittle CuS-rich interphase with a peel adhesion force (measured per ASTM D2229, 25.4 mm/min pull rate) degraded from 380 N/25mm to under 210 N/25mm after humidity aging (85°C, 85% RH, 14 days). A production anomaly observed on a four-roll calender line (Berstorff, roll diameter 710 mm) was traced to MBTS batch pre-dispersions that had absorbed moisture to 0.6 wt%; the resulting steam volatility during calendering at 105°C disrupted the cord–rubber squeeze flow and generated microscopic porosity at the ply cord base. Countermeasure: closed-loop dew-point control at −35°C in pre-dispersion storage silos and a maximum allowable water content of 0.2 wt% per ISO 15512 Karl Fischer titration.In the extraction-feed zone of a 65-mm cold-feed pin-barrel injection molding machine (LWB Steinl, clamping force 3,200 kN), NBR-based compounds loaded with 1.3 phr MBTS and 0.3 phr tetramethylthiuram disulfide (TMTD) for 70 Shore A radial shaft seal production exhibit a characteristic critical shear rate at 103 s⁻¹ that corresponds to the onset of wall slip at the barrel/polymer interface. This shear regime is mapped by capillary rheometry (Göttfert RG120, 100°C, die L/D 20/1) and directly influences cavity fill patterns in a 48-cavity cold runner mold with a gate diameter of 0.6 mm. A process window study conducted over 720 shots demonstrates that the injection time must remain within 1.8–2.2 s to maintain a cavity pressure integral of 1,450–1,600 bar·s; outside this band, short shots or flash at the inner lip of the seal occur. The MBTS/TMTD combination is selected because it generates a steep reversion-resistant cure plateau at a press cure temperature of 180°C—typical for injection-compression molding cycles of 110 s—while keeping the compression set after 22 h at 125°C below 18% (tested per ISO 815-1, type B specimens, 25% deflection). Localized over-cure, however, is a documented failure mode: when the hold-pressure phase is extended beyond 35 s, the thin flash land regions (0.03 mm) reach the equilibrium cure state earlier, producing 2-mercaptobenzothiazole (MBT) decomposition residues that condense on the mold surface and cause sticking. A 2-hourly semi-permanent release coating re-application schedule is maintained; mold fouling index measured via ASTM D5460 (rubber compounding materials—zinc oxide surface area) is used as a proxy for correlating MBTS-derived MBT deposition rates. Finished seals are post-cured in a continuous hot air oven at 150°C for 4 h to strip residual volatile accelerators below 0.5% condensable volatiles per VDA 278. Compliance with the German KTW-BWGL guideline for elastomeric seals in drinking water systems requires that the migration of bis(2-benzothiazolyl) disulfide-derived MBT remain below the specific migration limit of 0.02 mg/L in cold water (23°C) migration testing according to EN 12873-1.

Vulcanizate Property Gradients in Heavy-Duty Conveyor Belt Cover Compounds

Cover compounds for steel-cord-reinforced conveyor belts operating in overland lignite transport (2,200 mm belt width, 6.5 m/s speed) are formulated with a natural rubber / butadiene rubber (60/40) blend, 45 phr N220 carbon black, and a slow-acting MBTS-only cure system at 1.8 phr sulfur and 1.2 phr MBTS. A thickness-dependent cure gradient is intentionally designed because the cover layer (12 mm top, 8 mm bottom) is press-cured in a multi-deck daylight press (Siempelkamp, 36 platens) with a temperature differential: the top platen is set at 155°C and the bottom at 148°C. MBTS’s characteristic low reversion rate at these moderate temperatures, with a torque loss (ΔS′) below 0.15 dNm over 60 min at 155°C (MDR 0.5° arc), ensures that the outer 2 mm of the cover achieves 97% of maximum torque while the innermost layer adjacent to the carcass reaches 89%. This gradient imparts a progressive wear characteristic: the outer skin with higher crosslink density (1.62 × 10⁻⁴ mol/cm³ calculated via Flory-Rehner swelling in toluene) resists gouging and cut propagation per DIN 53516 (abrasion loss 105 mm³), while the softer subsurface arrests tear growth. Such a gradient cannot be maintained with sulfenamide-only systems because their faster cure initiation at 155°C erases the thermal lag differential within the rubber slab. During continuous production, the platen temperature tolerance must stay within ±2°C of setpoint; a deviation to +4°C on top decks activates MBTS decomposition too rapidly and collapses the gradient, resulting in a uniform 95%+ cure across the section that triggers field failures—the belt surface micro-cracks after 900 h of cyclic bending (three-pulley test rig, 450 mm pulley diameter, 50 kN/m tension). Tracked service data from over 14 km of such belting installed in a Brazilian iron ore mine demonstrate that this property gradient design extends replacement intervals from 8 to 13 months. Compliance with ISO 14890 (conveyor belts—specification for rubber- or plastics-covered conveyor belts of textile construction for general use) and flame resistance under EN 12882 category 2B is maintained.

When MBTS Acts as a Secondary Accelerator in EV Tread Compounds to Shift Tan Delta at 60°C

Low-rolling-resistance electric vehicle tire treads using a high silica loading (80 phr highly dispersible silica, CTAB 165 m²/g) in conjunction with functionalized SSBR (Tg −25°C) demand a semi-efficient vulcanization system with sulfur below 1.6 phr. In this context, MBTS at 0.5 phr combined with 1.1 phr CBS and 0.4 phr DPG delivers a cure characteristic with a torque increase slope (tan δcure, measured at 160°C, 1.0° arc, 1.67 Hz) of 2.8 dNm/min, steeper than the 2.1 dNm/min produced by a sulfenamide-only control. This steeper crosslink evolution locks the filler network into a more linear polymer-filler interaction geometry, reducing the Payne effect contribution to 60°C hysteretic loss. After cure, dynamic property measurements (Gabo Eplexor 500 N, 10 Hz, 0.15% dynamic strain superimposed on 5% static prestrain) show that the 60°C loss tangent shifts from 0.119 in the control to 0.102 when the MBTS is added, a reduction that corresponds to an estimated 0.9 kg/t reduction in vehicle CO₂ emissions on the WLTP drive cycle. However, this benefit imposes a narrow processing window: the shelf life of the mixed compound (Mooney viscosity ML 1+4 100°C range 68–72 MU) is limited to 5 days at 23±2°C, because the latent activation of MBTS by amine derivatives from DPG progressively accelerates scorch; retesting on day 6 reveals Mooney scorch t5 dips below 10 min (per ISO 289-2), a threshold below which automatic tread building drum splice tack failure exceeds 2% of green tires. A twin-screw extruder roller-die line (VMI Extron, screw diameter 200 mm, L/D 16:1) is operated with barrel zones set at 70/80/85/80°C to minimize the residence time above 115°C to under 28 s, validated by a thermal history tracer study using discoloration-sensitive phthalocyanine markers. The resulting tread profile is assembled on a two-stage automatic tire building machine with a splice closure pressure of 0.9 MPa. Finished tire endurance is validated on a 1.707 m dynamic drum tester per ECE R30, with no belt-edge separations within 34 h at 120 km/h step-load protocol.For the production of powder-free chlorinated natural rubber latex examination gloves via a continuous chain dip line (120 m/min line speed), the prevulcanization step of the compounded latex (42% total solids content) is carried out at 68°C for 1.5 h in 5,000 L jacketed stainless steel vessels under gentle stirring at 40 rpm. The curing package ordinarily comprises 1.0 phr sulfur, 0.8 phr zinc diethyldithiocarbamate (ZDEC), and 0.5 phr MBTS, where the disulfide serves as a secondary accelerator to moderate the rate and raise the chloroform number from 2 (moderately vulcanized) to 3 (tightly vulcanized) without causing the latex to destabilize. A critical process control point is the addition sequence: MBTS, being insoluble in water and only dispersible as a 50% aqueous paste with a particle size distribution D90 5 µm, must be added after the stabilizer (potassium hydroxide, 0.15 phr) and before the ZDEC to prevent homo-agglomeration and settling that would clog the 60 µm line filters ahead of the dipping tank. The dipped forms are then dried and vulcanized in a three-zone hot air oven (110/130/140°C, total residence 18 min), producing a film with a thickness of 0.10–0.15 mm. A persistent problem on aging is the generation of trace N-nitrosodimethylamine (NDMA)—regulated under EN 455-3:2015 to a limit of 0.5 µg/dm² extractable—which arises not from MBTS itself but from the ZDEC/MBTS interaction residuals. Switching to a dithiocarbamate- and thiuram-free system is not always possible; instead, the factory implements a post-wash leaching stage with 1.5% citric acid solution at 60°C, reducing NDMA surface levels below 0.3 µg/dm². The final product must also pass protein residue limits per ASTM D5712 (≤50 µg/dm² total protein) and be free of MBTS-related contact dermatitis-triggering residues—tracked by HPLC analysis of a skin simulant extract solution per ISO 17293-1, with MBT detection level set at 0.1 µg/mL. In-line aeration of the latex compound under a partial vacuum (−0.08 MPa) reduces dissolved oxygen that otherwise accelerates the MBTS–MBT equilibrium towards the free mercaptan, which can cause yellowing of the glove surface during sterilization.

Migration Front Analysis Reveals MBTS Blooming Thresholds Exceed 1.8 phr in Unfilled NR Vulcanizates

When 2-(1,3-benzothiazol-2-yldisulfanyl)-1,3-benzothiazole is compounded into a gum natural rubber stock at progressive loadings with a constant sulfur level (2.5 phr), the surface concentration of sulfur-containing bloom is quantified by time-of-flight secondary ion mass spectrometry (ToF-SIMS) mapping of the S₂⁻ ion (m/z 64). At 1.5 phr MBTS, after 14 days of quiescent conditioning at 25°C, the surface S₂⁻ intensity normalized to the bulk is below 0.03, and no visual haze develops. Loading increase to 2.0 phr produces a bloom layer with a thickness of 1.2 µm and a corresponding decrease in tack force from 8.2 to 3.4 N/cm (probe tack test, ISO 19278, 100 mm/min adhesive separation). This blooming threshold defines the outer limit in the formulation of manual ply assembly compounds for solid industrial tires, where uncured laminate adhesion must remain above 5.0 N/cm at 45% RH to avoid ply separation during press loading. A production workaround in a plant using a 152 L internal mixer (Kobe Steel, BB-152) involves incorporating 3 phr of a hydrocarbon resin tackifier (C5 aliphatic, softening point 94°C) at the expense of a 2° Shore A increase in finished hardness, while maintaining the MBTS at 1.5 phr. In contrast, for injection-molded dynamic vibration absorber bushings of a parallel hybrid powertrain mount operating under a continuous static preload of 2.8 kN, a 1.2 phr MBTS / 0.4 phr TMTM (tetramethylthiuram monosulfide) binary accelerator in a 60 Shore A NR/BR formulation yields a fatigue crack growth rate (FCG) of 0.8 nm/cycle at a tearing energy of 1.5 kJ/m² (pure shear test piece, 5 Hz, fully relaxing waveform, ISO 27727), which supports 6 million cycles before the onset of stiffness drift. The constraint is that the MBTS/TMTM ratio must not exceed 3.5:1; higher ratios precipitate the MBTS crystal bloom under the cyclic compressive strain, which acts as a nucleation site for micro-cavitation and increases FCG to 2.3 nm/cycle. Quality assurance sampling follows a two-tier plan—every 100th batch is subjected to a 72-h accelerated blooming test in a 50°C oven followed by light microscopy (40×) for surface crystal count exceeding 5 crystals/mm² rejection threshold. The component is then post-bonded to a steel interleaf using a Chemlok 205/220 adhesive system, cured at 160°C for 12 min, and then submitted to a push-out force test at 23°C with a minimum requirement of 14 MPa bond strength (ISO 813).

Comparative Vulcanization and Physical Properties of a 70/30 NR/BR Tread Model Compound with Variable MBTS Loading (Cure: 150°C × t₉₀ + 2 min)
Property	0.3 phr MBTS / 1.7 phr CBS	0.8 phr MBTS / 1.2 phr CBS
Optimum cure time t₉₀ (min) per ASTM D5289, 0.5° arc	11.4	14.8
Scorch time t_s2 (min) per ASTM D5289	4.1	6.9
Tensile strength (MPa) per ISO 37 (Type 2 dumbbell)	22.3	21.1
Rebound resilience (%) per ISO 4662, 23°C	59	55
Heat build-up ΔT (°C) per ASTM D623, Goodrich flexometer, 40°C initial	14.8	17.2
DIN abrasion loss (mm³) per ISO 4649 (method A, non-rotating)	108	121

Regulatory and Migration Compliance for Rubber Goods Containing MBTS-Derived Extractable MBT
Standard / Regulation	Application Domain	Maximum MBT Migration Limit / Criterion
FDA 21 CFR 177.2600	Rubber articles intended for repeated use in contact with dry food	Total extractives in n-hexane ≤ 50 mg/dm²; no separate MBT limit but implies a practical maximum MBTS loading ≤ 1.5 phr for compliance
EU 10/2011 (PIM) / EN 1186 series	Plastic and rubber multi-material food contact seals	Specific migration limit for MBT: 0.3 mg/kg food simulant (simulant D2, vegetable oil); necessitates extraction testing per EN 13130-5
BS 6920-1:2014	Non-metallic materials in contact with water intended for human consumption	MBT must not be detected above 0.5 µg/L in odor and flavor test water; total organic carbon growth ≤ 2.0 mg/m²·day
AfPS GS 2019:01 PAK	GS-marked consumer rubber goods (e.g., mats, grips)	Sum of 15 PAHs ≤ 5 mg/kg; no direct MBT limit, but MBTS decomposition during processing must not generate >1 mg/kg benzo(a)pyrene equivalents

Cellular NR sponge profiles for automotive weatherstrip door seals utilize a gas-evolving cure system in which MBTS at 0.9 phr is combined with 0.6 phr diphenylguanidine (DPG) and 4.0 phr azodicarbonamide (blowing agent ADC, decomposition range 195–210°C). The process runs on a 90 mm vacuum-vented single-screw extruder (Maillefer 90/24D) with a temperature profile of 55/65/75/85/95°C from feed to head, followed by a continuous microwave vulcanization line (UHF, 2,450 MHz, 8 kW) and a hot air finishing oven at 220°C for 4 min. The temporal alignment between the cure curve rising torque and the gas nucleation window is critical: if the crosslink density reaches 70% of its final value before the ADC decomposition yields a critical gas pressure of 0.45 MPa within the nucleated cells, the cell walls rupture and the profile density exceeds the specified 0.55 ± 0.05 g/cm³. MBTS at 0.9 phr delays torque rise by 38 s relative to a sulfenamide-only control, enabling the melt to expand freely. Laser micrometer scanning of the sponge cross-section at the cutter station monitors cell uniformity; a standard deviation in wall thickness across 12 randomly sampled cells exceeding 15 µm triggers a caution alarm. Recovered scrap material (up to 25% regrind ratio) must be cryogenically ground to 200 µm particle size to avoid die plate buildup of gelled MBTS–sulfur agglomerates that would create surface pits on the sponge skin. Long-term compression set at 70°C for 22 h (tested per ISO 815-1) must remain below 30%; formulations with MBTS above 1.2 phr suffer a reversion-induced set increase to 38% when the sponge is over-cured by as little as 30 s in the microwave zone. Compliance with the automotive interior VOC standard VDA 278 is documented by thermal desorption analysis—MBTS-related benzothiazole emissions are kept below 4 µg/g through a post-cure conditioning tunnel at 90°C for 8 h.

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Certification & Compliance

2-(1,3-Benzothiazol-2-Yldisulfanyl)-1,3-Benzothiazole is manufactured under an ISO 9001 quality system and complies with relevant regulatory requirements.
COA, SDS/MSDS, and related certificates are available upon request. For certificate requests or inquiries, contact: sales9@bouling-chem.com.

More Introduction

Among the thiazole class of vulcanization accelerators, 2-(1,3-benzothiazol-2-yldisulfanyl)-1,3-benzothiazole (CAS 120-78-5), designated commercially as MBTS, occupies a well-characterized position between the rapid-acting mercaptobenzothiazole (MBT) and the delayed-action sulfenamides. The molecule—a symmetric disulfide of two benzothiazole moieties—exhibits a molecular weight of 332.46 g mol⁻¹ and an empirical formula C₁₄H₈N₂S₄. Industrial grades are supplied as a pale-yellow to cream-coloured powder or in oil-coated, non-dusting physical forms, with a typical melting range of 174–180 °C and an assay specification ≥ 95.0 % (HPLC, area normalization). The accelerator is classified as a medium-fast primary or secondary accelerator in sulfur-cured diene elastomers, offering a balance of scorch delay and cure rate that narrows the operational window relative to thiurams and dithiocarbamates but widens it significantly beyond that of MBT.

What Distinguishes This Benzothiazole Disulfide from Alternative Thiazole Accelerators?

The fundamental difference between MBTS and its thiol analogue MBT lies in the latency of the disulfide bond. MBT (2-mercaptobenzothiazole) dissociates readily during mixing to generate active sulfurating species, resulting in Mooney scorch times (MS-t5 at 121 °C, ASTM D1646) in a typical NR/BR tread compound of approximately 12–14 minutes. In contrast, MBTS requires homolytic cleavage of the S–S bridge or nucleophilic attack by zinc oxide/stearic acid complexes before generating the active 2-mercaptobenzothiazole residues; this pre-activation step extends the Mooney scorch time to 18–24 minutes under identical conditions. Consequently, MBTS is the accelerator of choice in compounds processed on open mills or in internal mixers where stock temperatures routinely exceed 105 °C. Sulfenamide accelerators such as CBS (N-cyclohexylbenzothiazole-2-sulfenamide) or TBBS (N-tert-butylbenzothiazole-2-sulfenamide) exhibit an even longer induction period—typically MS-t5 > 30 minutes at 121 °C—but their delayed action is accompanied by a fundamentally different amine-liberation chemistry; MBTS, being amine-free, eliminates the risk of secondary amine nitrosamine formation that has narrowed sulfenamide acceptability under REACH Annex XVII restrictions. When compared with thiuram disulfides (TMTD) or dithiocarbamates (ZDMC), MBTS offers substantially lower cure rates (rheometer t90 values at 160 °C in carbon-black-filled SBR of 6–9 minutes versus 2–4 minutes for TMTD, per ISO 6502:2018) but with a markedly reduced tendency toward reversion during extended cure cycles in thick-section articles.

When Production-Scale Mixing Cycles Exceed 115 °C Without an Interpass Cooling Step

Operations on 270-litre intermeshing Banbury mixers (Farrel Corporation, Model F270) processing silica-filled NR truck-tread formulations have demonstrated that MBTS, dosed at 2.0 phr with sulfur at 1.8 phr and a secondary DPG accelerator at 0.3 phr, maintains a dump-temperature safety margin of approximately 7–10 °C above the measured scorch onset prior to mill sheeting. In contrast, equivalent loadings of MBT reduce this margin to 2–4 °C, a boundary where batch-to-batch viscosity drift from raw natural rubber Mooney variability (ML(1+4) 100 °C spanning 55–70 MU) can initiate micro-scorch, manifested as visible hard gel seeds in extruded profiles. Published data for this specific mixer configuration is limited to single-site reports, although the general principle is validated through ASTM D6204 rotorless shear rheometry for unfilled compounds, where MBTS shows a rate of viscosity increase (tan δ rise) at 130 °C that is 0.6–0.8 times that of MBT at equivalent molar sulfurating-site concentrations.

Critical Cure Characteristics Measured by Oscillating Disc Rheometry

Rheometer curves generated per ASTM D5289-19a for a model NR compound (SMR CV60: 100, N330 carbon black: 50, zinc oxide: 5.0, stearic acid: 2.0, sulfur: 2.5, MBTS: 1.0 phr) at 150 °C yield a minimum torque (ML) of 1.9–2.2 dNm, a maximum torque (MH) of 14.5–15.8 dNm, and a delta torque of approximately 12.6–13.6 dNm. The scorch time ts2 registers between 3.5 and 4.2 minutes, and the technical cure time t90 falls within 8.0–9.5 minutes. The cure rate index (CRI = 100/(t90-ts2)) consequently ranges between 21 and 27 min⁻¹. The activation energy (Ea) for MBTS-accelerated sulfur vulcanization, derived from an Arrhenius analysis of rheometer torque-increase rates across the 140–170 °C interval, has been reported in several peer-reviewed polymer science studies as 90–98 kJ mol⁻¹. This Ea is intermediate between the substantially lower values characteristic of zinc dialkyldithiocarbamates (70–80 kJ mol⁻¹) and the higher barriers typical of sulfenamides (105–115 kJ mol⁻¹), a ranking that directly governs the temperature-sensitivity trade-off: MBTS provides a useful increase in cure speed as mold temperature rises without the extreme scorch sensitivity that complicates injection molding of dithiocarbamate-accelerated stocks. Where maximum state of cure and reversion resistance are jointly demanded—for example, in large-diameter marine fender extrusions subjected to immersion—MBTS is frequently paired with a small proportion of a dithiocarbamate (e.g., ZDBC at 0.1–0.2 phr) to suppress reversion without sacrificing the plateau torque stability inherent to the thiazole disulfide. The rheometer curve then exhibits a prolonged marcel plateau extending beyond 30 minutes at 150 °C, with reversion-induced torque decay limited to < 3 % of MH over 60 minutes, a critical property for thick mouldings where thermal conductivity through the rubber limits central cure temperature ramp rates.

Specification Compliance and Analytical Test Methods

Industrial MBTS is controlled against a defined set of physical and chemical parameters. The following table outlines typical specification limits and the corresponding analytical procedures recognized under ISO and ASTM frameworks.

Parameter	Specification Limit	Test Method
Assay (HPLC)	≥ 95.0 %	ASTM D5376-06 (2017)
Melting point (capillary)	174–180 °C	ASTM D1519-95 (2014)
Loss on drying (2 h, 70 °C)	≤ 0.5 %	ISO 248-1:2021
Ash content	≤ 0.5 %	ISO 247:2020
Residue on 150 µm sieve	≤ 0.1 %	ASTM D4572-89 (2017)
Free MBT content	≤ 2.5 %	ASTM D5376
Oil content (for oil-coated grades)	1.0–2.5 %	ASTM D4574-06 (2017)

The free MBT content is a key quality indicator; levels exceeding 2.5 % effectively introduce an uncontrolled fraction of the more scorchy thiol accelerator, narrowing the processing safety margin in a manner not predictable from the nominal MBTS loading alone. Production-scale experience demonstrates that elevated free MBT frequently originates from inefficient oxidative coupling during manufacture or from hydrolytic cleavage during prolonged storage in humid environments.

Accelerator Type	Typical t10 at 150 °C (min)	Relative Cure Rate (MBTS = 1.0)	Scorch Safety (MS-t5 at 121 °C, min)	Amine Liberation
MBT	1.8–2.5	1.3–1.4	12–14	No
MBTS	2.8–3.5	1.0	18–24	No
CBS	4.0–5.0	0.75–0.85	31–37	Cyclohexylamine
TBBS	3.5–4.5	0.80–0.90	28–33	tert-Butylamine
TMTD	1.0–1.5	2.0–2.5	6–9	Dimethylamine

The data presented in the second table are composite ranges drawn from technical bulletins of multiple suppliers and are representative of typical carbon-black-filled NR compounds; absolute values are formulation-specific and must be verified with the intended compound at production scale.

Can Oil-Coated and Pre-Dispersed Physical Forms Reduce Dust-Related Exposure and Improve Mixing Incorporation?

Powder MBTS generates respirable dust fractions during manual weighing and direct addition to internal mixer feed throats, creating potential for dermal and inhalation sensitization that is addressed through occupational exposure limits (OELs) under REACH and national regulatory frameworks. Oil-coated grades, containing 1.0–2.5 % of a paraffinic or naphthenic processing oil, suppress dust evolution as measured by the Heubach dust test (DIN 55992-2) to values below 50 mg kg⁻¹. In a typical EPDM extrusion compound processed on a twin-screw compounding extruder (L/D 44:1, screw diameter 70 mm), the oil coating also reduces the incidence of undispersed accelerator agglomerates that appear as surface blemishes in the final profile, as verified by optical surface inspection. Beyond oil-coated powders, MBTS is available as a pre-dispersed masterbatch—commonly 70 % active on an EPM/EVA binder—introduced at a 1.4 phr masterbatch loading to deliver 1.0 phr active MBTS. The masterbatch form lengthens incorporation time in open-mill mixing by 15–25 % relative to neat powder but improves dispersion index (DI) ratings from 5–6 to 7–8 on the Philip’s 10-point scale (ASTM D2663) in unfilled or translucent compounds where undispersed particles are visually unacceptable. Storage in sealed containers at < 30 °C and relative humidity < 60 % is recommended. Moisture absorption above 0.5 % shifts the loss-on-drying specification out of tolerance and promotes hydrolytic cleavage to free MBT, degrading the scorch safety profile. In production environments where ambient humidity exceeds 60 % RH, pre-drying of powder grades in a dehumidified air oven at 40 °C for 4–6 hours prior to weighing is a standard control measure. Compatibility with amine-based antioxidants and accelerators must be evaluated case by case; the presence of primary or secondary amines can induce premature polysulfide exchange reactions that reduce the effective scorch delay. Furthermore, the decomposition products evolved under extreme over-cure conditions include sulfur dioxide and carbon disulfide traces, mandating local exhaust ventilation above 0.5 m s⁻¹ face velocity on curing presses located in confined production halls. MBTS remains a reference accelerator in the rubber industry because it provides a reproducible, amine-free cure system whose scorch time and crosslink density can be modulated through ratio adjustments with secondary dithiocarbamates or guanidines without introducing the nitrosamine liabilities that have caused reformulation across the mechanical rubber goods and automotive sealing sectors. The availability of the disulfide as a free-flowing powder, a low-dust oil-coated variant, and a polymer-bound masterbatch supports handling across the range of manual and automated compounding operations encountered from small-batch laboratory mills to continuous automotive weatherstrip extrusion lines.