N-Cyclohexyl-2-Benzothiazole
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HS Code |
554268 |
| Chemical Formula | C13H14N2S2 |
| Molecular Weight | 262.39 |
| Appearance | Typically a solid |
| Color | May be off - white to light yellow |
| Odor | Characteristic sulfur - containing odor |
| Melting Point | Around 160 - 165 °C |
| Solubility In Water | Insoluble in water |
| Solubility In Organic Solvents | Soluble in many organic solvents like benzene, toluene |
| Stability | Stable under normal conditions, but may react with strong oxidizing agents |
| Vapor Pressure | Low vapor pressure at room temperature |
As an accredited N-Cyclohexyl-2-Benzothiazole factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | N - Cyclohexyl - 2 - Benzothiazole packaged in 5 - kg bags. |
| Shipping | N - Cyclohexyl - 2 - Benzothiazole is shipped in well - sealed, corrosion - resistant containers. Transport follows strict chemical safety regulations, ensuring protection from physical damage and environmental exposure during transit. |
| Storage | **Storage of N - Cyclohexyl - 2 - Benzothiazole** Store N - Cyclohexyl - 2 - benzothiazole in a cool, dry, well - ventilated area away from heat sources and open flames. Keep it in tightly sealed containers to prevent moisture absorption and contact with air, which could potentially lead to degradation. Avoid storing near reactive chemicals to ensure its stability and safety. |
How CBS Influences Cure Reversion in Natural Rubber/Butadiene Rubber Tread CompoundsA passenger car radial tread formulation—typically a 70/30 or 80/20 blend of natural rubber and high-cis butadiene rubber—employs N-cyclohexyl-2-benzothiazolesulfenamide as the primary accelerator to balance the contradictory demands of high-speed mixed-phase extrusion and deep-section vulcanization. Dosing of CBS into a 1.5–2.0 phr sulfur system falls within 0.8–1.2 phr, adjusted by the carbon black structure; an N339 or N234 grade loaded at 50–65 phr with aromatic oil extension shifts the scorch onset by influencing accelerator adsorption on filler surfaces. Mixing is sequenced in an intermeshing tangential internal mixer with an effective chamber volume of 270 L (Farrel F270 or HF Mixing Group GK270), where polymer and black are masticated to dump temperatures 155–165 °C in the masterbatch stage, and the sulfenamide together with sulfur and activators is added on a 660 mm two-roll mill kept at 45–55 °C front roll to prevent thermal decomposition of the benzothiazole sulfenamide moiety into free 2-mercaptobenzothiazole. A dump temperature ceiling of 105 °C on the final pass is enforced; excursions beyond 112 °C are documented in plant shift logs to correlate with a 17–22 % reduction in Mooney scorch time (MS-t5 at 127 °C, ASTM D1646) and an unacceptably narrow processing window at the extruder die. Extrusion through a pin-type cold-feed extruder or a duplex triplex head requires a Garvey die exit temperature not exceeding 87 °C and a head pressure below 13.5 MPa; the CBS-dependent induction time must deliver a T5 exceedence of 22 min at 127 °C to survive residence time variations of ± 4 min originating from start-stop cycles on a dual-cavity tire-building machine. The vulcanization kinetics captured by a moving-die rheometer (MDR 2000, ASTM D5289) at 160 °C typically register a torque rise exceeding 1.8 dN·m/min between t10 and t50, followed by a plateau that descends into reversion when the isothermal hold is extended beyond 25 min. In the absence of an anti-reversion agent such as hexamethylene-1,6-bis(thiosulfate) disodium salt at 0.8–1.2 phr, the percentage reversion at 180 °C continuously vulcanized in a nitrogen-pressurized autoclave reaches 6.5–8.0 % measured as the drop from peak MH, compromising the tan delta at 60 °C and the laboratory abrasion resistance index against an ISO 4649 reference compound. Production-scale tire-building and curing presses operating at platen temperatures of 170–185 °C utilize bell-type or segmented mold technology where the reversion gradient from the tread surface to the sub-surface becomes the practical determinant of the scrapped rate; CBS-based compounds with a reversion resistance index (RRI, constructed from MDR torque decay) below 82 % are flagged by statistical process control. REACH registration of the sulfenamide (EC No. 202-411-2) demands a workplace exposure scenario that defines a derived no-effect level (DNEL) for inhalative exposure of 1.8 mg/m³, integrated into mixing-room air-extraction design to stay below an eight-hour time-weighted average of 0.25 mg/m³ as recommended by the manufacturer’s extended safety data sheet Section 8. Terminal performance testing of the cured tread stipulates tensile strength retention at ≥ 95 % after 72 h at 100 °C (ISO 188, method A) along with DIN abrasion loss below 115 mm³. The CBS molecule—owing to its cyclohexyl amide substituent—liberates cyclohexylamine during vulcanization, and the residue above 0.15 wt% determined by headspace GC/MS according to a modified VDA 278 protocol becomes a controlled substance in interior vehicle air quality specifications aligned with ISO 12219-1. Laboratory data from a leading tier-1 tire manufacturer’s published quality manual indicates that a 0.1 phr upward deviation in CBS addition shifts the storage modulus at 30 °C by 0.7–1.1 MPa, measurable on a dynamic mechanical analyzer (DMA) at 10 Hz, stiffening the tread edge and reducing wet-skid performance on a British Pendulum tester (BS EN 13036-4) by a statistically significant margin. Steel cord adhesion in a standard passenger car belt skim compound, where a high-sulfur, high-zinc oxide matrix meets a cobalt salt adhesion promoter, presents a distinct set of accelerator constraints. The skim formulation typically begins with 100 phr natural rubber (TSR 20 or SIR 20) filled with 55–60 phr N326 carbon black and includes 7–9 phr active zinc oxide alongside 4.5–5.2 phr insoluble sulfur. CBS is introduced at a restrained level of 0.5–0.8 phr, never exceeded because free amine buffering from its decomposition can compete with the cobalt carboxylate complex at the brass-coating interface and degrade the CuxS crystalline layer required for adhesion. The partial substitution of CBS by dicyclohexyl-2-benzothiazolesulfenamide (DCBS) at 0.2–0.4 phr is frequently employed to further delay the scorch without inducing an overcured network state in the 3–5 mm rubber interstice between adjacent steel cords. A tangent rotorless curemeter (ISO 6502) run at 145 °C must yield a t10 of 6.5–9.0 min and a t90 of 28–34 min to align with a high-pressure bladder press cycle of 22–26 min at 160 °C. A critical processing bottleneck emerges in the single-pass internal mixing routine where the cobalt naphthenate (10–12 % cobalt content) and sulfenamide are added early enough to ensure dispersion but late enough to avoid a temperature spike above 108 °C; an exotherm triggered by the accelerator-accelerated sulfur ring opening can lead to a localized viscosity collapse that, according to an internal quality audit at a European calendering plant, increased wire-coating void count by 3.2 % per thousand meters of skim-coated cord fabric inspected via X-ray transmission at 30 kV. Adhesion is quantified under steam-cure conditions (20 min at 165 °C) using an Instron pull-out fixture according to ASTM D2229, and the minimum acceptable pull-out force for 2+2x0.30 brass-plated cord at 23 ± 2 °C is set at 58 N; any CBS batch lot showing a melting-point depression below 98 °C (pure standard 99–103 °C) must be quarantined and retested for free 2-mercaptobenzothiazole contamination interfering with the sulfur-to-cobalt ratio at the adhesive interphase. When High-Temperature Conveyor Belt Cover Stocks Demand Delayed-Action AccelerationA rubber cover compound destined for a continuous-belt sinter-plant conveyor operating at a material surface temperature of 170–190 °C for 12 000 h accumulated service couples styrene-butadiene rubber (SBR 1502) with a minor natural rubber phase (15–20 phr) to confer green strength. The sulfenamide CBS concentration is deliberately elevated to 1.2–1.6 phr because the prevailing belt-press cure—a Rotocure drum or an Auma continuous double-belt press running at 0.3–0.8 m/min with a 200–220 °C surface contact temperature—imposes a heat-transfer-limited induction period that must be extended yet followed by a rapid cure rate once the compound passes the nip. A pre-vulcanization inhibitor N-(cyclohexylthio)phthalimide (CTP) is co-dispensed at 0.15–0.30 phr via a masterbatch chip form to increase the Mooney scorch safety margin by an additional 9–14 min without flattening the torque curve from the CBS activation. Compounding is executed in a low-ram-piston internal mixer of 190 L net volume (GK190E) where the final mixing stage is downward-temperature-controlled to a dump of 98–102 °C; mixed stock is subsequently strained through a gear-pump screen changer fitted with 120 mesh filters to catch undispersed agglomerates that could nucleate thermal-oxidative failure under ISO 1431 DCB testing. The cured cover requires a tensile strength retention of at least 65 % after hot-air aging for 168 h at 125 °C (ISO 188, cell method) and an abrasion loss below 130 mm³ per ISO 4649:2021 with a non-rotating sample. Because the benzothiazole sulfenamide sulfur donor system generates polysulfidic crosslinks that rearrange into mono- and disulfidic bonds during the belt’s thermal service, the CBS loading is precisely traded off against secondary accelerators: a co-catalytic system of tetramethylthiuram monosulfide (TMTM) at 0.25 phr reduces the post-cure network maturation drift in Shore A hardness from +4 points to +1 point over the first 4 000 h of operation, as confirmed by periodic ultrasonic thickness-gauge measurements and hardness logs from haulage-side maintenance crews. An incompatibility is noted with zinc-free systems attempting to use magnesium oxide solely; CBS activation requires a sufficient zinc oxide reservoir (4–6 phr indirect ZnO) to generate the active zinc–accelerator complex, and concentrations below 3 phr lead to an unanticipated trough in the vulcanization isotherm that the MDR detects as a secondary torque dip interpretable as premature decomposition of the intermediate 2-mercaptobenzothiazole zinc salt before crosslinking proceeds to completion. EPDM profiles extruded for automotive weatherstrips, characterized by an ethylene-norbornene terpolymer backbone with an ENB content of 4.5–6.5 wt% and a medium Mooney viscosity (55–70 ML 1+4 at 125 °C), utilize CBS at 0.8–1.2 phr to synchronize vulcanization with microwave-hot-air-line throughputs of 18–25 m/min. The accelerator is fed in a predispersed 75 % active microgranule format to eliminate dust and improve weighment accuracy within ± 0.02 phr on a gravimetric dosing unit bolted to the throat of a pin-barrel cold-feed extruder equipped with a 120 mm screw of 20:1 L/D. A spout-fluidized-bed vulcanization unit downstream combines a 2.45 GHz microwave cavity with a 6 m hot-air zone, maintaining a profile temperature ramp of 12 °C/s; the CBS-specific scorch delay of 40–55 s at 180 °C ODR torque rise prevents pre-crosslinking at the die land that otherwise manifests as melt fracture in a micro-diamond-polished die with a gap of 0.8 mm. A documented operational boundary involves the solubility limit of CBS in EPDM above 1.5 phr—measured by quantitative FTIR microscopy of bloom on a pressed plate stored for 30 days at 25 °C and 60 % relative humidity—exceeding the threshold of 0.12 absorbance units at 1460 cm⁻¹, which corresponds to visible surface frost unacceptable in German Association of the Automotive Industry (VDA) Class A visible sealing surfaces. The final sponge or dense profile is tested for compression set under constant deflection according to ISO 815-1:2019 after conditioning at 100 °C for 24 h; CBS-synergized formulations utilizing a secondary guanidine (DPG at 0.4 phr) routinely achieve a set value below 35 % for dense compounds, while the omission of CBS in favor of an ultra-fast thiuram-only system increases the set to 52–58 % and creates an unacceptable fish-scale surface in a Haake rheometer extrudate recorded at a shear rate of 500 s⁻¹. All raw materials covered by a FDA 21 CFR 177.2600 reference for “rubber articles intended for repeated use” are selected where the sealing line interfaces with painted metal, and CBS residual-free amine limits are validated by aqueous Soxhlet extraction followed by HPLC-MS to remain below the specific migration limit of 0.05 mg/kg food-simulant. Anti-Vibration Mount Compounds: Balancing Dynamic Stiffness and Fatigue Life Through Accelerator SynergyNatural rubber formulations for large-diameter shear-type anti-vibration mounts supporting stationary diesel generators and railway coach underframes rely on an efficient or semi-efficient vulcanization regime where the sulfur level is reduced to 0.6–0.9 phr and the CBS dosage raised sharply to 2.2–2.8 phr, complemented by a small quantity of tetrabenzylthiuram disulfide (TBzTD) at 0.15 phr to cap the cyclic-shear storage modulus drift below 0.18 MPa per decade of frequency sweep from 1 to 15 Hz (ISO 10846-2). High-performance mixing is carried out in a 320 L interlocking-rotor internal mixer with ram pressure maintained at 0.55–0.65 MPa and rotor speed modulated from 40 to 25 rpm after carbon black incorporation to prevent a temperature excursion beyond 82 °C when CBS is added—a critical constraint derived from differential scanning calorimetry data showing onset of accelerator decomposition at 92–96 °C in an air atmosphere at 10 K/min. The compound must survive 3×10⁶ cycles on a servo-hydraulic dynamic test frame at a static pre-compression of 1.8 MPa superimposed with a dynamic amplitude of 0.45 mm without crack nucleation visible at × 5 magnification under a stereo microscope, a criterion that a full-CBS system achieves when the crosslink density, measured by equilibrium swelling in toluene (Flory-Rehner calculation per ISO 1817), rests between 4.5×10⁻⁵ and 5.2×10⁻⁵ mol/cm³. The CB spring-hardening artifact observed at CBS concentrations above 3.0 phr is ascribed to monosulfidic over-crosslinking catalyzed by residual cyclohexylamine, which attacks the polysulfidic bridges in a S8-starved environment; a quantitative NMR analysis of the vulcanizate after pyrolysis confirms an increase in the ratio of mono- to disulfidic linkages from 1.6 to 2.7, degrading the elongation-at-break from 580 % to 470 % in a standard ring test at 500 mm/min (ISO 37 Type 2). Therefore, the upper CBS ceiling in mount recipes is enforced by statistical process control at the weigh-station rather than by laboratory after-cure rheometry. A manufacturing-side experience documented in a bearing producer’s non-conformance report describes a batch where a weigh-belt fault delivered 3.3 phr CBS; the subsequent mounts exhibited a 19 % reduction in fatigue crack initiation life in a prototype testing program, traced to the formation of a brittle oxidized skin identifiable by energy-dispersive X-ray microanalysis of sulfur-zinc ratios at the torn surface. The mounts are post-cured for 4 h at 70 °C to complete the rearrangement of the crosslink architecture and subjected to REACH-restricted substance screening for any benzothiazole derivatives classified as skin sensitizers category 1.
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Introduced to industrial rubber compounding in the 1960s, N-Cyclohexyl-2-Benzothiazole (abbreviated CBS, CAS 95-33-0) is the primary sulfenamide accelerator of choice where an extended scorch safety margin must be preserved through high-temperature processing stages. Supplied as a pale-yellow to greyish-white granule or powder with a melting onset of 96–101 °C and an ash content below 0.3 % (ISO 1125), the compound functions by a thermally triggered decomposition that releases 2-mercaptobenzothiazole and a cyclohexyl amine radical at vulcanization temperatures. Its molecular weight of 264.41 g mol⁻¹ and density of 1.27 g cm⁻³ (at 20 °C) facilitate homogeneous metered feeding in continuous mixer lines, but the sensitivity of the sulfenamide bond to moisture demands storage below 30 °C and at relative humidity not exceeding 60 %—failure to observe this leads to premature hydrolysis, acid by-product formation, and a measurable reduction in accelerator activity as verified by oscillating disc rheometry per ASTM D2084-19a.
In a twin-screw extruder fed with a natural rubber/butadiene rubber masterbatch, CBS routinely yields a Mooney scorch time (MS-t5 at 121 °C, ASTM D1646-19a) exceeding 28 minutes at 0.8 phr loading, compared to 19 minutes for N-tert-butyl-2-benzothiazolesulfenamide (TBBS) at equivalent molar dose. This differential in processing latency is exploited in the manufacture of large off-the-road tyre sections, where heat build-up in the core of a 150 kg blank can initiate crosslinking prior to full mould fill if the scorch window is inadequate. Plant data recorded on a 55 L intermeshing mixer with a ram pressure of 0.6 MPa show that dump temperatures reaching 155 °C are tolerated without incipient scorch when CBS is paired with 0.2 phr of cyclohexylthiophthalimide (CTP) as a prevulcanization inhibitor, whereas the same masterbatch with TBBS exhibited visible grain formation at the batch surface.
Measurements on a moving die rheometer (MDR, ASTM D5289-19a) at 170 °C for a silica-reinforced solution SBR compound containing 2.0 phr CBS reveal a maximum torque (MH) retention of 94 % after 10 minutes post-cure plateau, whereas an equivalent formulation accelerated with TBBS drops to 86 % under identical conditions. The broader stability window is attributed to the relatively slower thermal cleavage of the cyclohexylamine-sulfur bond, which moderates the concentration of active crosslinking species and reduces the rate of polysulfidic crosslink shortening. This property translates directly into improved blow-out resistance in high-speed passenger tyre shoulders, where internal temperatures can exceed 130 °C under sustained highway operation. Thermal ageing studied per ISO 188:2023 (100 °C for 72 h) confirms that CBS-cured vulcanizates retain 78 % of original tensile strength (ISO 37:2017, Type 2 dumbbell), outperforming TBBS-based stocks by 11 percentage points under the same protocol, albeit with a slightly lower absolute crosslink density as inferred from equilibrium swelling in toluene.
Continuous spiral oven curing of ethylene-propylene-diene monomer (EPDM) profiles at line speeds of 12 m min⁻¹ and a hot air temperature of 230 °C represents a processing regime where the delayed action of CBS can become a liability without formulation adjustments. Screw plastication prior to the die head generates shear heating that elevates stock temperature to 108–114 °C; at this range CBS alone reaches only 8 % of its ultimate cure state upon entry to the oven, causing dimensional instability in the first metre of the haul-off. By substituting 20 % of the CBS content with the ultra-fast thiuram accelerator tetrabenzylthiuram disulfide (TBzTD), the early-stage crosslink density at the die exit increases by 3.2 dN m of torque (MDR, 180 °C), sufficient to eliminate sag. This dual-accelerator approach must be balanced against a shortened scorch time, as t2 at 121 °C falls from 36 min to 14 min when TBzTD is introduced—a shrinkage in the safe processing envelope that forces batch scheduling into a just-in-time sequence.
The European tyre industry’s drive toward zinc oxide reduction (EU 2016/1005 amendment to REACH Annex XVII) has compelled reformulation of many accelerator packages. CBS retains comparable vulcanization efficiency down to 1.5 phr ZnO in a NR/BR conveyor-belt cover compound when combined with a zinc glycerol complex as a soluble zinc donor, generating a t90 value of 4.8 min at 160 °C compared to 4.2 min with a conventional 5 phr ZnO system. Below 1.0 phr ZnO, however, the accelerator begins to lose selectivity; crosslink distributions measured via thiol-amine chemical probe analysis show an increase in the proportion of monosulfidic to polysulfidic crosslinks from 0.25 to 0.42, correlating with a drop in elongation at break below 420 % (ISO 37). This threshold represents a hard formulation boundary: published data for CBS at sub-stoichiometric zinc levels in high-abrasion furnace black-filled matrices is limited, and trial lines frequently record a sharp rise in compression set (ASTM D395-18, Method B, 70 °C/24 h) from 22 % to 41 % once the zinc oxide fraction dips beneath the critical 1.0 phr mark.
Secondary amine-derived sulfenamide accelerators are subject to nitrosamine control under German TRGS 552 and the French Arrêté of 15 November 2016 because volatile N-nitrosamines can form during curing and migrate into rubber articles. CBS, derived from cyclohexylamine, yields N-nitrosocyclohexylamine at a level of 0.8–1.2 µg g⁻¹ in a carbon-black-filled NR compound cured at 160 °C for t95, as detected by GC-TEA according to ISO 29941:2010. This value sits below the typical range for N-nitrosodiphenylamine from the benzothiazyl disulfide (MBTS)-diphenylamine system but notably above the 0.1 µg g⁻¹ threshold enforced for baby bottle teats under Directive 93/11/EEC. Consequently, CBS is excluded from closed-loop food-contact applications that lack a washing or extraction step, while it remains acceptable for industrial rubber goods under a general migration limit of 10 mg dm⁻² (EU 10/2011). For nitrosamine-sensitive applications, the non-nitrosatable dibenzylamine-derived accelerator DCBS (N,N-dicyclohexyl-2-benzothiazolesulfenamide) is often substituted, though DCBS exhibits a substantially slower cure rate, shifting t90 from 5.2 min to 11.4 min at 150 °C.
The interaction between CBS and silica-silane coupling agents is central to the “green tyre” concept. When CBS is dosed at 1.4 phr into a highly-dispersible silica-filled SSBR/BR tread with bis(triethoxysilylpropyl) tetrasulfide (TESPT, 6.4 phr), the accelerator participates in a complex competition: the silanization reaction consumes ethoxy groups and releases ethanol, which can protonate the basic amine cleavage products of CBS and shift the vulcanization pH downward. This pH drift reduces the rate of sulfur crosslinking unless compensated by an alkaline co-agent. Factory monitoring data from a 320 L tangential mixer show that ethanol concentration in the dump gas rises to 140 ppm within 90 s of CBS addition; when diphenylguanidine (DPG) is incorporated at 1.8 phr as a secondary accelerator and alkalinity buffer, the ethanol peak drops to 95 ppm and the crosslink density (MRD Δtorque) climbs by 12 %. This synergy, however, narrows the mixing temperature window to 145–155 °C—exceeding 160 °C triggers premature silane coupling, which immobilizes the filler surface and prevents the efficient dispersion of CBS agglomerates below 2 µm primary particle size.
| Accelerator | ts2 (min) | t90 (min) | MH‑ML (dN·m) | Tensile strength (MPa) | Elongation at break (%) |
|---|---|---|---|---|---|
| CBS, 1.2 phr | 7.8 | 12.3 | 18.2 | 24.6 | 521 |
| TBBS, 1.0 phr | 5.2 | 8.7 | 19.5 | 25.9 | 487 |
| DCBS, 1.5 phr | 15.4 | 26.1 | 17.1 | 22.8 | 558 |
In closed-cell sponge profiles for automotive weatherstripping, the delayed gas-release behaviour of CBS creates a different set of constraints. Nitrogen evolved from the decomposition of the sulfenamide contributes to cell nucleation, but the timing of peak gas generation must align with the polymer matrix’s minimum viscosity when the expansion agent decomposes. Rheological profiles obtained via Rubber Process Analyzer (RPA) at 180 °C indicate that CBS produces a maximum gas evolution rate at 2.8 min, whereas azodicarbonamide-based blowing agents reach peak decomposition at 3.5 min. This mismatch results in coarse, irregular cell structures unless a kicker—typically a small addition of zinc dibenzyldithiocarbamate—is used to advance the CBS decomposition. Published plant trials from a continuous microwave/hot-air line confirm that co-adding 0.3 phr of the dithiocarbamate reduces the density of the EPDM sponge from 0.68 g cm⁻³ to 0.51 g cm⁻³ without surface collapse, a result directly reflected in compression set improvement from 38 % to 21 % (ASTM D1056-20).
While CBS remains the sulfenamide anchor for general-purpose industrial rubber goods ranging from vibration dampers to hydraulic hose covers, its performance in wholly saturated hydrocarbon elastomers such as ethylene‑vinyl acetate copolymer (EVM) is marginal. Peroxide‑cured EVM systems do not engage the sulfur‑donor mechanism of CBS, and the residual amine by‑products have been observed to neutralize acidic coagents, leading to a cure state depression of up to 18 % in MH (MDR, 180 °C) when CBS is inadvertently added through equipment cross-contamination. For this reason, dedicated production cells with sealed feed hoppers and separate carbon black transport lines are mandated when CBS is part of the material portfolio, as even 0.1 % carryover into a peroxide stream triggers unanticipated hardness drift and elevated tension set in finished goods.
