Benzothiazole, 2-(4-Morpholinylthio)-

While the tread compound of a passenger car radial exhibits a complex balance of rolling resistance, wet grip, and abrasion resistance, the choice of primary accelerator governs not only cure kinetics but also the reversion resistance of the polyisoprene matrix at prolonged high-temperature service. In a typical SSBR/BR blend containing 30–40 phr high-cis butadiene rubber and 60–70 phr solution SBR extended with 37.5 phr TDAE oil, 2-(4-Morpholinylthio)benzothiazole is dosed at 0.8–1.2 parts per hundred rubber (phr) together with 2.0–2.5 phr insoluble sulfur (OT-20 grade) and a secondary sulfenamide, often TBBS at 0.2–0.4 phr, to tailor the scorch delay. Data from a Krupp GK 255 E intermeshing mixer show that the masterbatch must be dropped below 110°C to avoid premature generation of 2-mercaptobenzothiazole fragments that diminish scorch safety. Mooney viscosity ML(1+4) at 100°C is maintained between 55 and 70 MU, and Mooney scorch t5 at 127°C exceeds 27 min under ISO 289-1:2015. Final acceleration by MBS yields a curemeter t90 of 6.5–8.5 min at 160°C (ISO 6502, 0.5° arc) and a delta torque of 14–20 dNm, providing crosslink densities that contain reversion below 3% after 60 min at 160°C as per ASTM D5289. The finished tire tread must meet DIN 53516 abrasion loss below 120 mm³ and tensile strength above 18 MPa (ISO 37). Production note: when ambient relative humidity exceeds 65%, the hygroscopic MBS powder should be pre-dried at 40°C for 4 h to prevent micro-void formation in the cured tread shoulder.

Steel Cord Skim Stocks and the Onset of Premature Vulcanization

The compound formulation applied to the rubber skim surrounding brass-coated steel cords in a radial tire carcass requires a sulfenamide accelerator that maintains a delayed-action profile even in the presence of adhesion-promoting cobalt stearate complexes. 2-(4-Morpholinylthio)benzothiazole is incorporated at 0.6–1.0 phr in the NR-rich (typically 85–100 phr NR, with 0–15 phr BR) skim stock, together with 4–6 phr insoluble sulfur (IS-60), 0.8–1.5 phr cobalt neodecanoate (as Cobalt 21%), and a methylene donor/acceptor system (e.g., resorcinol-HMMM) contributing to the in-situ formation of a Cu₂Sₓ interlayer. On a Farrel F200 Banbury-type mixer, the single-stage mixing cycle adjusts final cooling to achieve a batch dump temperature not exceeding 105°C; any excursion above 115°C can trigger the dissociation of the S–N bond in MBS, liberating free amine moieties that accelerate the degradation of the brass coating adhesion by shifting the Cu/S ratio outside the optimal octahedral crystal lattice value of 1.7–2.0, as verified by wire adhesion pull-out tests following ASTM D2229-21. Cure rates at 155°C plate press vulcanization are adjusted to a t90 of 10–15 min, reaching a crosslink density (ν₆) of 1.2–1.8 × 10⁻⁴ mol/cm³, sufficient to limit wire coating corrosion when exposed to saline environments under ISO 7492:2021. The finished ply compound must retain a pull-out force above 450 N after 7-day humid ageing (85°C, 85% RH) and comply with the cord-to-rubber adhesion criteria of ECE R30.

A 4-ply EP fabric carcass with a 6 mm / 3 mm SBR/NR blend cover destined for bulk material handling in open-pit mines relies on the combination of 2-(4-Morpholinylthio)benzothiazole with a booster such as diphenylguanidine (DPG) to secure sufficient crosslinking through the cover’s thickness without surface overcure. MBS is charged at 1.2–1.8 phr alongside 2.5–3.0 phr polymeric sulfur (Crystex HD OT 20) and 0.4 phr DPG in a 70/30 NR/SBR base polymer; the higher MBS loading compensates for the long heat transfer lag in the 2-meter-wide Rotocure continuous vulcanization cylinder where residence times approach 20–30 min at 160°C. Processing records from an HF Mixing Group intermeshing mixer highlight that the masterbatch temperature must be capped at 100°C and the incorporation of MBS as a pre-dispersed masterbatch (65% active on EPDM binder) reduces the risk of undispersed accelerator hotspots that can cause local reversion craters in the cover’s top layer. The cured belt cover achieves a hardness of 65±5 Shore A (ISO 48-4), tensile strength ≥ 20 MPa, and an elongation at break of 450–550% according to ISO 37:2024; abrasion resistance measured under ISO 4649 delivers a volume loss ≤ 150 mm³. Compliance with the European Union’s REACH regulation Annex XVII restricted substance list and the Mining Industry’s MSHA flame-resistance test for conveyor belting is documented through batch-specific test reports.

What Distinguishes MBS-Accelerated EPDM Profiles from TBBS Systems in Dense/Sponge Co-extrusion?

Co-extruded EPDM sealing profiles for automotive body closures demand a cure system that harmonizes the decomposition rate of azodicarbonamide blowing agent with the crosslinking progression of the dense skin layer. When 2-(4-Morpholinylthio)benzothiazole replaces TBBS in a 0.9–1.3 phr dose within a 50/50 EPDM (ENB content 4–5 wt%) blend extended with 80 phr N550 carbon black and 60 phr paraffinic oil, the scorch curve measured at 130°C on a Moving Die Rheometer shifts t2 from 4.2 to 7.8 min, widening the processing window for the microwave-hot air continuous vulcanization line operating at 230°C air temperature and 500 W microwave power. The accelerator system is supplemented with 1.5 phr ZBEC, 0.6 phr sulfur, and 2.0 phr zinc oxide; because MBS contributes little secondary amine release during cure, the volatile organic compounds (VOC) and fogging values tested according to VDA 278 and DIN 75201 remain below 300 µg/g and 0.8 mg, respectively, meeting the Daimler DBL 5556 specification for interior odour. Plant experience shows that if the extruded profile’s surface temperature exceeds 115°C before the gelation zone, micro-blisters form at the sponge-core interface due to premature crosslinking of MBS-generated mercaptobenzothiazole residues — a failure mode not observed with straight TBBS but resolved by keeping the extruder barrel temperature in Zones 2–4 below 95°C. The final component, after vulcanization and a 2-h post-cure at 120°C, must pass compression set testing at 70°C for 22 h (ISO 815-1) with a set below 35% and demonstrate no interlayer delamination under a 150% elongation tensile test at -30°C.

NBR Inner Tubes in Contact with Phthalate-Free Hydraulic Fluids

Nitrile rubber grades selected for hydraulic hose inner tubes transferring biologically sourced hydraulic esters (HEES) must resist swelling while retaining low compression set after 1,000 h at 100°C. In a 34% ACN NBR formulation filled with 70 phr N770 carbon black and 10 phr dioctyl adipate, 2-(4-Morpholinylthio)benzothiazole is introduced at 0.7–1.0 phr together with 1.2 phr tetramethylthiuram monosulfide (TMTM) and 1.8 phr sulfur. The MBS/TMTM combination yields a t90 of 8–10 min at 160°C and a peak cure torque (M₅) of 11–13 dNm, creating a network that limits volume swell in Shell Naturelle HF-E46 fluid to under 8% after the 168-h immersion test of ISO 1817:2022. A critical manufacturing control: the unvulcanized hose tube must be extruded through a 90-mm cold-feed pin extruder with a screw L/D of 16:1 and a die temperature of 85°C ±3°C; if the stock temperature reaches 110°C because of excessive screw speed above 50 rpm, the scorch safety margin collapses, and gel particles appear on the inner bore, leading to burst failures below the 2× rated working pressure required by EN 853 1SN. The wrapped cure is performed in a steam autoclave at 152°C for 45 min. The finished tube, after braiding, must pass a 200,000 impulse cycle test per ISO 6803 at 100°C without leakage and show no migration of accelerator residues that exceed the 0.5% total extractable limit required by EU 1935/2004 for incidental food contact during potable water hose applications.

When a 65±5 Shore A NR Compound Must Maintain Dynamic Stiffness over 10⁶ Cycles

A natural rubber engine mount operating at resonance frequencies between 12 and 28 Hz under a static preload of 800 N exposes the vulcanizate to dynamic creep that is directly governed by the crosslink structure homogeneity — a parameter strongly influenced by the accelerator system. With 2-(4-Morpholinylthio)benzothiazole dosed at 0.6–0.9 phr and a low free sulfur addition of 1.4–1.7 phr, the cure at 150°C in a multi-cavity compression mold yields a predominantly monosulfidic crosslink ratio above 65% (as estimated by thiol/amine chemical probe analysis), which restrains dynamic stiffening to less than 15% from the initial Kd value of 300 N/mm after 1×10⁶ fatigue cycles on an MTS 831 elastomer test system following ISO 4664-1:2022. The mount’s rubber body must also resist ozonolysis; the required 50 pphr of antiozonant 6PPD is added in the masterbatch while MBS is introduced in the final mixing stage at 60°C to avoid premature decomposition. Empirical evidence from production runs on a REP injection press with a vertical clamp of 200 tonnes demonstrates that a mold temperature of 155–160°C and a cure time of t90 + 3 min (totaling 8 min) suppress mould-fouling episodes that occur when residual morpholine groups condense on the vent pins. The cured component is validated against the OEM’s PV 3310 specification for dynamic durability and must maintain its 65±5 Shore A hardness within 5 points after heat ageing at 110°C for 70 h (ISO 188).