Acrylonitrile-butadiene copolymer (NBR) is a random elastomer produced by hot or cold emulsion polymerization of acrylonitrile and butadiene. Bound acrylonitrile content in commercial direct-supplied grades typically spans 18–50 wt%, while raw polymer Mooney viscosity ML(1+4) at 100°C ranges from 25–95 MU when tested per ISO 289-1:2018 or ASTM D1646. Cold-polymerised NBR, polymerised below 10°C, contains lower gel and a narrower branching distribution than hot-polymerised grades; this difference appears in extrusion head pressure and in the surface roughness of unsupported fuel hose after crossheading. Direct supply of NBR bales or compacted crumb is therefore specified not only by acrylonitrile content and Mooney viscosity but also by package geometry, pallet load stability, and maximum warehouse temperature. Bale cold flow can weld adjacent bales above 30°C, and the mill-room practice of pre-blending bales from multiple containers is necessary when lot-to-lot Mooney variation exceeds ±7 MU. The polymer is designated NBR under ISO 1043-1:2011 and ASTM D1418; compounding for evaluation follows ASTM D3182.

How Does Bound Acrylonitrile Content Govern Solvent Uptake and Low-Temperature Flexibility?

The bound acrylonitrile group raises the polar component of the solubility parameter, which controls equilibrium swelling in aliphatic and aromatic hydrocarbon media. In cured compounds containing 50 phr carbon black and 10 phr plasticizer, volume swell after 70 h in ASTM Reference Fuel C at 23°C per ASTM D471 typically ranges from 10–20% for 45 wt% ACN, 25–40% for 33 wt% ACN, and 50–80% for 18 wt% ACN. The same structural feature reduces low-temperature segmental motion. TR-10 values per ASTM D1329 shift from approximately -20°C to -30°C as ACN increases from 33 wt% to 45 wt%, while an 18 wt% ACN grade can remain flexible below -50°C. This inverse relationship is a property cliff-edge in fuel hose covers: a compound selected for sour gasoline resistance at 45 wt% ACN may crack on a cold-weather assembly line at -25°C even though its room-temperature tensile strength is higher. Compounders use differential scanning calorimetry per ISO 11357-2 to verify glass-transition width in direct-supplied NBR because broad Tg dispersion can produce brittle failure at temperatures 10–15°C above TR-10. Table 2 presents representative compounded ranges after 50 phr carbon black N550 and 10 phr plasticizer; exact values require grade-specific datasheet normalisation.

If the exact fluid combination or compounding package differs, published data for that specific configuration is limited; the ranges above should be used as ranking logic rather than acceptance limits.

During direct NBR supply to a rubber mixing facility, bale dimensions and palletised unit loads determine whether a receiving plant can feed an internal mixer without staging. Raw wrapped bales are frequently 700 × 350 × 150 mm, stacked 48 per EUR pallet to a gross unit load of approximately 1,200 kg. If incoming bales are exposed to relative humidity above 60% on a non-climate-controlled dock, surface moisture adsorption can exceed 0.5 wt%; pre-drying at 70–80°C for 2–4 h is required before adding carbon black to avoid steam porosity in hot-air-cured sheet. The weighing system on a 49 L intermeshing mixer has a tolerance of ±0.5 phr on carbon black; deviations above 1 phr alter modulus and compression set, therefore lot-to-lot compound density checks per ISO 2781 are used as a receiving control. A Mooney viscosity shift of 10 MU at constant screw speed on a cold-feed pin barrel extruder can alter output by more than 8% and raise melt temperature by 4–6°C. That temperature shift is sufficient to consume scorch safety time on a sulfur-donor cure package, which is usually specified with a moving-die rheometer ts2 of 1.5–2.5 min at 180°C per ISO 6502.

Direct NBR Supply: Incoterms, Payment Terms & Risk Allocation Table

Direct NBR supply contracts executed under Incoterms 2020 (ICC Publication 723E) allocate physical risk at defined points; payment terms allocate financial risk and are usually documented under UCP 600 or URC 522. Under EXW, the buyer bears all risk once baled NBR is placed at the seller’s warehouse. Under FCA, the seller completes export clearance and delivers to the buyer’s nominated carrier; risk transfers when the carrier receives the goods. Under CIP, the seller pays carriage to the destination but risk transfers to the buyer at the origin-handover point, and the seller must provide cargo insurance covering 110% of the contract value under Institute Cargo Clauses (A) or equivalent. Under DAP, delivery occurs when the goods are placed at the destination terminal ready for unloading, so the seller bears transport risk to that point. Under DDP, the seller carries risk through import clearance and import duty payment. Payment instruments typically include an irrevocable confirmed letter of credit at sight, documents against payment at sight, or open account after a registered audit; the documentary requirements depend on the Incoterm because a CIP transaction requires proof of insurance but a FCA transaction does not. A shipment of raw NBR under 30% advance payment and 70% against copy documents leaves the buyer exposed to non-delivery risk even when the Incoterm is EXW, confirming that payment terms and Incoterms govern different failure modes.

When the receiving compounder is in the European Union, the seller’s export documentation must be sufficient to support REACH registration or exemption, and the product must be classified under the correct Combined Nomenclature. If the NBR compound is intended for repeated food-contact uses, evidence under FDA 21 CFR 177.2600 or European Union Regulation (EU) 10/2011 may have to be secured by the party handling import clearance; otherwise, the shipment can be held at the port. These regulatory obligations are non-delegable by Incoterm unless the chosen rule explicitly places import clearance on one party, as DDP does for the seller and EXW does for the buyer.

When Carbon Black Dispersion Falls Below 4 µm in NBR Compounds

When carbon black dispersion in an NBR masterbatch is not maintained below the 4 µm threshold, cured tensile strength and extrusion surface quality deteriorate in direct-cut hose and profile lines. Dispersion per ASTM D2663 method B or reflected-light microscopy counts agglomerates larger than 5 µm; a compound with more than 10 agglomerates per 100 cm² at 100× cannot reliably pass burst-pressure requirements in high-pressure fuel hose tested per ISO 1402. Internal mixing with a 49 L tangential mixer requires carbon black N550 to be added at a ram pressure of 0.4–0.6 MPa and a dump temperature of 110–130°C; plasticizer is split-added after black incorporation because early addition reduces shear and leaves undispersed agglomerates above 20 µm. On a co-rotating twin-screw extruder with an L/D ratio of 40:1 and segmented screw elements, the feeding order of NBR crumb, zinc oxide, stearic acid, and carbon black in the first 4 D of barrel length is followed by atmospheric venting at 20 D. Injection moulding of these compounds requires clamp force of 0.4–0.6 kN/cm² of projected part area and nozzle melt temperature of 90–110°C, depending on cure system; if fill time exceeds 2 s, scorch at the gate produces surface laminations and the part must be rejected for dimensional non-conformance under ISO 2768-1.

For peroxide-cured NBR compounds, mixing controls differ because amine-based antioxidants and amine-containing processing aids can scavenge free radicals and reduce crosslink density. The cure package is commonly dicumyl peroxide at 4–6 phr on a polymer basis, with peroxide concentration verified by assay; a moving-die rheometer at 180°C per ISO 6502 should show a maximum torque increase of at least 10 dN·m over minimum torque. High-ACN NBR grades in peroxide systems often develop a scorch safety time below 1.5 min, which is insufficient for thick-section transfer moulding; semi-EV sulfur systems or sulfur-donor systems are then substituted, but the substitution sacrifices hot-air ageing retention. In a sulfur-donor cure with 0.8 phr sulfur and 2.5 phr tetrabenzylthiuram disulfide, tensile strength after 70 h at 125°C per ASTM D573 may drop by 20–30%, whereas a peroxide cure retains 80% of original tensile strength under the same conditions. The boundary for amine-containing additives is therefore strict: if a compound is to be peroxide-cured, the supplier must certify that the NBR is not coagulated with an amine-modified antioxidant.

Hot Tear Resistance Falls Abruptly Above 150°C in Sulfur-Cured NBR

Hot tear resistance in sulfur-cured NBR is governed by crosslink type and elastomer chain scission. The measured tear strength per ASTM D624 die C at 150°C can be 60–70% lower than the 23°C value for an N550-filled 33 wt% ACN compound. Above 150°C, polysulfidic crosslinks and weaker butadiene units undergo thermal degradation, producing a further loss of tear resistance and higher compression set. The processing window for sulfur-cured NBR is therefore effectively bounded by the onset of cure system reversion, which can be measured on a moving-die rheometer as a negative torque slope after T90 at 180°C. Compounds with total sulfur below 0.5 phr and a semi-EV accelerator ratio exhibit lower reversion but require mould temperatures of 160–170°C and longer cycles. Injection-moulded seals exposed to brief surface temperatures of 160–170°C can tolerate the condition only if the curing system is reversion-resistant and the part is post-cured for 4 h at 150°C.

In receiving-plant laboratories, immersion testing of NBR components in ASTM IRM 903 and Reference Fuel C provides a method to separate polymer quality from compound quality. A compound with bound ACN at 33 wt% immersed in IRM 903 for 70 h at 125°C per ASTM D471 should exhibit volume swell below 35%; if the same lot shows swell above 45%, the fault may originate from low bound ACN content, insufficient carbon black reinforcement, or plasticizer migration. Extraction in ASTM D297 can identify an overplasticized compound, and Fourier-transform infrared spectroscopy can confirm the bound nitrile level on the extracted rubber. For fuel-contact seals, a volume swell of 20–30% in Fuel C is often accepted because the seal remains swollen in service; the limiting property is not low swell but the retained tensile strength after drying, which can fall below 50% of the original when a low-ACN grade is exposed to oxygenated fuel. Direct-supplied NBR lots are therefore accepted only when the supplier’s certificate of analysis lists bound ACN by nitrogen analysis per ASTM D3533 or calibrated FT-IR traceable to ISO 17034, Mooney viscosity by ISO 289-1, and ash content by ISO 247, along with the lot-specific mixing date and bale traceability code.