Acrylonitrile-butadiene copolymer (NBR) is an emulsion-polymerized random elastomer whose bound acrylonitrile content controls equilibrium swelling in aliphatic hydrocarbons, low-temperature stiffening, fuel permeation, and cured-modulus response. Commercial cold polymerization is typically conducted between 5 °C and 25 °C to limit gel formation and branching while preserving accelerator response. Raw polymer characteristics are reported by Mooney viscosity ML(1+4) 100 °C, specific gravity near 0.98–1.00, and ash content below 0.5 wt% when calcium chloride or aluminum sulfate coagulants are controlled. NBR is supplied as compressed bales, crumbs, dusted powder, or oil-extended bales, and each form imposes distinct mixing, conveying, weighing, and pre-blending constraints in downstream manufacturing.

Request an NBR Quotation: What We Need From You to Quote in 24 Hours

The quotation workflow for an NBR compound requires a defined set of raw polymer parameters, target vulcanizate performance values, and the applicable compliance framework. Without a bound acrylonitrile value and Mooney range, batch selection cannot be aligned to either oil resistance or flow characteristics. A 24-hour response is practicable when the data in the following table accompanies the inquiry. Hardness alone is insufficient because Shore A does not define oil swell, cure state, low-temperature retraction, or dynamic load-bearing behavior.

For custom compounds containing carbon black N220, N330, N550, or N774, the filler loading and aggregation characteristics should be declared because carbon black surface area changes tensile modulus, compression set, and dynamic heat build-up. Plasticizer type—DOP, DINP, DOS, TOTM, or ether-thioester—must be specified when low-temperature performance or fuel extraction is relevant. If the compound is destined for drinking-water contact, medical use, or food contact, the relevant migration declaration under FDA 21 CFR 177.2600, EU 10/2011, or ISO 10993 should be declared at the inquiry stage, as these constraints exclude certain antioxidants, accelerators, and processing aids.

How Do Bound Acrylonitrile and Mooney Viscosity Shape the Processing Envelope?

Bound acrylonitrile is the principal structural variable. At 18% ACN, volume swell in ASTM IRM 903 after 168 h at 100 °C commonly exceeds 45 volume %; at 45–50% ACN the same test usually yields values below 10 volume %. The trade-off appears in low-temperature behavior: higher ACN raises glass transition toward -20 °C, while lower ACN retains flexibility below -50 °C but loses barrier performance. A shift of 5% ACN can alter temperature retraction TR-10 by 6–10 °C depending on filler loading and plasticizer selection. Mooney viscosity determines shear heating, die swell, mold filling, and the ability to incorporate high filler volumes without exceeding mixing torque limits.

The tabulated ranges reflect supplier technical bulletins and historical compounding data rather than a universal grade certificate. Specific grade values control batch selection. Where an application requires simultaneous low-temperature flexibility and low swell, published data for raw NBR alone is insufficient; compounded data using the intended plasticizer and filler system are mandatory.

Curative selection determines the crosslink architecture and thermal-oxidative stability of the vulcanizate. Conventional sulfur systems at 1.5–2.5 phr sulfur with sulfenamide accelerators produce mixed sulfide crosslinks and provide high tensile and tear strength. Efficient vulcanization and sulfur-donor systems favor monosulfidic crosslinks and improve heat resistance but reduce fatigue life under dynamic strain. Peroxide-cured NBR compounds develop carbon-carbon crosslinks with superior compression set at temperatures above 100 °C, yet the cure reaction is sensitive to oxygen and is inhibited by amine antidegradants, certain aromatic process oils, and acidic fillers. Moving-die rheometer data according to ASTM D5289-19a or ISO 6502-2 should define minimum torque, scorch time ts2, and optimum cure time tc90 for each batch.

Processing of NBR begins with mastication and incorporation of carbon black, plasticizer, zinc oxide, stearic acid, and antioxidant in an intermeshing internal mixer. Fill factors of 0.70–0.80 and ram pressures below 0.50 MPa are common for high-viscosity grades; mixing is typically discharged at 105–125 °C to prevent scorch when sulfur donors are included. Two-roll mill addition of curatives requires roll temperatures of 35–55 °C and friction ratios near 1.15:1; tight nip settings below 0.5 mm improve accelerator distribution but raise local shear heating. Injection molding of NBR compounds at Mooney ML(1+4) 100 °C below 50 MU is generally feasible with barrel temperatures from 60 °C to 90 °C and mold temperatures from 160 °C to 200 °C. Higher-viscosity stocks may require transfer or compression molding; clamp force above 2,500 kN may be necessary for large seal plates to maintain flash control. Batch-to-batch Mooney drift of ±5 MU alters injection-molding shot weight stability and requires barrel temperature correction on production lines with shot-mass consistency limits below 1%.

Low-Temperature Flexibility and Oil Resistance Are Balanced by ACN Ratio

Low-temperature flexibility is measured by brittleness temperature in ASTM D2137, temperature retraction in ISO 2921, or Gehman stiffness in ISO 1432. A high-ACN NBR at 40–50% ACN produces good barrier and lower swelling but begins to stiffen below -25 °C, which can cause lip seal leakage in cold crankcase applications. A low-ACN grade at 18–21% ACN retains flexibility near -50 °C but swells more than 50% in IRM 903. For outdoor sealing, NBR compounds are susceptible to ozone cracking because the unsaturated butadiene backbone reacts with atmospheric ozone. Para-phenylenediamine antidegradants at 1–2 phr can extend static ozone resistance under ASTM D1149 but cannot provide continuous dynamic ozone protection; moving components exposed to ozone require blending with polyvinyl chloride, epichlorohydrin, or a more saturated polymer.

Raw NBR bales stored under ambient ozone, ultraviolet light, or in proximity to copper and manganese salts undergo surface oxidation and gel formation. ISO 2230:2017 recommends storage below 35 °C, relative humidity below 65%, and stock rotation within 24 months from production. Condensation moisture on cold bales should be avoided; if bales are transferred from cold storage to a warmer compounding area, a conditioning period of 12–24 h is typical before internal mixing. Pre-drying at 60–80 °C for 2–4 h is required when compound moisture exceeds 0.5 wt% or when molding porosity is detected. Peroxide-cured stocks must exclude air-retarding amine antidegradants and certain sulfur donors, as premature free-radical scavenging leads to lower crosslink density and higher compression set.

When NBR Is Specified for Fuel System Components, Additional Data Required

Fuel hose, diaphragm, and seal compounds require more than raw polymer ACN and Mooney data. The target compound must be tested against ASTM D471-16a in ASTM Fuel A, Fuel B, Fuel C, or ethanol-blended fuels. Permeation coefficients determined by ASTM D814-95 or cup methods should be stated if the part is subject to evaporative emission limits. Higher ACN grades at 40–50% reduce aromatic fuel swelling and permeation but exhibit elevated TR-10; a cold-climate fuel seal specified below -30 °C may require an HNBR or low-ACN blend, which in turn raises permeation. Biodiesel and aggressive oxygenated fuels can extract plasticizer and accelerate aging; published long-term data for high-FAME biodiesel NBR fuel lines is limited, and immersion testing at 40–60 °C for 1,000 h is commonly required before production release. Compression set testing under ASTM D395-18, method B, for 22 h at 100–125 °C is a standard screening procedure for fuel injector seals. SAE J30 hose constructions impose cover, tube, and reinforcement specifications rather than raw polymer certificates.

Compression-molded gasket compounds for water/glycol service are typically based on 28–33% ACN NBR with carbon black N550 or N774 at 40–90 phr, plasticizer at 0–20 phr, and a sulfur or sulfur-donor cure system. The target hardness range of 60–80 Shore A is measured according to ASTM D2240-15, tensile properties according to ASTM D638-14 or ISO 37:2017, and tear resistance according to ASTM D624-12. Finished parts intended for potable water or food contact require FDA 21 CFR 177.2600 or EU 10/2011 migration declarations, and these restrictions exclude many conventional thiuram and carbamate accelerators unless specific migration data support the formulation.