Oil-contact sealing components, hydraulic hoses, and pump diaphragms require an elastomer that balances moderate oil resistance, processing latitude, and acceptable low-temperature flexibility. Acrylonitrile‑butadiene rubber 3305E is positioned in the medium-acrylonitrile segment of NBR, classified under ASTM D1418 as NBR and under ISO 1629 as NBR. The polymer is produced by cold emulsion polymerization and is supplied as baled crumb with a non-staining stabilizer. In supplier nomenclature the code 3305E denotes a nominal bound acrylonitrile content of 33 ± 1.5 wt% and a nominal Mooney viscosity ML(1+4) at 100 °C of 50 ± 5. Unlike high-ACN grades that sacrifice low-temperature properties for aromatic fuel resistance, 3305E is selected where the fluid is a paraffinic or naphthenic mineral oil, a water-glycol hydraulic fluid, or a mild aliphatic solvent. The following technical profile defines the limitations of mixing, milling, extrusion, and vulcanization for this grade.

What Raw-Polymer Specifications Define 3305E?

Supplier-published raw-polymer limits for 3305E are summarized in Table 1. The bound acrylonitrile content controls the balance between oil swelling and low-temperature retraction and should be verified by nitrogen analysis because variations within the ± 1.5 wt% limit produce measurable shifts in cured modulus and swell behaviour. The Mooney viscosity band of 50 ± 5 defines the initial molecular-weight distribution and correlates with compound viscosity during mixing and extrusion; a lot near 55 MU may require rotor-speed reduction or a 5–10 phr increase in plasticizer to maintain a target compound Mooney of 60–70 MU. Volatile matter and ash limits of ≤ 0.5 % minimize defects in thin-gauge calendered sheet and molded parts, but they do not remove the need to screen or filter compounds when surface-critical parts are specified.

Property	Test method	Typical or limiting value
Bound acrylonitrile content	Supplier nitrogen method; ISO 1656	33 ± 1.5 wt%
Mooney viscosity ML(1+4) at 100 °C	ASTM D1646	50 ± 5
Volatile matter	ASTM D5668	≤ 0.5 %
Ash	ASTM D5667	≤ 0.5 %
Specific gravity	ASTM D297	0.98 ± 0.01
Stabilizer type	Supplier datasheet	Non-staining

When the polymer is transferred from bale storage to a production-scale internal mixer with intermeshing or tangential rotors, the initial mastication peak occurs within the first 30–60 s. A typical bale pre-heat is not required when the storage temperature is above 15 °C. Mixer charging at 40 °C, a ram pressure of 0.4 MPa, and rotor speeds of 35–50 min⁻¹ produce dump temperatures of 110–135 °C for a first-pass masterbatch containing carbon black and plasticizer. A representative first-pass masterbatch loading sequence loads the polymer, zinc oxide at 5.0 phr, stearic acid at 1.0 phr, and half of the carbon black at time zero; the remaining carbon black and plasticizer are added after the compound reaches 80–90 °C. The medium Mooney viscosity of 3305E allows a wide one-pass or two-pass mixing window, but a second pass at low rotor speed is preferred when sulfur donor and sulfenamide accelerator are added below 100 °C to avoid premature crosslinking. On a two-roll mill the grade bands cleanly at front-roll temperatures of 45–55 °C; a friction ratio of 1:1.15 to 1:1.25 is sufficient for tight-nip sheeting below 0.5 mm. At high mill speeds and low nip, tack may increase; addition of 0.5–1.0 phr of stearic acid or microcrystalline wax stabilizes the band without shifting cure kinetics. For cold-feed extrusion, barrel temperatures from 45 °C at the feed throat to 65 °C at the head, with a screw L/D of 20:1, produce moderate die swell and smooth surfaces for unsupported hose compounds. Batch-to-batch variation within the stated Mooney range is most visible in extrudate swell, not in final hardness; therefore extruder screw speed should be trimmed before changing the formulation.

Compound Design Boundaries in Sulfur-Cured Sealing Articles

Sulfur-cured sealing compounds built on 3305E require attention to cure-system stoichiometry because the raw polymer does not contain curative or reinforcing filler. A conventional reference compound with N330 black at 40 phr, zinc oxide at 5.0 phr, stearic acid at 1.0 phr, sulfur at 1.5 phr, and N-tert-butylbenzothiazole-2-sulfenamide at 1.2 phr reaches t₉₀ at 160 °C in 8–12 min when tested on a moving-die rheometer per ASTM D5289. The scorch time t_s2 at 125 °C is typically 6–10 min for this cure system, allowing pot-temperature operation below 100 °C for compression transfer and short injection cycles at mold temperatures of 170–190 °C. At 180 °C the same cure system typically reaches t₉₀ in 1.5–3.0 min; this short vulcanization window supports high-output injection molding but narrows the thermal operating band of the tool. Mold temperature control within ±3 °C is required to avoid under-cure at the cold edge and reversion at the hot gate. Tensile strength measured per ASTM D412 on die-cut dumbbells is generally reported in supplier reference formulations in the range of 18–22 MPa, with elongation at break 350–450 %; the spread reflects dispersion quality and carbon black structure rather than the polymer alone. Compression set after 24 h at 100 °C per ASTM D395 Method B is typically 15–25 % for a properly post-cured sulfur cure. Replacing part of the sulfur with a thiuram donor below 0.5 phr reduces set but raises nitrosatable amine concerns that must be assessed under REACH and workplace exposure limits. Peroxide-cured 3305E compounds require coagulant-stabilizer screening because residual soap and water-soluble ash can reduce crosslink efficiency; a low-ash lot is preferred for peroxide systems with trimethylolpropane trimethacrylate at 0.5–1.5 phr.

When 33% Acrylonitrile Content Becomes the Limiting Variable for Fuel Exposure

The nominal 33 wt% bound acrylonitrile content creates a predictable inflection point in fluid swell behaviour. In aliphatic mineral-oil service the grade performs well because the polarity of the nitrile groups resists swelling by nonpolar hydrocarbons; however, exposure to aromatic fuels, alcohol-blended gasoline, and high-aniline-point hydraulic fluids shifts the swell curve beyond the range acceptable for precision seals. Volume change measured per ASTM D471 after 70 h at 100 °C in IRM 903 for a black-filled medium-ACN vulcanizate typically falls in the 15–25 % range, whereas a 40 wt% ACN grade reduces the same measurement to 5–12 %. The penalty for the higher ACN grade appears in low-temperature retraction: TR-10 measured per ASTM D1329 shifts from approximately −40 °C to −35 °C for 3305E to −25 °C to −18 °C for a 40 wt% ACN compound. Table 2 summarizes the structural trade-off. For fuel pump diaphragms and fuel hose inner liners, a 3305E-based compound is not automatically suitable; published data for this specific configuration is limited and the final choice must be validated against the actual fuel blend, evaporative emission requirements, and low-temperature starting torque. The comparison in Table 2 is a structure-property engineering approximation compiled from published NBR literature and typical black-vulcanizate studies; supplier-certified values for 3305E in a specific cured formulation may differ.

Parameter	28 wt% ACN NBR	3305E, 33 wt% ACN NBR	40 wt% ACN NBR
Bound ACN	28 ± 1.5 wt%	33 ± 1.5 wt%	40 ± 1.5 wt%
Mooney ML(1+4) at 100 °C	50 ± 5	50 ± 5	50 ± 5
TR-10 in a 40 phr N330 black compound, ASTM D1329	−48 °C to −44 °C	−40 °C to −35 °C	−25 °C to −18 °C
Volume swell after 70 h at 100 °C in IRM 903, ASTM D471	30–45 %	15–25 %	5–12 %
Primary fluid resistance boundary	Low-temperature glycols, paraffinic oils	Mineral oils, water-glycol, mild aliphatics	Mild aromatics, fuels with low oxygenates

Qualification of 3305E for hydraulic seals, gaskets, and pump diaphragms should be confirmed against the finished compound rather than the raw polymer. A mineral-oil seal compound based on 3305E can be tested for tensile change and hardness change after dry-heat aging at 100 °C for 70 h, with a typical requirement of tensile change within ±30 % and hardness change within ±15 points. For water-glycol hydraulic fluids, the compound should be immersed in the actual fluid at 60 °C for 168 h per ASTM D471, because water-glycol stability depends on inhibitor chemistry and can vary between OEM formulations. Tear strength per ASTM D624 Die C is relevant for gland-loaded O-rings and should be assessed before replacing a higher-Mooney NBR. Abrasion resistance per ISO 4649 Method A may be specified for dynamic applications such as rotating shaft lips; 3305E can be compounded with N220 or N234 carbon black at 45–60 phr to raise abrasion performance, but the resulting compound Mooney rises and may require a processing plasticizer such as dioctyl phthalate at 5–15 phr. Dioctyl phthalate additions above 10 phr increase low-temperature flexibility but can reduce oil resistance by plasticizer extraction in ASTM D471 testing; the measured swell then reflects plasticizer loss rather than polymer-fluid interaction. The raw polymer is not compliant with food-contact or potable-water standards as supplied; any such use must be supported by compound-specific migration testing under FDA 21 CFR 177.2600 or equivalent national regulations. Bale storage should remain below 40 °C, out of direct sunlight, and away from copper, manganese, or ozone-generating equipment because these agents accelerate oxidative degradation of the unsaturated butadiene backbone. Although 3305E is supplied with a non-staining stabilizer, prolonged storage beyond 24 months may shift Mooney viscosity and should be re-tested per ASTM D1646 before production. Condensation on chilled bales can introduce moisture into internal mixers and cause porosity in calendered sheet; if bales are transferred from cold storage at ≤ 10 °C to a warm mixing room, warm-up time sufficient to reach surface temperature above the dew point is required. The grade should not be blended with natural rubber or SBR in the same mixer batch without adjusting the cure system, because the unsaturated backbones differ in accelerator demand and sulfur solubility.