What Is Acrylonitrile Used For? Eight Downstream Chains from ABS to Carbon Fibre

Acrylonitrile (CAS 107-13-1, CH₂=CHCN) is produced primarily by propylene ammoxidation over fluidized-bed bismuth molybdate or antimony-based catalysts at 400–510 °C and 1–2 bar. Commercial monomer is typically 99.5% minimum purity, inhibited with monomethyl ether hydroquinone at 35–45 ppm. The liquid has a boiling point of 77.3 °C, density of 0.806 g/cm³ at 20 °C, and water solubility of 7.35 g/100 mL. Flammability limits in air are 3.0–17.0 vol%; autoignition temperature is 481 °C. The vinyl and nitrile groups allow the monomer to be routed into eight downstream chains: acrylonitrile-butadiene-styrene, styrene-acrylonitrile, nitrile rubber, acrylic fibre, acrylamide, adiponitrile/hexamethylenediamine, high-acrylonitrile barrier resins, and polyacrylonitrile-based carbon fibre.

Acrylonitrile-Butadiene-Styrene and the Rubber-Grafting Window

In emulsion ABS production, polybutadiene latex with a mean particle size of 0.25–0.35 µm is grafted with a styrene-acrylonitrile shell and then compounded with separately polymerised matrix SAN. The SAN phase contains 20–35 wt% acrylonitrile; total rubber content in the finished compound is typically 10–30 wt%. Grafting prevents rubber particle agglomeration when the grafted powder is melt-blended with matrix SAN on a co-rotating twin-screw extruder with L/D 32–40. Bulk-mass ABS, in contrast, dissolves polybutadiene in styrene and acrylonitrile and relies on phase inversion during prepolymerisation to generate rubber particles of 0.5–1.5 µm. Injection moulding grades are pre-dried at 80 °C for 2–4 h to maintain moisture below 0.1%. Melt temperatures of 210–250 °C and mould temperatures of 25–80 °C are used; melt volume-flow rate under ISO 1133-1:2022 at 220 °C/10 kg is usually 2–30 cm³/10 min. Under ISO 527-2, tensile yield stress is 35–55 MPa; notched Izod impact under ISO 180 is 15–35 kJ/m². Thermal stabilisers such as hindered phenols at 0.1–0.3 phr with phosphite costabilisers are melt-compounded into outdoor grades. Processing above 280 °C degrades the butadiene phase and liberates acrylonitrile, requiring local exhaust ventilation and upper melt-temperature interlocks. On injection moulding lines, clamp force is typically 4–7 kN/cm² of projected area for medium-viscosity ABS. Residence time at melt temperature should not exceed 5 min because yellowing increases with thermal history. Thick-section parts with wall thickness above 4 mm typically use lower-rubber ABS to avoid sink marks and reduced heat-deflection temperature.

Comparatively, styrene-acrylonitrile copolymers are produced by bulk or suspension polymerisation without the polybutadiene phase, yielding transparent grades with acrylonitrile mass fractions of 24–33%. Higher acrylonitrile content improves resistance to oils, detergents, and stress cracking, but requires slightly higher melt processing temperatures. Vicat softening temperature under ISO 306/B50 is typically 105–110 °C; tensile stress at break under ISO 527-2 is 65–80 MPa. Water absorption after 24 h at 23 °C under ISO 62 is near 0.2%. In food-contact applications, EU Regulation (EU) No 10/2011 sets an acrylonitrile-specific migration limit of 0.01 mg/kg. Industrial bulk finishing units reduce residual acrylonitrile to below 5 mg/kg by vacuum devolatilisation at 220–240 °C. Light transmittance through a 3 mm plaque under ISO 13468 is 88–90%. The polymer is melt-processed for appliance housings, cosmetic packaging, medical device components, and disposable laboratory articles. Its lack of butadiene improves ultraviolet stability and lowers odour but reduces room-temperature impact strength relative to ABS. Glass-fibre reinforced SAN is available for structural parts, though the addition of 20–30 wt% glass fibre sacrifices transparency and raises tensile modulus to 8–10 GPa.

What Controls the Oil Resistance and Low-Temperature Limit in Nitrile Rubber?

Acrylonitrile-butadiene rubber is emulsion-polymerised at 5–40 °C, with bound acrylonitrile content controlled from 18–50 wt%. Cold polymerisation at 5–15 °C produces more linear chains and higher tensile properties; hot polymerisation at 30–40 °C increases branching and gel content. The nitrile group provides resistance to aliphatic hydrocarbons and vegetable oils, while higher bound acrylonitrile raises the glass transition and reduces low-temperature flexibility. ASTM D1418 designates NBR; ISO 1629 provides the rubber nomenclature. Mooney viscosity ML(1+4) at 100 °C is commonly 30–100. Sulfur cure with sulfenamide accelerators and peroxide cure with dicumyl peroxide are standard; peroxide-cured NBR is preferred for hot air ageing up to 120 °C. Under ASTM D412, filled vulcanisates have tensile strength of 10–25 MPa and elongation at break of 250–600%. Compounding uses internal mixers with ram pressure of 0.4–0.6 MPa; first-stage dump temperature is held at 100–120 °C, and curatives are added in a second stage at 70–80 °C to prevent scorch. Plasticiser migration in fuel-contact service can distort oil-swelling measurements, so ASTM D471 immersion limits are applied to a defined test fluid such as IRM 903. Table 1 gives representative property ranges for sulfur-cured NBR; actual values depend on cure state, filler type, plasticiser load, and test temperature.

Because fibre-grade polyacrylonitrile begins cyclization and chain scission at 180–200 °C before melting, it is not melt-spinnable. Copolymers containing at least 85% acrylonitrile are dissolved in dimethylformamide, dimethylacetamide, 45–55% aqueous sodium thiocyanate, or aqueous nitric acid. Dope solids content is typically 20–30 wt%. Wet-spinning spinnerets contain 20,000–100,000 holes and feed the solution into a coagulation bath where solvent concentration and temperature are controlled to avoid macrovoid formation. Coagulation bath temperature is often held at 5–25 °C, with solvent-to-water ratio managed in countercurrent cascades. Drawing at 3–12× aligns the fibrillar network and increases tenacity; heat-setting under steam at 120–150 °C stabilises the oriented structure. Typical acrylic staple after hot drawing has a tenacity of 2.0–3.0 cN/dtex and elongation at break of 30–50% under ISO 5079. Residual solvent is removed by countercurrent washing and drying below 140 °C to limit yellowing. Finish application at 0.2–0.6% on tow surface controls static and downstream carding friction. ISO 2076 defines acrylic and modacrylic generic fibre names. Acrylic staple and tow are used in wool-like knitwear, outdoor fabrics, and filters; fibre density of about 1.17 g/cm³ provides bulk without excessive weight.

Converting Acrylonitrile to Acrylamide with Immobilised Nitrile Hydratase

Hydration of acrylonitrile to acrylamide is carried out either over fixed-bed copper catalysts at 90–120 °C or with immobilised nitrile hydratase biocatalysts operating below 30 °C in continuous stirred-tank reactors. The biocatalytic route achieves conversion above 99% and avoids cyanide-bearing side reactions, but requires strict control of acrylonitrile concentration and dissolved oxygen to maintain enzyme stability. In fixed-bed copper catalyst hydration, unconverted acrylonitrile is separated and recycled to maintain nitrile conversion across the bed. The immobilised-cell route uses alginate or polyacrylamide beads and operates at near-neutral pH; nitrile hydratase activity is measured in units per gram of dry catalyst. The resulting 40–50% aqueous acrylamide is then polymerised to polyacrylamide for drinking-water clarification, papermaking retention, and enhanced oil recovery. Molecular weight of polyacrylamide for enhanced oil recovery can reach 5–25 million g/mol, which demands low monomer residuals and controlled shear dissolution. Residual acrylonitrile in acrylamide monomer is a critical exposure parameter; closed-loop reactor design and continuous monitoring are used because acrylonitrile volatility increases with temperature. This downstream chain transfers the production hazard from monomer flammability and nitrile toxicity to polymer dust and residual monomer control. Compliance for drinking-water-grade polyacrylamide is assessed under protocols such as NSF/ANSI/CAN 60.

Electrochemical hydrodimerization of acrylonitrile to adiponitrile is conducted in divided cells with a catholyte containing quaternary ammonium salts and an oxygen-evolving anode. Acrylonitrile concentration, catholyte pH, and current density are controlled to suppress propionitrile and 3-cyanopropanal by-product formation. Published industrial selectivities to adiponitrile above 90% are reported for electrohydrodimerization, although butadiene hydrocyanation has displaced much of this capacity due to lower energy consumption. Adiponitrile is hydrogenated to hexamethylenediamine over nickel or cobalt catalysts at 60–150 °C, and the diamine is combined with adipic acid to produce polyamide 66. Polyamide 66 moulding materials are specified under ISO 16396-1; relative viscosity in 90% formic acid is assessed by ISO 307. Hexamethylenediamine is stored under inert gas to prevent carbamate formation with carbon dioxide. Salt preparation with adipic acid is controlled to pH 7.5–8.0 in aqueous solution before evaporation to nylon salt. Melt processing of polyamide 66 typically occurs at 280–290 °C, with the processing window bounded by polymer degradation above 300 °C. This chain therefore supplies engineering thermoplastics for under-hood automotive parts and electrical connectors requiring dimensional stability and high-temperature mechanical performance.

In barrier packaging extrusion, high-acrylonitrile resins containing 70–75% acrylonitrile with methyl acrylate or styrene comonomers provide low oxygen and solvent permeability. The high nitrile content raises the glass transition to 80–95 °C, so melt extrusion is maintained at 190–210 °C with minimal residence time; thermal exposure above 220 °C can release hydrogen cyanide and discolour the resin. Oxygen permeation under ASTM D3985 at 23 °C and 0% RH is typically below 1.0 cm³·mm/(m²·day·atm), whereas transparent SAN grades are generally 4–8 under the same conditions. The resins are processed by extrusion blow moulding and thermoforming for agricultural chemical containers, pharmaceutical blister base layers, and beverage overpackaging. Extrusion blow moulding requires controlled parison swell and low-shear mixing to avoid thermal damage; screw designs with compression ratios of 2.5–3.0 and barrier flights are used. Moisture level in pellets should be below 0.05% before melt processing; drying at 70–75 °C for 2–3 h in desiccant dryers is sufficient. Chemical resistance to toluene, methanol, and petrol is used to justify packaging for aggressive formulations, but compatibility testing against the actual packaged product is required. Regrind ratios above 30% can reduce impact strength and barrier uniformity.

When Polyacrylonitrile Precursor Becomes a Carbon Fibre

Polyacrylonitrile precursor for carbon fibre is a solution-spun copolymer containing 90–98% acrylonitrile with methyl acrylate or itaconic acid comonomers that moderate cyclization. Tows such as 3K, 12K, 24K, and 50K are oxidatively stabilised in air at 200–300 °C under tension. The heating rate must stay between 0.2–5 °C/min; faster rates create a skin-core oxygen gradient that leaves an unreacted core and causes filament fusion or low carbon yield. Stabilised fibre is carbonised in nitrogen or argon at 1000–1600 °C, then graphitised at 2000–3000 °C for high-modulus grades. Carbon yield from the precursor is 45–50% by mass.

Filament diameter after carbonisation is 5–7 µm. Under ISO 10618:2004, standard-modulus carbon fibre has tensile modulus of 230–240 GPa and tensile strength of 3.5–5.0 GPa; intermediate-modulus fibre is 290–300 GPa; high-modulus fibre is 350–450 GPa with elongation at break below 1.0%. The surface is electrochemically oxidised and sized with an epoxy-compatible emulsion at 0.5–1.5% by mass to improve handling and matrix wetting. In filament winding, the tension on a 12K tow is typically maintained below 15 N to limit fuzz generation. The thermal stabilisation step is the throughput bottleneck: commercial ovens must balance exothermic cyclization, tow tension, and oxygen diffusion. Published data for specific precursor-oxidation configurations is limited because winding and stabilisation line parameters are treated as proprietary by fibre producers.