Unreinforced nylon 11 (PA11) is produced by melt polycondensation of 11-aminoundecanoic acid obtained from castor oil through transesterification, pyrolysis, and hydrolysis of ricinoleic acid. The repeating unit contains eleven methylene groups per amide group, placing PA11 in the long-chain aliphatic polyamide family. Representative commercial unreinforced PA11 grades include Rilsan BESNO P40 TL for injection molding and Rilsan BESNO P20 TL for extrusion; both omit glass-fiber and mineral reinforcement codes. Commercial materials under this product overview are designated under ISO 1874-1 as PA11, M, with viscosity-number blocks separating tube and pipe extrusion resins from thin-wall injection grades. Typical density is 1.03–1.05 g/cm³ according to ISO 1183-1:2019, and the peak melting endotherm by differential scanning calorimetry is reported near 189 °C using ISO 11357-3:2018. The dry-as-molded tensile stress at yield generally falls between 40 MPa and 50 MPa when tested at 50 mm/min per ISO 527-1:2019 and ISO 527-2:2012.

Unlike short-chain PA6 or PA66, the lower amide density of PA11 reduces hydrogen-bonding density and lowers equilibrium moisture uptake. Crystallinity in unfilled PA11 extrudate commonly falls between 30 % and 40 % when measured by heat of fusion using ISO 11357-3:2018, and this crystallinity fraction contributes to chemical barrier and dimensional stability. The amorphous phase retains enough chain mobility after moisture conditioning to support high elongation at break, but dry-as-molded parts can exhibit notch-sensitive behavior.

Which Engineering Property Ranges Are Reported for Dry-as-Molded Unreinforced PA11?

The table below consolidates typical property ranges for unfilled PA11 across injection and extrusion grades. Values are dry-as-molded unless otherwise noted.

The spread in these ranges reflects differences in viscosity number, stabilizer package, and crystallinity. High-viscosity extrusion grades for air-brake tubing typically report melt volume-flow rates below 10 cm³/10 min at 235 °C and 2.16 kg, while injection grades for thin-wall connectors may exceed 15 cm³/10 min under the same load. Conditioned values are generated after storage at 23 °C and 50 % relative humidity to equilibrium per ISO 291:2008.

After conditioning at 23 °C and 50 % relative humidity, unreinforced PA11 reaches an equilibrium moisture content near 1.8 wt%; the corresponding equilibrium for PA6 is approximately 2.8–3.2 wt%, and saturation in water for PA6 reaches 9–10 wt% when tested to ISO 62:2008. This lower water uptake limits the dry-to-conditioned loss in tensile modulus and permits components to maintain more stable dimensions in humid service. The coefficient of linear thermal expansion for unreinforced PA11 is typically 100–140 × 10⁻⁶ K⁻¹ between 23 °C and 60 °C per ISO 11359-2:1999, and mold shrinkage in flow direction is commonly 0.8–1.5 % depending on wall thickness and gate geometry.

When PA11 Is Extruded into Air-Brake and Fuel Tubing at Production Scale

Unreinforced PA11 is specified for nylon air-brake tubing qualified to SAE J844 and for fuel and vapor lines evaluated under SAE J2260. In production-scale single-screw extrusion, pellets are dried in a desiccant dryer with a dew point below -30 °C at 80–90 °C for 4–6 h, targeting residual moisture below 0.08 wt%. Extruder barrel profiles from 230 °C to 260 °C, screw L/D ratios of 24:1 to 30:1, and screen packs of 100–150 µm are representative. Die land length ratios of 10:1 to 15:1 and vacuum calibration at 0.06–0.08 MPa are used to control ovality and concentricity. Melt temperatures above 270 °C or residence times exceeding 10 min can shift molecular weight distribution and reduce finished tube burst pressure; qualification of the finished tube is performed using the burst, cold-impact, and flexibility procedures of SAE J844 because published data for this specific configuration is limited.

In offshore unbonded flexible pipe, unfilled PA11 pressure sheaths are qualified under API Spec 17J. Melt temperature, residence time, and residual moisture are controlled because hydrolytic degradation during extrusion reduces long-term pressure retention. Production-scale lines use grooved feed sections and barrier screws to limit shear heating; published data for specific line configurations is limited to operator qualification files.

Injection molding of unfilled PA11 connectors, cable ties, and snap-fit housings uses mold temperatures from 30 °C to 60 °C, with high mold temperatures above 80 °C used when maximum crystallinity and dimensional stability are required. Melt volume-flow rates of 10–20 cm³/10 min at 235 °C allow thin-section filling with injection pressure below 120 MPa. Hot-runner manifolds should avoid sharp radius changes and dead spots because unfilled long-chain polyamides can deposit low-molecular-weight fractions when residence time exceeds 8 min. Post-mold conditioning at 50 % RH for 48–72 h is commonly applied before snap-fit assembly or impact testing because dry-as-molded parts may exhibit brittle failure at notches. The absence of glass fiber reduces melt anisotropy and produces more uniform shrinkage than 30 wt% glass-filled PA11, but lowers flexural modulus from approximately 3000–6000 MPa for reinforced grades to 900–1300 MPa for this unreinforced class.

Chemical Resistance in Hydrocarbon Fuel, Chloride, and Weak Acid Service

Unreinforced PA11 is evaluated for hydrocarbon fuel contact by immersion and permeation methods under ISO 175:2010 and SAE J2260, using ASTM Reference Fuel C at temperatures from 40 °C to 60 °C. The long aliphatic segment reduces swelling relative to shorter-chain polyamides; however, the magnitude depends on stabilizer package and wall thickness, and published data for oxygenated fuels above E15 at elevated temperature remains limited. Stressed components exposed to road-salt chloride solutions are screened by environmental stress-cracking procedures such as ISO 22088-3:2006; unfilled PA11 is generally less sensitive to zinc chloride stress cracking than PA6 and PA66, but notched or high-hoop-stress designs still require part-level validation. Continuous contact with strong acids, phenols, and oxidizing agents is not recommended, and hydrolysis accelerates in hot water above 80 °C.

In wire and cable sheathing, low equilibrium moisture uptake and abrasion resistance are evaluated by thermal aging and scrape-abrasion procedures, with automotive cable specifications such as ISO 6722 used for qualification. Unreinforced PA11 is also supplied in powder form for fluidized-bed and electrostatic spray coating; particle size distributions differ from pellet extrusion grades and require separate melt-flow and dry-flow characterization.

Relative to unreinforced PA12, PA11 is reported with a higher peak melting point of approximately 189 °C versus 176 °C and a density higher by 0.02–0.03 g/cm³, while saturation water uptake is slightly higher at 1.8–2.0 wt% compared with 1.5–1.6 wt% for PA12. These differences make PA11 the usual selection when thermal margin in under-hood tubing is required, while PA12 may be selected when lowest water uptake and density are dominant. Compared with unreinforced PA6, PA11 offers approximately 80 % lower saturation water uptake and a lower dry-state tensile modulus; PA6 dry-as-molded tensile stress at yield is typically 70–80 MPa, but this advantage narrows after moisture conditioning.

Comparative ranges are typical for unfilled grades; specific commercial compounds differ by viscosity number, stabilizer, and nucleating system. Processors who run PA66 before PA11 should purge thoroughly with a low-viscosity PA11 or dedicated purge compound because residual PA66 can cause gel-like inclusions and delamination in extruded tube. Unreinforced PA11 should not be combined with reactive chain extenders or certain amine-based additives without torque-rheometry validation because the amide end groups can participate in chain-extension reactions. Published data for long-term hot-water aging above 80 °C in chlorinated potable water is limited, and components exposed to such conditions require grade-specific testing per ISO 175:2010.