Arkema Rilsan MB 3000 NAT is a natural-colour, high-viscosity polyamide 11 extrusion compound specified for cable sheathing, flexible pipe outer jackets, and protective sleeving. The polymer is produced from 11-aminoundecanoic acid derived from castor oil; the repeating unit contains 11 methylene carbons per amide group, giving a lower amide density than PA6 or PA66. This molecular architecture is the basis for reduced equilibrium water absorption and improved dimensional stability under humid service conditions. Public technical data for unfilled PA11 sheathing grades in this product family report a density of 1.03 g/cm³ to 1.04 g/cm³ per ISO 1183-1:2019, a melting peak of 183°C to 189°C per ISO 11357-3:2018, tensile yield stress near 42 MPa at 5 mm/min per ISO 527-2:2012, tensile modulus near 1,200 MPa per ISO 527-1:2019, flexural modulus near 1,100 MPa per ISO 178:2019, Shore D hardness near 72 per ISO 868:2003, and notched Charpy impact at 23°C above 6 kJ/m² per ISO 179-1:2010. The MB 3000 NAT designation identifies a natural, unpigmented base resin optimised for melt-extruded sheathing; the high molecular weight imparts elevated melt strength to limit sag and draw-down on vertical wire coating lines. Published data for the exact molecular-weight distribution of this specific grade are limited; however, its sheathing designation implies a melt viscosity above that of comparable injection-moulding PA11 grades.

What Separates Rilsan MB 3000 NAT from PA12, PA6, and HDPE in Flexible Cable Armour?

Selection among PA11, PA12, PA6, and HDPE sheathing commonly turns on moisture uptake, low-temperature ductility, and hydrocarbon barrier behaviour. PA6 and PA66 absorb water above 2.5 wt% at 50% RH and above 8 wt% after immersion per ISO 62:2008; the resultant plasticization shifts tensile modulus and can produce dimensional instability in multi-layer cable constructions. PA11 sheathing compounds typically equilibrate below 1.9 wt% at 50% RH and below 2.5 wt% after saturation, which reduces the magnitude of property drift. PA12 offers similarly low water uptake but has a lower melting peak, commonly 175°C to 180°C, and some PA12 cable grades require external plasticizer to approach PA11 impact at −40°C. At that temperature, PA11 sheathing retains ductile behaviour without plasticizer, while unmodified PA6 exhibits a ductile-to-brittle transition near 0°C to −10°C. Compared with HDPE, PA11 sheathing has higher abrasion resistance, lower permeability to methane and aromatic hydrocarbons, and a higher continuous service temperature in dry air above 90°C, whereas HDPE is generally limited below 80°C depending on the stabiliser package.

Moisture control remains the principal processing boundary for MB 3000 NAT. The compound must be pre-dried to 0.15 wt% residual moisture before entering the extruder; above this threshold, hydrolytic chain scission in the melt produces surface pitting, gas bubble formation, and loss of tensile elongation after cooling. Desiccant dryers are specified with an inlet air dew point below −40°C, a specific airflow of 3.7 m³/h per kg/h of resin, and a residence time of 4 h to 6 h at 80°C. A vented barrel under 100 mbar absolute can remove trace volatiles, but it does not correct hopper moisture on a single-screw extruder. Processors running 60 mm extruders with 24:1 to 30:1 L/D screws report die-head pressure excursions above 200 bar when regrind levels exceed 15 wt%; controlled regrind at or below this level holds batch-to-batch melt-pressure drift within ±8% at constant screw speed.

When Ambient Relative Humidity Exceeds 60% During Hopper Charging

When ambient relative humidity exceeds 60%, dried PA11 granules can regain surface moisture within 20 min to 30 min when exposed to open air. The feed hopper should therefore be blanketed with dry air at a dew point below −30°C, or a desiccant dryer should be mounted directly above the feed throat. Conveying lines should be cleaned or replaced if angel hair is observed; velocity above 25 m/s generates fines that later carbonise in the melt stream. A heated hopper set at 70°C to 80°C reduces condensation on granule surfaces when pellets move from a cold warehouse to a warm plant. Moisture analyser readings taken at the dryer outlet should be below 0.12 wt%, allowing an increase of 0.03 wt% before the screw; if the reading is higher, residence time must be extended or the desiccant bed replaced. Visual inspection of the pellet is not a reliable control because PA11 can appear dry while carrying sufficient surface moisture to hydrolyse amide bonds.

Melt Rheology and Sheathing Extrusion Window

The extrusion window for Rilsan MB 3000 NAT is bounded by melt temperature, die-head pressure, and shear rate. Manufacturer processing guidance for unfilled PA11 sheathing typically specifies a barrel profile from 210°C in the feed zone to 235°C in the metering zone, with die-head temperatures between 230°C and 245°C. Melt temperatures above 260°C accelerate thermo-oxidative degradation, producing yellowing and a measurable reduction in notched impact; melt temperatures below 205°C raise head pressure and leave unmelts in thick sheathing. Screws of 24:1 to 30:1 L/D with a compression ratio of 2.5:1 to 3.0:1 are common for high-viscosity PA11. Die-land shear rates are held between 100 s⁻¹ and 500 s⁻¹; above this range, melt fracture may appear as surface roughness on the sheath. At screw speeds above 100 rpm on a 60 mm extruder, shear heating can raise melt temperature by 10°C to 15°C above barrel setpoint, and a melt pump may be required to stabilise output. A vacuum sizing tank at 15°C to 30°C is used for round cable jackets, with turbulent water flow to prevent local boiling and asymmetric cooling. At sheath wall thicknesses above 3 mm, residual stress from asymmetric cooling can produce longitudinal shrinkage above 1.5%, and line speed is then limited by cooling capacity rather than screw output. Similar PA11 sheathing compounds exhibit an MVR below 20 cm³/10 min at 235°C and 2.16 kg per ISO 1133-1:2022, while injection-moulding PA11 grades can exceed 40 cm³/10 min under the same conditions. Published data for this specific grade at high shear rates are limited; die trials are recommended to confirm pressure drop and die swell.

Hydrocarbon exposure is a primary service condition for PA11 sheathing in offshore control lines and automotive fuel-adjacent covers. The lower amide density of PA11 reduces solubility in aliphatic hydrocarbons compared with PA6; qualification for oil and gas applications is typically performed against API 17J for unbonded flexible pipe outer sheaths and ISO 23936-2 for thermoplastic components in production fluids. However, PA11 is not a universal barrier material; explosive decompression resistance of neat PA11 sheathing is lower than dedicated PA12 or PVDF grades formulated for high-pressure gas service. Continuous contact with concentrated hydrochloric acid, strong oxidising agents, or polar solvents such as methanol above 40°C should be avoided because swelling and amide bond attack can occur. For UV resistance, the natural NAT form must be compounded with carbon black or a stabiliser masterbatch to meet ISO 4892-2:2013 xenon-arc requirements; the uncoloured variant is intended for masterbatch tinting or applications not exposed to direct sunlight.

Accelerated Ageing Retention Values Are Measured Under IEC 60811 and ISO 527

Qualification for wire and cable sheathing commonly uses IEC 60811-501:2012 for mechanical property measurements and IEC 60811-401:2012 for thermal ageing. Retention of tensile strength and elongation at break after ageing is evaluated at 100°C for 7 days; PA11 sheathing compounds typically retain more than 70% of original elongation per ISO 527-2:2012. Low-temperature impact tests are conducted at −40°C according to ISO 179-1:2010, and long-term weathering uses ISO 4892-2:2013 xenon-arc exposure. The following matrix summarises the typical qualification checks for a natural PA11 sheathing grade used in cables.

On offshore flexible riser outer sheathing lines, MB 3000 NAT is extruded over cable cores or flexible pipe armour at line speeds dictated by cooling tank capacity; the natural grade is usually combined with 2 wt% to 5 wt% carbon black masterbatch to achieve UV stabilisation and lower surface resistivity. Without antistatic additives, the volume resistivity remains above 10¹² Ω·m per IEC 62631-3-1, so static-dissipative applications require a dedicated conductive formulation rather than the natural sheathing grade.