Evonik Vestamid L-R9-MHI Antistatic, Black, Electrically Conductive Nylon 12 is a heat-stabilized polyamide 12 compound supplied for injection moulding and profile extrusion. The designation places the material in the Vestamid L PA12 family, with a conductive carbon-black filler system that provides bulk electrostatic dissipation rather than a removable surface coating. Typical as-moulded density is 1.03 g/cm³ when tested according to ISO 1183-1; the crystallite melting point is usually reported near 176 °C by ISO 11357-3. Because the base polymer is PA12, the grade absorbs less moisture than carbon-black-filled PA6 or PA66, with equilibrium moisture uptake commonly below 0.7 % at 23 °C and 50 % RH under ISO 62. The black color is intrinsic to the conductive filler and is not a separate pigment layer. The compound is specified for injection-moulded electronic carriers, conveyor rollers, cable-protection parts, and housings in static-sensitive assembly or potentially explosive atmospheres where surface resistivity must remain below the charge-accumulation threshold.

Which electrical performance envelope is specified for the R9-MHI grade?

The compound is positioned in the conductive to static-dissipative range rather than in the insulating range. Surface resistivity is typically measured between 10² Ω/sq and 10⁵ Ω/sq on injection-moulded plaques conditioned at 23 °C and 50 % RH using IEC 62631-3-2 or ASTM D257 electrode configurations. Volume resistivity is correspondingly low, often below 10⁴ Ω·m. Unlike post-moulded antistatic coatings, the conductive carbon-black network remains active after abrasion or machining because it is distributed through the polymer matrix. However, the measured value is not isotropic. High shear, long residence time, flow-front hesitation, and weld-line orientation can change local surface resistivity by up to two orders of magnitude. Electrical testing should therefore be performed on the actual part rather than only on a standardized plaque. A common release protocol uses a concentric-ring electrode or four-point probe at 100 V DC after 48 h conditioning at 23 °C and 50 % RH. Moisture depresses surface resistivity, so parts moulded and tested immediately after production may give lower readings than dry-as-moulded parts. The grade is intended for electrostatic charge dissipation, not for broadband electromagnetic interference shielding.

Mechanical performance reflects the trade-off between carbon-black loading and the inherent ductility of PA12. Tensile modulus is usually reported in the 1100 MPa to 1600 MPa range to ISO 527-2. Tensile stress at yield is commonly between 30 MPa and 45 MPa. Notched Charpy impact at 23 °C is typically 5 kJ/m² to 10 kJ/m² when tested to ISO 179-1/1eA. At −30 °C, PA12 retains a larger fraction of room-temperature impact strength than PA6 or POM-C, which makes the material suitable for cold-climate transport components. The carbon-black network can act as a notch initiator in thin sections below 1.0 mm, so ribs, bosses, and sharp corners should be radiused. Mould shrinkage is generally between 0.8 % and 1.2 % in the flow direction and 1.0 % to 1.4 % transverse; final values depend on gate position, mould temperature, and wall thickness.

The conductive filler narrows the moulding window relative to unfilled PA12

Processing before melt compounding or moulding is governed by moisture control. The material is dried in a desiccant dryer at 80 °C for 4 h to 6 h until residual moisture is below 0.10 %. Closed-loop drying with a dew point below −30 °C is required; hot-air tray dryers are not reliable for this moisture level. Injection-moulding melt temperatures are typically held between 190 °C and 240 °C, with mould temperatures from 50 °C to 80 °C. Higher mould temperatures improve weld-line strength and surface appearance but extend cycle time. Screw peripheral speed should remain below 0.25 m/s to limit shear heating of the filler. If the machine is stopped for more than 10 min, the barrel is purged with unfilled PA12 to prevent carbon-black agglomeration and black-spec formation. Extrusion operations commonly use a three-zone screw with an L/D ratio of 24:1 to 30:1 and a compression ratio of 2.5:1 to 3.0:1. Tool steel should be hardened or coated because carbon-black-filled melts are mildly abrasive. Cold-slug wells and hot-runner channels should be designed without dead spots, because stagnant melt can produce local increases in resistivity and visible black specks.

Chemical compatibility limits relevant to fuel-vapour and humid service

The PA12 base provides high resistance to aliphatic hydrocarbons, mineral oils, greases, and many industrial solvents. In fuel-vapour exposure, the material is less prone to swelling than many PA6 grades, although the conductive filler slightly increases permeability. Continuous contact with hot water above 80 °C or saturated steam can hydrolyze the PA12 backbone and should be evaluated by tensile-impact testing to ISO 527-2 and ISO 179-1/1eA. Strong inorganic acids, chlorinated solvents, and phenolic compounds can attack the polymer; the carbon black does not provide barrier protection. The material is not suitable for continuous exposure to strong oxidizing acids or to media that cause stress cracking in PA12. For applications involving repeated flexing, fatigue testing on welded or overmoulded specimens is necessary because carbon black can concentrate at weld interfaces and reduce local ductility. Published data for this specific grade under long-term hot-water immersion is limited, so end-use validation is required when the part will operate above 60 °C in high humidity.

Applications are usually injection-moulded trays, tote boxes, conveyor system components, cable-protection parts, and housings used in electronics assembly lines. In ATEX/IECEx zones, conductive PA12 is used for rollers and guides where static discharge could ignite solvent vapors. The low moisture uptake of PA12 reduces dimensional change in humid air, which is an advantage over PA6 and PA66 in precision handling parts. Compared with conductive POM-C, the PA12 grade generally offers lower density, lower hardness, better low-temperature impact, and higher elongation, but lower stiffness and wear resistance. Compared with carbon-black-filled PA6, the PA12 grade offers lower moisture absorption, better resistance to hydrocarbons, and lower processing temperature, but lower tensile strength and typically higher material cost. Compared with static-dissipative UHMWPE, the PA12 compound can be injection moulded into complex geometries and is easier to weld, although UHMWPE has better abrasion resistance in sliding applications.

When weld-line resistivity must be verified before production release

A conductive PA12 part can exhibit non-conductive weld-line regions even when the bulk material is within specification. Weld lines are formed where two melt fronts meet; the carbon-black network may not knit across the interface if the melt-front temperature is too low or if mould venting is insufficient. In such locations, surface resistivity can remain in the insulating range even if the rest of the part reads below 10⁵ Ω/sq. The condition is detected by mapping the part with a two-point probe or by examining cryo-fractured sections under a scanning electron microscope. Production release is more reliably based on IEC 61340-2-3 charge-decay measurements on the assembled component. Tooling corrections include increasing melt temperature by 10 °C to 20 °C, raising mould temperature to 80 °C, adding overflow wells at weld locations, or changing gate position to reduce the number of merging fronts. Published data for this specific R9-MHI grade’s weld-line conductivity is limited; process validation on the actual mould is required before series production. Regrind levels above 30 % can shift resistivity and mechanical properties because repeated heat history degrades the carbon-black structure and PA12 molecular weight.

Material compliance is usually evaluated under REACH Regulation (EC) No 1907/2006 and RoHS Directive 2011/65/EU. Food-contact or potable-water service requires grade-specific confirmation, because carbon black and heat stabilizers may not be automatically covered under FDA 21 CFR 177.1500 or EU Regulation (EU) No 10/2011. Bags should be kept sealed and stored at 15 °C to 25 °C. Storage above 60 % RH increases moisture pickup and may require re-drying before processing. The compound is not formulated for medical implant applications and should not be combined with amine-based antistatic masterbatches unless compatibility is specifically validated.