The dry-property designation assigned to Evonik Vestamid L2121 sw 9.7507 identifies a carbon-black-pigmented, heat-stabilized polyamide 12 compound supplied as cylindrical pellets for extrusion and injection molding. The suffix 9.7507 refers to the specific carbon black colour concentrate incorporated into the L2121 base resin, not to a filler content or a separate regrind stream. Dry properties are measured on test specimens sealed in moisture-barrier packaging immediately after drying to a residual moisture content of 0.10% or less and conditioned at 23 °C. In the dry-as-molded state, the polar amide groups in PA12 remain unplasticized by absorbed water, so tensile modulus and yield stress are higher than conditioned values, while elongation and notched impact are lower. Published data for this specific configuration is limited; therefore, critical design values must be confirmed against the lot-specific certificate of analysis and the current Evonik technical datasheet.

What Dry-State Mechanical Values Anchor Initial Design Allowables for L2121 sw 9.7507?

For initial part design, the dry-property set for high-viscosity PA12 can be referenced only after the selected test standard and specimen geometry are fixed. The following values are representative of manufacturer-published dry-state data for Vestamid L2121-type black compounds and must be verified for the 9.7507 lot in use. Density at 23 °C is approximately 1.01 g/cm³ when measured according to ISO 1183-1. Tensile modulus in the dry state is commonly reported in the range of 1,400 MPa to 1,600 MPa under ISO 527-1/-2, with yield stress near 44 MPa and yield strain near 5%. Nominal strain at break generally exceeds 50%. Charpy notched impact at 23 °C under ISO 179-1/1eA is typically positioned between 5 kJ/m² and 8 kJ/m². The melting peak recorded by differential scanning calorimetry under ISO 11357-1/-3 is normally observed between 170 °C and 178 °C. Because black pigmentation can shift crystallisation kinetics slightly, moulders should not transfer cooling-time data from natural PA12 grades without experimental verification.

Design calculations using dry values must not be applied to continuously wet or coolant-immersed service without conditioning factors. When specimens are conditioned at 23 °C and 50% relative humidity until equilibrium, tensile modulus may decrease by roughly 10% to 20% and elongation increases, because absorbed water acts as a plasticizer. Moisture uptake kinetics in unfilled PA12 at wall thicknesses below 3 mm approximate Fickian diffusion; thin-walled tube sections therefore reach equilibrium faster than solid injection-molded bosses. Published data for this specific configuration is limited, so end-use validation should measure conditioned properties after moisture equilibrium has been established by gravimetric analysis.

Moisture absorption of PA12 under water immersion at 23 °C typically reaches between 1.0% and 1.5% by mass when tested according to ISO 62. This uptake is substantially lower than that of PA6 or PA66, which absorb on the order of two to three times more water. The lower moisture level explains why black PA12 tube and cable protection parts maintain tighter dimensional stability during humidity swings than equivalent PA6 constructions. In dry-state specifications, the absence of moisture is not an absolute physical state; it is a controlled test condition defined by residual moisture content below 0.10%, not by zero hydroxyl interaction.

When Pre-Drying Is Omitted from Extrusion of the 9.7507 Black Compound

Desiccant drying is mandatory for open storage. The granulate should be dried at approximately 80 °C for 4 h to 6 h to a target moisture content below 0.10%. Dew point in the drying hopper should be maintained below -30 °C. Carbon black can absorb infrared energy unevenly, so hopper temperature uniformity and air distribution must be verified rather than inferred from setpoint alone. On a single-screw extruder with an L/D ratio of 25:1 to 30:1, typical barrel settings rise from 220 °C in the feed zone to 245 °C at the die. Direct melt-temperature measurement after the breaker plate is required because barrel setpoints do not account for shear heating generated in the compression and metering zones. Melt temperature should not exceed 260 °C; prolonged exposure above 270 °C initiates oxidative gel formation and generates black specking that is easily misread as pigment dispersion failure. For tube extrusion, a barrier screw with a Maddock mixing section improves distribution of the 9.7507 carbon black package without adding excessive shear energy. Water-ring pelletising is not relevant to extruded product, but regrind from start-up scrap can be reused only after re-drying to the same moisture specification and only at inclusion rates that do not exceed 20% by mass unless process capability data demonstrate otherwise.

In black polyamide 12 tube extrusion, the 9.7507 pigmentation provides ultraviolet resistance for outdoor cable protection and pneumatic line covers. Vacuum calibration is used to maintain wall-thickness control during unsupported draw-down. The high-viscosity L2121 base resin gives sufficient melt strength for corrugated tube forming, but the die gap and haul-off speed must be matched to prevent internal melt fracture at high shear rates. Compared with low-viscosity PA12 grades intended for thin-wall injection molding, L2121 sw 9.7507 is selected where sag resistance and calibration stability are more important than shortest cycle time. Compared with glass-fibre-reinforced PA12 grades, the dry modulus of L2121 is significantly lower and elongation at break is significantly higher, making the 9.7507 variant unsuitable for structural brackets with high creep requirements but appropriate for snap-fit clips and tubing clamps that require repeated flexural deformation without cracking.

Compliance and Lot-Specific Confirmation Points

Storage above 60% relative humidity in open containers accelerates moisture uptake and can bring pellet moisture above 0.15% within short handling periods, depending on air temperature and pellet surface area. Wet granulate produces splay in injection-molded parts and porosity in extruded tube walls. If moisture-related surface defects appear, closed-loop desiccant drying with dew-point instrumentation must be used rather than increasing melt temperature. The carbon black package in 9.7507 can complicate visual inspection of polymer degradation, so pressure filtration index and offline melt viscosity monitoring are more reliable than black speck counting alone. Process boundaries should be revalidated for each lot because the particle-size distribution of the carbon black masterbatch affects low-shear viscosity more strongly than high-shear viscosity. Equipment purging between materials should use a PA12-compatible purge compound; direct transition from PVC or POM without purging can generate thermal degradation products that reduce melt stability in the L2121 base resin.