Evonik VESTAMID® X7293 BK 9.7507 is a black, dry-as-packaged polyamide 12 compound specified for melt extrusion and certain injection-molding processes where low moisture uptake and retention of ductility below 0°C govern material selection. The grade identifier combines the base compound family X7293, the black color code BK, and the finish/package identifier 9.7507. The term “Dry” refers to controlled pellet moisture at the time of packaging, not to a separate polymer backbone. The product belongs to the PA12 family, whose repeat unit places 11 methylene groups between amide linkages; this structure yields lower equilibrium water absorption than PA6 or PA66 and contributes to impact resistance at low temperature. In the dry-as-molded state, representative published values include a density of 1.01 g/cm³ per ISO 1183-1, a DSC melting peak near 176 °C per ISO 11357-1/-3, a tensile modulus of approximately 1500 MPa per ISO 527-1/-2, and a notched Charpy impact at 23 °C of about 5.5 kJ/m² per ISO 179-1/1eA. These values are typical for dry-as-molded test specimens and shift after moisture conditioning; they are not to be read as guaranteed specification limits.

The moisture-conditioned state is not addressed by dry-as-molded data. When specimens are stored at 23 °C and 50% RH to equilibrium, tensile modulus decreases and impact resistance increases. Design calculations that use dry tensile modulus without a moisture correction overstate snap-fit stiffness in humid service. Conditioning according to ISO 291 or ASTM D618 is therefore recommended before dimensional or mechanical verification.

What Differentiates a Dry PA12 Tube Grade from Its Unstabilized Base Resin?

Compared with an unstabilized PA12 homopolymer, the X7293 compound carries a heat-stabilization package that reduces chain scission during repeated residence in the melt at 220 °C to 250 °C. Single-screw extrusion at 25:1 L/D with a grooved-barrel feed section produces a more stable melt-pressure trace for the BK-pigmented pellet than for unpigmented PA12 of similar molecular weight. The carbon black in the BK concentrate provides ultraviolet screening in thin-wall tubing; however, the pigment network also lowers notched impact energy by approximately 10% to 15% relative to unpigmented PA12 at equal melt-flow ratio. Dispersion quality at the die lip remains the controlling variable: pigment agglomerates larger than 10 µm create surface roughness and reduce hoop stress resistance in 1.0 mm wall tube. The exact antioxidant and lubricant package is not disclosed here. Incoming batch control therefore relies on Charpy impact per ISO 179-1/1eA, melt volume-flow ratio per ISO 1133-1, and melt-pressure drift on a reference single-screw line rather than on additive identity.

Residual moisture in the dry-as-packaged state is typically below 0.10% by weight. Storage in ambient plant air above 60% RH raises surface moisture within 24 h to 48 h because the PA12 amide linkage remains hygroscopic despite the long aliphatic chain. Pre-drying in a desiccant dryer with a dew point of -40 °C to -30 °C and an air temperature of 80 °C for 4 h to 6 h restores the extrusion moisture limit. Vacuum drying at 80 °C under 20 mbar is acceptable for clean regrind fractions up to 20% by weight. Moisture above 0.15% by weight converts to steam at the die, producing splay, microvoids, and unacceptable wall-thickness variation in tubes below 0.50 mm wall. Tray dryers without dew-point control are insufficient because the equilibrium moisture of PA12 at 50% RH is near 0.7% to 0.9%; the process-critical fraction is only the first 0.15%. On production single-screw tubing lines, melt-pump suction-pressure instability above ±0.5 bar has been recorded when the hopper throat is left open to humid plant air during extended runs. The appropriate control is a closed hopper with dry-air purge, not longer drying time alone. A desiccant dryer with a return-line dew-point sensor and a hopper residence time not exceeding 2 h at 80 °C is appropriate when regrind is present.

Extrusion Melt-Temperature Bounds for Single-Screw Tube Lines

Melt temperature settings for X7293 fall within 220 °C to 250 °C for polished-tube dies and up to 260 °C for profile dies with restrictive breaker plates. Barrel profiles are normally set as a rising ramp from 200 °C at the feed throat to 240 °C at the metering section, with adapter and die held at 235 °C to 245 °C. A single-screw extruder with 24:1 to 30:1 L/D and a three-zone screw at a compression ratio of 2.5:1 to 3.0:1 is sufficient for unfilled PA12; a grooved feed section improves solids conveying but adds 5 K to 10 K of melt-temperature rise from shear heating. Because PA12 melt is pseudoplastic, raising screw speed from 40 min⁻¹ to 80 min⁻¹ reduces apparent viscosity; die melt-pressure fluctuations should nevertheless remain below ±1.0 bar to hold a wall-thickness tolerance of ±0.05 mm in a 6 mm × 1 mm tube. Above 260 °C, discoloration and molecular-weight loss accelerate; below 210 °C, unmelted granules or poor dispersion of the black concentrate can appear. For injection-molded fittings, mold temperatures of 40 °C to 80 °C and clamp force of approximately 5 kN to 7 kN per cm² of projected area are adequate; hot-runner tips above 250 °C may raise local residence-time degradation risk. Regrind management further influences stability. Up to 20% clean, dry regrind is frequently re-introduced on tube extrusion lines without altering melt-pressure stability. Higher levels, or regrind containing dust and moisture, broaden the molecular-weight distribution and shift notched Charpy by as much as 15%. A screen pack of 60 mesh or finer should be used to remove carbonized particles; PA12 can form black specks if dead spots in the adapter exceed 250 °C for more than 20 min.

Fuel vapor lines, pneumatic tubing, cable sheathing, and snap-fit connectors made from VESTAMID® X7293 BK 9.7507 are selected where low water absorption and cold-impact ductility matter. In air brake tubing conforming to SAE J844, PA12 compounds of this class are heat-aged at 125 °C to evaluate burst retention; published data for this exact BK formulation in the specific wall construction is limited, so line validation must include burst and elongation after aging. For contact with aliphatic hydrocarbons, the grade shows the expected PA12 resistance. For glycol/water mixtures above 120 °C, hydrolysis becomes kinetically significant over thousands of hours and should be screened by weight-loss coupons per ASTM D1384. Strong acids, concentrated formic acid, and polar solvents attack the amide linkage and are outside the intended use envelope. Because saturation water absorption is approximately 1.5% per ISO 62, a humid enclosure shifts dimensions and tensile modulus less than does PA6 or PA66. The long methylene sequence also lowers surface free energy, which reduces moisture wettability but also lowers printability and adhesive bond strength without pretreatment.

When PA12 Replaces PA6 or PA66 in Cold-Impact Applications

Compared with PA6 and PA66, the X7293 compound offers lower density and lower equilibrium moisture uptake but sacrifices stiffness and upper service temperature. A dry-as-molded tensile modulus near 1500 MPa places it below typical PA6 at 2900 MPa to 3200 MPa and PA66 at 3000 MPa to 3400 MPa. The notched Charpy impact at -30 °C above 4.0 kJ/m² per ISO 179-1/1eA is the primary mechanical differentiator in cold-weather clips and tubing; many short-chain polyamides lose ductility in that range. The melting point near 176 °C restricts continuous service in air to roughly 100 °C to 120 °C, below the 220 °C to 230 °C ceiling indicated for heat-stabilized PA66. In humid environments, PA6 may lose more than 30% of its dry tensile modulus at 50% RH, whereas PA12 retains a higher fraction because its saturation moisture is about one-sixth that of PA6. Snap-fit closing-force calculations based on dry properties therefore remain more representative after installation for PA12. The property shift after moisture conditioning is still measurable and must be included in dimensional tolerance stacks; it is not eliminated.

Regulatory classification of VESTAMID X7293 BK 9.7507 as supplied does not, by itself, establish compliance for finished articles. REACH and RoHS conformance must be confirmed with the current supplier declaration. The black colorant and stabilizer package are incorporated at the compounding stage and do not impose an automatic restriction under EU 10/2011 or FDA 21 CFR 177.1500, but conversion-specific migration testing is required for food-contact use. The grade is not intended for sustained immersion in hot aqueous acid or alkaline solutions above 60 °C, because the amide linkage hydrolyzes and mechanical properties decline. For welding operations, hot-plate welding at 220 °C to 240 °C with a joint pressure of 0.4 bar to 0.8 bar is common for PA12 tubing, but specific parameter trials must be made on the actual wall thickness. Published data for the specific BK 9.7507 carbon black package under buried or continuously wet service is limited; long-term design should therefore include appropriate safety factors on burst and fatigue strength.