Vestamid L1621 sw is a plasticized polyamide 12 (PA12) injection-moulding compound supplied in black. The suffix “sw” denotes black pigmentation; “dry properties” refers to the reference state obtained after drying to a moisture content below 0.1 wt% and verified by Karl Fischer titration according to ISO 15512. Dry as-moulded data represent the upper stiffness boundary for design because absorbed water in PA12 acts as a plasticizer. The inherent low moisture uptake of PA12—typically 1.0 % to 1.5 % at saturation under ISO 62—limits the dimensional and mechanical shift between dry and conditioned service compared with PA6 or PA66. The grade is not a glass-filled or impact-modified system; it is a plasticized PA12 with a reduced tensile modulus and a ductile low-temperature failure mode.

Dry-Property Data Set for Vestamid L1621 sw

The values in Table 1 are representative dry as-moulded results and should be confirmed against the current manufacturer data sheet and lot-specific certificate of analysis.

The dry condition should not be confused with conditioned values obtained after ISO 1110 accelerated moisture conditioning; conditioning lowers modulus and often raises notched impact response.

Polyamide 12 is produced from laurolactam by ring-opening polycondensation. The longer alkane segment between amide groups reduces density and moisture affinity compared with PA6 and PA66. L1621 sw compounds a plasticizer phase into the PA12 matrix, disrupting interchain hydrogen bonding and lowering dry tensile modulus from unplasticized-PA12 levels near 1,400 MPa to approximately 400 MPa. The plasticizer phase also depresses the brittle-ductile transition and contributes to the no-break Charpy response at −30 °C. The carbon-black pigment serves principally as an ultraviolet screening agent; it does not act as a reinforcing filler, so the low modulus of L1621 sw should not be corrected upward for pigmentation. Compared with impact-modified PA12 grades, L1621 sw achieves flexibility through plasticization rather than elastomer toughening; plasticizer migration behaviour must therefore be considered in hot or solvent-contact service.

What Distinguishes L1621 sw from Unplasticized and Glass-Filled PA12 Grades?

Selection of L1621 sw over an unplasticized PA12 grade changes dry tensile modulus from approximately 1,400 MPa to 400 MPa and yield stress from approximately 40 MPa to 25 MPa. The trade-off is intentional: snap-fit assemblies that would crack after repeated engagement in unplasticized PA12 can accept the lower load-bearing capacity because the plasticizer phase increases elongation at break to >200 % and suppresses brittle fracture. Against short-glass PA12 compounds, L1621 sw sacrifices modulus and creep resistance; glass-filled grades can exceed 2,000 MPa in dry tensile modulus, but they produce higher abrasive wear in screw and barrel components and exhibit notch sensitivity. Against PA66, the PA12 backbone of L1621 sw reduces saturation water uptake from 8–9 % to 1.0–1.5 % under ISO 62, which reduces the shift in dimensions from dry to conditioned service in humid environments. The black pigmentation in L1621 sw also provides opacity and ultraviolet screening, but unpigmented PA12 grades are preferred where colour-neutral translucency is required.

In injection-moulding operations, three processing boundaries determine part quality. First, pre-drying in a desiccant dryer at 80 °C for 4 h to 8 h to a dew point of −30 °C or lower is required when regrind content exceeds 20 wt% or storage relative humidity is above 60 %; failure to dry plasticized PA12 can generate surface splay and shot-weight variation. Second, melt temperature should be maintained between 210 °C and 250 °C; barrel residence above 260 °C increases plasticizer volatilization and black-speck formation. Third, mould surface temperature should be held between 20 °C and 60 °C for moderate crystallinity and dimensional stability; lower mould temperatures reduce cycle time but increase frozen-in stress in thick sections. On production-scale toggle-clamp machines with general-purpose screws in the 18:1 to 22:1 L/D range, the lower melt viscosity of L1621 sw relative to unplasticized PA12 permits gate pressures approximately 15–25 % lower for identical wall-stock geometries. The low-shear melt is prone to drool with open nozzles; positive shut-off nozzles are recommended for hot-runner systems. Mould shrinkage after 48 h at 23 °C and 50 % RH generally falls between 1.0 % and 1.5 % when measured per ISO 294-4, but shrinkage is strongly dependent on gate freeze time and cavity thickness, so a prototype cavity trial is required for tolerance-critical features.

Capillary rheometry according to ISO 11443 shows pseudoplastic flow; at shear rates above 100 s⁻¹ the shear-thinning effect becomes pronounced. The Cross-WLF parameters supplied with commercial flow-simulation databases should be used for gate-pressure prediction. The plasticizer phase reduces die swell relative to unplasticized PA12, but also reduces screw friction; low back pressure in the 30–60 bar range is typical, and screw recovery time should be monitored to detect feed-throat bridging or screw slippage.

Automotive snap-fit clips and cable retainers use L1621 sw where installation in an engine compartment combines low-temperature assembly and vibration. For these parts, low-temperature impact is assessed with Charpy notched specimens at −30 °C per ISO 179-1/1eA; the grade typically records no break. The same ductility supports living-hinge designs in industrial enclosures where repeated flexural cycles at 23 °C and 50 % RH are specified. Fluid-contact applications are limited primarily to fuels and aliphatic hydrocarbons because plasticizer extraction in polar solvents or strong alkaline media can reduce low-temperature ductility; published data for this specific configuration in methanol or glycol-based fluids is limited, and compatibility testing under ISO 175 is required. Applications in medical device housings may require grade-specific confirmation against ISO 10993-1, because the plasticizer system and carbon black pigment are part of the biocompatibility package. Regulatory status under FDA 21 CFR 177.1500 for nylon resins is available only if the supplier issues a grade-specific compliance statement; the base PA12 chemistry should not be assumed to cover the plasticizer package.

Thermal-ageing behaviour for L1621 sw is governed by plasticizer retention rather than oxidation induction. Long-term heat ageing should be assessed under ISO 188 at candidate service temperatures; continuous use above 90 °C can accelerate plasticizer migration and surface tack. The black grade is not inherently flame-retarded; any flame-class claim requires grade-specific testing under IEC 60695-11-10 or UL 94. Electrical connectors using this grade should be qualified on the finished assembly, because comparative tracking index and volume resistivity values are geometry- and processing-dependent.

When Moisture Conditioning Occurs, Dry-Property Values Shift to Lower Modulus

Because PA12 contains amide groups, moisture uptake shifts dry-property data to conditioned values. After accelerated conditioning under ISO 1110 at 70 °C and 62 % RH, the tensile modulus of plasticized PA12 can decrease by 10–30 % relative to the dry condition, while notched impact strength often increases. Dry-property data should therefore be used for initial snap-fit design only with a moisture correction, or conditioned values supplied by the manufacturer should be requested. For dimensional analysis, the water-absorption value under ISO 62 remains the critical input; changes in relative humidity from 20 % to 80 % can produce measurable width changes in long, thin sections. The grade is not recommended for continuous use above 90 °C without additional ageing data from the manufacturer, because plasticizer migration kinetics accelerate with temperature and can lead to embrittlement over time.