Evonik Vestamid L1640 nf (as-conditioned) is an unplasticized, medium-viscosity polyamide 12 homopolymer supplied in natural fine-granule form. The “as-conditioned” designation refers to the moisture-equilibrated state obtained after exposure to 23 °C and 50 % RH in accordance with ISO 291 or after accelerated conditioning under DIN EN ISO 1110. In this state, polyamide 12 absorbs significantly less atmospheric moisture than polyamide 6 or polyamide 66; equilibrium moisture uptake in standard climate is commonly reported in the range 0.7–0.9 wt% for PA12, compared with 2.5–3.0 wt% for PA6 and 2.0–2.5 wt% for PA66 per ISO 62. The lower amide-group density along the aliphatic C12 backbone reduces the rate of property shift caused by humidity cycling, which is relevant for dimensionally stable extruded profiles and injection-molded connectors exposed to condensation. The grade is typically characterized by a density near 1.01 g/cm³ at 23 °C according to ISO 1183-1 and a crystalline melting temperature between 176 °C and 180 °C by ISO 11357-1/-3. Lot-specific values on the Evonik certificate of analysis should be used for process capability studies.

The L1640 nf grade is intended for extrusion and injection moulding of semi-finished profiles, cable sheathing, pneumatic tubing, fluid connectors, and technical clips. The nf code identifies natural fine granulate; it does not denote a nucleation package or plasticizer content. Because the material is unmodified and unpigmented, converters can introduce additive masterbatches for UV stabilization, color, or processing aid without the interference of a pre-existing nucleant load. The medium-viscosity melt is positioned between high-flow injection-moulding grades and high-viscosity extrusion grades. In thin-wall components with flow-length-to-thickness ratios above 150:1, a higher-flow PA12 grade may be required; published data for this specific configuration is limited and should be confirmed by spiral-flow trials on the target tool.

Processing of the as-conditioned grade follows standard PA12 drying practice. If the moisture content exceeds 0.10 wt% by Karl Fischer titration per ISO 15512, pre-drying in a dehumidified-air hopper dryer or vacuum oven at 80 °C for 4–8 h is recommended to bring residual moisture below 0.05 wt%. Molten PA12 exposed to excess moisture shows a reduction in melt viscosity and can generate surface splay or voiding in extruded wall sections. On single-screw extruders with 25:1 to 30:1 L/D and grooved feed sections, barrel zone temperatures from feed to die are commonly set at 220 °C, 230 °C, 240 °C, 245 °C, and 240 °C, with melt temperature held between 220 °C and 250 °C. Residence time above 250 °C should not exceed 10 min to avoid chain scission and color shift. Injection moulding requires melt temperatures of 220–250 °C and mould temperatures from 40 °C to 80 °C. Higher mould temperatures within this range increase spherulite size and reduce post-mould shrinkage, but they extend cooling time. Clamp force settings follow the projected area and the expected cavity pressure of 600–800 bar; specific process capability data for this grade on high-speed packaging tools is limited and should be generated from pressure-transducer studies.

Rheological characterization of L1640 nf under capillary viscometry per ISO 11443 shows shear-thinning behavior typical of linear polyamide 12. At melt temperature 230 °C, apparent shear viscosity curves crossing 10²–10³ Pa·s at shear rates from 10² s⁻¹ to 10³ s⁻¹ guide die design. Melt strength is sufficient for tube extrusion with draw-down ratios up to 3:1; published data for specific draw ratio limits on this exact natural fine grade is limited. For profile extrusion, a compression screw with a 2.5:1 compression ratio and a screen pack combination of 60/80/100 mesh is commonly used to build melt pressure and homogenize the melt. When regrind content exceeds 20 wt%, melt pressure fluctuation on single-screw extruders with 25:1 L/D has been observed by production personnel because of irregular feeding of uncrystallized granule; the addition of 0.5–1.0 wt% of a processing aid masterbatch or reduction of screw speed by 15–20 % is normally required.

How does the as-conditioned L1640 nf differ from nucleated, plasticized, and glass-filled PA12 grades?

The unfilled L1640 nf does not contain a nucleating package that accelerates crystallization; therefore, it produces a wider processing window in thick-wall parts and a higher coefficient of linear thermal expansion than glass-filled grades but less dimensional stiffness than 30 wt% glass fibre reinforced PA12. A glass-filled PA12 typically exhibits tensile modulus above 4500 MPa and strain at break below 5% under ISO 527-1/-2, whereas as-conditioned unfilled PA12 retains elongation at break values above 200%, allowing snap-fit features and cyclic flexural applications; flexural fatigue should be validated per ISO 178 or ASTM D790-17. Plasticized PA12 compounds can reduce Shore D hardness below 60, while unplasticized L1640 nf usually measures 70–72 Shore D per ISO 868 after conditioning. The medium viscosity of L1640 nf positions the melt between high-flow injection-moulding grades and high-viscosity extrusion grades; this limits its use in ultra-thin-wall connectors where very high-flow PA12 is required but supports consistent wall-thickness control in tubing with 1.0–2.0 mm nominal wall.

Because the nf code refers to natural fine granule, the product does not include carbon black or stabilizer packages intended for long-term UV exposure unless specified by the converter’s masterbatch addition. In artificial weathering tests under ISO 4892-2, unprotected natural PA12 shows surface chalking and reduction in tensile elongation before black pigmented PA12 grades; weatherable parts require adequate UV stabilizer masterbatch and validation of retention of elongation after 1000 h xenon-arc exposure.

Mechanical response of the as-conditioned material is governed by absorbed moisture rather than plasticizer migration. When specimens are conditioned per DIN EN ISO 1110 and tested at 23 °C under ISO 527-1/-2, the tensile modulus is typically lower than the dry-as-moulded value by 20–30 %. This shift must be accounted for in snap-fit design because the apparent flexural stiffness decreases and strain recovery is delayed. The following table lists representative values for unplasticized PA12; lot-specific values and the relevant certificate of analysis should be used for tolerance calculations.

Electrical insulation performance of unmodified PA12 is adequate for low-voltage cable sheathing; volume resistivity under IEC 60093 is typically in the range 10¹¹–10¹² Ω·m at 23 °C after conditioning. Dielectric strength measured by IEC 60243-1 is typically 20–25 kV/mm on 1.0 mm plaques. These values decrease with moisture uptake; for electrical applications, the designer should use the upper end of the conditioned moisture range. Linear thermal expansion of unfilled PA12 between 23 °C and 60 °C is approximately 110–130 × 10^-6 K⁻¹ per ISO 11359-2. Compared with 30 wt% glass-filled PA12, which may show 30–50 × 10^-6 K⁻¹, unfilled L1640 nf demands wider clearance gaps in assemblies exposed to temperature gradients.

Dynamic mechanical analysis of unfilled PA12 in the conditioned state shows a glass transition below 50 °C, often reported around 40–45 °C depending on moisture content. The damped tan δ peak shifts downward by absorbed water, meaning that room-temperature impact performance is ductile but stiffness at 80 °C is lower than at 23 °C; design calculations should not use the 23 °C tensile modulus for continuous service above 60 °C.

Pneumatic tubing extruded from unfilled PA12 is commonly qualified to ISO 7628-2 or ISO 14743, with minimum burst pressure requirements validated on finished tube at 23 °C and at 80 °C. The as-conditioned state reduces tensile strength by 10–15 % relative to dry-as-moulded tube; therefore, burst pressure values measured immediately after extrusion may not represent equilibrium service performance. For automotive air brake tubing, the finished article must meet SAE J844 or SAE J1394; resin compliance alone is insufficient.

Thermal ageing, chemical exposure, and regulatory testing demand grade-specific verification

Continuous heat resistance of unmodified PA12 is limited by oxidative degradation rather than melting. Under ISO 188 accelerated heat ageing at 100 °C, unmodified PA12 shows progressive loss of tensile elongation after 500–1000 h; stabilizer packages shift the embrittlement point beyond 2000 h. The natural, unmodified L1640 nf is therefore not specified for under-hood applications exceeding 100 °C in continuous contact with hot air unless an appropriate antioxidant masterbatch is used and validated by heat-ageing trials. Chemical resistance follows the general PA12 profile. The material is resistant to aliphatic hydrocarbons, diesel fuel, lubricating oils, greases, and many hydraulic fluids at temperatures up to 60 °C; resistance must be confirmed under ISO 175 with the actual process fluid. Strong mineral acids, concentrated formic acid, phenol, and chlorinated solvents at elevated temperature are incompatible and should be excluded from contact. Stress cracking resistance to aqueous salt solutions, including zinc chloride, should be assessed by ISO 22088-2 or ISO 22088-3 when the component is used in winter road-salt environments. Published data for the specific zinc chloride threshold of L1640 nf is limited; targeted testing is required.

A compliance review for L1640 nf must separate resin-level test data from finished-article certification. Polyamide 12 is covered by FDA 21 CFR 177.1500 for polyamide resins in food-contact applications and by EU 10/2011 when specific migration limits are met by the final article. No claim of conforming to a specific migration limit is transferred automatically from the resin grade; the converter must run migration tests on the finished part under EN 1186 and EN 13130. REACH registration for polyamide 12 monomers and polymers is managed by the supplier; the downstream user retains responsibility for SVHC communication under Article 33 when candidate-listed substances are present above 0.1 wt% in the final object. For drinking-water contact, the specific national approvals, such as DVGW W270, WRAS, or ACS, must be tested on the finished component, not on the resin alone.