Evonik VESTAMID® L1833 black 9.7623 is a heat-stabilised polyamide 12 (PA12; nylon 12) injection-moulding compound reinforced with 20% by weight short glass fibre. The grade designation identifies the L-series PA12 base, the glass-fibre modification and the ready-colour black formulation 9.7623; the filler is dispersed as short fibres with a nominal length distribution that depends on screw work, back pressure, gate geometry and regrind content. The material is normally converted by injection moulding on three-zone reciprocating-screw machines, because the short glass fibre raises melt viscosity relative to unfilled PA12 and reduces the processing window for profile extrusion to a limited range of high-pressure, low-shear operations. The product occupies a specified position between unfilled PA12 and 30% glass-fibre-filled PA12: it retains the low moisture absorption, low specific gravity, hydrocarbon tolerance and low-temperature impact properties of polyamide 12 while adding the tensile modulus, tensile strength, creep resistance and heat-deflection performance needed for rigid connectors, brackets, fittings, cable-management parts and fluid-handling hardware. Representative mechanical and thermal results are generated on injection-moulded ISO 3167 multipurpose specimens prepared according to ISO 294-3, conditioned according to ISO 291, and tested under the specific methods named in Table 1. Results from standard specimens should not be treated as component design allowables; fibre orientation, weld lines, thickness-dependent crystallinity and local processing history alter each property in the final moulded part.

What limits the use of 20% glass-fibre reinforcement in semi-crystalline PA12?

The transition from unfilled PA12 to a 20% glass-fibre-filled PA12 changes the deformation mode from ductile yielding to fibre-dominated micro-cracking and brittle or quasi-brittle rupture at low strain. Under ISO 527-2 tensile loading, the tensile modulus of the filled grade is approximately 5,000 MPa, while unfilled PA12 typically lies between 1,300 MPa and 1,600 MPa under the same conditioning state; tensile strain at break is reduced to roughly 4% to 6%, and the strain-rate sensitivity of the compound is more pronounced than that of the unfilled matrix. Reinforcement raises density from approximately 1.01 g/cm³ to approximately 1.24 g/cm³ (ISO 1183-1) and shifts heat deflection temperature under 1.80 MPa (ISO 75-2/A) from the range 50–60 °C to approximately 150–160 °C. The filled grade also exhibits lower mould shrinkage and more anisotropic shrinkage than unfilled polyamide 12; weld lines formed at the meeting of two melt fronts can retain as little as 50% of the un-notched tensile strength when fibres orient perpendicular to the flow front. Notch sensitivity increases: sharp radii, flow marks, gate vestiges and poorly vented areas become more significant in the filled system. The mechanical envelope is therefore useful for semi-structural parts, but finite-element models must include fibre-orientation tensors from mould-filling simulation rather than isotropic material properties.

Table 1 lists representative single-point data for dry-as-moulded VESTAMID® L1833 black 9.7623. The figures are not specification minima or design maxima; they are reference values from current technical literature and may vary with batch and conditioning.

These values apply only to the dry-as-moulded state. Conditioning in water or humid air reduces stiffness and strength but can increase toughness; the degree of change is smaller than in unfilled PA12 and short-chain polyamides because the PA12 matrix absorbs less water. For parts with long flow paths or multiple gates, the actual tensile modulus in the flow direction can deviate from the isotropic specimen value by more than 30%, depending on local fibre-orientation tensors. Creep testing under ISO 899-2 is therefore recommended for pressure-loaded fittings and snap-fit arms; short-term tensile data do not capture the time-dependent loss of interference at temperatures above 80 °C.

Preliminary drying in a dehumidifying hopper dryer is required if sealed packaging has been opened for more than 30 min. The granulate should be dried at 80 °C for 4 h to 6 h to a moisture content below 0.10% by weight, and inlet air dew point should be maintained below -30 °C. Processing at moisture contents above 0.15% leads to hydrolytic chain scission, visible splay, reduced tensile properties and inconsistent surface gloss. A flat melt temperature profile of 230 °C to 270 °C is typical at the nozzle; higher temperatures up to 280 °C may be used for thin-wall parts below 1.0 mm, but residence time at temperatures above 280 °C should not exceed 10 min. Mould temperature is set at 40 °C to 80 °C for rapid cycles or 80 °C to 100 °C when maximum crystallinity, surface quality and dimensional stability are more important than cycle time. The screw should have an L/D ratio between 18:1 and 25:1, a compression ratio of approximately 2.0:1 to 2.5:1, and a low-shear metering zone; peripheral screw speed should be held between 0.1 m/s and 0.3 m/s to limit fibre fracture. Back pressure of 2 MPa to 6 MPa improves melt homogeneity but higher back pressure reduces fibre length. Cushion control should maintain 2 mm to 5 mm of melt ahead of the screw tip, and hold time should be set by weight-stability trials rather than by fixed timer alone. Gate freeze occurs earlier than in unfilled PA12; therefore holding pressure must be transferred to the cavity before the gate solidifies. Hot-runner systems with externally heated manifolds are acceptable if dead spots and stagnant melt regions are eliminated; cold-runner systems should keep the sprue and runner diameter large enough to avoid excessive shear heating. Regrind from sprues and runners can be added at 20% to 30% by weight, but each regrind pass reduces fibre length distribution and shifts tensile and impact properties.

Incoming inspection of VESTAMID L1833 black 9.7623 should verify pellet moisture by Karl Fischer titration according to ISO 15512, glass content by ash determination according to ISO 3451-1, density according to ISO 1183-1, and melt volume-flow rate on a capillary rheometer or melt indexer according to ISO 1133-1 at 235 °C under 5 kg load. Fibre-length distribution is not generally controlled by the supplier as a lot-release specification, but it can shift during material handling, long regrind chains or aggressive screw designs. Batch-to-batch variation in black pigmentation is normally controlled by the supplier’s colour code 9.7623; visual colour control should be quantified by spectrophotometric measurements on plaques rather than by subjective inspection. In high-volume production, in-mould pressure sensors are recommended for detecting differences in melt viscosity or gate freeze caused by moisture or regrind variation; short-shot trials after material changes should be repeated because the filled grade has a shorter flow length than unfilled PA12 under the same injection pressure.

When hydrocarbon resistance and low moisture uptake are selected, how does L1833 compare to PA6/PA66-GF20 and PBT-GF20?

At equivalent 20% glass-fibre loading, polyamide 12 retains lower saturated water absorption than PA6 or PA66 matrices. Under ISO 62 immersion at 23 °C, PA12 mouldings typically absorb approximately 1.0% to 1.5% by weight at saturation, whereas PA6 or PA66 can exceed 8% to 10% depending on formulation, plate thickness and conditioning history. At 50% RH, PA12 absorbs roughly 0.5% to 0.8%, while PA66 absorbs approximately 2.5% to 3.0%. The practical result is that L1833 components retain a larger fraction of their dry stiffness and show smaller dimensional expansion when moved from dry storage to humid service; however, conditioning before snap-fit assembly remains necessary because interference and insertion-force calculations must use the conditioned modulus. Relative to PBT-GF20, L1833 has lower density (1.24 g/cm³ versus approximately 1.42–1.45 g/cm³), lower heat-deflection temperature, and lower short-term stiffness, but it usually offers better impact behaviour at temperatures below 0 °C under ISO 179-1/1eA and greater resistance to hydrolysis in hot-moist environments. PBT-GF20 has lower equilibrium moisture uptake, but its higher density and more limited low-temperature ductility can be disadvantages in vehicle underbonnet hardware. Against unfilled PA12, the 20% glass-fibre grade replaces the high ductility of unfilled resin with a substantial gain in creep resistance and heat-deflection temperature; unfilled PA12 is generally limited to lower continuous service temperatures under load. Against 30% glass-fibre PA12, L1833 has lower melt viscosity, easier filling in thin-wall sections, lower tool wear and less severe anisotropic shrinkage, but lower modulus, strength and heat-deflection temperature. The choice between 20% and 30% glass-fibre PA12 therefore involves a trade-off between stiffness and processability.

Typical production-scale applications for VESTAMID L1833 black 9.7623 include injection-moulded quick connectors and couplings for hydrocarbon vapour lines, pneumatic push-in fittings, cable ducts, cable ties, brackets, clips, sensor housings and fasteners where combined low-temperature impact and elevated-temperature short-term resistance are required. Average injection moulding clamp force is normally calculated from projected area at 0.5 kN/mm² to 1.0 kN/mm², with higher pressures needed for thin walls, long flow lengths and multicavity tools. Weld lines are inherent in any filled moulding with multiple gates or interruptions; gate placement should force weld lines into low-stress regions, and if weld-line strength is critical, local wall thickening or overflow wells are often necessary. Because the compound contains 20% glass fibre, tool steels with hardened cavities or wear-resistant inserts are recommended for production runs exceeding 500,000 cycles. Mould venting must be more generous than for unfilled PA12, with land depths below 0.03 mm to avoid gas burning and fibre-induced vent clogging. Compliance with RoHS Directive 2011/65/EU and REACH Regulation (EC) No 1907/2006 should be confirmed from current supplier declarations for the specified colour code; food-contact, potable-water or medical use requires separate written confirmation because the black formulation may contain carbon black and processing additives that are not covered by a generic statement.

Thermal ageing tests on injection-moulded specimens according to ISO 188 at 150 °C generally show progressive loss of tensile strain at break before a sharp decline in tensile strength; carbon black grade 9.7623 provides UV stabilisation for outdoor use, but surface chalking and gloss change occur after prolonged weathering according to ISO 4892-2 or ISO 4892-3. Glass fibre reinforcement reduces the coefficient of linear thermal expansion from approximately 120 × 10⁻⁶ K⁻¹ for unfilled PA12 to roughly 40 × 10⁻⁶ K⁻¹ in the flow direction and 60 × 10⁻⁶ K⁻¹ normal to flow, depending on fibre orientation; this difference must be considered in metal-to-plastic assemblies with wide temperature cycles. Electrical volume resistivity and surface resistivity are consistent with a reinforced polyamide insulator, but carbon black can reduce surface resistivity relative to natural grades; electrical safety requirements should be verified under the component standard rather than inferred from base-polymer data.

Chemical resistance boundaries and incompatibilities in glass-filled PA12

Polyamide 12 is resistant to many aliphatic hydrocarbons, oils, greases, fuels and hydraulic fluids at ambient temperature, but it is not a barrier material. Strong mineral acids, polar organic solvents, and oxidising media attack the matrix, and the glass-fibre phase can be affected by alkaline aqueous solutions at elevated temperature. Concentrated acetic acid, formic acid, m-cresol, and some chlorinated solvents cause swelling, surface attack or environmental stress cracking; the risk increases with high residual moulded-in stress, sharp radii, weld lines and hot-wet exposure. Continuous contact with hot aqueous glycol mixtures or engine coolants may plasticise the PA12 matrix and reduce tensile properties; specific chemical resistance for the black 9.7623 formulation must be verified in the intended fluid at worst-case service temperature. The material should not be dried above 100 °C in circulating air because thermo-oxidative surface degradation can occur; vacuum or dehumidifying dryers are preferred. Regrind reuse should be limited to 20% to 30% by weight and must be combined with mechanical evaluation because fibre-length reduction and matrix degradation change failure behaviour. The use of amine-based additive masterbatches is not recommended without trials, as polyamide chain scission or side reactions can produce odour, surface deposits and inconsistent mechanical data. Published data for long-term hydrothermal ageing of this specific grade in aggressive biodiesel or alcohol-blended fuel at temperatures above 80 °C is limited; component validation under production tooling and actual fluid exposure is required before design release.