EMS-GRIVORY Grilamid L 16 GM nat is a natural-colour, glass-microsphere-modified polyamide 12 injection-moulding grade based on poly(lauryllactam). The PA12 backbone contains an 11-carbon methylene sequence between amide groups; this lower amide density reduces equilibrium moisture uptake compared with PA6 or PA66. For unfilled PA12, water absorption at 23 °C and 50 % relative humidity is commonly 0.6–0.8 % when tested to ISO 62, while PA66 can exceed 2.5 %. In the GM variant, spherical glass microspheres are dispersed in the matrix to reduce anisotropic mould shrinkage and improve dimensional stability. The suffix nat denotes an unpigmented natural colour.

Under ISO 16396-1, the grade is specified as a polyamide 12 injection-moulding compound with glass microsphere filler; the exact designation block, filler mass fraction and viscosity class should be taken from the supplier datasheet because the trade name does not encode the complete ISO designation. The base PA12 melting point is approximately 178 °C by ISO 11357-3. The glass filler does not eliminate the PA12 crystalline endotherm but reduces the volume fraction of crystallisable polymer. This lowers free shrinkage after ejection; typical mould shrinkage for a 2 mm plaque tested to ISO 294-4 is 0.4–0.7 % for this type of glass-bead PA12, compared with 1.0–1.5 % for a comparable unfilled PA12.

What Distinguishes Glass Microspheres from Milled Glass and Short Glass Fibres in Shrinkage Control?

Glass microspheres are roughly spherical and typically have diameters in the 10–50 µm range; they do not orient strongly along the melt-flow direction. Short glass fibres align in flow and produce anisotropic shrinkage, with longitudinal values often 0.1–0.3 % and transverse values above 0.8 % depending on fibre content and gate geometry. The GM filler therefore suppresses planar shrinkage differences in circular connectors, sensor housings and thin-walled clamps where roundness must be retained after ejection. Milled glass is intermediate in aspect ratio and provides less optical isotropy than microspheres but higher modulus than unfilled resin.

This isotropic dimensional control reduces warpage after annealing or humid ageing but carries a mechanical trade-off. Under ISO 527-1/-2, a 30 % short-glass-fibre PA12 can exceed 7,000 MPa tensile modulus, while a glass-microsphere PA12 generally remains below 3,000 MPa. Notched Charpy impact under ISO 179-1/1eA is lower than unfilled PA12 because the spherical filler can act as a stress concentrator at the interface. Selection of L 16 GM nat is therefore appropriate for dimensional stability and moderate stiffness, not for maximum tensile strength or snap-fit impact.

Compared with unfilled PA12, the glass-microsphere grade reduces mould shrinkage and post-mould warpage, raises compressive stiffness, but reduces ductility and increases surface haze on polished tooling. Compared with short-glass-fibre PA12, it offers lower tensile modulus but reduced anisotropy and better surface finish. Against PA6 or PA66 glass-bead grades, this PA12 product exhibits lower water absorption, lower density, and better retention of modulus under humidity ageing, but lower dry-state heat deflection temperature and hardness. Material substitution from PA66 to PA12 requires recalculating snap-fit insertion force and clearance fits because the tensile modulus is lower.

Melt Rheology, Screw Plastication, and Barrel Thermal Profiling in Injection Moulding

PA12 has a narrow melting range and lower melt viscosity than PA6/PA66 at equivalent molecular weight. Glass microspheres increase low-shear viscosity less than high-aspect-ratio glass fibre and generate less shear heating. Typical barrel settings for this grade are 220–240 °C at the rear, 240–260 °C in the centre, and 250–270 °C at the nozzle; air-shot melt temperature should be 230–280 °C. Mould temperature may be set from 30 °C to 80 °C. Lower mould temperatures shorten cycle time; higher mould temperatures increase crystallinity and dimensional stability. Mould-surface temperature variation above ±3 °C can produce differential post-shrinkage near the gate and at flow-path ends.

On a 40 mm, 20 L/D general-purpose injection screw, the feed depth should be cut for PA12 semi-crystalline resin, and the compression ratio should be 2.2:1–2.6:1 to avoid microsphere attrition. Back pressure between 30 bar and 80 bar hydraulic and screw speed below 300 rpm limit filler breakage. Production-scale glass-bead polyamide moulding has shown that high back pressure or undersized feed zones crush microspheres into angular fragments, raising viscosity unpredictably and increasing moulded-in stress. Screw recovery time should be shorter than cooling time by at least 5 s; if recovery exceeds 15 s, barrel residence time becomes the limiting factor and colour changes may show yellowing.

The glass microspheres require distributive mixing, not high-shear dispersion, because they are already discrete particles. Screws with aggressive Maddock mixers are generally unnecessary and can create excessive shear heating; low-shear mixing elements with moderate compression ratio are preferred. The melt volume-flow rate for medium-viscosity PA12 grades is commonly determined at 275 °C under 5 kg load to ISO 1133-1; glass microsphere filler reduces MVR relative to unfilled PA12 at the same temperature. Capillary rheometry at 250 °C and shear rates 100–5,000 s^-1 is used for mould-filling simulation; a single-mode viscosity model is often insufficient for glass-bead PA12 at high shear and should be replaced by a multi-mode fit.

Crystallisation of PA12 proceeds rapidly below 160 °C; the cooling rate controls the α/γ phase ratio. Mould temperatures below 40 °C freeze the surface layer before full crystallisation, reducing crystallinity and increasing dimensional sensitivity to later annealing. For metering bodies and bearing housings, annealing at 130–150 °C for 1–2 h in oil or nitrogen is used to stabilise dimensions before final machining. Glass microspheres can act as heterogeneous nucleation sites and refine spherulite size, but they do not prevent weld-line weakness.

Weld lines downstream of cores or multiple gates show reduced tensile strength because the glass microspheres do not bridge the flow front and reduce effective load-bearing cross-section. Strength retention at a weld line can fall below 70 % of the unwelded value under ISO 527-1/-2. Therefore gates should be sequenced so that weld lines move away from snap-fit features and sealing faces; external gas assist or sequential valve gating is preferred for thin-wall round parts.

When Residual Moisture Exceeds 0.1 % Before Plastication

PA12 absorbs water through hydrogen bonding at amide groups; glass microspheres reduce the hygroscopic polymer fraction but do not eliminate moisture uptake. Predrying at 80 °C in a desiccant dryer with a dew point below -30 °C is required when residual moisture exceeds 0.1 %. Virgin material in a 50 mm bed depth typically requires 4–8 h; cold regrind or material stored above 60 % RH requires 8–12 h. Water at melt temperature hydrolyses the PA12 chain, shifting molecular weight lower and reducing notched impact strength. Splay, silver streaks, and nozzle drool indicate severe moisture but are not reliable for marginal levels; Karl Fischer titration or a TGA moisture balance should be used for lot release.

Drying above 90 °C for extended periods can yellow natural material and consume heat-stabiliser reserves. The hopper dryer should be interlocked to prevent setpoint drift, and return air from the drying hopper should be checked for fines because microsphere dust can accumulate in the desiccant bed. Regrind above 30 % by weight may increase melt viscosity variation and lower impact; if regrind is used, the ratio should be fixed in the batch record and the granulate screened to remove fines below 0.5 mm.

Automotive fuel-system connector bodies, clips and quick-connect retainers are a principal use of PA12 because of resistance to aliphatic fuels, diesel, engine oil and zinc-free coolant. The glass-microsphere modification allows moulders to maintain roundness of clip bores and connector sealing faces without the anisotropic warpage seen with glass fibre. In pneumatic quick couplings and compressed-air line fittings, the grade is selected where dimensional stability under humidity changes is required; lower water absorption than PA6/PA66 retains hardness and friction more uniformly. Cable sheathing clamps, sensor brackets and gear encoder housings benefit from reduced shrinkage and less post-mould distortion during warehouse storage at uncontrolled humidity.

In automotive fuel-contact applications, PA12 grades are commonly validated against OEM material standards that reference ISO 16750-4 for thermal cycling and ISO 9227 for salt spray. Resistance to diesel, biodiesel blends and engine oil should be confirmed by immersion testing at the upper use temperature because glass filler can expose additional interfacial surface for fuel diffusion and reduce post-exposure elongation. Published data for this specific configuration under biodiesel immersion is limited; component validation should include post-exposure tensile testing to ISO 527-1/-2 and dimensional measurement at 23 °C and 50 % RH.

Chemical Resistance Limits and Processing Incompatibilities

PA12 resists aliphatic hydrocarbons, mineral oils, greases and dilute alkaline solutions, but is attacked by strong mineral acids, phenols and concentrated formic acid. Zinc chloride solutions, including de-icing brines containing zinc chloride, can initiate environmental stress cracking in stressed PA12 components. The glass microsphere interface may provide a preferential path for crack propagation if filler-matrix adhesion is degraded by acid or water exposure. Hot-water contact should be limited to 60 °C continuous for typical unfilled PA12; glass microspheres do not improve hydrolysis resistance, and applications above 80 °C in aqueous media require a hydrolysis-stabilised grade or a different polymer.

Combination with amine-based additives, metal salts or excessive fatty acid mould-release agents may shift crystallisation behaviour or reduce filler-matrix adhesion. Additive migration kinetics in the PA12 matrix are Fickian; low-molecular-weight amide slips or metal soaps can bloom to the surface and alter frictional behaviour in connector retaining features. Electrical connector applications require supplier data for comparative tracking index and dielectric strength; PA12 generally provides high surface resistivity but can accumulate static charge unless an antistatic or conductive grade is used.

Food-contact use of the glass-microsphere-filled material is not automatically covered by base-polymer approvals under FDA 21 CFR 177.1500 or EU Regulation (EU) No 10/2011, because the filler surface sizing and any migration of processing aids must be assessed. A supplier regulatory statement should be obtained for each article configuration. The material is typically supplied with a EU REACH (EC) No 1907/2006 and RoHS Directive 2011/65/EU statement, but specific SVHC content should be confirmed in the supplier’s technical documentation.

Continuous use temperature in air for unfilled PA12 is often specified as 80–100 °C depending on additive package and test duration. Glass microspheres do not improve oxidative stability; above 120 °C, surface yellowing and loss of elongation occur unless the heat-stabiliser package is adequate. In engine-compartment locations with air temperature 135 °C under load, PA12 may soften or creep excessively, and a PA46 or PPA material may be required. For parts under constant load, creep testing to ISO 899-1 is necessary because glass microspheres do not suppress the viscoelastic response of the PA12 matrix.

For North American comparative data generation, ASTM D638-14 tensile testing is sometimes substituted for ISO 527-1/-2; values are not directly comparable because of specimen geometry and strain rate. The L 16 GM nat grade is not recommended for applications requiring optical clarity, high tensile impact, or continuous service above 100 °C in air. Process capability for narrow tolerances below ±0.1 % of nominal dimension must be established by tool trials, because published data for this specific configuration under high-humidity cycling is limited. Thin-wall connectors with wall thickness from 0.8 mm to 2.5 mm are typical; for a 1.5 mm wall, pin-point gate diameter should not be below 0.8 mm, and land length should be 0.5–1.0 mm. The mould should be vented to 0.01–0.03 mm depth on the parting line to avoid burn marks from trapped volatiles.