What Causes Zinc Chloride Stress Cracking in Coextruded Vapour Recovery Lines?

Grilamid® L 20H FWA nat is specified as the inner functional layer in coextruded multi-layer vapour recovery lines where resistance to zinc chloride derived from road de-icing brines and underbody corrosion products is the limiting design factor. In a three-layer construction comprising an impact-modified outer PA12 layer, a central EVOH barrier layer, and an inner Grilamid® L 20H FWA nat layer, the inner layer is run on a 30:1 L/D single-screw extruder with a barrier feed section at a barrel temperature profile of 210 °C, 225 °C, 235 °C, 240 °C, and 245 °C. Melt temperature at the die is held between 238 °C and 245 °C. Pre-drying at 80 °C for 4–6 h to a residual moisture content below 0.10 wt% is mandatory because higher moisture levels depress melt viscosity and produce hydrolysis-induced surface defects at die exit. Layer thickness distribution is controlled by spiral mandrel die geometry, with the inner PA12 layer maintained at 0.20–0.35 mm and total wall thickness at 1.0–1.5 mm. Adhesion to EVOH requires a maleic anhydride-grafted tie resin; without the tie layer, delamination occurs during post-extrusion corrugation because PA12 and EVOH differ in crystalline shrinkage by approximately 1.2–1.5% in the transverse direction. Permeation limits under SAE J2260 and CARB evaporative emission protocols are achieved only when EVOH layer continuity is verified at 100% via optical inspection after vacuum calibration. Burst testing on production lines is carried out at 23 °C and 121 °C according to ISO 7628-1, with minimum burst pressure requirements derived from the service rating of the line. The zinc chloride stress cracking resistance of PA12 is evaluated using the bent strip method of DIN EN ISO 22088-3 after 200 h immersion in 50 wt% ZnCl₂ at 60 °C. The L 20H FWA nat grade retains tensile elongation at break above 120% at 23 °C in dry-as-moulded condition when tested per ISO 527-2:2012, but that value declines if moulding moisture exceeds 0.15 wt%. In production, barrel residence time is limited to 8–12 min to prevent thermo-oxidative yellowing of the natural grade, and purging with a high-viscosity HDPE is performed before shutdown to minimise black specks from degradation.

Across heavy-truck air brake circuits, Grilamid® L 20H FWA nat is extruded into plain polyamide tubing with outside diameters of 6 mm, 8 mm, 10 mm, 12 mm, and 16 mm, used for compressed air service at working pressures up to 1.25 MPa. Unlike PA6 and PA66, the PA12 backbone provides a low equilibrium moisture absorption of 0.7–0.8 wt% at 23 °C and 50% relative humidity per ISO 62:2008, which limits swelling-induced changes in internal diameter to below 1.0% after 1,000 h of humid exposure. Extrusion lines employ a 25:1 L/D single-screw extruder with a three-zone screw and a grooved feed section, barrel temperatures from 200 °C at the feed zone to 250 °C at the metering zone and head, and a die temperature of 245–250 °C. Post-die sizing uses a vacuum water tank held at 20–30 °C and a haul-off ratio between 1.02 and 1.08 to set residual longitudinal orientation. For SAE J844 Type A non-reinforced tubing, production lots are burst tested at 23 °C and after low-temperature impact at −40 °C, with acceptance criteria fixed by the OEM but normally not less than four times the rated working pressure of 1.25 MPa. The heat-stabilised package of Grilamid® L 20H FWA nat allows continuous service at 100 °C in dry air, but exposure to zinc chloride-rich road spray under sustained tensile stress above 5 MPa should be assessed for stress cracking resistance before approving underbody routing. Hose insertion force is governed by outer diameter tolerance of ±0.05 mm for 8 mm OD; this is achieved by maintaining a melt pump before the die to limit output variation to ±1.5%.

Flexible Potable Water and Beverage Dispensing Lines Under EU 10/2011

The FWA designation denotes the food-contact and potable-water formulation of EMS-Grivory Grilamid® L 20H FWA nat, used in post-mixer beverage tubes, espresso machine water lines, and carbonated water feeds where low extractable content and low taint transfer are critical. Compliance is assessed under Commission Regulation (EU) No 10/2011 as amended by Regulation (EU) 2020/1245, with overall migration limits of 10 mg/dm² for plastics in contact with aqueous foods under test condition OM2 at 40 °C for 10 days. The resin is evaluated under 21 CFR 177.1500(b) for nylon homopolymers and copolymers used in food-contact articles, subject to end-use extraction testing because the natural grade contains a heat stabiliser package that must be confirmed as complying with the positive list. In extrusion, processing temperatures are held at 225–240 °C to avoid generation of low-molecular-weight laurolactam oligomers above sensory threshold; vented barrels with a vacuum of −0.08 MPa are used to strip residual monomer. The tube is cooled in a warm water bath at 60 °C for the first 2 m, then at 20 °C, to limit surface crystallinity and maintain transparency of the natural grade. Dimensional specifications for 4 mm OD × 2 mm ID beverage lines require a concentricity of at least 0.1 mm and an inner surface roughness Ra below 0.4 µm to prevent biofilm adhesion. In-line pressure testing at 1.5 MPa for 30 s is performed after laser marking, with no leakage allowed. For carbonated water service, the tubing must withstand repeated pressure cycling between 0.2 MPa and 0.8 MPa at 5 °C for 100,000 cycles; published data for this specific cycling configuration is limited, so validation is carried out on the final assembled dispenser under NSF/ANSI 51 criteria. Long-term hot-water exposure at 80 °C shows tensile strength retention above 60% after 1,000 h per ISO 527-2:2012. Beyond 90 °C, hydrolysis rate increases and service life drops quickly. The grade is not supplied with UV stabilisation, so natural tubing installed in direct sunlight requires a light barrier or additional stabiliser masterbatch.

Chemical dosing circuits for chlorine-based sanitising solutions employ Grilamid® L 20H FWA nat as an extruded tube and injection-moulded fitting material where polyolefins fail on stress cracking and fluoropolymers carry excessive cost. The tubing is produced in outside diameters from 4 mm to 12 mm, with wall thickness selected for a maximum working pressure of 1.0 MPa at 23 °C in sodium hypochlorite solutions up to 200 ppm free chlorine. Extrusion runs on a 24:1 L/D single-screw machine with a melt temperature of 225–235 °C and a screw speed of 30–50 rpm; the die is fitted with a 0.4 µm melt filter because gel particles from moisture-contaminated regrind cause fish-eye defects that reduce burst pressure. Chemical resistance is evaluated by immersion in 200 ppm NaOCl at 40 °C for 1,000 h, with retention of tensile strength above 80% when tested per ISO 527-2:2012. The grade is not recommended for strong mineral acids such as 20% hydrochloric acid at temperatures above 40 °C because amide hydrolysis causes a rapid loss of molecular weight and a drop in notched Charpy impact strength below 3 kJ/m². For dosing lines carrying citric acid at pH 3 and 60 °C, the maximum continuous service temperature is limited to 50 °C; at pH 9–11, sodium hydroxide solutions up to 1% are tolerated only at ambient temperature. Fittings are moulded with a mould temperature of 60 °C and connected by push-in or barbed fittings, with pull-out force specified at greater than 120 N for 6 mm OD tubing after 24 h conditioning at 23 °C. Published data for dynamic fatigue of this specific grade in chlorine-dosed potable water is limited; accelerated validation is therefore performed using end-use assemblies rather than isolated material specimens.

When Loose Tube Fibre Buffers Require Hydrolysis Resistance Below 60% Relative Humidity

In optical fibre cable construction, Grilamid® L 20H FWA nat serves as a loose tube buffer material because its low water absorption reduces post-extrusion shrinkage in humid installation environments. The compound is extruded as a 1.7–2.2 mm OD loose tube over a gel-filled bundle of 12–24 fibres, with a wall thickness of 0.20–0.30 mm and a concentricity of ≥95% relative to the fibre bundle axis. A 25:1 L/D single-screw extruder fitted with a 3.0–4.0 mm round die and a fibre-guide tip is run at a melt temperature of 235–240 °C and a line speed of 200–400 m/min; the melt is pressure-screened through a 30 µm breaker plate to remove gels that would produce point defects. After extrusion, the tube is quenched in water at 25–35 °C and wound with back-tension controlled to 0.5–1.0 N. Post-extrusion shrinkage is measured according to IEC 60794-1-2 method E11 after 24 h at 85 °C, with target values below 0.5% for indoor cable and below 1.0% for outdoor cable designs. The heat-stabilised formulation permits intermittent exposure to 120 °C during jacketing operations; continuous exposure above 100 °C in dry environments should be limited to avoid thermo-oxidative degradation of the natural grade, which lacks carbon black UV protection. Compatibility with thixotropic hydrocarbon gels used in loose tube filling is evaluated by gel ageing tests at 85 °C for 30 days, with retention of tensile elongation at break above 100%. If the cable is specified for outdoor aerial use, the natural grade must be protected by an outer UV-stabilised polyamide or polyethylene jacket because unmodified natural PA12 degrades on prolonged UV exposure under ASTM G154 cycling. Moisture-driven dimensional change in the installed tube is governed by ISO 62:2008 water absorption of 0.7 wt% at saturation, compared with 1.8–2.2 wt% for PA6 at 23 °C in water, which is the primary design reason for selecting PA12 in high-humidity duct environments.

A reciprocating screw injection moulding machine with a 20:1 L/D screw processes Grilamid® L 20H FWA nat into quick-connect couplings, fluid sensor housings, and chemical-resistant clips for water handling systems. Barrel temperature zones are set from 210 °C at the feed zone to 250 °C at the metering zone, nozzle at 255 °C, and mould temperature is held between 40 °C and 80 °C depending on part wall thickness. Pre-drying at 80 °C for 4–6 h to a residual moisture below 0.10 wt% is mandatory before moulding; if granulate remains open to a production environment above 60% relative humidity for more than 30 min, re-drying is required because PA12 absorbs surface moisture quickly. Injection speed is 30–60 mm/s for wall sections of 1.0–2.5 mm, and holding pressure is set to 60–70% of the injection peak pressure to minimise sink marks around seal seats. Weld lines in the sealing area are avoided by gate placement at the thickest cross-section, and the resulting weld line strength is checked on a tensile bar per ISO 527-2:2012, with a minimum retention of 60% of the unwelded strength. Moulded parts are allowed to crystallise for 1–2 h at 80 °C when dimensional stability is critical, because PA12 continues slow post-crystallisation after ejection and can shrink an additional 0.3–0.5% within 48 h. Leak-tightness of assembled quick connectors is verified by an air-under-water test at 0.6 MPa for 30 s with no bubble formation. For pressurised hot-water fittings, published data for long-term creep of this specific natural grade is limited; qualification therefore relies on pressure cycling based on ISO 9080-derived strength curves or customer-specific test plans, not on extrapolated long-term hydrostatic strength curves.