In six-layer automotive fuel tank coextrusion, Braskem HDPE SGF4950 is used as the virgin high-density polyethylene carrier in both the outer skin and inner contact layers. The grade is selected on the basis of a reported melt flow rate of 0.30 g/10 min at 190°C under 5 kg load per ISO 1133-1:2022 and a density of 0.948 g/cm³ per ISO 1183-1:2019. These values position SGF4950 at the high molecular weight end of extrusion blow moulding grades, where parison sag is reduced and die swell is stable on accumulator heads with shot capacities of 5–10 kg. The outer skin typically occupies 15–20% of the shell thickness, the inner contact layer 35–40%, and the buried regrind layer 25–35%. Barrier control is provided by an EVOH layer at 3–5% volume fraction, flanked by two maleic anhydride-grafted tie layers each at 1.5–2.5%. On a production-scale coextrusion line, a 90 mm grooved-barrier extruder with 30:1 L/D delivers the SGF4950 melt to the inner and outer channels, while a 65 mm coextruder supplies EVOH and tie resin. Melt temperature is held at 200–220°C, die temperature at 190–210°C, and blow air pressure at 0.7–0.9 MPa. The mould circuit is set to 10–15°C, with total cycle time for a 60–80 L tank between 90–130 s. Target shell thickness is 4.0–8.0 mm in corner regions and 2.5–4.0 mm in flat sidewalls, as checked by ultrasonic gauge per ASTM E797.

The regrind layer is the critical boundary for lot-to-lot consistency. Internal flash, deflash heads, and rejected tanks are granulated and routed into the buried regrind layer at 25–35 wt%, and the melt flow rate of the reclaimed fraction is monitored per ISO 1133-1:2022. A shift greater than 0.05 g/10 min from virgin SGF4950 measurably increases parison sag on shot lengths above 800 mm, and upper-corner wall thickness falls from 3.0–3.5 mm to 2.0–2.5 mm when the regrind fraction exceeds 35 wt%. The environmental stress crack resistance of the regrind layer also declines because repeated heat history reduces the high molecular weight fraction; published production data for similar HMW-HDPE fuel tank grades show ESCR values under ASTM D1693-15 condition B falling from >1000 h on virgin material to 600–800 h on a 35 wt% regrind blend at 100% Igepal CO-630. This is the technical reason why regrind ratio is not increased to reduce material cost without re-qualification. Under CARB LEV III and EPA 40 CFR Part 86 evaporative emission protocols, a six-layer tank shell is designed to maintain hydrocarbon permeation below 0.5 g/m²/day at 40°C with CE10 fuel. The EVOH layer must remain continuous through deep-draw corners; local thinning to <1.5% of shell thickness triggers permeation failure before mechanical failure.

When a 25 L UN-certified jerrycan is blow moulded with SGF4950 and internal trim is reused

The 25 L monolayer jerrycan for Packing Group II liquids is qualified under 49 CFR 178.509 and ADR 6.1.5.3, with a drop test height of 1.2 m onto the closure edge after filling to 98% capacity with water at 18°C. The production cell uses a long-stroke reciprocating blow moulding machine with a clamp force of 300–400 kN, an accumulator head shot capacity of 1.5–2.5 kg, and a die bushing diameter of 35–50 mm. SGF4950 is fed through a 75 mm extruder with 25:1 L/D, a barrier mixing screw, and screen pack with 60/80/100 mesh configuration. Melt temperature is 200–215°C, die temperature 190–200°C, and blow air pressure 0.6–0.8 MPa. The mould is chilled to 10–25°C. Axial programming uses 10 points, with a target minimum sidewall of 2.2–2.5 mm and a shoulder minimum of 1.8 mm. In high-humidity coastal storage, 1.5–2.5 wt% of UV-stabilised carbon black masterbatch is compounded into SGF4950; dispersion is controlled at <10 µm agglomerate size by film-failure testing under ISO 18553. Post-consumer recyclate is excluded from the monolayer structure unless the UN design qualification is repeated with the recyclate blend, because a 0.05–0.10 g/10 min upward MFR shift can transfer failure from sidewall puncture to shoulder splitting in the 1.2 m drop test.

For Packing Group II liquids with specific gravity above 1.2, the UN drop height is reduced to 0.8 m, but the sidewall flexural modulus of SGF4950 at 1000 MPa under ISO 178:2019 must still support stacked warehouse loading. The jerrycan is tested for stacking under 40°C for 28 days with a superimposed load equivalent to 3.0 m of identical packages. ESCR remains the controlling resin property because the shoulder pinch-off weld is exposed to the hydrocarbon fill line; SGF4950 in this geometry exhibits no environmental stress crack failure before 1000 h under ASTM D1693-15 condition B when the pinch-off die temperature is not below 190°C.

For a 220 L tight-head L-ring drum, the accumulator discharge sequence determines whether the top chime and bottom chime survive a -18°C drop on the closure edge. The parison for a 220 L drum weighs 4.0–4.8 kg and is dropped from an accumulator head with 5–8 kg shot capacity through a die bushing of 220–280 mm. The blowing station uses clamp force of 800–1200 kN, and the extruder is typically a 120 mm grooved-barrier machine with 30:1 L/D. Melt temperature for SGF4950 is maintained at 205–225°C, die temperature at 195–215°C, and mould water temperature at 10–25°C. The blow air pressure is 0.6–0.8 MPa, with a pre-blow delay of 0.5–1.5 s and a final blow time of 15–25 s. Total cycle time is 120–160 s. Wall thickness distribution is controlled by 20–30 axial programming points; the top chime must retain 2.8–3.5 mm and the sidewall 2.0–2.5 mm. Capacity is checked gravimetrically per ISO 3507, and leakage is tested under 20 kPa internal air pressure with the drum immersed in water.

The top chime is the failure site that forces cycle-time discipline. When mould temperature in the chime area exceeds 25°C, the outer surface freezes at a slower rate, and the post-blow shrinkage differential between chime and sidewall reaches 1.5–2.0% as measured by comparative dimensional scans under ISO 15270. At -18°C, a sidewall with 2.0 mm minimum thickness survives the 1.2 m drop, but a chime below 2.5 mm fails by brittle splitting at the pinch-off weld. The relationship between wall thickness and cold-drop impact energy is non-linear: reducing top-chime thickness from 3.0 mm to 2.5 mm lowers absorbed energy by 20–30% due to stress concentration at the inner radius. This is why parison programming must direct extra material to the chime during the first 10% of the shot discharge. Regrind is limited to 20–30 wt% for tight-head drums carrying corrosive liquids, because higher regrind levels reduce ESCR below 600 h when tested per ASTM D1693-15 condition B and can move the ductile-to-brittle transition temperature upward by 5–10°C.

What limits the regrind fraction in surface-fluorinated monolayer agrochemical containers?

Surface-fluorinated monolayer containers based on SGF4950 are used for ester-based and aromatic solvent formulations where coextruded barrier layers are not available on small blow moulding machines. The container body is blow moulded from unfilled SGF4950 with a melt temperature of 200–215°C and a die temperature of 190–200°C, then exposed inline to a fluorine–nitrogen atmosphere at 0.1–1.0 vol% F₂ for 30–120 s. The fluorination reactor is operated under controlled vacuum or pressure swing, and the resulting surface fluorine-to-carbon ratio is measured by X-ray photoelectron spectroscopy. A fluorine barrier layer of 50–200 nm is sufficient to reduce weight loss of xylene-based formulations below 0.1 wt% over 28 days at 40°C in container permeation testing. Published data for SGF4950-specific fluorination kinetics is limited, so the line is qualified by permeation testing of each container geometry according to ASTM D2684 or internal chemical weight-loss protocols.

The regrind fraction in the fluorinated monolayer is the limiting formulation variable. Fluorination changes the surface energy and creates a partially cross-linked outer layer; that layer must not be granulated back into the feed stream unless the fluorinated portion is segregated, because melted fluorinated surface fragments can reduce interlayer adhesion and create micro-laminations in the pinch-off weld. Production practice caps closed-loop regrind at 10–15 wt% for fluorinated containers, compared with 25–35 wt% for non-fluorinated monolayer containers, and the fluorinated scrap is either sold as lower-grade regrind or directed to non-barrier applications. ESCR remains the acceptance criterion under ASTM D1693-15 condition B; containers filled with 100% Igepal CO-630 must reach >1000 h on virgin SGF4950 and >800 h on the 15 wt% regrind blend. Agricultural chemical packaging is qualified for resistance to stack compression under ISTA 3E or ASTM D4169 truck vibration profiles, with closure torque retention tested after 14 days at 40°C.

For diesel exhaust fluid tank blow moulding, the stress-cracking environment shifts from hydrocarbon swelling to polar urea solution and ammonia vapour. SGF4950 is processed on accumulator-head machines similar to automotive fuel tank lines, but the inner surface is not exposed to CE10 fuel, so the barrier requirement is replaced by long-term resistance to 32.5 wt% urea solution at temperatures up to 60°C during under-hood operation. The material must pass immersion testing under ISO 22241-4:2019 for urea solution compatibility, with tensile yield strength retention above 80% and elongation at break retention above 70% after 500 h at 60°C. The tank wall is typically 3.0–5.0 mm, with additional thickness at the filling neck and sensor bosses. The melt temperature is 200–220°C, and the mould temperature is 10–20°C. Cycle time for a 10–20 L DEF tank is 60–90 s. This application uses the same SGF4950 high melt strength for large parison, but the absence of EVOH barrier coextrusion allows a monolayer design with up to 30 wt% internal regrind if the regrind passes the same ISO 22241-4:2019 immersion test.

Parison swell and drawdown thresholds for SGF4950 in small technical blow mouldings

Small technical blow mouldings such as automotive fuel filler necks, air ducts, and chain saw oil tanks use SGF4950 when the part combines thick-wall rigidity with stress-crack resistance. The limiting processing window is narrower than in large containers because the shot size is below 500 g and the parison length is below 400 mm. Under such conditions, die swell for SGF4950 is observed in the range 30–50% depending on shear stress at the die lip, and drawdown is less than 10 mm/s at 200°C melt temperature. The die gap is set to 1.5–3.0 mm, and axial parison programming is performed with 10 segments. The blow pressure is 0.6–0.8 MPa, and the mould temperature is 10–20°C. If the melt temperature exceeds 225°C, the parison becomes too fluid on vertical drops longer than 300 mm; if the melt temperature falls below 195°C, the pinch-off weld becomes brittle because the high molecular weight fraction does not interdiffuse across the weld line. The lower temperature limit is confirmed by notched Charpy impact at 23°C being below 15 kJ/m² on weld-line specimens under ISO 179-1, while the bulk material remains above 20 kJ/m².