LyondellBasell HDPE H4620 is processed as a high-molecular-mass low-melt-flow blow molding and thick-sheet extrusion grade. Nominal melt-flow rate is 0.20 g/10 min at 190°C/2.16 kg (ISO 1133-1:2022), and nominal density is 0.946 g/cm³ (ISO 1183-1:2019). The low melt index indicates a molecular architecture that resists parison drawdown in large-shot blow molding and limits sheet sag in deep-draw thermoforming. Downstream applications concentrate in large-part blow molding, multilayer coextrusion, thick sheet extrusion, and regrind-based profile extrusion.

Extrusion blow molding of 25–220 L UN-rated tight-head drums is a demanding downstream segment because parison stability and pinch-off weld strength determine regulatory test outcomes. Accumulator-head machines dominate production; the typical configuration includes a 90–120 mm barrier-screw extruder with 24:1 L/D ratio and a spiral-grooved feed section, twin platens, and an accumulator shot capacity of 4.5–12.0 kg. Die melt temperature is held between 190°C and 215°C. Temperatures above 225°C produce visible parison necking, top-wall thinning, and increased oxidized gel formation; temperatures below 180°C raise melt pressure and reduce die-lip surface quality. Blow mold cooling water is set to 8–14°C. A 220 L drum of 10.5–11.5 kg final weight typically runs at 120–180 s cycle time, excluding automated flash removal. The bottom pinch-off weld and the top chime area are the principal failure origins during cold-drop testing.

UN certification for 1H1 drums requires sequential validation lots. Drop testing follows 49 CFR 178.603 or ADR 6.1.5.3; for Packing Group II liquids, the drop height is 1.2 m at -18°C, and three drums are conditioned and dropped to strike the top seam, sidewall, and bottom seam. Leakproofness testing under 49 CFR 178.604 applies internal air pressure of 30 kPa for 10 min. Stack compression testing under 49 CFR 178.606 is conducted for 24 h at 40°C with the superimposed load calculated for the transported product. The mold design must maintain sidewall thickness above 1.2 mm at every point, because local thinning below this value reduces top-load and cold-impact safety margins.

Stress-cracking resistance is the central material property. ASTM D1693-15 condition B immersion in 10% Igepal solution at 50°C typically gives nominal ESCR values above 1000 h for 2 mm compression-molded plaques, but actual drum-wall values after extrusion oxidation and regrind incorporation are lower. Therefore the maximum post-industrial regrind fraction is controlled at 30 wt% for dangerous-goods drums unless factory-specific melt-flow and ESCR data support a higher level. Concentrated nitric acid, hydrogen peroxide above 30%, and freely draining xylene or toluene are not recommended as continuous loads without independent permeability and stress-crack validation.

Multilayer Coextrusion Blow Molding of Automotive Fuel Tanks

The outer and inner skins of a five-layer automotive fuel tank use H4620 to provide cold-impact strength and hydrocarbon resistance outside the EVOH barrier layer. The barrier is a 32–38 mol% ethylene-vinyl alcohol copolymer with a target layer thickness of 0.10–0.20 mm. Maleic anhydride-grafted polyethylene tie layers, each 0.10–0.30 mm thick, connect the polar EVOH to the non-polar HDPE. Total wall thickness is ordinarily 4.0–6.0 mm for 55–110 L tanks. The density of 0.946 g/cm³ is at the lower end of the automotive fuel tank range; this improves low-temperature impact but requires stronger ribbing and side-wall geometry than a 0.952 g/cm³ grade would require for the same burst and pressure-pulse performance.

The process constraint is thermal separation. EVOH degrades above 240°C, while H4620 requires at least 205°C to suppress melt fracture. The coextrusion feedblock is designed so that the two melt streams meet only in the final manifold. If EVOH temperature exceeds 235°C, gels form and create pinholes through the barrier; if HDPE temperature falls below 200°C, higher backpressure produces shear heating in the extruder, which is detectable as a rising pressure trend at the gear pump. The inner layer may contain up to 30 wt% of in-plant regrind from trimmed flash; above this level, MFR broadening and inner-wall defect formation after fuel conditioning become more likely. Melt temperatures for the five-extruder configuration are usually split as HDPE at 210–220°C, tie resin at 200–215°C, and EVOH at 220–235°C.

Hydrocarbon permeation testing is system-level rather than grade-specific. A five-layer structure with an intact EVOH layer reduces CE10 permeation by 70–90% relative to monolayer HDPE, but published SAE J1737 data for H4620 in a defined tank construction is limited. Cold-impact testing is performed after fuel soak at -40°C; the HDPE skins must avoid crack propagation through the pinch-off weld and insert bosses. The regulatory drivers are CARB LEV III and EPA 40 CFR Part 86 evaporative emission limits, with tank-level durability validated by OEM-specific pressure-pulse and low-temperature impact sequences.

For thick-sheet extrusion into thermoformable stock of 4–12 mm, H4620 is processed on a 75–100 mm, 30:1 L/D barrier screw fitted with a gear pump and flexible-lip sheet die. Melt temperature is held at 200–215°C. The vertical three-roll polishing stack is set to 70–90°C on the top roll, 60–80°C on the middle roll, and 40–60°C on the lower roll. Roll temperatures above 90°C produce sheet surface roughness and vacuum voiding; roll temperatures below 50°C freeze in residual stress that is released during the first heating cycle in the thermoformer. The extruded sheet is used for plug-assisted thermoformed industrial battery housings, machine guards, and material-handling dunnage. In plug-assisted forming, sheet surface temperature is brought to 150–170°C; the plug is heated to 100–120°C and is commonly made from syntactic foam because aluminum plugs chill the HDPE too quickly and cause corner cracking. Draw ratios are kept below 3:1 for corner radii below 5 mm.

The terminal parts are not loaded under constant internal pressure; the main requirements are puncture resistance, hydrolytic stability, and flatness after conditioned exposure at 80°C for 24 h. Dimensional stability is tested by ISO 75-2 method B at 0.45 MPa; HDPE H4620 shows large deflection compared with mineral-filled polypropylene but also has a higher coefficient of linear thermal expansion of 1.0–1.3 × 10⁻⁴ K⁻¹. Steel inserts or bossed mounts therefore require isolation washers to prevent thermally induced cracking. Hot-plate welding at 230–250°C plate temperature and 0.15–0.30 MPa joining pressure is the preferred joining method; vibration welding produces wider flash but acceptable short-term strength in non-cosmetic industrial parts.

What Limits the Use of H4620 in Fluorinated Agrochemical Jerrican Production?

When a 20–60 L extruded jerrican must retain toluene, xylene, or cyclohexanone-containing formulations, monolayer HDPE fails the permeation requirement and inline fluorination is applied to the inner wall before filling. The jerrican is blow molded from H4620 on a monolayer accumulator machine and then treated with a 0.5–2.0 vol% fluorine-in-nitrogen mixture at 25–40°C for 10–60 s, producing a fluorinated surface layer 20–80 nm thick. The treatment converts surface C–H bonds to C–F bonds and reduces solvent uptake by barrier densification. It does not improve barrier performance after deep scratches or surface abrasion; capping systems with metallic friction rings can remove the fluorinated layer at the neck, which is the most common leak path in field returns.

The blow molding process uses an accumulator machine with shot size 1.5–4.0 kg, melt temperature 195–210°C, and fluorine-resistant mold venting if fluorination is performed in-mold. Additive packages are limited: metal stearate lubricants above 0.05 wt% react with elemental fluorine and create smoke; external release agents must be removed before surface treatment. Regrind from fluorinated scrap is limited to 15 wt% because the fluorinated layer releases hydrogen fluoride during re-extrusion, which embrittles the molecular weight distribution and corrodes chrome-plated screw surfaces. The resulting jerricans are tested gravimetrically for solvent loss under fixed storage at 40°C; the acceptable threshold depends on the active substance and package size, and published data for H4620 with specific solvent systems is limited.

On high-capacity accumulator machines with shot sizes above 30 kg, H4620 is used to blow mold vertical storage tanks of 2,000–10,000 L for aqueous fertilizers, cooling water, and mild alkali solutions. Wall thickness is distributed over the entire parison length, and the mold must be designed with graduated ribbing because the 0.946 g/cm³ density grade has lower ring stiffness than 0.954 g/cm³ pipe grades. Sidewall panels are reinforced with curved ribs at 300–500 mm intervals; flat panels without ribs exhibit long-term creep at 0.25 MPa hoop stress. The end product is not pressurized and is not classified as pressure piping, so EN 12573 welded thermoplastic tank design rules apply. For outdoor installations, 2.0–3.0 wt% of a 40–50% carbon black masterbatch is metered at the feed throat to meet UV stabilization requirements; insufficient dispersion leaves visible streaks and reduces notched impact at -20°C.

Failure during service usually initiates at the drain-thread weld or the manway flange, not at the shell. Welded spigot fittings are joined by hot-plate welding at 230–250°C; the weld is pressure-tested at 30–50 kPa for 10 min. Chemical exposure limits are similar to those for drums: sulfuric acid above 50% and sodium hydroxide above 30% require elevated-temperature validation; continuous exposure to strongly oxidizing agents is not advised. Published long-term creep data for H4620 at 40°C and 0.25 MPa hoop stress are limited.

When Closed-Loop Regrind Is Re-Extruded Into Non-Critical Drainage Profiles

Post-industrial H4620 flash, trim, and rejected parts are densified and re-extruded into corrugated drainage culverts, trench liners, and protective sleeving. The regrind fraction entering the profile extruder is controlled by the melt-flow rate shift: each heat history increases the 190°C/2.16 kg MFR by approximately 0.03–0.08 g/10 min, depending on extrusion temperature and residence time. For non-pressure drainage products, a blend containing 30–50 wt% regrind and 50–70 wt% virgin H4620 maintains acceptable ring stiffness and impact resistance. The profile line uses a grooved-barrel extruder with 30:1 L/D screw, a screen changer with 100–150 µm mesh, and a gear pump. Melt temperature is reduced to 180–195°C to suppress further chain scission; this requires lower screw speed and longer barrel residence time than virgin processing.

The corrugated profile is produced with a vacuum calibrator and water spray cooling at 20–30°C. Dimensional checks follow ASTM D2412 for pipe stiffness and ASTM D2444 for impact, but these products are not rated for sustained internal pressure. If the same regrind stream is considered for pressure-rated pipe, ASTM F714 hydrostatic design basis data must be generated for that specific compound; published data for H4620 in pressure pipe applications is limited, and using the grade in that service without such data is not supported.