Borealis HDPE BOREALIS HE3366 is a bimodal high-density polyethylene produced in a Borstar dual-reactor cascade. The grade belongs to the manufacturer’s HE series for extrusion blow moulding and large-part industrial packaging. Nominal values from the technical datasheet include a density of 0.946 g/cm³ when tested per ISO 1183-1:2019 and a melt mass-flow rate of 0.60 g/10 min at 190 °C under a 2.16 kg load per ISO 1133-1:2022. The bimodal molecular weight distribution is not expressed as a single certificate value but appears in dynamic rheology as a higher low-frequency storage modulus relative to unimodal high-density polyethylene of the same melt index. The high-molecular-weight fraction contributes melt strength, parison stability, and environmental stress crack resistance; the shorter-chain fraction lowers shear viscosity and stabilises accumulator-head extrusion.

The Borstar process uses a slurry-loop primary reactor and gas-phase secondary reactor in series. In HE3366, the reactor split is controlled to produce a high-molecular-weight copolymer fraction and a lower-molecular-weight fraction. The result is a bimodal molar mass distribution that cannot be matched by single-reactor unimodal HDPE without sacrificing either processability or environmental stress crack resistance. Independent control of the reactor split also enables the manufacturer to maintain MFR₂ at 0.60 g/10 min while keeping density at 0.946 g/cm³, a combination that in conventional chromium-catalysed technology would require higher comonomer levels and lower catalyst activity.

On a 60 mm grooved-feed extruder with a 25:1 L/D screw and an accumulator head, a flat barrel temperature profile between 180 °C and 210 °C is used. The accumulator tool and die are held at 200 °C to 210 °C. Melt pressure at the head inlet is observed between 25 MPa and 35 MPa at a screw speed of 40–60 min⁻¹. Melt temperature should not exceed 220 °C; after 45 min of stagnant hold-up at 240 °C, gel particles and yellowness index increase measurably. Specific energy consumption on this line is typically 0.25–0.32 kWh/kg. Head pressure should not exceed 45 MPa; above this threshold, viscous dissipation raises melt temperature and accelerates wear of the grooved feed bush.

Primary packaging applications include industrial containers from 5 L to 30 L, agricultural chemical canisters, detergent bottles, and lubricant containers. The grade is also used for intermediate bulk packaging components where UN certification requires high environmental stress crack resistance and impact strength. During colour change, purging with a high-viscosity polyethylene purge compound at 200 °C for 15–20 min reduces streak defects. Screen packs of 80/120/80 mesh are common for head protection, but the final screen should be 60 mesh if a fluoropolymer-based processing aid is used.

What Limits Slow Crack Growth Performance in Aggressive Liquid Packaging?

The critical performance boundary for HE3366 in detergent, surfactant, and agricultural chemical packaging is environmental stress cracking. The manufacturer technical datasheet reports a full-notch creep value exceeding 1000 h under ISO 16770:2016 at 4 MPa and 50 °C in a nonylphenol ethoxylate test fluid. This value is a comparative material property, not a guaranteed service life, because stress-cracking severity depends on wall stress, moulded-in strain, and the specific surfactant package. Tensile yield stress is reported as 24 MPa per ISO 527-2:2012, and tensile modulus as 850 MPa. Notched Charpy impact strength at 23 °C is reported at 32 kJ/m² per ISO 179-1/1eA. The manufacturer datasheet also lists Vicat softening temperature at 126 °C per ISO 306/A50 and Shore D hardness of 62 per ISO 868:2003. These values place the grade in the intermediate-stiffness segment of the blow moulding HDPE range, with impact resistance prioritised over maximum top-load strength.

Stress crack resistance of high-density polyethylene is associated with tie-molecule concentration and lamellar orientation in the spherulitic structure. Bimodal HDPE with a high-molecular-weight copolymer fraction promotes tie-molecule formation across adjacent lamellae, which resists crack propagation under high stress. A unimodal HDPE of higher density has fewer tie molecules and crystallises with a more brittle spherulitic structure, resulting in lower environmental stress crack resistance. Chemical compatibility for detergent packaging is evaluated with test fluids that model nonionic surfactants; ISO 16770:2016 applies a constant tensile load to a notched specimen immersed in the fluid. The stress level of 4 MPa is selected to reproduce the wall stress in a filled container under stacking at ambient temperature. Converters should not use the full-notch creep value as the sole criterion for concentrated formulations above 30% surfactant because the fluid can plasticise the amorphous phase and reduce effective tie-molecule mobility.

Package-level qualification for aggressive liquids is not established by resin data alone. A 25 L container must pass hydraulic pressure tests, leakproofness, and drop tests at 1.2 m for packing group II or 0.8 m for packing group III under Chapter 6.1 of the UN Model Regulations. The resin contributes through its environmental stress crack resistance and low-temperature impact response, but wall-thickness distribution, pinch-off weld quality, and closure torque remain the dominant manufacturing variables.

Because the grade is formulated for high-molecular-weight blow moulding, addition of post-industrial reclaim below 30 wt% does not require a viscosity offset, provided the regrind is dried to below 0.10 wt% moisture at 80 °C for 2 h. Above 30 wt% regrind, the melt flow rate can shift and the notched Charpy impact strength may decline because of repeated shear history and partial loss of the high-molecular-weight fraction. Colour concentrates based on polyethylene carriers are preferred; concentrates containing metal stearates or amine-based processing aids should be evaluated, as they can alter surface wetting and reduce the environmental stress crack resistance of the finished container. Silicone-based external lubricant addition is typically limited to 0.5–1.0 wt%; higher levels can interfere with hot-plate welding of closures and spouts.

Swell, Sag, and Molecular Architecture in Large-Part Extrusion Blow Moulding

Parison sag in a 210 g shot for a 25 L canister on a 90 mm accumulator machine with a 30:1 L/D screw is the principal process control variable. At a melt temperature of 195 °C to 205 °C, the parison extends at an average rate of 8–12 mm s⁻¹ depending on die gap and accumulator speed; this is balanced against a die swell ratio of approximately 1.5–1.8 measured at the die exit. The bimodal distribution increases zero-shear viscosity and therefore reduces sag relative to a low-molecular-weight injection moulding HDPE at the same melt index. The same high-molecular-weight fraction generates visible sharkskin below 190 °C, which is suppressed by raising the die temperature to 205 °C and maintaining the die land length at 15–20 times the die gap.

During parison wall-thickness programming of a 20 L jerrycan, the die gap profile is divided into at least 10 segments because the parison length variation from top to bottom requires more melt strength near the pinch-off. The top pinch-off area should be programmed with a 10–15% thicker parison to compensate for flash compression; the bottom pinch-off is programmed with a 5–10% thinner parison to maintain a smooth tail weld. Shot-size utilisation is kept between 60% and 80% of accumulator capacity to avoid hold-up variability and inconsistent part weight.

The comparison above is not a design-allowable table; it is a lot-derived orientation for material substitution trials and should be revalidated for the specific packaging geometry and wall stress. Compared with a chromium-catalysed unimodal HDPE of the same MFR₂, HE3366 exhibits approximately 2–3 times higher full-notch creep environmental stress crack resistance, but the tensile modulus is 20–30% lower. A container designed for unimodal HDPE cannot be redesigned in HE3366 simply by changing resin; sidewall ribbing may be required to maintain the same top-load force. Conversely, a container designed for HE3366 may lose drop impact performance if a unimodal HDPE is substituted without increasing wall thickness.

Production-scale observation on accumulator-head lines indicates that the most common failure associated with this grade is intermittent fold-in at the blow pin during high-speed parison inflation. When the pre-blow pressure is below 0.6 MPa, the parison can contact the blow pin before the mould closes, producing a local weld line that reduces drop impact resistance at -20 °C. This failure mode is controlled by increasing the pre-blow pressure to 0.8 MPa and adjusting the blow delay to 0.4 s. At low temperatures, mould and die temperatures should be held at the upper end of the range, and the blow pin should be pre-heated to 40 °C to prevent local cooling-induced brittleness at the pinch-off. If the part is to be filled and stored below -30 °C, a separate low-temperature impact study using ISO 179-1/1eA is required; published data for this specific configuration is limited.

When PE100 Pipe-Grade HDPE Is Used Instead of HE3366 in Blow Moulding

Substitution of a PE100 pipe-grade HDPE into an extrusion blow moulding tool designed for HE3366 is not a direct drop-in. Pipe-grade PE100 resins typically have an MFR₂ below 0.30 g/10 min and a higher zero-shear viscosity; the accumulator head pressure can rise by 10–20% at the same screw speed, and the parison becomes more resistant to elongation but also more sensitive to die-lip build-up. Surface finish deteriorates because the pipe-grade molecular architecture is optimised for slow crack growth and hydrostatic strength, not for high-shear die throughput. Conversely, using a high-flow injection moulding HDPE with an MFR₂ above 2.0 g/10 min produces excessive parison sag, low melt strength, and poor wall-thickness control in containers larger than 5 L. HE3366 occupies the intermediate rheological window: melt strength is sufficient for 10–30 L containers, while shear viscosity remains low enough for accumulator-head extrusion without pre-compounding.

Quality control of incoming lots should include density by ISO 1183-1:2019, melt flow rate by ISO 1133-1:2022, and moisture by Karl Fischer titration below 0.05 wt%. The certificate of analysis typically controls density within ±0.002 g/cm³ and MFR₂ within ±0.05 g/10 min. Lot-to-lot variation within these ranges does not normally require process parameter changes, but a shift from 0.55 g/10 min to 0.65 g/10 min can alter parison sag by several millimetres in large containers and may require die gap adjustment. The base stabilisation is designed for extrusion blow moulding heat history. Addition of phenolic or phosphite stabiliser masterbatches should be limited to the supplier-recommended ratio because excess phosphite can hydrolyse and create plate-out on the die lip. The grade is supplied as natural pellets; black or coloured compounds are produced by let-down with approved masterbatches at 2–3 wt%.

At the packaging validation stage, the resin must be evaluated against the relevant food-contact or industrial chemical packaging requirements. For food-contact use, the grade should be assessed under EU Regulation (EU) No 10/2011 and Commission Regulation (EC) No 1935/2004, but the converter must obtain the relevant statement of compliance for each specific lot and package design. For industrial chemical packaging, the UN Model Regulations Chapter 6.1 drop and stack tests are the operative framework. Published data for specific configurations involving aggressive organic solvents above 50% concentration is limited, and aromatic hydrocarbons should be excluded from the packaging matrix unless package-level compatibility testing demonstrates no stress-cracking failure.