LyondellBasell HDPE L4904LS is a high-molecular-weight high-density polyethylene supplied as pelletised resin for extrusion blow moulding. The product is characterised by a nominal density of 0.949 g/cm³ according to ASTM D1505 and a high-load melt index of 4.9 g/10 min at 190 °C under 21.6 kg load according to ASTM D1238. The low conventional melt index and moderate high-load melt index imply a broad molecular weight distribution with a high entanglement density; this molecular architecture is the principal reason for the grade's elevated melt strength and environmental stress cracking resistance relative to narrow-distribution blow moulding resins. The material is normally supplied without a UV stabiliser package unless specifically ordered; carbon black or hindered amine stabiliser masterbatch can be added at the converter for outdoor exposure.

Mechanical property values are lower-bound estimates from compression-moulded specimens and are not directly transferable to blow moulded walls, where orientation and frozen-in stress alter both yield stress and environmental stress cracking resistance. In a blow moulded container, the hoop direction may exhibit a yield stress that is 5–10 % higher than the machine direction when parison inflation is balanced; unbalanced die gaps shift this asymmetry and can reduce effective drop impact. Therefore, incoming resin certification under ISO 19069-2 or ASTM D4976 should be supplemented by section-weight mapping of the finished container and drop testing at 0 °C to −20 °C for industrial formulations.

The density of 0.949 g/cm³ corresponds to a crystalline fraction of approximately 60–65 % determined by differential scanning calorimetry at 10 K/min using the 293 J/g reference enthalpy for linear polyethylene. The broad melting endotherm typically shows a peak between 130 °C and 134 °C, with secondary lamellar melting between 118 °C and 126 °C. The bimodal distribution produces a mixed lamellar morphology: thick lamellae from the low-molecular-weight fraction provide stiffness, while the high-molecular-weight fraction ties the lamellae through the amorphous phase and raises slow crack growth resistance.

Processing Behaviour in Extrusion Blow Moulding

On accumulator-head extrusion blow moulding machines with grooved-feed extruders of 24:1 to 30:1 L/D, L4904LS is typically processed at a melt temperature of 190 °C to 220 °C. A representative barrel profile is 170 °C in the rear zone, 185 °C in the centre zone, and 195 °C to 205 °C in the metering zone and die head. Under these conditions, head pressure is controlled between 20 MPa and 35 MPa depending on screw speed, die gap, and accumulator fill speed. Die head temperature stability within ±5 °C is required for consistent parison length; larger excursions lead to variable wall-thickness distribution and weld-line movement. Pre-drying is not normally required for HDPE, but surface condensation after storage at relative humidity above 60 % RH can be removed by drying in a desiccant hopper at 80 °C for 2 h.

Capillary rheometry at 190 °C shows a shear viscosity at 100 s⁻¹ on the order of 1,400–1,800 Pa·s, declining to 250–300 Pa·s at 1,000 s⁻¹. The power-law index between those shear rates is approximately 0.35–0.42, indicating pronounced shear thinning. In extensional flow, the melt exhibits a longer extensional rupture time than a unimodal grade of the same high-load melt index; this is expressed as lower sag velocity in constant-load parison sag tests.

Regrind from closed-loop in-house scrap can be used up to 30 % by mass without significant reduction in environmental stress cracking resistance if the regrind is free of moisture, fine particles, and contamination. At regrind levels above 50 %, parison sag becomes more pronounced and melt-pressure fluctuations increase; this is most visible as ovalisation in the neck area of 20 L to 60 L containers. A screw mixer section of at least 4 L/D is recommended to homogenise the melt and to avoid streaks from colour or additive masterbatch. Processors transferring from a general-purpose HDPE should anticipate a moderate increase in extruder torque and should verify that the screw drive has sufficient thermal overload margin.

Common production failure modes when processing L4904LS include melt-pressure spikes from cold pellet bridging in the hopper, parison curl from asymmetric die temperature, and blow-pin displacement due to high melt stiffness. These are corrected by maintaining hopper throat temperature below 50 °C, verifying die land temperature uniformity across quadrants, and using a blow pin with positive mechanical centring. A shift in high-load melt index of more than 0.5 g/10 min between lots is sufficient to alter parison hang time by several seconds on a 60 L accumulator machine; converters should therefore monitor lot-to-lot melt index and adjust die gap or melt temperature as needed.

In rigid industrial containers where the filled product is a surfactant-based formulation, a dilute bleach solution, or an agricultural emulsifiable concentrate, the environmental stress cracking resistance plateau of L4904LS is used to reduce brittle failure at the pinch-off weld and handle attachment. Moulded part weight typically ranges from 0.5 kg to 9 kg, corresponding to container volumes from 5 L to 60 L. The resin is suitable for closed-head jerricans and agricultural chemical canisters produced by extrusion blow moulding. Specific container qualification for dangerous goods must be performed according to ADR 6.1.5.3 drop test and ADR 6.1.5.4 leakproofness test; no resin alone can guarantee UN certification. In drop tests on 20 L containers moulded at a minimum wall thickness of 2.8 mm, fracture typically initiates at the pinch-off weld if flash compression is insufficient; this failure mode is controlled more by mould close speed, flash thickness, and melt temperature than by resin density. For automotive fuel tank service, published multi-layer permeation data for L4904LS in the structural layer is limited; end users should request supplier data for specific layer structures and perform evaporative emission testing under the applicable CARB or EPA protocol.

How Does L4904LS Compare to Unimodal Blow Moulding Grades of Similar Melt Index?

A comparison with conventional unimodal HDPE blow moulding grades of similar density and high-load melt index shows that L4904LS shifts the processing/property balance toward higher environmental stress cracking resistance at equivalent density and melt index. The molecular weight distribution is broader, which raises the concentration of tie molecules between crystalline lamellae and increases slow crack growth resistance. At the same time, the lower-molecular-weight fraction in the distribution maintains shear thinning and processability in an extruder.

In production terms, the broader distribution and lower melt index produce a more stable parison but also increase head pressure at a given screw speed. A die gap increase of 0.5 mm to 1.0 mm or a die temperature increase of 5 °C may be required to maintain target parison weight when replacing a conventional grade. The difference is especially relevant in thin-wall containers below 2.0 mm minimum wall thickness, where the higher melt strength allows a longer parison hang time but may require higher blowing air pressure to achieve full mould definition.

When Environmental Stress Cracking and Sag Limits Exclude Commodity HDPE

When storage conditions combine elevated temperature, aggressive filling media, and high stacking loads, commodity HDPE blow moulding resins may show environmental stress cracking after several weeks to months, particularly at the pinch-off weld and embossed logos. L4904LS is selected for such conditions because its environmental stress cracking resistance plateau delays crack initiation and allows the container to deform rather than split. The resin is also used in multi-layer structures as the structural layer with an inner polyamide or EVOH barrier layer and a pigmented outer layer; the layer distribution should be set according to drop-impact testing under ASTM D2463 and top-load compression testing under ASTM D2659.

For outdoor storage of agricultural chemicals, a UV stabiliser masterbatch is usually required, as the base resin is not supplied with a weathering package. Without stabilisation, surface chalking and a decline in impact strength may appear after 12–24 months of continuous ultraviolet exposure; published data for L4904LS in unstabilised outdoor service is limited. The grade is not optimised for thin-wall injection moulding and should not be processed on high-pressure injection moulding equipment without the addition of a flow-enhancing masterbatch or a change in part design to increase wall thickness.

When the resin is evaluated for food-contact or pharmaceutical packaging, a supplier statement is typically required to confirm compliance with FDA 21 CFR §177.1520(c) for olefin polymers, including end-use extraction limits under 21 CFR §177.1520(d) and 21 CFR §177.1520(e) where applicable. In the European Union, finished articles are evaluated under Regulation (EU) No 10/2011 and its amendments; overall migration into food simulants must not exceed 10 mg/dm² of contact area under the intended time and temperature conditions. Containers for hazardous materials require design-type testing under ADR/RID, IMDG, or 49 CFR Part 178 as applicable, and the resin must be verified in the final moulded article at the specified wall-thickness distribution. The limitations of L4904LS include its reduced flow in thin-wall injection moulding and its lack of an intrinsic UV stabiliser package; both must be addressed by process or formulation modification rather than by the resin itself.