LyondellBasell HDPE L5840 is a high-density polyethylene grade assigned to extrusion blow moulding of rigid containers. The resin is characterised by a nominal density of 0.955 g/cm³ when measured under ASTM D1505 and a melt flow rate below 1.0 g/10 min at 190 °C and 2.16 kg according to ASTM D1238. This places the grade in the high-molecular-weight HDPE class, where parison stability and environmental stress-crack resistance are prioritised over melt fluidity. Reported applications include household and industrial chemical containers, detergent packaging, agrochemical bottles, and medium-to-large rigid vessels produced on shuttle and accumulator-head blow-moulding lines. All values given here are representative trade-literature data unless the working lot certificate requires different limits.

Material specification and rheological boundary conditions specified by the producer

The property set is standardised around a density window of 0.954 g/cm³ to 0.956 g/cm³ and a melt flow rate window of 0.5 g/10 min to 0.8 g/10 min. The low melt flow rate is intentional: it corresponds to a high weight-average molecular weight and a broad molecular weight distribution that increase melt strength during parison extrusion. The table below summarises representative published data and test references. These are not specification maxima or minima; the producer’s certificate of analysis is the binding document.

The combination of a density near 0.955 g/cm³ and a melt flow rate below 1.0 g/10 min is deliberate. Increasing density in HDPE raises modulus and barrier performance but usually lowers environmental stress-crack resistance unless comonomer placement and molecular weight distribution are adjusted. In L5840, a sufficiently high comonomer incorporation and broad molecular weight distribution are used to retain stress-crack resistance at a density that would otherwise produce brittle failure in aggressive detergent and oxidising chemistries.

Thermal analysis by differential scanning calorimetry, if supplied in the lot technical note, typically shows a single melting peak in the range 128 °C to 134 °C under ASTM D3418. This melting point does not define the blow-moulding melt temperature; the processing range is wider because parison shaping requires sufficient melt elasticity. The high-molecular-weight tail provides melt strength for parison hang-up and contributes to slow crack growth resistance, while the lower-molecular-weight fraction plasticises the melt during extrusion and reduces die-head pressure. A high-load melt index measured at 190 °C and 21.6 kg under ASTM D1238 is commonly two orders of magnitude larger than the 2.16 kg value for such grades, but the ratio is lot-dependent.

What limits the usable parison window when running L5840?

The first processing boundary is melt fracture. For the high-molecular-weight HDPE class to which L5840 belongs, sharkskin onset is commonly observed at wall shear stresses of 0.14 MPa to 0.20 MPa in a clean die. A high-shear extrusion run can therefore generate visible surface roughness before the melt reaches the die exit. The condition is managed by reducing screw speed, increasing die-land temperature, widening the die gap, or adding a fluoropolymer processing aid to the melt at dosages from 200 ppm to 1,000 ppm.

The second boundary is parison sag. High melt strength suppresses sag, but the molecular weight remains finite, and long-drop containers above roughly 250 mm in parison length can exhibit measurable diameter taper. Sag is temperature- and time-dependent; a melt temperature reduction of 5 °C may reduce sag, but it increases extruder torque and die-head pressure. Accumulator-head machines are therefore operated with a melt temperature window of 200 °C to 220 °C for L5840, with die-head zones kept 5 °C to 10 °C hotter than the extruder discharge to prevent surface fracture.

Die swell must also be accounted for during tool set-up. High-molecular-weight HDPE grades typically produce swell ratios of 1.5:1 to 2.0:1 at shear rates in the 100 s⁻¹ to 500 s⁻¹ range. For L5840, the exact swell ratio depends on die gap, land length, and temperature; no single published figure applies to all accumulator-head configurations. The die gap on a 60 mm to 80 mm grooved-feed extruder is normally set between 1.5 mm and 3.0 mm, but a gap increase of 0.2 mm can alter the parison drop time and the effective wall thickness distribution. These interactions make the useful parison window narrower than a simple melt-flow number would suggest.

Because HDPE is not hygroscopic in the same manner as polyamide or PET, L5840 does not require forced-air drying when stored in a dry warehouse. If pellets are exposed to relative humidity above 60 % or condensation is observed, a short dehumidified-air or hot-air drying step at 80 °C for 1 h to 2 h removes surface moisture. Venting of the extruder hopper and barrel is usually sufficient to eliminate water streaks during continuous operation.

When L5840 is substituted for a lower-modulus HDPE in an existing 10 L industrial container tool, the first measurable difference is an increase in sidewall stiffness and top-load resistance under ASTM D2659 conditions. The higher modulus permits a reduction in wall thickness if the packaging specification allows it. That same substitution increases melt pressure and may shorten the stable drop time because of the higher melt viscosity at low shear; processors often compensate by increasing die-head temperature by 5 °C or by adjusting the parison programmer to shift material from the pinch-off area to the shoulder. Environmental stress-crack resistance in a 10 % Igepal solution tested according to ASTM D1693 Condition B can remain above 300 h, which is the basis for selecting L5840 over lower-cost HDPE grades when containers are exposed to aggressive hydrocarbons or concentrated detergents.

Compared with HDPE grades designed for injection moulding, L5840 exhibits a melt flow rate that is one to two orders of magnitude lower. Injection moulding HDPE commonly falls in the 10 g/10 min to 50 g/10 min range at 190 °C and 2.16 kg, which permits short cooling cycles and thin-wall filling but sacrifices ESCR and melt strength. L5840 is therefore unsuitable for injection moulding of thin-wall closures and should not be processed on standard injection moulding machines without substantial screw and check-ring modification. Film HDPE grades, by contrast, are designed for high-speed extrusion with narrower molecular weight distribution to control bubble stability; they generally do not require the same level of parison hang-up. Pipe HDPE grades may have a higher density and are formulated for long-term hydrostatic strength under ISO 9080, and are not interchangeable with L5840.

For food-contact or pharmaceutical packaging, the resin must be evaluated under the finished-article rules rather than as a pellet. United States Food and Drug Administration 21 CFR 177.1520 permits olefin polymers for food-contact use when the finished article meets the prescribed extractive and end-use limits. European packaging is assessed under Commission Regulation (EU) No 10/2011, with an overall migration limit of 10 mg/dm² for plastics intended for food contact. Compliance depends on converter processing temperatures, regrind content, and the specific food simulant; a lot certificate from the producer does not by itself certify the final blow-moulded container. REACH Annex XVII and RoHS Directive 2011/65/EU should also be checked against the current lot documentation for restricted substances.

When the same grade is moved from a shuttle press to an accumulator-head line

Shuttle presses with single or dual parison heads expose the melt to shorter residence times and lower accumulated shot mass. A transfer to an accumulator-head line changes the thermal history of the melt because the accumulator holds a complete shot between extrusion and discharge. For L5840, the melt should not be held above 220 °C for longer than 10 min to 15 min when using a machine without a nitrogen blanket, because long residence time can increase yellowness and reduce melt strength through oxidative chain scission. Extruder barrel profiles should be flat to slightly decreasing from 200 °C to 220 °C, and the accumulator temperature should be set near 205 °C to 215 °C. Fill speed and discharge speed are set independently; a slow accumulator fill with a fast discharge reduces parison sag but can amplify melt fracture if the discharge shear rate is high.

In practice, a 2.5 L to 5 L bottle mould line may use a 60 mm grooved-barrel single-screw extruder with a 24:1 L/D barrier screw and a Maddock mixing section to complete plastication. Screw speeds are often limited to 50 min⁻¹ to 80 min⁻¹ on such configurations because higher speeds reduce melt temperature control and can exceed the melt fracture threshold. For containers above 20 L, an accumulator head with a diverging ram and programmed die gap is preferred. The transition from shuttle to accumulator is not only a scale-up change; it alters parison drop time, swell ratio, and the cooling rate of the final article.

Material changes on a line running L5840 may be accomplished with a lower-viscosity HDPE purge or a commercial purging compound. The purge should be run at the upper end of the melt temperature range, 220 °C to 230 °C, and the screw should be allowed to clear the accumulator head until no visible gel or white specks remain in the parison. Because L5840 has a high viscosity, a shut-down with a heat-soak period can degrade the retained melt; the extruder should be discharged and purged before an extended halt.

A statistically valid qualification for a 5 L agrochemical container should include environmental stress-crack resistance testing to ASTM D1693, top-load to ASTM D2659, and drop impact at -18 °C according to ASTM D2463, using a sample size of at least five containers per production condition. Wall thickness distribution should be mapped by sectioning or ultrasonic gauging, because high-molecular-weight HDPE can develop thin spots at the pinch-off and the lower chime if the parison programme is not adjusted. Regrind content above 20 % by weight has been reported to reduce ESCR in blow-moulded HDPE parts; if L5840 is run with in-house regrind, the blend should be validated against the same ESCR test rather than assuming linear property retention. Published data for this specific configuration is limited at regrind fractions above 30 %, and the safe limit for any given package depends on the aggressiveness of the fill chemical and the storage temperature.