LyondellBasell HDPE 50-2000 is a high-flow, injection-moulding-grade high-density polyethylene. The grade designation encodes the two principal specification boundaries: 50 corresponds to a nominal density of 0.950 g/cm³ when tested according to ISO 1183-1, and 2000 corresponds to a nominal melt flow rate of 20.0 g/10 min at 190 °C under a 2.16 kg load according to ISO 1133-1:2022. These nominal values place the resin in the high-flow segment of HDPE and restrict its primary conversion route to injection moulding, where low melt viscosity under shear shortens fill time and reduces hydraulic pressure demand.

The material is classified as high-density polyethylene because its density exceeds the 0.940 g/cm³ boundary used in ISO 11420 and ASTM D4976. The density of 0.950 g/cm³ is relatively low within the HDPE band, so crystallinity is lower than that of 0.960 g/cm³ pipe or sheet grades. A two-phase density model using an amorphous phase density of 0.855 g/cm³ and a crystalline phase density of 1.000 g/cm³ yields a crystallinity of approximately 65%. The lower crystallinity reduces stiffness and heat resistance but improves the deformation capacity of the moulded part.

The high melt flow rate indicates a lower weight-average molecular mass than general-purpose HDPE. Consequently, the melt strength is insufficient for continuous extrusion blow moulding of large containers because parison sag becomes uncontrollable. The grade should not be used in film blowing, pipe extrusion, or rotational moulding applications that require high shear viscosity or zero-shear melt strength. Conversely, for thin-wall food containers, overcaps, housewares and stackable tote boxes, the short cycle and low injection pressure are process-relevant properties.

Molecular architecture should not be inferred solely from the melt flow rate. Melt flow rate is a single-point capillary measurement and does not report molecular weight distribution, long-chain branching, or comonomer distribution. Published capillary rheometry data for this grade under ISO 11443 is limited. Processors developing hot-runner systems should request the full shear-viscosity curve at 190 °C and 210 °C from the producer. In injection moulding, gates commonly expose the melt to apparent shear rates between 10³ s⁻¹ and 10⁵ s⁻¹; the pseudoplastic shear thinning of polyethylene controls cavity balance more reliably than the melt flow rate alone.

Because polyethylene is non-hygroscopic, HDPE 50-2000 does not require desiccant drying in sealed packaging. Surface condensation may occur when cold pellets are transferred into a humid production hall with relative humidity above 60%. A hopper dryer set to 70–80 °C for 1–2 h removes surface moisture. Drying should not be used to correct contamination from fines, dust, or incompatible regrind; those require melt filtration or material segregation.

How does the 50-2000 designation translate to melt-index and density specifications?

The leading 50 denotes the nominal density class, with the convention producing 0.950 g/cm³. The trailing 2000 denotes the melt flow rate class in tenths of a gram per 10 min, yielding 20.0 g/10 min. These are nominal values and do not describe the full specification. Actual lot-to-lot variation is reported on the certificate of analysis and is controlled by the producer’s internal quality system. When a converter uses regrind, the melt flow rate and density of the blend should be rechecked because contamination changes both values.

At a density of 0.950 g/cm³, the melting peak measured by differential scanning calorimetry under ISO 11357-3 typically falls between 125 °C and 135 °C. The Vicat softening temperature A50 under ISO 306 is expected near 120–125 °C. These thermal values do not define maximum service temperature under load; creep under continuous stress should be evaluated by ISO 899-1 when a part is used above 60 °C.

Injection moulding of HDPE 50-2000 on a 40 mm diameter single-screw machine with a 22:1 L/D general-purpose screw commonly uses a barrel profile from 160 °C in the feed zone to 220 °C at the nozzle. Melt temperature above 230 °C should be limited because thermo-oxidative chain scission can produce yellowing, odour, and reduced impact. The high melt flow rate may allow a lower injection pressure than an 8 g/10 min HDPE grade, but the holding pressure and screw cushion must still be controlled to avoid sink marks. A screw cushion below 5 mm is associated with inconsistent packing.

Mould temperature controls cooling rate and final crystallinity. A mould surface below 10 °C can freeze the skin too rapidly and produce flow lines, jetting, and poor weld-line strength. A mould surface above 35 °C increases cycle time and post-ejection shrinkage. A starting range of 15–30 °C is appropriate for many thin-wall tools, but the exact value should be determined by part weight stability and cavity pressure measurement. Turbulent-flow water channels should maintain a temperature differential below 2 °C across the mould face.

Shrinkage, gate freeze-off, and tool-temperature boundaries in thin-wall tooling

Semi-crystalline polyethylene shrinks during cooling and after ejection. For a nominal 2.0 mm wall section, flow-direction shrinkage is often between 1.2% and 2.0% and transverse shrinkage between 1.0% and 1.8%, but these values are part-tool interactions rather than material constants. Moulding trials on the target tool are mandatory. A plaque test according to ISO 294-4 gives comparative shrinkage data but cannot predict shrinkage in a stackable container because constraints and flow orientation differ.

Gate freeze-off defines the hold-pressure duration. For a cold gate, hold pressure must be maintained until the gate solidifies; otherwise the cavity loses pressure before the part has compensated for volumetric shrinkage. Premature hold release produces sink marks, voids and post-ejection dimensional drift. Hot-runner systems should use positively shut-off valve gates or balanced manifolds. Because HDPE 50-2000 has low melt viscosity, an overheated hot runner can cause drool and stringing at the gate.

Weld lines are zones of reduced chain interpenetration. In unreinforced high-flow HDPE, weld-line strength is lower than the bulk because the merging flow fronts have already cooled and oriented. Multi-gated tools should place weld lines in low-stress areas, and melt temperature should be kept in the upper half of the processing window to promote interdiffusion at the front. Published data for weld-line strength of this specific grade is limited; a tensile test on a double-gated plaque under ISO 527-2 should be used for verification.

When 50-2000 replaces a lower-melt-index HDPE in stackable container production

Substituting a 20.0 g/10 min HDPE for a 5 g/10 min or 8 g/10 min HDPE of the same density changes the balance between processability and solid-state properties. The high-flow resin reduces fill pressure and permits thinner walls or more cavities on the same clamp force, but its lower molecular weight can reduce environmental stress-cracking resistance and notched impact. Applications involving detergents, surfactants, essential oils, or constant strain should be qualified under ASTM D1693 or ISO 22088-2 on the moulded article, not only on pelletised resin.

The lower viscosity of HDPE 50-2000 also means that a hot-runner balance established for a lower-MFR grade does not transfer directly. The pressure redistribution among cavities changes, and the first filled cavity may experience overpacking before the last cavity fills. Flow simulation using shear-viscosity data under ISO 11443 reduces the number of tool trials required.

Within the same density class, a grade with a melt flow rate of 12 g/10 min would show higher molecular weight and better stress-cracking resistance than HDPE 50-2000, but require higher injection pressure and longer cycle time. Conversely, a 30 g/10 min grade would fill longer flow lengths but exhibit lower impact and reduced chemical resistance. HDPE 50-2000 therefore occupies a mid-high flow position in injection MFR lines; the final selection must be made with the complete property set and not by melt flow rate alone.

For a 1.0 mm wall thickness, flow length is governed by melt temperature and injection speed. With HDPE 50-2000, a flow-to-thickness ratio above 200:1 may be achievable in simple geometries, but the gate and runner system must provide adequate pressure at the last fill point. As wall thickness decreases, the material’s lower melt viscosity reduces pressure demand relative to a 5 g/10 min grade, making it possible to fill thin ribs without increasing tonnage.

For pigmentation, a concentrate with a carrier resin of equal or higher melt flow should be used. A conventional masterbatch let down at 2 wt% may change the effective melt flow rate because the carrier often has a higher melt index than 20.0 g/10 min. The finished blend should be tested under ISO 1133-1:2022 and ISO 1183-1 before production. Concentrates containing high loadings of calcium carbonate or incompatible carriers can increase brittleness and reduce low-temperature impact.

For food-contact applications in the European Union, compliance must be demonstrated under Regulation (EU) No 10/2011 as amended. Overall migration is measured according to EN 1186 and must not exceed 10 mg/dm². In the United States, the resin may be evaluated under 21 CFR 177.1520, but the final article, colourants, additives, and recycled content have separate compliance obligations. A food-contact statement should be obtained for the specific lot.

Industrial applications may require additional declarations for RoHS recast Directive 2011/65/EU, particularly for electrical and electronic equipment. HDPE 50-2000 is not expected to contain lead, mercury, cadmium, hexavalent chromium, PBB or PBDE as intentionally added substances; nevertheless, lot-specific confirmation is necessary because additives and processing aids can introduce trace substances.

Use with strong oxidising agents, chlorinated hydrocarbons at elevated temperature, or prolonged contact with polar solvents under stress can accelerate environmental stress cracking. The material should not be welded with extrusion welding rod of a much higher molecular weight grade because fusion across the interface depends on chain entanglements and equivalent melt flow. For machining, low cutting speeds and sharp tools are required because the high-flow grade softens at relatively low frictional heating.

Common processing defects observed on injection machines with HDPE 50-2000 include jetting, gate blush, and surface sharkskin at excessive injection speed. Jetting appears as a serpentine flow mark when the melt front enters the cavity at high velocity without swelling against the walls. Reducing injection speed from 150 mm/s to 60–80 mm/s and enlarging the gate can suppress jetting. Sink marks arise when hold pressure decays before gate freeze; maintaining an adequate screw cushion and increasing hold time are corrective actions.

In compounds containing recycled HDPE, the melt flow rate and density shift according to the source and contamination level. Replacement of more than 10 wt% of virgin HDPE 50-2000 with low-viscosity regrind should be validated by testing the blend under ISO 1133-1:2022 and by moulding stress-crack specimens under ISO 22088-2. Published data for this specific configuration is limited; therefore, lot-specific validation is the only reliable basis for converting from virgin HDPE 50-2000.