LG Chem LUTENE-H ME5500 is a high-density polyethylene injection-moulding grade produced by low-pressure olefin polymerisation and marketed under the LUTENE-H family. The material is specified for rigid injection-moulded articles in which the part must sustain stacking loads, repeated impact, and moderate environmental contact: industrial pails, crates, tote boxes, pallet components, caps, and closures. The manufacturer’s published datasheet lists a melt flow rate of 5.0 g/10 min at 190 °C under 2.16 kg load when measured according to ISO 1133-1:2022, and a density of 0.955 g/cm³ under ISO 1183-1:2019. These values locate the grade in the medium-molecular-weight, medium-flow segment of high-density polyethylene, placing it between fractional-melt blow-moulding and pipe grades on one side and high-flow thin-wall packaging grades on the other.

Table 1. Representative published property profile for LG Chem LUTENE-H ME5500.

The data are not specification limits. They are generated on standard specimens and may drift with pigment levels, regrind loading, processing temperature, and post-mould conditioning. A supplier certificate of analysis should be referenced for lot-to-lot comparison.

Regrind incorporation in injection-moulding operations is common for HDPE crates and pallets. At 20 wt% clean, thermally stable regrind, the melt flow rate may shift by 0.5–1.0 g/10 min depending on prior heat history and masterbatch dilution. The processing window should be re-verified after changing regrind loading because gate seal time and part mass are sensitive to the lower viscosity of degraded regrind. Gravimetric dosing is preferred over volumetric mixing to avoid variations in bulk density.

Mould design influences orientation, weld-line position, and shrinkage. A single submarine gate or fan gate across a side wall can create an asymmetric orientation pattern and produce bow after conditioning. Multi-gate arrangements improve filling symmetry but introduce weld lines at flow-front interactions. Cavity pressure sensors near the gate and in the last-filled impression provide the data needed to set holding pressure and gate-seal time; this is more reliable than machine hydraulic pressure alone. Simulation of filling and packing with measured viscosity data for the selected lot reduces the number of tool trials but does not eliminate the need for moulded-part qualification.

What Limits the Flow Path in Thin-Wall Closure and Crate Tooling?

For a resin with a melt flow rate of 5.0 g/10 min, filling of thin-wall crates and closures is usually constrained by the shear-rate dependence of viscosity and by the onset of crystallisation at the mould wall. On a general-purpose reciprocating-screw machine with a 20:1 to 25:1 L/D screw and compression ratio of 2.5:1 to 3.0:1, barrel temperatures are typically set from 180 °C in the feed zone to 220 °C at the nozzle. The material does not require desiccant drying if internal moisture is below 0.05 wt%; surface condensation from outdoor storage can be removed by 2 h at 70 °C in a desiccant-bed hopper dryer.

The most common processing limitation is gate freeze before the holding-pressure stage has compensated volumetric shrinkage. This is particularly severe in thick bosses, ribs, and latch features. A mould temperature below 10 °C accelerates surface solidification and intensifies weld-line visibility, while a mould temperature above 40 °C prolongs cooling time and can generate sink marks in thick sections. In multi-cavity crate tools with a nominal wall of 2.0 mm, hydraulic injection pressures of 80–120 MPa are common, and cavity pressure transducers are used to identify the gate-seal point. Clamp force sizing for this material class is often based on a cavity pressure of 30–50 MPa; a projected cavity area of 1,000 cm² therefore calls for clamp force in the range 3,000–5,000 kN.

Production lines running multi-cavity crates on toggle-clamp machines typically find that cooling time, not screw recovery, controls the cycle when wall stock exceeds 3 mm. The high crystallisation rate of HDPE shortens the time required to form a stable part surface but also narrows the holding window. Processing of ME5500 should be stabilised with back pressure in the range 0.5–2.0 MPa and screw surface speeds of 0.1–0.3 m/s. These settings are typical for medium-flow HDPE and limit excessive shear heating while preserving melt homogeneity.

When lower-melt-index HDPE is substituted into a nucleated tool without gate modifications

Substitution of a fractional-melt HDPE into tooling originally sized for ME5500 usually moves the process into a pressure-limited mode. A 0.3 g/10 min grade has substantially higher viscosity at equivalent temperature and shear rate; the same gates and runner diameters then require longer filling time and higher pressure. Premature gate freeze may occur before the packing phase is complete, leading to high sink marks or dimensional variation in thick sections. On a 1,500 kN machine, the replacement resin may not maintain the same shot size at the same clamp force, while ME5500 remains inside the available pressure envelope. Conversely, a 20 g/10 min high-flow injection grade may reduce filling pressure and enable thinner walls, but the trade-off is generally lower notched impact and increased shrinkage anisotropy. The choice is therefore governed by the tool’s gate depth, runner balance, and the load-bearing requirement of the moulded article.

A direct side-by-side comparison of ME5500 with all other LUTENE-H grades in an identical tool is not available in published form. However, the melt flow differential provides a first-order estimate of processing change. At constant barrel settings, a lower-melt-index grade generates higher shear heating and longer screw recovery; a higher-melt-index grade shortens recovery but may require lower melt temperature to prevent flash. For medium-flow HDPE such as ME5500, rectangular gate depths of 0.6–1.2 mm are common in crate-tool design, but the final dimension must be confirmed by pressure-drop studies because wall thickness, flow length, and pigmentation move the effective processing window.

Under short-term tensile loading, the grade exhibits a yield point followed by cold-drawing. The published tensile yield stress is 28 MPa under ISO 527-2:2012, and flexural modulus is approximately 1,150 MPa under ISO 178:2019. These values support stacking stiffness in crates and industrial pails, but the modulus is lower than that of glass-reinforced polypropylene, so flat panels under heavy static load require ribbing or increased section. Notched Izod impact strength at 23 °C is reported as 4.0 kJ/m² under ISO 180/A:2000. The impact resistance of high-density polyethylene is strongly dependent on notch sharpness, mould temperature, and pigment dispersion; sub-zero performance should be tested on moulded parts, not on compression-moulded plaques.

Environmental stress-cracking resistance under ASTM D1693-21, condition B, is process-dependent. Rapid quench, high melt temperature, regrind degradation, and contact with polar liquids reduce the failure time. Published ESCR data for this specific injection-moulding configuration is limited, so parts that contact detergents, lubricants, or wetting agents should be evaluated under actual service stress rather than by standard laboratory coupons alone.

Chemical resistance follows general HDPE behaviour. Dilute acids, alkalis, and salt solutions are often acceptable at ambient temperature, but strong oxidising acids, chlorinated solvents, and hydrocarbons can produce swelling, creep rupture, or environmental stress cracking. Immersion testing according to ISO 175:2010 should reproduce the moulded-in stress condition when the article is used for chemical containment. Continuous exposure to ketones or unsaturated hydrocarbons at temperatures above 40 °C is not recommended.

Thermal ageing under stacked load introduces creep and ESCR coupling.

At temperatures above 40 °C, the failure criterion shifts from short-term yielding to long-term creep rupture or slow crack growth. For design of crates, pallets, and pails under static load, creep modulus measured according to ISO 899-2:2003 is more relevant than tensile yield. High-density polyethylene typically retains only 40–60% of its short-term flexural modulus after 1,000 h of loading at room temperature; published data for this specific grade is limited, so prototype verification is necessary. When the stressed part is exposed to detergents or other ESCR-active agents, creep and environmental stress cracking combine, and failure can occur below the short-term yield point. Testing should therefore use actual service load, temperature, and chemical environment rather than extrapolating from standard notched impact or tensile data.

Mould Shrinkage, Annealing, and Dimensional Tolerance Stack-Up

Injection-moulded plaque shrinkage for ME5500 is published in the range 1.5–2.0% under ISO 294-4:2018. Shrinkage is anisotropic; flow-direction shrinkage is typically lower than transverse shrinkage because of molecular orientation. For a rectangular crate base with a nominal cavity length of 600 mm, differential shrinkage can produce several millimetres of bow or twist if cooling and gating are asymmetric. Packing pressure, hold time, mould temperature uniformity, and regrind loading all influence final dimensions. Post-mould annealing at 80 °C for 2 h reduces frozen-in stress but may add 0.2–0.5% secondary shrinkage. Dimensional tolerance stack-up should include cavity dimensions, injection pressure variation, pigment dispersion, and post-mould storage temperature.

Colour masterbatches and nucleating agents shift both rheology and crystallisation. A nucleating package can increase flexural modulus by 5–15% and reduce mould shrinkage by 0.1–0.3%, but it can also lower impact strength and change the gate-seal time. Pigment dispersions based on high-flow carriers can increase melt flow rate; therefore the final moulded article’s properties should be measured on the production compound rather than on natural resin. Ultraviolet stabilisers are not present at weathering-protection levels in the base grade; outdoor service requires a separate UV-stabilised masterbatch or grade selection.

Regulatory compliance must be assessed at the finished-article level because colour masterbatches, regrind, and processing aids alter the solvent-extractable profile. The base polyolefin may be eligible for food-contact use under 21 CFR 177.1520 and Regulation (EU) 10/2011 Annex I, but the final article requires migration testing against the applicable overall migration limit. Industrial applications are documented under Regulation (EC) 1907/2006 for REACH and Directive 2011/65/EU for RoHS restrictions. Table 2 summarises the documentation matrix.

In non-food technical applications, the supplier safety data sheet should be checked for REACH registration status and any substance of very high concern above the 0.1% weight threshold. If recycled content is used, RoHS screening by X-ray fluorescence is advisable because heavy-metal contamination cannot be ruled out from polymer chemistry alone.

In service, ME5500 is better suited to cold and ambient-temperature load-bearing containers than to hot-fluid handling or continuous solvent exposure. The Vicat softening temperature of 123 °C under ISO 306:2022 method A50 is not a continuous-use limit. Creep modulus and stress-rupture data should be consulted for pallet racking or long-term stacking. Weld-line regions exhibit lower toughness than the bulk material; short-shot studies, cavity pressure curves, and hold-pressure sweeps are required to define the final processing window for each multi-cavity tool.