PetroChina Dushanzi HDPE HD5218EA is a high-density polyethylene resin formulated for high-speed injection moulding of thin-wall rigid packaging and materials-handling articles. The melt mass-flow rate is nominally 18 g/10 min when determined at 190 °C under a 2.16 kg load according to ISO 1133-1:2022, and the nominal density is 0.952 g/cm³ by ISO 1183-1:2019 method A. These two indices define the processing profile: the high flow reduces injection-pressure demand and permits multi-cavity filling at wall thicknesses from 0.6 mm to 2.5 mm, while the density contributes adequate flexural modulus and top-load resistance for returnable crates, dairy crates, caps, closures, and storage totes. The material is not a pressure-pipe or blown-film resin; the melt strength is too low for continuous extrusion processes requiring sag resistance. The following sections characterise the grade against standardised test methods, production-scale moulding practice, and release-to-food-contact obligations.

Which standardised property values are reported for HD5218EA?

Producer documentation lists the representative values shown in Table 1. These are statistically derived from injection-moulded or compression-moulded test specimens and are not lot-release specifications unless stated in the certificate of analysis. Conformance to the corresponding test standard does not guarantee part-level performance; moulded-part testing remains necessary for structural applications.

The tensile yield stress of 23 MPa and flexural modulus of 1000 MPa support stacking loads in distribution packaging, whereas the Charpy notched impact strength of 4 kJ/m² at 23 °C implies a lower-energy failure mode than high-molecular-weight HDPE grades used in pressure pipe. The Vicat softening temperature of 123 °C under ISO 306:2022 method A50 indicates that the grade is not suitable for retort or autoclave sterilisation above 121 °C; hot-fill applications above 80 °C should verify package deformation under load. Shore D hardness of 62 provides scratch resistance in reusable containers but does not eliminate surface marking in high-abrasion returnable logistics loops.

The solid-state morphology of HD5218EA is governed by a fast crystallisation rate at typical mould temperatures of 10–40 °C. Differential scanning calorimetry under ISO 11357-3:2018 for HDPE of this density typically yields a crystallisation onset near 110–115 °C, but published data for this specific grade is limited. In thin-wall parts, rapid cooling freezes orientation before full relaxation; the result is higher flow-direction modulus and lower flow-direction elongation than isotropic compression-moulded specimens suggest. This morphological anisotropy is why design allowables derived from ISO 527-2:2012 tensile bars should not be directly applied to thin-wall geometries without orientation-specific testing. The narrow molecular weight distribution reduces low-molecular-weight tail content, which helps to limit extractables and odour in food-contact parts, but also narrows the processing window for shear-induced gloss variation in coloured mouldings.

Capillary rheometry data for HDPE with MFR near 18 g/10 min show shear-thinning such that apparent viscosity at 1000 s⁻¹ is roughly an order of magnitude below the zero-shear value; however, grade-specific master curves for HD5218EA are not publicly available. The practical consequence is that injection-rate increases are more effective at reducing pressure than melt-temperature increases, because the viscosity decreases with shear rate faster than with temperature in the processing window. This supports the use of high injection velocities for thin-wall filling, provided the tool is vented correctly and the melt front does not create jetting or weld-line weakness at converging fronts.

Processing behaviour observed in high-speed thin-wall injection moulding cells

On high-speed thin-wall moulding cells using 250–400 t clamp force machines with 25–45 mm screw diameters, the grade is typically processed at melt temperatures between 190 °C and 220 °C, with mould temperatures between 10 °C and 40 °C. Higher melt temperatures lower viscosity further but increase the risk of odour formation when regrind is used; the upper limit of 230 °C is recommended. Back pressure should be maintained between 0.3 MPa and 0.7 MPa to ensure melt homogeneity without excessive shear heating. The cushion position should be held at 3–6 mm to avoid screw bounce and fill-weight variation. For hot-runner valve-gated tools, nozzle and manifold temperatures of 210–230 °C are used, but published data for this specific configuration is limited; start-up with lower manifold temperatures and stepwise increase is advised.

Because the melt viscosity is low, decompression settings are critical. A suck-back distance below 5 mm is usually required to prevent nozzle drool and stringing in open nozzles; when hot-runner needle valves are used, decompression may be reduced further. Vent depths of 0.02–0.03 mm on the parting line are consistent with supplier guidance for HDPE of this MFR range to avoid gas entrapment and burn marks. On multi-cavity cap tools with 48 or more cavities, fill imbalance often originates from runner pressure loss rather than resin viscosity; hot-runner suppliers recommend geometrically balanced manifolds and positive melt-pressure sensors at the nozzle.

Primary application geometries include caps and closures with internal threads, where the high MFR permits low injection pressure and reduced moulded-in stress around unscrewing cores, and returnable transport packaging such as dairy crates, bread trays, and beverage crates. In pails and containers with wall thickness above 2.0 mm, hold-pressure time should be extended until gate freeze is confirmed by part-weight stabilisation; premature gate freeze produces sink marks and top-load scatter. For thin-wall containers below 1.0 mm, injection velocities of 200–300 mm/s and hold-pressure times of 0.5–1.5 s are typical for similar-MFR HDPE grades; the actual values depend on part geometry, runner system, and machine response. Shrinkage allowances of 1.5–2.5 % in the flow direction and 1.0–2.0 % transverse are often used in tool design, but part-specific trials are mandatory because anisotropy varies with gate location and wall thickness.

When HD5218EA replaces lower-flow injection-moulding HDPE grades

The principal difference is the melt mass-flow rate. Relative to an HDPE with MFR in the 5–8 g/10 min range, HD5218EA reduces injection-pressure demand, permits shorter hold-pressure time, and allows higher cavitation for the same available clamp force. The trade-off is a lower melt strength, which narrows the processing window for thick-wall sections and eliminates extrusion blow-moulding or blown-film use. Table 2 summarises the differentiating process-structure characteristics.

Density and solid-state stiffness remain comparable to other HDPE grades at 0.952 g/cm³; therefore the choice of HD5218EA over a lower-flow grade should be driven by wall thickness, cavitation, and cycle-time requirements rather than by differences in final part rigidity. In applications where impact toughness is critical, a lower-MFR HDPE with higher molecular weight may deliver higher Charpy notched impact, but published data for this specific configuration is limited and lot-specific testing under ISO 179-1:2020 is required. Compared with high-density polyethylene grades designed for pipe extrusion, HD5218EA has a higher MFR and lower molecular weight; pressure-pipe grades require long-term hydrostatic strength under ISO 9080 and are usually MFR below 1 g/10 min. Compared with unimodal blow-moulding HDPE, the grade lacks the melt strength and strain-hardening required to withstand parison sag. Compared with medium-density polyethylene film grades, the density of 0.952 g/cm³ reduces impact but increases stiffness and creep resistance in rigid mouldings.

High ambient humidity or condensation on cold pellets can cause surface splay in thin-wall mouldings. Where outdoor silo storage or unheated material handling is used, predrying at 70–80 °C for 1–2 h with a dry-air hopper dryer having a dew point below −20 °C is required. Pellets below 10 °C should be equilibrated to ambient to prevent condensation on screw root surfaces. The melt temperature should not exceed 240 °C for residence times longer than 5 min; oxidative degradation under those conditions reduces impact strength and can generate aldehydic odour. Regrind addition above 30 % by weight is not recommended for food-contact or colour-critical parts unless the converter validates lot-to-lot consistency.

Regulatory and food-contact compliance profile

HD5218EA is supplied as an olefin polymer within the scope of FDA 21 CFR 177.1520(c) for food-contact articles, provided the finished article meets the extractive limitations and end-use conditions described in that section. For the European Union, finished packaging must comply with Regulation (EU) No 10/2011, including overall migration limits of 10 mg/dm² and specific migration limits for any added substances. Compliance with REACH registration obligations and absence of substances of very high concern above 0.1 % w/w should be confirmed through the supplier safety data sheet. The grade is outside the scope of RoHS unless it is incorporated into electrical and electronic equipment; in such cases Directive 2011/65/EU applies to the finished product. No statement in this paragraph substitutes for converter-specific migration testing because the final colourant, additive, and processing aid package is outside the resin producer’s control.

Colour concentrates containing acid scavengers and neutral pH fillers are preferred. Compatibility with amine-based additives is not a primary concern for HDPE, but converters should validate organoleptic properties when such additives are used in food-contact articles. High back pressure above 0.7 MPa and high shear screw elements should be avoided to prevent local melt-temperature overshoot and molecular weight reduction. These boundaries define the operational envelope for the grade; however, no producer recommendation replaces machine-specific process development on the actual moulding cell.