Iran Petrochemical HDPE 52518 is a pelletized high-density polyethylene injection-moulding grade with a nominal melt flow index of 18 g/10 min at 190°C under a 2.16 kg load as per ISO 1133-1 and a nominal density of 0.952 g/cm³ as per ISO 1183-1. The material is specified for thin-wall injection-moulded packaging, closures, caps, housewares, and general-purpose articles. Relative to lower-flow grades in the same Iranian HDPE portfolio, frequently specified at MFR values of 0.2–0.5 g/10 min for extrusion blow moulding and pipe, HDPE 52518 exhibits lower melt viscosity during cavity filling. This rheological profile supports reduced filling pressure and shorter cycle times in multi-cavity tools, but it carries measurable reductions in melt strength, environmental stress crack resistance, and continuous-wall extrusion blow-moulding suitability.

Manufacturer documentation for HDPE 52518 indicates food-contact suitability under FDA 21 CFR 177.1520 and EU Regulation 10/2011 when processed without non-compliant colorants or additives; final article compliance remains the downstream converter’s responsibility. The product is supplied as natural or white pellets in 25 kg bags or bulk containers. Pellets should be stored in sealed packaging below 40°C to avoid surface condensation, because cold-pellet moisture can generate splay defects when the material is moved from unheated storage into a warm production hall.

Why Does a Melt Flow Index of 18 g/10 min Narrow the Processing Window?

The effect of high MFR on processing is most visible in the relationship between melt viscosity and injection pressure. In capillary rheometry, HDPE with an MFR of 18 g/10 min at 190°C shows a shear-thinning region that becomes pronounced above 10² s⁻¹. For thin-wall tools with wall stock between 0.5 mm and 0.8 mm, this viscosity enables filling at melt temperatures of 180–230°C and hot-runner temperatures of 190–210°C, provided gate diameters are maintained between 0.3 mm and 0.5 mm. The same low-viscosity behaviour narrows the boundary between a complete part and flash. On hydraulic injection moulding machines with general-purpose screws of 20:1 L/D and non-return valves, barrel zone temperature drift greater than ±5°C can alter shot weight by more than 1.0% on thin-wall parts, causing either underfilling or flash at the parting line.

Melt temperature for HDPE 52518 should be controlled within 180–230°C. Below 170°C, residual crystalline domains increase screw torque and may leave unmelted pellets in the shot. Above 250°C, oxidative chain scission accelerates, raising MFR, reducing drop-impact performance, and increasing the potential for taste-and-odour defects in food-contact articles. Mould temperature is conventionally set between 10°C and 50°C; each 10°C increase in mould surface temperature can add 0.5–1.5 s to cycle time on thin-wall geometries while improving weld-line strength and gloss. These interactions make the practical operating window narrower than the raw melt-temperature envelope suggests.

Production-scale troubleshooting records show that short-shot events in thin-wall HDPE caps are frequently traced not to melt temperature alone but to gate freeze-off and screw-recovery limitations. When cycle time falls below the screw plasticising capacity, melt delivery becomes intermittent; screw-recovery time should be kept below the cooling time by at least 0.5 s to maintain a stable melt cushion. If a 30% regrind fraction is used, pellet-to-pellet bulk density variation may alter screw feed and require an increase in back pressure of 5–10 bar to restore melt density.

Property Specification and Test Method Mapping

These figures are manufacturer-published typical lot averages and are not contractual minima. Tensile properties are determined on injection-moulded or compression-moulded specimens prepared according to ISO 1872-2 and conditioned for 40 h at 23°C and 50% RH before testing. The density value is measured after 24 h annealing to stabilise crystallinity; fast-cooled thin-wall mouldings may exhibit density values 0.001–0.003 g/cm³ lower than the annealed nominal value because cooling-rate-dependent crystallinity affects stiffness, permeability, and shrinkage.

Environmental stress crack resistance is not routinely published for high-MFR HDPE injection grades. When ESCR data are required for detergent, alcohol, or surfactant-containing products, testing should be conducted on moulded plaques in accordance with ASTM D1693 under 100% Igepal CO-630 at 50°C. Published data for HDPE 52518 under this specific configuration is limited; users should not extrapolate from lower-MFR blow moulding grades, which may exhibit ESCR values above 100 h under the same test. High MFR and higher density generally reduce ESCR, so HDPE 52518 is not the first selection for aggressive chemical packaging.

Melt Temperature, Residence Time, and Gate Geometry Are Not Independent.

The processing window for HDPE 52518 is best described as an interaction among melt temperature, residence time, and gate geometry. Extended residence time at 230°C can produce viscosity reduction equivalent to a 10°C melt-temperature increase on a machine with a barrel capacity too large for the shot weight. A shot weight below 20% of barrel capacity prolongs residence time and increases the probability of chain-scission-related MFR drift; converter trials on thin-wall tubs have recorded MFR increases of 2–4 g/10 min after 20 min of interrupted purging at 250°C. Such drift alters cavity packing and produces variable part weight. Where possible, barrel capacity should be selected so that shot mass falls between 35% and 75% of the rated capacity.

Gate design for HDPE 52518 must account for the grade’s low melt strength and rapid crystallisation. Edge gates, submarine gates, and hot-runner valve gates are used; gate diameters below 0.3 mm may restrict flow and generate shear-heating defects, while gates above 1.0 mm extend cycle time and increase gate vestige. For a 0.6 mm wall, gate depth is often set at 60–70% of wall thickness. Short-shot risk increases when the flow-length-to-wall-thickness ratio exceeds 200:1 without flow leaders; reductions in melt temperature below 180°C and mould temperature below 10°C lower the critical ratio further. Flash formation, by contrast, is governed by clamp force availability and parting-line fit; for multi-cavity thin-wall tools, a clamp force of 80–120 tonnes is commonly selected for projected areas of 150–250 cm², depending on cavity count and peak injection pressure.

Mould shrinkage for HDPE 52518 is typically reported in the range 1.5–2.5% in the flow direction and 1.5–2.0% transverse, measured according to ISO 294-4 after 24 h at 23°C. Shrinkage anisotropy arises from molecular orientation and cooling gradients; lower mould temperatures increase anisotropy and may promote warpage in rectangular tubs. Post-moulding dimensional checks should be made no earlier than 24 h after demoulding because HDPE crystallinity evolves after ejection. For tight-fit closures, cap diameter tolerance is typically held within ±0.05 mm, which requires stable packing pressure and consistent cooling time.

When HDPE 52518 Replaces a Lower-Flow Blow Moulding Grade in Thin-Wall Applications

Substitution of HDPE 52518 for a lower-flow HDPE grade is technically valid only in injection-moulded thin-wall applications, not in extrusion blow moulding. Extrusion blow-moulding grades in the Iranian HDPE product line are typically specified at MFR values of 0.2–0.5 g/10 min; their higher melt strength supports parison stability in intermittent or continuous blow moulding. HDPE 52518 at 18 g/10 min lacks sufficient melt strength for stable parison formation under normal die swell and draw-down conditions, and attempts to use it on shuttle or accumulator blow-moulding machines with parison lengths above 200 mm produce measurable thickness variation and draw-down instability.

In injection-moulded caps and thin-wall containers, the product’s high flow provides a different balance. Cycle-time reductions can be achieved through reduced injection pressure and shorter hold times, but the grade’s stiffness and impact response differ from lower-flow grades of similar density. For applications requiring snap-fit assembly, the lower molecular weight associated with 18 g/10 min MFR tends to reduce tensile elongation and notched Izod impact relative to 0.5 g/10 min material. A processor evaluating the change should compare notched Izod impact according to ISO 180/A and drop-impact performance of the finished article under ASTM D2463 or customer-specific drop geometries. Published data for HDPE 52518 in finished-cap drop-impact configurations is limited; a moulding trial followed by statistical capability analysis is required before specification approval.

Density matching is not sufficient to predict performance. Two HDPE grades with the same 0.952 g/cm³ density can differ in molecular weight distribution, comonomer type, and catalyst formulation. The 18 g/10 min MFR of HDPE 52518 indicates a lower average molecular weight than blow-moulding grades; this reduces entanglement density and therefore reduces slow-crack-growth resistance. In service conditions involving repeated stacking loads or internal pressure, long-term creep and crack propagation should be evaluated using ASTM F1473 or equivalent slow-crack-growth methods. These tests are not part of routine lot release for the grade.

Regulatory status for HDPE 52518 is documented against the following frameworks. Converter-specific conditions, additive loadings, and food-contact surface-to-volume ratios may require supplementary testing.

For food-contact compliance under EU Regulation 10/2011, overall migration limits of 10 mg/dm² apply to the finished article, but HDPE 52518 lot-specific documentation does not replace migration testing on actual packaging because surface-area-to-volume ratio and processing aids influence the result. Published data for this specific film-extrusion configuration is limited; the grade is not intended for film. Applications requiring continuous-wall extrusion blow moulding, ESCR under aggressive surfactants, or parison stability should use lower-flow HDPE grades. HDPE 52518 is limited to injection-moulded article fabrication within the melt-temperature and gate-geometry constraints described.