ARPC (Iran) HDPE EX5 is a high-density polyethylene extrusion grade produced by Amirkabir Petrochemical Company and supplied as natural cylindrical pellets. The resin belongs to the PE-HD class under ISO 17855-1:2016 and is positioned for blown-film, sheet, and non-pressure extrusion processes in which melt strength and draw stability are required rather than injection-moulding flow. Supplier-published nominal data place the density at 0.954 g/cm³ when determined under ISO 1183-1:2019. The melt mass-flow rate is reported in the range of 0.75 g/10 min to 0.85 g/10 min at 190 °C with a 5.0 kg piston load under ISO 1133-1:2022. These values position EX5 as a medium-viscosity extrusion grade, distinct from high-flow injection HDPE grades in the 20 g/10 min class and from very low-flow blow-moulding grades that depend on higher zero-shear viscosity for parison stability.

Does the EX5 Melt Flow Index Align with Blown-Film or Thick-Sheet Extrusion Requirements?

The melt flow index of EX5 is low enough to support the bubble stability required in high-stalk blown-film operations but high enough to avoid excessive backpressure on conventional single-screw extruders. For blown film, the practical melt-fracture window typically narrows above 1.2 g/10 min for high-density grades because lower molecular weight reduces elongational viscosity and increases the risk of bubble sag. EX5, with a nominal melt flow index near 0.8 g/10 min, remains inside the process window commonly used for heavy-duty sacks and packaging films. In thick-sheet extrusion, the same rheology permits a stable draw from the die lip without pronounced neck-in or edge-thickness variability. The density of 0.954 g/cm³ gives the sheet higher stiffness than lower-density polyethylene films but also reduces impact absorption at low temperature unless orientation or blending is applied.

These values are lot-specific and should be confirmed against the supplier certificate of analysis. The table is not a finished-part specification; conversion-induced molecular orientation, additive package, and filler level alter final mechanical response. The melt flow index test under ISO 1133-1:2022 uses a 5.0 kg load because low-load values in the 0.1 g/10 min range would not discriminate adequately among extrusion HDPE grades. The high-load melt index, if requested for pipe or large-part evaluation, is not a direct substitute for capillary rheometry when assessing die swell.

When EX5 is compared with an injection-moulding HDPE of 20 g/10 min, the difference is not only flow rate. EX5 retains higher melt elasticity, a wider die swell envelope, and longer relaxation time after shear. These are practical differences in a plant: the injection grade will fill a multi-cavity tool at lower pressure but may show warpage in thick sections; EX5 will generate higher extruder torque at the same screw speed and may require a melt pump for thickness uniformity. The molecular architecture also affects shrinkage. Semi-crystalline HDPE with 0.954 g/cm³ density typically exhibits mould shrinkage between 1.5% and 3.0%, but extrusion sheet made from EX5 can show anisotropic shrinkage if the take-off speed is not matched to calender roll temperature.

When the Extruder L/D Drops Below 24:1, Barrier-Screw Melt Temperature Control Becomes Critical

On production-scale blown-film lines with a 24:1 L/D single-screw extruder, ARPC HDPE EX5 is normally processed with a barrel profile ramped from 160 °C in the feed zone to 210 °C in the metering zone. Die temperature is held between 200 °C and 220 °C. If the line uses a barrier screw, shear heating can raise melt temperature by 5 °C to 8 °C above the barrel set point at high screw speed. The operator response should be to reduce screw speed or adjust the downstream cooling, not to lower the feed-zone set point below the crystalline melting region. A cold feed zone can leave unmelted granules in the melt stream and produce gel-like defects in the film, even though the barrel readout appears stable.

Screen packs of 60/80/100 mesh are typical in the adapter to remove char and crosslinked particles. Pressure before the screen pack is kept below 350 bar during continuous operation. A rising pressure trend at constant screw speed indicates screen blockage, polymer degradation, or feed-bridge formation; a sudden drop in pressure with a simultaneous rise in motor load may indicate screw wear or melt leakage across a damaged barrel liner. For extrusion of 50 µm blown film with a 1.0 mm die gap and a blow-up ratio of 3.5:1, frost-line height is commonly maintained between 1.5 and 3.0 die diameters. A frost line that remains too high is often caused by insufficient air-ring flow or excessive melt temperature, not by the resin alone.

HDPE EX5 does not normally require desiccant drying. If the pellets are stored at relative humidity above 60% for more than 72 h, or if regrind is introduced into the hopper without surface drying, moisture can create splay and reduce film clarity. In this condition, hopper-air drying at 70 °C for 2 h is adequate. Drying temperature should not exceed 80 °C to avoid pellet softening and feed-throat bridging. Extended residence time above 240 °C should be avoided because it can initiate chain scission, shift the melt flow index upward, and increase the volatiles measured under ISO 11358-1:2022 thermogravimetric analysis.

In thick-sheet extrusion, the roll-stack temperature is commonly set between 70 °C and 90 °C. Lower roll temperatures increase cooling rate and sheet haze but also increase residual stress. Higher roll temperatures improve surface gloss but can cause blocking if the sheet is wound too tightly. The die gap is typically set 10% to 20% wider than the final sheet thickness to compensate for draw-down. A die gap too narrow at high line speed can raise die pressure above 300 bar, increase shear heating, and produce melt fracture. If melt fracture appears, increasing die temperature by 5 °C is preferred over increasing line speed because line speed amplifies draw resonance.

Unlabelled application data are equally important for blown-film conversion. Machine-direction tensile strength on 50 µm film is measured under ISO 527-3:2018. The machine-direction tensile stress at yield is typically near 28 MPa, while transverse-direction yield stress is commonly 2 MPa to 4 MPa lower due to orientation. Elongation at break remains above 600% in both axes when the film is processed below 220 °C melt temperature. The ratio of machine-direction to transverse-direction tensile stress should be monitored; a ratio above 1.3 may indicate excessive molecular orientation and can cause weak transverse tear resistance. Dart impact on 25 µm film under ASTM D1709, Method A, commonly lies between 120 g and 180 g depending on frost-line height, but published data for EX5-specific film in this configuration is limited. Formulators seeking low-temperature impact resistance should not rely on HDPE EX5 alone; blending with LLDPE or adding an elastomer modifier may be required for freezer-grade packaging.

ESCR, Oxygen Transmission, and Food-Contact Compliance Boundaries

Environmental stress crack resistance under ASTM D1693-21 is a critical differentiator between extrusion HDPE and low-molecular-weight HDPE. EX5’s reported F50 value above 500 h in 100% Igepal is relevant for rigid sheet and container sidewalls exposed to surfactants and oils. However, the test is strain-dependent and lot-sensitive; finished articles with sharp corners or moulded-in stress may crack below the reported value. For aggressive organic hydrocarbons, aromatic solvents, or strong oxidising acids, HDPE is not recommended as a continuous service material. The material is compatible with dilute aqueous acids, alkalis, and many polar solvents at ambient temperature, but the service temperature should remain below the Vicat softening point under load and below 60 °C for continuous creep-prone applications unless validated by a long-term hydrostatic test.

For direct food-contact use, the finished article must be tested under the applicable jurisdiction. The resin may meet the general requirements of FDA 21 CFR 177.1520(c) 3.2a and European Commission Regulation (EU) No 10/2011, but resin-grade compliance is not equivalent to finished-article compliance. Extraction testing under ISO 1186-1 and ISO 1186-14 is required on the actual packaging. Heavy-metal and specific migration limits should be confirmed using the final colour masterbatch, because pigments and processing aids migrate, not the base resin alone.

Water-vapour transmission rate for HDPE at 0.954 g/cm³ is lower than LDPE, but oxygen barrier is poor. Packages made from EX5 are not a substitute for EVOH, PVDC, or metallised film when oxygen exclusion is critical. In barrier coextrusions, EX5 may serve as the structural skin layer with an EVOH core, but tie-layer adhesion must be verified under ASTM F904 or equivalent peel testing. The difference in melt flow index between skin and core layers should not be excessive; a mismatch above 1.5 g/10 min can create interfacial instability and layer-thickness variation in the die.

Outdoor exposure of EX5 without ultraviolet stabilisation leads to embrittlement within months under ISO 4892-2:2021 accelerated weathering. For outdoor film or sheet, carbon black loading of 2.0 to 2.5 wt% or a hindered-amine light-stabiliser package is required. Carbon black dispersion must be evaluated under ISO 18553 or equivalent microscopy; poor dispersion creates agglomerates that act as stress concentrators. The addition of processing aids should be limited to those that do not interfere with surface treatment. If the film is printed or laminated, corona discharge treatment above 38 mN/m surface tension is typical, but the treatment decays with time and should be rechecked before ink application.

Compared with a bimodal pipe grade, EX5 does not provide the same long-term hydrostatic strength under ISO 9080:2022 and should not be substituted for PE 100 or PE 100-RC pipe formulations without full validation. Compared with a high-flow HDPE film grade, EX5 requires higher torque and produces higher die pressure, but it yields better bubble stability and greater downgauging potential in applications where film stiffness and creep resistance are governing variables. The rheological difference appears most clearly in capillary rheometry: at 190 °C and an apparent shear rate of 100 s⁻¹, EX5 typically exhibits higher shear viscosity than a 1.8 g/10 min film grade, and the onset of gross melt fracture shifts to a higher shear stress. This is a measurable processing advantage in thick-gauge sheet, where flow instabilities at the die lip create gauge bands.

Melt Strength and Die Swell Contrast with Injection-Moulding HDPE Grades

In extrusion-grade high-density polyethylene, melt strength is not directly measured by melt flow index. It is inferred from extensional rheometry, die swell, and bubble stability. EX5, with its lower melt flow index and higher molecular weight relative to injection HDPE, displays higher melt strength and a broader stable draw region. On a blown-film line, this permits higher blow-up ratios without bubble flutter. On a sheet line, it permits higher draw ratio with less sag. In contrast, an injection-moulding HDPE of 20 g/10 min shows low die swell and short relaxation time, which is desirable for mould filling but undesirable for maintaining a stable annular parison or film bubble.

The practical result is that EX5 is used where the part is formed in the melt state over a relatively long open path, such as blown film between the die and the collapsing frame, or sheet between the die and the roll stack. It is less suitable for thin-wall injection-moulded containers with wall thickness below 0.8 mm, because the higher viscosity may create short shots or require excessive melt temperature. If injection moulding is attempted, a barrel temperature above 220 °C and an intensification pressure above 1000 bar may be needed, but the product is not sold for that purpose and the resulting mechanical properties may be outside the design window.

For sheet and film conversion, gauge control is improved when the extruder is equipped with a gear melt pump. On a 90 mm single-screw extruder with a 30:1 L/D ratio, throughput fluctuations of ±1.5% without a melt pump can produce transverse gauge variation of ±4% to ±6% after draw-down. Adding a melt pump reduces fluctuation but introduces shear heating; melt temperature increase across the pump is typically 2 °C to 4 °C. The extruder screw speed is then trimmed to maintain pump inlet pressure between 80 bar and 120 bar. These are field-level settings, not resin absolute limits, but they are observed on production equipment when processing HDPE in the 0.7 g/10 min to 0.9 g/10 min range.

Regrind use alters the property balance. Up to 20 wt% clean post-industrial regrind is commonly introduced into the feed stream without a major loss of tensile yield, provided the regrind is not thermally degraded. Above 30 wt%, melt flow index may shift upward by 0.1 g/10 min to 0.2 g/10 min and the F50 environmental stress crack resistance may fall. The regrind fraction should be controlled by lot, not by visual appearance alone. Addition of a high-flow HDPE scrap into EX5 lowers viscosity and die swell; this may be acceptable for thick sheet but can destabilise thin-film bubble geometry.

Processing of EX5 with peroxide additives is not recommended unless the converter has validated the modification. Peroxide-induced chain scission or crosslinking can shift the molecular weight distribution outside the design range and alter die swell. If reactive modification is required for adhesion or branching, laboratory-scale torque rheometry under ASTM D3795 or equivalent is required before production.