Before grade qualification in thin-wall closure and rigid crate applications, the converter verifies the melt-flow response of Lotte Chemical HDPE HIVOREX E308 under ISO 1133-1:2022. The grade is positioned as a medium-flow high-density polyethylene injection-moulding material with a reported melt-flow rate of 8.0 g/10 min at 190 °C and 2.16 kg, and a solid-state density of 0.956 g/cm³ under ISO 1183-1. Manufacturer datasheet values place the tensile yield stress near 24 MPa under ISO 527-2 and the flexural modulus near 800 MPa under ISO 178. The product is used in rigid crates, pails, caps, housewares, and thin-wall containers; it is not a blow-moulding or film-extrusion grade. Compared with low-flow HDPE grades in the 0.3–0.8 g/10 min range used in extrusion blow moulding, E308 provides lower melt viscosity and faster cavity filling but lower melt strength. Compared with high-flow HDPE grades in the 20–40 g/10 min range used for ultra-thin lids, E308 retains higher notched impact strength and greater creep resistance under sustained load. Raw-grade property data do not establish food-contact compliance; finished-article verification under the applicable regulation is required.

What processing window governs stable filling in hot-runner multi-cavity tools?

On production-scale injection-moulding machines with clamp force from 1,200 kN to 5,000 kN, barrel-zone settings for E308 are commonly established with a flat or reverse profile: feed throat below 180 °C, compression zone at 200–220 °C, and nozzle at 220–230 °C. Melt temperature measured by insertion pyrometer should remain between 200 °C and 230 °C. At melt temperatures below 190 °C, short shots become more frequent when the flow-length-to-wall-thickness ratio exceeds 180:1; above 240 °C, oxidative degradation during extended hold time reduces tensile elongation at break under ISO 527-2 and increases yellowing. Mould temperature is maintained between 10 °C and 40 °C; elevated mould temperatures above 50 °C are not normally required and lengthen cycle time without a measured increase in notched Charpy impact strength under ISO 179-1/1eA.

Rheological characterisation under ISO 11443 at 190 °C and 210 °C is used to construct viscosity models for mould-filling simulation. HDPE in this melt-flow class displays shear-thinning between 100 s⁻¹ and 10,000 s⁻¹; at gate shear rates above 100,000 s⁻¹, melt fracture or gate blush becomes more probable. For E308, published numerical viscosity curves for every shear rate are often not supplied in standard datasheets; converters can measure the flow curve on the specific lot before designing precision thin-wall tools.

Injection velocity is profiled to prevent jetting and to fill thin walls before freeze-off. A low initial velocity of 30–60 mm/s during sprue entry, a high velocity of 80–150 mm/s during main cavity filling, and a reduced velocity before transfer to hold pressure are typical for wall sections below 1.0 mm. Back pressure is limited to 0.3–0.7 MPa; screw speed is kept between 80 min⁻¹ and 150 min⁻¹ on general-purpose screws with L/D 20:1–25:1. These values are starting points, not validated process limits for a specific mould. If E308 is pre-compounded with colour masterbatch or additives, a co-rotating twin-screw extruder with L/D 36:1–44:1 may be used when high additive loadings require dispersive mixing; for direct moulding, a single-stage screw with a dispersion head is sufficient.

Surface moisture is managed even though HDPE is not hygroscopic. When pellets are stored in unheated silos at relative humidity above 60%, condensation can produce splay and internal voids. A drying step of 2 h at 80 °C in a desiccant hopper dryer is applied under these conditions; drying above 100 °C for extended periods risks agglomeration at the hopper magnet or feed throat. Regrind is typically limited to 20 wt% when clean and dry; higher regrind fractions can alter the effective melt-flow rate and reduce notched Charpy impact strength, but published data for E308 at specific regrind levels is limited.

Reported physical property envelope and test methodology for ISO-conditioned specimens

Table 1 summarises representative values for injection-moulded E308 specimens conditioned at 23 °C and 50% relative humidity under ISO 291. Values are taken from standard polyolefin datasheet reporting and are not a substitute for certificate-of-analysis data for a specific lot.

Notched Charpy impact strength under ISO 179-1/1eA is sensitive to notch tip radius and moulded-in stress; values obtained with a 0.25 mm notch radius should not be compared directly with values generated with a different radius. Tensile elongation at break is measured at a nominal test speed of 50 mm/min under ISO 527-2 and is reduced in weld-line regions. Density is measured on the solid moulded part, not on the pellet, and lot-to-lot variation of approximately ±0.001 g/cm³ can be expected in normal production.

Material substitution from polypropylene or from lower-flow HDPE requires revision of tool shrinkage. Because E308 is a semi-crystalline polyolefin, mould shrinkage is anisotropic; for this melt-flow class, typical mould shrinkage is 1.5–2.0% in the flow direction and 1.0–1.5% transverse to flow, measured on plaques under ISO 294-1. These values are higher than polypropylene shrinkage and must be compensated before a polypropylene tool is re-used. Compared with HDPE grades below 1.0 g/10 min, E308 is unsuitable for extrusion blow moulding because its lower melt strength allows parison sag; conversely, it is easier to fill thin injection-moulded sections. Table 2 places these differences in a class-level context.

The comparisons in Table 2 are generic class descriptions, not direct grade specifications. Substitution into existing E308 tooling should not be based solely on nominal melt-flow rate; mould-filling simulation, gate shear-rate, and post-moulding shrinkage must be verified on the target machine.

If low-temperature impact resistance dominates the end-use requirement, polymer molecular architecture becomes the critical variable.

At service temperatures below -20 °C, the notched impact performance of HDPE depends on molecular weight distribution, short-chain branching, and processing-induced orientation. E308 is a medium-flow grade and is not specified for cryogenic impact service; its notched Charpy impact strength at -20 °C is lower than that of high-molecular-weight HDPE grades with melt-flow rates below 1.0 g/10 min. Frozen-food packaging and cold-climate crates can still employ E308 when the article has radii above 3 mm, no sharp gate vestige, and uniform wall sections above 1.5 mm; however, pails or industrial containers subjected to drop impact at sub-zero temperatures should be evaluated against a lower-flow HDPE grade. Slow-crack-growth resistance under ISO 16770 or notched pipe test methods is not the primary design basis for E308; published data for long-term hydrostatic or aggressive-chemical exposure of this specific grade is limited.

Design features control the practical performance of E308. Rib-to-wall ratios below 0.6:1, corner radii above 2 mm, and uniform wall-thickness transitions reduce moulded-in stress. Sharp internal corners in pail bases act as stress concentrators and should not be specified without a radius of at least 2 mm; otherwise, notched Charpy impact strength measured on a standard specimen overestimates service performance under ISO 179-1/1eA. Weld lines in handle regions should be positioned away from tensile loads because weld-line tensile strength is 70–85% of the un-welded tensile yield stress in HDPE under ISO 527-2. For continuously loaded stacked crates, design calculations should use creep modulus rather than short-term flexural modulus; creep modulus under ISO 899-1 at 23 °C declines with time and stress. Published data for E308 at 1,000 h and 10 MPa is not typically provided on standard datasheets and should be measured if crate loads exceed 20% of the tensile yield stress.

Chemical environment compatibility is a separate design input. In contact with aliphatic hydrocarbons such as hexane or with aromatic solvents such as xylene at temperatures above 60 °C, E308 undergoes solvent uptake and a corresponding reduction in tensile yield stress; this is a solubility-parameter limitation of HDPE generally. In aqueous detergent solutions at temperatures below 40 °C, surface stress cracking of moulded-in stress regions is possible if the part contains sharp corners or weld lines; environmental stress-cracking tests under ISO 22088-3 are therefore specified for containers holding non-ionic surfactants. Published data for E308 under specific detergent concentration gradients is limited.

From a regulatory standpoint, polyethylene homopolymers used in food-contact articles are often evaluated under FDA 21 CFR §177.1520 and Regulation (EU) No 10/2011. The datasheet for E308 should be checked for the specific additive package and catalyst residues, because individual species may have specific migration limits. Overall migration limits under Regulation (EU) No 10/2011 are 10 mg/dm²; specific migration testing is performed according to EN 1186-1 or equivalent. REACH and RoHS 2011/65/EU apply to electrical and electronic equipment enclosures only if the moulded part is part of an EEE; restricted substances are not normally a concern for unpigmented HDPE, but converters must verify pigment masterbatches separately. A supplier certificate of composition does not replace finished-article migration testing.

On multi-cavity lines, three field failure modes recur when E308 is processed outside its thermal and rheological limits. Gate blush appears when initial injection velocity is too high at the gate; reducing the first-stage velocity to 30 mm/s or increasing gate diameter usually removes the defect. Weld-line brittleness in handles and bosses occurs when melt temperature is below 200 °C or when venting is inadequate; vent depth of 0.02–0.03 mm and land length of 6–12 mm are typical for HDPE, but the vent depth must be machined for the specific melt viscosity and not exceed flash tolerance. Ejection-induced deformation on pails and crates is observed when the core region is ejected above 80 °C; the correction is additional cooling time or reduced mould temperature, not increased mould temperature. Batch-to-batch melt-flow-rate variation for commercial HDPE injection grades is generally within ±0.5 g/10 min; a lot shift from 7.5 g/10 min to 8.5 g/10 min requires adjustment of cushion and transfer pressure but is not a defect. These operational boundaries are provided for process establishment and incoming material qualification.