Chevron Phillips Chemical HDPE EHM 6004 is a pelletized high-density polyethylene resin based on a hexene-1 copolymer architecture. The nominal density is 0.960 g/cm³ determined under ASTM D1505, and the nominal melt index is 0.65 g/10 min at 190 °C/2.16 kg using ASTM D1238. The nominal high-load melt index is 35 g/10 min at 190 °C/21.6 kg using ASTM D1238. These values place the resin in the high-stiffness, high-molecular-weight segment of HDPE, where melt viscosity is suited to accumulator-head extrusion blow molding and thick sheet extrusion rather than high-speed injection molding.

The hexene-1 comonomer introduces short-chain branching that disrupts uniform lamellar growth and increases interlamellar tie-molecule formation relative to a homopolymer of equivalent melt index. The practical consequence is that environmental stress crack resistance under ASTM D1693 is higher than that of a comparable linear homopolymer at equal density. Published data for the specific branch distribution of EHM 6004 is limited; however, the grade is positioned as a hexene copolymer rather than a butene copolymer for this reason.

Nominal Mechanical Properties, Thermal Transitions, and Standard Test Methods

The property set below is consolidated from manufacturer technical literature and uses standard specimen preparation practices. Conditioning follows ASTM D618 at 23 °C and 50% RH for 40 h unless otherwise noted. Tensile yield and elongation use ASTM D638 Type IV specimens at a crosshead speed of 50 mm/min. Flexural modulus uses ASTM D790 Procedure A at 2 mm/min with a 1% secant definition. The notched Izod value is generated under ASTM D256 at 23 °C after notch preparation on injection-molded plaques.

The Vicat softening point under ASTM D1525 should not be interpreted as a continuous service temperature. For pressure-bearing applications, long-term hydrostatic strength must be calculated using ISO 9080 or ASTM D2837 with service-specific hoop stress and temperature inputs. The brittleness temperature under ASTM D746 is a comparative low-temperature ranking, not a minimum use temperature for impact events.

In molecular terms, the conventional melt index of 0.65 g/10 min and high-load melt index of 35 g/10 min yield a melt flow ratio of 54. This ratio is not a direct measure of polydispersity, but it is used in resin qualification and lot-release documentation to monitor lot-to-lot consistency. The melt density of HDPE at 190 °C is approximately 0.766 g/cm³; the melt volume-flow rate under ISO 1133-1:2022 is therefore lower than the mass-flow rate by the density correction. This distinction is significant when translating melt index values to volumetric throughput in grooved-feed extruder calculations.

On a capillary rheometer at 190 °C, EHM 6004 displays a shear-thinning viscosity profile typical of a high-molecular-weight extrusion resin. A broad molecular weight distribution is used in large parison blow molding because the high-molecular-weight fraction contributes extensional viscosity and sag resistance, while the lower-molecular-weight fraction lowers extrusion head pressure. The trade-off is that a broad distribution can reduce melt extensibility and increase the onset of surface haze in thin-walled sections when compared with narrow-distribution grades used for cast film.

For multilayer coextrusion, processors should verify the compatibility of EHM 6004 with adjacent tie resins and barrier polymers. Layer-to-layer viscosity mismatches above roughly 2:1 at the relevant shear rate can produce interfacial instability in the die and visible weld lines in the finished article. Elongational rheometry data for this specific EHM 6004 formulation is not widely published; the practical approach is to measure apparent viscosity over a shear rate range of 50 s⁻¹ to 500 s⁻¹ on a capillary rheometer and compare the curves with the adjacent layer resins.

Where Does EHM 6004 Differ from HHM 5502BN and HXM 50100?

Relative to Chevron Phillips Chemical HHM 5502BN, a standard blow molding grade with nominal density 0.955 g/cm³ and nominal melt index 0.35 g/10 min, EHM 6004 has a higher melt index and a higher density. The lower melt viscosity can reduce extruder head pressure and can permit faster parison extrusion on thin-wall parts, but it also increases parison sag if melt temperature is not reduced accordingly. The higher density of EHM 6004 increases flexural modulus and may allow down-gauging in stiffness-limited applications, while the lower molecular weight can reduce ESCR when compared with HHM 5502BN at identical part geometry and stress levels.

Compared with HXM 50100, a high-flow HDPE film resin used on high-speed cast film lines, EHM 6004 has a much lower melt index and is not suitable for thin-gauge film production at high line speeds. The two grades are not interchangeable. EHM 6004 is intended for thick-walled extrusion blow molding, sheet extrusion, and thermoforming processes where melt strength and parison uniformity are required.

Processing on Accumulator-Head Extrusion Blow Molders

On a single-screw extruder with a grooved feed zone and an L/D ratio from 24:1 to 30:1, the following starting temperature profile is common: feed zone 180 °C, compression zone 190 °C, metering zone 200 °C, head 200 °C, die 200 °C. The melt temperature measured at the die exit should be held between 190 °C and 220 °C. At melt temperatures below 190 °C, die pressure rises and the parison surface can show sharkskin melt fracture. Above 220 °C, oxidative degradation can reduce melt strength and generate gel particles. Processing window constraints in this grade are therefore approximately ±5 °C around the mid-range melt temperature during long production runs.

The die gap is set between 1.5 mm and 3.0 mm depending on part weight and die swell. Blow pressure between 0.4 MPa and 0.7 MPa is typical for continuous wall consolidation. Blow time is adjusted until the inner surface reaches the mould temperature and the wall does not recoil on deflation. Premature deflation at pressures above 0.7 MPa can produce pinch-off flash thinning, especially near mould parting lines.

Accumulator-head machines with shot capacities from 10 kg to 45 kg are used for large containers, intermediate bulk packaging, and agricultural chemical tanks. The extruder should be capable of uniform throughput within ±2% to avoid parison length variation. Wall thickness control through a programmable head is recommended for parts longer than 1.0 m; manual die gap adjustments are usually insufficient to control thinning at the top and bottom pinch-off zones.

Die swell for EHM 6004 is lower than that of low-melt-index blow molding grades because the lower molecular weight reduces elastic recovery. Die swell values in practice are influenced by die geometry, land length, and shear history. On a spiral mandrel die with a land length ratio of 10:1, processors have noted a die swell range of 20% to 40% depending on extrusion rate. Published data for this specific resin in such dies is limited; die swell must be measured on the production tool.

If Moisture Content Exceeds 0.05% by Weight, Pre-Drying Is Required

HDPE is not hygroscopic, but surface condensation on cold pellets and regrind can introduce moisture at relative humidity above 60%. Moisture levels above 0.05 wt% can produce surface splay, pinholes, and internal bubbles in thick blow-molded walls. In such conditions, pre-dry the resin and regrind at 80 °C for 2 h in a desiccant dryer with a dew point of -30 °C. Pellets transferred from outdoor silos should be allowed to equilibrate indoors for 24 h before hopper loading.

Regrind addition should not exceed 20 wt% without a production trial. Higher regrind fractions can reduce melt strength and broaden residence time distribution. Fines and dust should be removed with a cyclone separator before blending. Lot-to-lot variation in melt index for commercial HDPE typically remains within ±0.05 g/10 min around the nominal value. When changing lots, the recommended procedure is to retain 10% of the previous lot as a transition batch and monitor head pressure and parison length for the first 30 min.

The olefin polymer base resin is manufactured to meet FDA 21 CFR 177.1520 for olefin polymers intended for food-contact applications, provided that the finished article meets the extraction limits and use conditions specified in the regulation. For the European Union, converters must verify compliance under Commission Regulation (EU) No 10/2011 and its amendments, including overall migration limits of 10 mg/dm² for plastic food-contact materials. These statements apply to the base resin as supplied; they do not automatically extend to the finished article after printing, lamination, or addition of masterbatch.

EHM 6004 is not an ultraviolet-stabilized grade unless explicitly specified by the supplier. Outdoor service applications requiring more than 2 years of exposure should use a carbon black masterbatch at 2.0 to 2.5 wt% carbon black with a primary aggregate size below 25 nm and good dispersion. Continuous contact with strong oxidizing acids, halogens, or aromatic hydrocarbon solvents above 60 °C can induce environmental stress cracking and should be evaluated through chemical resistance testing under ASTM D543.

What Are the Critical Failure Modes in Large Parison Extrusion?

Three failure mechanisms are commonly monitored when EHM 6004 is run on large-part blow molding lines: parison sag, melt fracture, and pinch-off weld line splitting. Parison sag is a viscoelastic response to gravitational loading during the hang time between parison extrusion and mould closure. The sag rate increases with melt temperature and parison length. On a parison length of 2.0 m, a melt temperature increase of 5 °C can produce a measurable diameter reduction in the lower quarter of the parison, causing wall thinning and an axial weld line. The remedy is to reduce melt temperature or increase extrusion speed, but both changes alter die swell and parison diameter.

Melt fracture in EHM 6004 occurs when wall shear stress exceeds the critical level at the die land, typically appearing as a regular small-amplitude surface roughness that becomes severe sharkskin at low melt temperature or high extrusion rate. The onset can be measured as a loss of surface gloss at shear rates above 500 s⁻¹ through a capillary die of 20:1 L/D. In production, sharkskin is controlled by raising die temperature, widening the die gap, or reducing screw speed. However, raising melt temperature beyond 220 °C accelerates thermo-oxidative degradation and can produce gel specks, so the practical response space is narrow.

Pinch-off weld line splitting occurs when the mould pinch-off region does not reach a sufficient fusion temperature and pressure. The weld line strength can be tested on cut sections using a tensile impact method or a bend test at 0 °C. Inadequate pinch-off compression can be caused by too low a melt temperature, insufficient clamp force, or contamination at the parting line. On accumulator-head machines with clamp force below 150 t, weld line thickness can be the limiting factor for containers with a pinch length greater than 1.5 m. Processors should verify the weld line thickness with an ultrasonic gauge and document it as part of production lot acceptance.

In thick-walled structural parts such as intermediate bulk container inner bottles, automotive fluid reservoirs, and chemical storage tanks, EHM 6004 is processed with wall thickness ranging from 2 mm to 8 mm. The combination of high density and hexene-1 copolymer architecture provides a measurable retention of impact resistance after exposure to surfactant solutions. Drop-impact testing following ASTM D2463 or ASTM D5276 is used to evaluate finished containers at 0 °C and -18 °C. For parts exposed to agricultural chemicals, ESCR testing under ASTM D1693 condition B is used as a screening tool, but field validation with the actual chemical mixture is required because stress-cracking agents vary widely in polarity and molar volume.

Sheet extrusion and thermoforming operations use EHM 6004 at melt temperatures from 200 °C to 230 °C through a flat die with a polished roll stack held at 80 °C to 100 °C. Sheet thickness from 3 mm to 12 mm is common for thermoformed pallet covers and dunnage trays. In these processes, the higher density of EHM 6004 permits lower thickness at equal flexural stiffness, but the reduced melt strength compared with lower-melt-index blow molding grades can cause sag across wide sheet dies. Published data for this specific configuration is limited.