Marlex HHM 5502BN (HDPE): Datasheet, Processing Window and What It Is Made For

Marlex HHM 5502BN is a high-density polyethylene grade classified as a high-molecular-weight hexene copolymer. The base resin is supplied for large-part extrusion blow molding, sheet extrusion, and thermoforming. Its melt index of 0.35 g/10 min at 190 °C/2.16 kg places it in the high-viscosity segment of the HDPE family, while the density of 0.955 g/cm³ contributes stiffness, chemical resistance, and resistance to creep under stacking loads. In blow molding operations, the low melt index indicates a highly viscous melt that resists parison sag; in sheet extrusion, the same viscosity requires appropriate screw design and head pressure management.

What Published Data Sheet Values Govern Grade Selection?

Representative published datasheet values for Marlex HHM 5502BN are summarized in Table 1. They should be read as typical manufacturer-published data and not as lot-specific specifications or a certificate of analysis.

Table 1. Representative published data for Marlex HHM 5502BN.

Above the crystalline melting region, these values define a grade with sufficient modulus for stacking and creep resistance in industrial packaging. The hexene comonomer introduces short-chain branches that reduce density-adjusted crystallinity relative to a homopolymer and improve slow crack growth resistance. The low melt index is associated with a broad molecular weight distribution and a high entanglement density, which are critical for extensional flow stability in large parisons.

The processing window for this grade is not a single-temperature interval but a three-dimensional envelope defined by melt temperature, shear rate, and residence time. At low melt temperature, viscosity remains high and head pressure rises sharply; at high melt temperature, the same viscosity deficit can produce parison droop. The standard production-line check is therefore to record melt temperature at the adapter, extruder screw speed, head pressure, accumulator fill time, and the programmed parison profile together, not as independent set points.

The Extrusion Melt Temperature Envelope

For large-part accumulation blow molding, the practical melt temperature window is bounded by 195 °C and 230 °C, with a preferred die-exit melt temperature of 200–220 °C. At melt temperatures below 195 °C, high melt viscosity produces excessive head pressure and a rough parison surface, and the accumulator head may not fill within the required cycle time. Above 230 °C, the onset of thermo-oxidative chain scission becomes measurable in long residence time equipment, particularly in the accumulator head and transfer lines. The extrusion barrel should be profiled from 170 °C in the feed zone to 210–220 °C in the metering zone, with adapter and die zones held within 200–225 °C.

On single-screw extruders with 25:1 to 33:1 L/D ratio and barrier screws, the melt temperature measured at the adapter should be controlled with a melt probe rather than inferred from barrel indicators. The difference between barrel set point and actual melt temperature can reach 15 °C because of shear heating in high-viscosity HDPE. Screen packs of 20/40/60 mesh are common, and head pressures of 20–35 MPa can be expected depending on die gap, parison programming, and shot size. Production-scale accumulator machines for 220 L drums typically use extruder diameters of 90–120 mm, shot sizes of 8–15 kg, and screw speeds from 30–60 min⁻¹. Mold temperatures for blow molding are set at 10–30 °C. For thick-walled containers, lower mold temperatures reduce cycle time but can increase frozen-in stress at pinch-off zones.

When Barrel Residence Time Exceeds 15 Minutes

Accumulator-head machines used for 220 L open-head drums can create long residence time distributions. With shot sizes of 8–15 kg, portions of the melt may reside in the head and transfer lines for 10–20 min. At melt temperatures above 230 °C, such residence times are sufficient to lower melt viscosity through chain scission, and the resulting melt pressure drift may require continuous adjustment of parison weight. If oxygen is not excluded, oxidized species can act as gel precursors. Production observations for similar high-molecular-weight HDPE grades indicate that gel formation appears as small fisheyes in sheet or as localized thinning in container pinch-off areas.

The safe operating boundary is therefore to maintain accumulator head metal temperatures at 200–215 °C and to purge the head when downtime exceeds 15 min. The base resin contains a phenolic/phosphite stabilization package; however, repeated reprocessing of regrind beyond 30 wt% can deplete antioxidant activity. Regrind reuse should be validated by melt index retention and oxidative induction time according to ASTM D3895. No additional pre-drying is normally required for HDPE pellets. Surface condensation on cold pellets exposed to high-humidity plant air can generate sheet splay; if observed, a hopper dryer at 70 °C for 1–2 h removes surface moisture.

Accumulator Head Tooling, Die Gap and Parison Weight

High-molecular-weight HDPE grades exhibit die swell of 15% to 30% and parison weight swell that must be compensated by tooling. Die land length-to-gap ratios of 15:1 to 25:1 are used to stabilize flow and reduce melt fracture. Accumulator head tooling with diverging die geometry can be set to a die gap of 2–5 mm for 10–60 L containers and up to 5–10 mm for 220 L drums. Parison programming is required to control wall thickness distribution in parts with varying blow ratio; programmed wall thickness profiles generally contain 50–100 points. A melt temperature of 210 °C combined with a shot speed of 0.5–1.5 kg/s can keep parison sag below 10% over a 1 m parison length.

The high viscosity of the 0.35 g/10 min resin also sets a lower practical die gap because shear rates above approximately 1000 s⁻¹ in thin die land regions can initiate melt fracture. Capillary rheometry of similar melt-index HDPE grades indicates that apparent shear viscosity decreases from roughly 20,000 Pa·s at 0.1 s⁻¹ to approximately 2,000 Pa·s at 100 s⁻¹ at 200 °C. These shear-thinning characteristics allow extrusion through a die while preserving high extensional viscosity for parison stability. The use of a static mixer between the extruder and accumulator head reduces thermal gradients and can narrow the observed melt temperature variation to ±3 °C.

For sheet extrusion and thermoforming, the grade is processed on a single-screw extruder of 30:1 to 33:1 L/D with a static melt mixer or melt pump. The recommended melt temperature is 210–230 °C. The melt is cast through a coat-hanger die into a three-roll stack. Roll temperatures from 80 °C to 100 °C control surface gloss and sheet crystallinity. This grade should not be processed without purging at start-up if a prior lower-viscosity polyethylene has carbonized in the system.

Where Environmental Stress Crack Resistance Controls Grade Selection

Environmental stress crack resistance is the primary mechanical risk in rigid chemical packaging. The ASTM D1693 test bends a notched specimen in a surfactant solution; a published F50 value above 600 h under Condition B is representative for this hexene-copolymer HDPE. The combination of high molecular weight and short-chain branching increases tie-molecule density and slows crack propagation. Applications that expose the polymer to non-ionic surfactants, aqueous agricultural chemicals, or mildly aggressive detergents use this resin when a homopolymer of similar density would fail by rapid crack growth under hoop stress.

The operational boundary remains that ESCR performance does not imply compatibility with strong oxidizing acids, chlorinated hydrocarbons, or aromatic solvents at elevated temperatures. Each chemical formulation should be tested under ASTM D1693 with the actual packaged fluid. Published data for this specific configuration is limited, and the use of generic ESCR rankings does not replace pack testing under filled-container stress conditions.

Container and Tank Applications Demand High ESCR and Controlled Swell

Specified applications for Marlex HHM 5502BN center on large blow molded containers, industrial drums, accessory tanks, and sheet for thermoformed pallets and dunnage. In 55 L to 220 L drums, the high melt strength maintains uniform wall thickness in the chime and pinch-off zones; the ESCR allows use with many surfactant-containing liquids. In sheet form, the material is formed into twin-sheet thermoformed parts such as pallets and cable reels, where flexural modulus and weld-line integrity are critical. The grade is also used in multi-layer blow molded containers where a high-ESCR HDPE layer is combined with barrier or regrind layers. Thin-wall injection molding, fiber spinning, and blown film are not appropriate processing routes because the melt index of 0.35 g/10 min produces excessive fill pressures and poor processability in high-shear capillary-dominated operations.

Table 2. Typical compliance matrix referenced for final articles.

Compliance is article-specific. Component manufacturing temperature, food-contact surface area, wall thickness, and intended food simulant influence migration test results. The base resin datasheet alone should not be used to certify final article compliance for food or dangerous goods packaging.

Design and processing limits for the grade are defined by oxidation and ultraviolet sensitivity. Continuous load-bearing service above 60 °C is not recommended for chemical storage under hydrostatic pressure. Outdoor exposure of unpigmented articles is limited to short-term service because ultraviolet radiation reduces elongation at break and accelerates surface microcracking; for outdoor weathering, 2.0–2.5 wt% carbon black or an equivalent UV stabilization package is required. Processing with regrind above 30 wt% should be validated for melt index drift and loss of ESCR. Contact with strong oxidizing acids, aliphatic chlorinated solvents, or aromatic hydrocarbons at the upper end of the processing-use range can soften and stress-crack the polymer. Documented high-purity applications require independent extraction and migration testing.