Chevron Phillips Chemical HDPE HHM 5502-04BN is a high-molecular-weight, hexene-copolymer high-density polyethylene supplied in pellet form for sheet extrusion, large-part thermoforming, industrial containment, and geomembrane fabrication. The resin is characterized by a nominal density of 0.955 g/cm³ under ASTM D1505 and a melt index of 0.35 g/10 min at 190°C with 2.16 kg under ASTM D1238. These values place the material in the HMW-HDPE class, where high molecular weight and broad molar mass distribution produce elevated melt strength, slow crack growth resistance, and high modulus relative to medium-molecular-weight high-density grades. The -04BN suffix identifies a specific formulation and additive package within the HHM 5502 series; direct interchange with other suffix grades should be avoided unless the converter has verified the additive, weathering, and compliance status of the finished article. In sheet and geomembrane applications, the grade is selected when stiffness, toughness, and resistance to environmental stress cracking are weighted above melt flow.

Morphologically, the density of 0.955 g/cm³ indicates a crystalline fraction near 65% to 70% when estimated from polyethylene density-crystallinity relationships. The crystallites contribute to flexural modulus and chemical permeation resistance while the amorphous tie-chain population influenced by the hexene comonomer supports environmental stress crack resistance. The melt index of 0.35 g/10 min is a low-shear indication only; high-load melt index is the more useful control for sheet extrusion because flow through the die occurs at shear rates orders of magnitude above the 2.16 kg condition. A high-load melt index near 35 g/10 min under 21.6 kg is reported for the HHM 5502 family; the ratio of high-load to normal melt index, near 100, reflects shear thinning that aids die flow while retaining melt strength.

What processing boundaries apply during sheet extrusion and thermoforming?

Sheet extrusion of HHM 5502-04BN is melt-viscosity limited rather than drying limited. Standard HDPE drying is unnecessary unless pellet surface condensation is present; if storage humidity exceeds 60% RH or pellets have moved from cold storage to a warm production area, pre-drying at 80°C for 2 h is a conservative starting point. Typical melt temperatures for HMW-HDPE sheet lines fall between 210°C and 250°C. Below 210°C, high melt viscosity can reduce output, increase head pressure, and produce sharkskin melt fracture at the die lip. Above 260°C, thermal-oxidative degradation accelerates, producing gels, yellowing, and reductions in environmental stress crack resistance. The effective processing window is therefore narrow; published data for this specific configuration is limited, and conversion of the grade on a given line should begin with melt temperature mapping rather than a fixed barrel profile.

Production-scale experience on single-screw extruders with 24:1 to 30:1 L/D indicates that barrier screws with a Maddock mixing section are preferred. Screen packs of 20/40/60 mesh are common; finer packs raise head pressure and may reduce output by 5% to 10% as screens blind. Head pressure should be monitored against the extruder manufacturer’s maximum rating, and rupture discs or pressure alarms should be set to prevent screen failure. Die gap settings are typically 0.8 mm to 1.5 mm for sheet thicknesses of 2 mm to 12 mm; polished chrome roll stacks at 70°C to 110°C are used to control gloss and sheet flatness. These values are not product-specific specifications but represent the envelope within which HMW-HDPE sheet grades are generally commercialized. If the resin is run on a twin-screw line, the screw configuration should be validated because excessive shear heating can raise melt temperature above the 260°C degradation threshold even when barrel setpoints are lower.

Thermoforming of HHM 5502-04BN sheet requires careful temperature uniformity. Sheet surface temperatures between 160°C and 190°C are typically used for HMW-HDPE; the lower bound minimizes sag and web formation, while the upper bound improves detail in deep-draw tools. Oven residence time should be adjusted to achieve through-thickness temperature uniformity within ±5°C. Draw ratios above 3:1 may produce localized thinning in male-tool corners, especially when sheet is at the high end of the forming range. Tooling with radii below 6 mm can act as stress concentrators and reduce environmental stress crack resistance in the final part. Mold temperatures of 40°C to 80°C are common for dimensionally stable parts; higher mold temperatures reduce frozen-in stress but increase cycle time.

Field data from HMW-HDPE sheet lines indicate that the most common processing-related failure modes are die-lip freeze-off, edge weave from nonuniform die temperatures, and gel formation from overheated resin. Die lip heaters should be zone-controlled; edge heaters often require a 5°C to 10°C higher setting than the center to compensate for heat loss at the deckles. If output is limited by head pressure rather than motor load, periodic screen changes are more effective than raising melt temperature. In thermoforming, batch-to-batch variation in high-load melt index can shift sag behavior; operators commonly adjust oven zone temperatures by 5°C to 10°C to compensate. These adjustments should be captured in the lot set-up record because they are indicators of molecular weight drift rather than random process noise.

The environmental stress crack resistance performance of HHM 5502-04BN is the controlling property for containment and geomembrane service. Under ASTM D1693 condition B in 100% Igepal CO-630, the grade typically exceeds 1,000 h before 50% of specimens fail. This slow crack growth resistance supports selection for storage tanks, secondary containment, and pond liners where localized stress, weld seams, and long service life intersect. However, ESCR is not a bulk strength guarantee; stress concentrations at sharp corners, weld start/stop points, and scratch defects can reduce time to brittle failure by orders of magnitude. Wall thickness below 2 mm in thermoformed corners may also reduce service life under sustained hoop stress. Published data for specific thickness-stress combinations in HHM 5502-04BN is limited; finite element or prototype stress-cracking evaluation is recommended before specifying the material for critical containment at continuous operating temperatures above 60°C.

Chemical resistance of high-density polyethylene is generally strong in dilute acids, alkalis, and polar solvents, but HHM 5502-04BN is not immune to all service fluids. Strong oxidizing acids, chlorinated solvents, liquid hydrocarbons, and surfactants can plasticize, oxidize, or stress crack the resin. Continuous exposure to diesel, gasoline, or organic solvents may lower tensile strength and promote environmental stress cracking. For geomembrane applications, oxidative induction time under ASTM D3895 and sustained pressure testing under ASTM D1598 may be required by project specifications; the resin alone does not establish these end-product values. The -04BN stabilization package is not a substitute for design review of chemical compatibility, and no single chemical resistance table should replace testing under actual service fluid composition and temperature.

Property, specification, and comparative differentiation of HHM 5502-04BN

Differentiation from other products in the Chevron Phillips Chemical HDPE portfolio is based on the combination of density, melt index, and molecular weight distribution. HHM 5502-04BN is not a general-purpose injection molding grade; its fractional melt index makes thin-wall mold filling impractical. Compared with HDPE grades of 0.942 g/cm³ or 0.949 g/cm³, the higher density of 0.955 g/cm³ increases flexural modulus and reduces permeability. Compared with bimodal HDPE grades above 0.958 g/cm³, the resin retains a broader ESCR window and avoids the rapid stiffness gain that can reduce slow crack growth resistance. Compared with lower-molecular-weight sheet grades with melt index above 1.0 g/10 min, HHM 5502-04BN provides higher melt strength and greater sag resistance in thermoforming, but requires higher extruder torque and melt temperature control.

The values in the table are typical and are not release specifications. For design, use the manufacturer’s current sales specification and not typical property data. Batch-to-batch variance in high-load melt index can be more relevant to sheet extrusion than nominal melt index because it reflects flow at shear rates closer to those in the die. Converters should request lot-specific high-load melt index and density data when qualifying HHM 5502-04BN for tight-thickness sheet or geomembrane welding.

For geomembrane specification, the resin is not supplied as a finished geomembrane; converters must qualify the sheet against GRI GM13 or equivalent. Components such as carbon black or UV stabilizers are compounded into the sheet, not necessarily present in the -04BN resin. A 2.0 mm HDPE geomembrane made from HHM 5502-04BN may be tested for thickness, density, tensile properties, tear resistance, puncture resistance, and stress crack resistance under ASTM D5397 or ASTM D1693. Published data for this specific resin in finished geomembrane form is limited; project-specific testing is required.

Food-contact status of HHM 5502-04BN is not established by resin type alone. HDPE homopolymers and copolymers with density above 0.94 g/cm³ may fall under FDA 21 CFR 177.1520(c), but the specific stabilization and processing aids in the -04BN formulation must be reviewed against the regulation. EU food-contact evaluation under Commission Regulation (EU) 10/2011 and its amendments is an end-product responsibility; migration testing on the finished article is required for fatty food simulants if the material is intended for direct food contact. For potable water, compliance with ANSI/NSF 61 must be established through the manufacturer’s listing or third-party certification; the absence of a listing means the product is not certified for this use. RoHS and REACH declarations may be available from the manufacturer, but they apply to the resin as supplied and do not cover colorants, fillers, or processing aids added by the converter.

When HHM 5502-04BN is welded, machined, or joined to dissimilar materials

Secondary fabrication requires qualification of weld integrity and residual stress. Hot wedge and extrusion welding of HMW-HDPE sheet are typically conducted at weld surface temperatures between 220°C and 260°C. Lower temperatures produce incomplete fusion at the weld root; higher temperatures can oxidize the polymer and reduce peel strength. Weld strength should be verified by ASTM D6392 peel and shear methods or ASTM D4437 field seam evaluation. Saw cutting and routing of thick sheet can introduce microcracks if tool speed is too high or if cut surfaces are not cleaned prior to welding. Mechanical fasteners should be isolated from sustained tensile stress because polyethylene cold-flows under load; torque retention and stress relaxation should be evaluated under service temperature. Adhesive bonding is generally not recommended for HDPE unless the surface has been corona-, plasma-, or flame-treated and a compatible primer is used; even then, bond strengths are low compared with welded joints. When HHM 5502-04BN is joined to polypropylene or PVC, differential thermal expansion and melt temperature mismatch prevent fusion welding; mechanical connection with elastomeric seals is the standard production approach.