Chevron Phillips Chemical HDPE HHM 5502-01 is a high-density polyethylene resin produced by slurry-loop polymerization with hexene-1 as the short-chain branching comonomer. The pelletized product is defined by a nominal density of 0.955 g/cm³ and a melt flow rate of 0.35 g/10 min at 190°C/2.16 kg when tested according to ASTM D1238 or ISO 1133-1:2022. These two indices position HHM 5502-01 as a fractional-melt, high-density material intended for thick-walled rigid packaging and industrial-container applications rather than thin-wall, high-speed molding. Reported uses include heavy-wall pails, crates, totes, trays, pallets, dunnage, and chemical containers, where long-term load-bearing behavior and environmental stress crack resistance carry more weight than cycle-time minimization. The suffix -01 denotes a standard pellet stabilization package; the exact additive identity and any reactive-processing restrictions should be confirmed through the manufacturer’s product stewardship documentation.

The hexene-1 comonomer differentiates HHM 5502-01 from butene-based HDPE copolymers of similar density. In a polyolefin of this density range, longer short-chain branches increase the probability of tie-molecule formation between lamellae, which alters slow crack growth behavior and environmental stress crack resistance without necessarily changing short-term tensile yield strength. High-flow HDPE molding grades with melt flow rates of 6–20 g/10 min fill thinner sections faster, but they typically sacrifice notched impact and stress crack resistance. Conversely, HHM 5502-01 has a low melt flow rate that increases injection pressure and recovery time. This trade-off is the central difference from other HDPE products and should be evaluated against the part’s wall thickness, chemical exposure, and service life.

What Constitutes the Manufacturer’s Published Property Envelope for HHM 5502-01?

The values tabulated below are nominal values from Chevron Phillips Chemical product literature and are not batch-release specifications. Density and melt flow rate are controlled on every lot; mechanical values are generated from injection-molded specimens under standard laboratory conditions and may vary with cooling rate, regrind content, and pigment dispersion. The tabulated data are not to be used directly for design calculations without safety factors and failure-mode testing.

Because the melt flow rate is 0.35 g/10 min, the resin falls into the fractional-melt category. This classification is significant for injection molders: screw torque, filling pressure, and shear heating become primary variables. The published viscosity curve shows pronounced shear thinning at typical injection shear rates, but the resin does not have the melt strength of a bimodal high-density blow-molding resin; parison sag is therefore a limitation in large extrusion blow-molding operations. Published data for this specific configuration in continuous extrusion blow molding are limited.

A density of 0.955 g/cm³ corresponds to a crystalline fraction in the range of 65–70% when calculated from the two-phase model using 1.000 g/cm³ and 0.852 g/cm³ for the crystalline and amorphous phase densities, respectively. This crystallinity level contributes to flexural modulus and chemical resistance but also produces mold shrinkage values in the range of 1.5–2.5% depending on part thickness, mold temperature, and gate design. Shrinkage anisotropy is typical; flow-direction and transverse-direction values can differ by 0.2–0.5%. Tooling allowances should be adjusted on the basis of molded plaque measurements rather than brochure values.

Injection Molding Equipment, Temperature Limits, and Flow-Length Constraints

Processing of HHM 5502-01 on production-scale injection molding equipment requires attention to melt temperature, screw design, and mold temperature. Reciprocating-screw machines with 20:1 to 30:1 L/D ratios and compression ratios of 2.5:1 to 3.5:1 are standard for high-density polyethylene. General-purpose screws with gradual transition zones are acceptable, but barrier screws provide better melt homogeneity at the low melt flow rate. Barrel temperature profiles commonly begin at 180–190°C in the feed zone and rise to 220–250°C at the nozzle, with melt temperatures measured by an infrared pyrometer not exceeding 260°C. Holding at 275°C or above for more than a few minutes produces chain scission and is observed as a reduction in die swell, viscosity, and mechanical properties. Mold temperatures of 10–40°C are used to balance crystallinity, shrinkage, and cycle time; higher mold temperatures above 60°C increase shrinkage and cycle time but improve weld-line strength in thick sections. Injection pressure at the nozzle is frequently in the 80–120 MPa range for thin sections, while thick-walled articles may fill at lower pressure and require longer hold times.

The low melt flow rate increases screw recovery time. For a 60 mm general-purpose screw, screw recovery times may extend to 10–20 s at 60 rpm depending on back pressure and screw design. Molding trials should confirm that recovery time does not exceed cooling time to avoid cycle-time extension. Screw speed should not exceed 100 rpm for high-molecular-weight HDPE to reduce shear heating; if melt temperature exceeds 260°C, screw speed or back pressure should be reduced. Pre-drying is typically unnecessary for HDPE stored at ambient conditions below 60% RH; if surface condensation or wet regrind is present, hopper drying at 70°C for 2 h prevents splay. The resin is incompatible with contamination by polypropylene, which forms separate phases and weakens weld lines and impact strength.

Weld lines in molded parts are a particular limitation because the low melt flow rate reduces molecular movement across the weld plane. In critical weld-line regions, higher mold temperature and moderate injection speed improve entanglement. Molded notched Izod impact at the weld line should be measured rather than assuming bulk values. Regrind from sprues and runners is commonly incorporated at levels up to 20 wt%; higher levels can reduce environmental stress crack resistance. Published data for this specific product at high regrind ratios is limited, so production trials with the actual regrind fraction are required before release of parts for stressed chemical service.

When Regulatory Compliance and Food-Contact Certification Enter the Specification

Regulatory compliance for HHM 5502-01 must be verified against the final article composition, including masterbatch, regrind, and processing aids. The resin is typically manufactured to meet the olefin polymer requirements of FDA 21 CFR 177.1520(c) for food-contact use, subject to end-use limitations and the conditions of use in 21 CFR 176.170(c) tables. For European Union applications, the base polymer may be evaluated under Regulation (EU) No 10/2011 and subsequent amendments, provided that the overall migration limit and specific migration limits for additives are confirmed on the finished article. Heavy metals restrictions under RoHS Directive 2011/65/EU and substance registrations under REACH are addressed through the manufacturer’s compliance statement; no finished-article certification should be inferred from resin compliance alone.

Because HDPE is a nonpolar polyolefin, it is resistant to aqueous chemical environments but is not suitable for sustained contact with strong oxidizing acids, aromatic solvents, or halogenated hydrocarbons at elevated temperatures. Swelling by aliphatic hydrocarbons can reduce tensile strength and should be evaluated by immersion testing under ASTM D543 for the specific chemical service. Outdoor weathering of natural resin requires additional UV stabilizer masterbatch; carbon black at 2–3 wt% is conventionally used for long-term outdoor service in HDPE, but the final dispersion and particle size determine weatherability. The standard -01 package should not be assumed to provide more than processing stabilization unless the manufacturer’s documentation explicitly states otherwise.

Comparative Position Among Butene Copolymer and High-Flow HDPE Grades

HHM 5502-01 differs from a butene-based HDPE of the same nominal density because the hexene-1 comonomer produces longer short-chain branches. Longer comonomer branches increase the probability of tie-molecule formation between adjacent lamellae; the practical result is improved slow crack growth resistance and environmental stress crack resistance. Under ASTM D1693 Condition A, HHM 5502-01 is specified with an F50 value above 600 h, while many butene-based grades of similar density and melt flow rate show lower ESCR values, often below 200 h. This difference does not necessarily translate into a higher tensile yield strength; both product architectures can reach the same density and similar yield stress, but the fracture and long-term load-bearing behavior separate them.

Relative to high-flow HDPE injection molding grades with melt flow rates of 6–20 g/10 min, HHM 5502-01 has a significantly higher molecular weight. High-flow grades fill thinner walls, produce shorter cycle times, and permit lower injection pressures; however, they are more susceptible to environmental stress cracking and may exhibit lower notched Izod impact. For a given part geometry, a high-flow HDPE may allow a wall thickness reduction from 4 mm to 2.5 mm, but the long-term ESCR and drop impact performance may not be equivalent. HHM 5502-01 is therefore selected when the part is thick-walled, when chemical exposure is expected, or when the load duration is measured in years rather than minutes. Conversely, for thin-wall consumer packaging with fast cycle requirements, a melt flow rate below 1 g/10 min creates avoidable processing cost.

Compared with polypropylene, HHM 5502-01 provides lower flexural modulus at equivalent thickness, but it retains better low-temperature impact. A typical polypropylene homopolymer can embrittle near 0°C, whereas high-density polyethylene of this molecular weight retains measurable impact below -20°C. The resin is not a drop-in replacement for polypropylene in thin-wall living-hinge applications. Compared with medium-density polyethylene grades below 0.940 g/cm³, HHM 5502-01 provides higher stiffness but generally lower intrinsic stress crack resistance. Direct comparative data generated on production-scale equipment for HHM 5502-01 against every alternative grade are limited in the published literature. Before substitution, the part should be evaluated by measuring notched Izod impact according to ASTM D256, ESCR according to ASTM D1693, and tensile yield according to ASTM D638 on production-representative specimens. In addition, the lower melt flow rate of HHM 5502-01 makes it unsuitable for high-cavitation small-part molds with very high flow-length/wall-thickness ratios; such geometries require high-flow grades or processing at the upper melt-temperature boundary, which may reduce molecular weight and compromise mechanical properties.