Chevron Phillips Chemical Marlex HDPE 9607D is an injection-moulding-grade high-density polyethylene supplied as pellets. The resin is positioned in the 0.960 g/cm³ density class and is typically associated with a melt index of 0.70 g/10 min when measured at 190 °C under a 2.16 kg load in accordance with ASTM D1238. Density is normally determined by ASTM D1505 or ISO 1183-1. Primary conversion routes are reciprocating screw injection moulding for rigid articles: industrial pails, crates, storage boxes, trays, housewares, and closures. The resin is specified where high wall stiffness, a relatively short cooling time, and acceptable low-temperature impact behaviour are required in medium-walled or thick-walled parts. It differs from lower-density HDPE copolymers in having higher tensile yield stress and flexural modulus but lower environmental stress-crack resistance. It differs from high-melt-index thin-wall injection grades in having higher melt viscosity and better toughness at equal wall thickness. Published supplier data should be verified against the current product data sheet and certificate of analysis for the specific lot, because nominal property ranges are not a substitute for conversion trials.

On production-scale injection moulding lines with general-purpose polyolefin screws of 20:1 to 24:1 L/D and 2.5:1 to 3.5:1 compression ratio, Marlex HDPE 9607D is normally processed at melt temperatures from 190 °C to 230 °C. The lower boundary is limited by incomplete homogenisation and the appearance of unmelted pellets in thick bosses or ribs; the upper boundary is limited by oxidative discolouration and broadening of the molecular weight distribution. Mold temperatures between 15 °C and 40 °C are typical. A mold temperature below 15 °C shortens surface cooling but increases frozen-in orientation and can reduce notched impact strength. A mold temperature above 40 °C extends the cooling-limited cycle time without a proportional gain in shrinkage uniformity. Back pressure should be held between 0.3 MPa and 0.7 MPa on open-loop hydraulic machines; higher back pressure can increase melt temperature by viscous dissipation and cause gate blush in multicavity tools. Screw retraction speed is set to prevent air entrapment in the feed zone. A melt cushion of 3 mm to 6 mm is maintained for consistent packing and to prevent screw bottoming. Published data for this specific configuration is limited for highly specialised hot-runner multi-gate systems; tool trials are recommended because the grade is not formulated for all thin-wall applications below 0.8 mm nominal wall thickness.

What Distinguishes the 0.960 Density Class from Lower-Density and Higher-Flow HDPE Resins?

The performance differences among HDPE products are dominated by molecular weight, molecular weight distribution, comonomer type, and density. Increasing density from 0.950 g/cm³ to 0.960 g/cm³ raises the crystalline fraction and increases flexural modulus, tensile yield stress, and hardness. That same crystallinity increase reduces the free volume available for chain relaxation under environmental stress. Consequently, the stress-crack resistance of a 0.960 density injection moulding grade is lower than that of a 0.950 density blow moulding grade. A lower-density blow-moulding class may provide better ESCR for aggressive liquid packaging, but it has lower stiffness and is formulated for parison sag resistance rather than injection fill. Pipe grades in the PE 100 class according to ISO 12162 have a broad or bimodal molecular weight distribution and slow crack growth resistance, but their melt index is often below 0.1 g/10 min, making them unsuitable for conventional injection moulding. High-flow injection moulding grades in the 20 to 40 g/10 min range reduce cycle time and allow thin-wall parts but exhibit lower impact resistance and lower chemical resistance because of reduced tie-molecule density. Marlex HDPE 9607D occupies an intermediate position: it offers higher stiffness than lower-density copolymers and better processability than fractional melt pipe resins, while retaining sufficient toughness for rigid packaging applications.

Table 1 provides the property envelope for a 0.960 density HDPE injection moulding class. Values are class-typical ranges and are not lot-specific guarantees.

Mould shrinkage in the flow and transverse directions for the 0.960 density HDPE class is typically reported under ASTM D955 or ISO 294-4 as 0.018 to 0.025 mm/mm. The high crystalline content increases shrinkage compared with lower-density copolymers and also increases the difference between shrinkage parallel and perpendicular to flow. Shrinkage anisotropy is a common cause of dimensional instability in containers with uneven wall thickness. In pail tools with a central hot-tip gate into the base, radial flow orientation can cause the pail rim to shrink less in the flow direction than in the hoop direction; ring-shaped stiffeners or cooling channels in the rim may be required to prevent ovality. On a multicavity crate tool with edge gates, differential packing can create cavity-to-cavity mass variation exceeding 0.5% and corresponding warpage. Maintaining uniform melt delivery and identical packing profiles across cavities is more critical than raising the overall hold pressure. Published data for this specific configuration is limited for complex geometries with thickness transitions exceeding 2:1; plaque values should not be extrapolated to a production tool without trial measurements.

When a Converter Needs FDA or EU Food-Contact Status for Rigid Packaging

For food-contact applications such as pails and containers, the converter must obtain the current food-contact statement for Marlex HDPE 9607D from the supplier. HDPE resins of this density class can be formulated to meet the compositional requirements of FDA 21 CFR 177.1520(c) for olefin polymers used in contact with aqueous, acidic, alcoholic, and fatty foods, provided the extraction tests on the completed article comply with the specified end-use conditions. In the European Union, the resin may be evaluated under EU 10/2011 and subsequent amendments, with overall migration limits and specific migration limits dependent on the final part geometry and food-contact ratio. REACH compliance is established through the supplier’s safety data sheet; no substance of very high concern should be present above the communication threshold. No part design assumption replaces the need to test the finished article for migration, organoleptic properties, and dimensional stability under the applicable food-simulant conditions.

The following checklist applies to a rigid injection-moulded article made from Marlex HDPE 9607D. It does not establish compliance by itself. Each item must be confirmed with supplier documentation and with tests on the finished part.

Lot-to-lot variation in melt index and molecular weight distribution can shift injection pressure and part mass. Converters should request the certificate of analysis for each lot and compare the melt index to the process window established during tool trials. A deviation of more than 0.1 g/10 min from the process set point may require adjustment of barrel temperature or injection speed. Such an adjustment is not a substitute for verifying part dimensions under ASTM D648 or ISO 75 for heat deflection. Infrared spectroscopy and density columns are used by incoming-quality laboratories to confirm resin identity against the original reference sample. Contamination with lower-density polyethylene reduces crystallinity and part stiffness; contamination with polypropylene can cause interfacial delamination and a reduction in notched impact strength under ASTM D256 or ISO 180. Because HDPE has a water absorption below 0.01% under ASTM D570, pre-drying is usually not required unless surface condensation occurs at relative humidity above 60% or after severe temperature cycling. A formal incoming-material inspection plan is therefore required for high-volume food packaging lines.

Rigid industrial pails and crates moulded from Marlex HDPE 9607D are typically produced with nominal wall thicknesses from 2.0 mm to 4.0 mm. The resin’s stiffness allows a pail to maintain stacking performance and compression resistance at lower weight than a lower-density HDPE. In chemical pails, however, the reduced ESCR of the 0.960 density class means that surfactant-based cleaning products, agricultural emulsifiable concentrates, and solvent-containing formulations can promote cracking at the gate or at sharp corners. Moulded-in stress should be minimised by generous radii, balanced cooling, and adequate packing time. The pail should not be specified for continuous exposure to aromatic hydrocarbons or strong oxidising acids unless testing under ASTM D543 or ISO 175 on the actual part demonstrates acceptable retention of properties. In closure applications, the resin provides a higher softening point than lower-density HDPE and maintains backoff torque within specification after repeated cycling. Cold impact in crates is affected by thickness and orientation; parts with flow-weld lines may fail at localised points even when the notched impact value of a plaque is acceptable. The material is not recommended for parts requiring low-temperature impact below -40 °C without a specific part-level impact test and a controlled heat history. The resin is compatible with clean HDPE rework and regrind at addition levels up to 20% in non-food packaging, provided the regrind is dried and free of polypropylene contamination. Polypropylene contamination in the regrind can reduce impact strength and cause delamination due to polymer incompatibility; melt filtration and source control are required.