Chevron Phillips Chemical HDPE HP076 is a high-molecular-weight high-density polyethylene blow moulding resin supplied in pellet form. The grade is characterised by a nominal density of 0.949 g/cm³ when tested to ASTM D1505 and a nominal melt index of 0.30 g/10 min at 190 °C/2.16 kg when tested to ASTM D1238. The high-load melt index at 190 °C/21.6 kg is approximately 30 g/10 min, which reflects the shear-thinning response required for accumulator-head blow moulding of large parts. The resin belongs to the HMW-HDPE family and is intended for applications in which parison hang strength, environmental stress crack resistance, and low-temperature impact resistance control part performance.

Nominal Property Envelope and Test Methodology

The following table lists the commonly referenced physical and mechanical properties for HP076. Values are nominal and should be confirmed against the manufacturer’s current certificate of analysis before production qualification.

The 0.949 g/cm³ density indicates a moderate comonomer content that lowers crystalline density relative to homopolymer HDPE while retaining sufficient stiffness for large structural containers. The 0.30 g/10 min melt index places the resin in the high-molecular-weight range; this contributes to high melt strength but also to elevated head pressure and shear heating during plastication. The 1,030 MPa flexural modulus is lower than that of 0.955–0.960 g/cm³ HDPE grades, a deliberate trade-off that shifts the property balance toward ESCR and impact performance. The ASTM D1693 ESCR result exceeding 1,000 h under Condition B with 100% Igepal is a primary specification for chemically aggressive contents such as agricultural formulations and industrial liquid packaging.

The high ESCR of HP076 is associated with high-molecular-weight fractions that form tie molecules between lamellae. In slow crack growth testing under ASTM F1473 or ISO 13479, the resin’s comonomer distribution and molecular weight distribution delay brittle failure; however, the exact molecular weight distribution is proprietary. The moderate density of 0.949 g/cm³ reduces lamellar thickness and increases amorphous tie-molecule density relative to homopolymer HDPE, which improves resistance to stress cracking but lowers the flexural modulus. This trade-off is consistent with the relationship between crystalline fraction and ESCR reported for high-density polyethylene pipe and blow moulding grades.

On production-scale accumulator-head blow moulding machines equipped with grooved-feed extruders of 24:1 to 30:1 L/D, HP076 is typically plastified with a barrel profile rising from 180 °C at the feed section to 200–220 °C at the die head. A constant melt temperature of 210–230 °C is maintained to avoid parison sag on parts with shot weights above 5 kg. Excessively low melt temperatures below 195 °C produce visible melt fracture and surface roughness on moulded parts, while temperatures above 240 °C for extended residence times can initiate oxidative chain scission and discolouration. The shear viscosity under typical extrusion rates requires head pressures of 20–35 MPa depending on die gap, mandrel diameter, and accumulator volume; pressure drops across spiral mandrel dies should be measured before specifying pump capacity. Published data for spiral-mandrel rheology of HP076 is limited; die design should be confirmed with in-house spiral-mandrel rheometry before final tooling manufacture.

Batch-to-batch variance in melt index and density is controlled within manufacturer specification limits, typically ±0.15 g/10 min for high-load melt index and ±0.002 g/cm³ for density. On automated blow moulding lines with closed-loop parison control, a shift of 2 g/10 min in high-load melt index can require die-gap adjustment of 0.3–0.5 mm to maintain pinch-off wall thickness. Inconsistent regrind addition is a more frequent source of process instability than pellet lot changes.

What Limits the Processing Window in Accumulator-Head Extrusion Blow Moulding?

The primary rheological limit is the temperature dependence of parison hang strength. Because the resin has a high weight-average molecular weight, the zero-shear viscosity is high, but the shear-thinning slope is significant. In practice, a die-head melt temperature of 220 °C produces a stable parison for containers with wall thicknesses from 4 mm to 10 mm; above 230 °C, the sag rate increases and programmed wall-thickness control may not compensate for thinning at the pinch-off zone. A second limit is moisture. Although polyethylene is not hygroscopic, surface condensation on pellets stored at ambient humidity above 60% RH can introduce volatiles that form splay or silver streaks. Pre-drying at 80 °C for 2 h is therefore recommended when silo or hopper conditions are uncontrolled. A third limit is additive interaction: the resin should not be blended with pro-oxidant transition metal stearates or with amine-based masterbatches unless long-term oxidative stabilisation has been evaluated by ASTM D3895 or equivalent oxidative-induction time testing.

Capillary rheometry at 190 °C and 210 °C demonstrates shear-thinning behaviour typical of HMW-HDPE. At apparent shear rates from 100 s⁻¹ to 1,000 s⁻¹, the shear viscosity decreases by approximately one order of magnitude. This non-Newtonian response supports flow through the die gap but complicates calculation of pressure drops using a single viscosity value. Melt strength measured by Rosand-type elongational rheometry or by parison sag tests on a 100 mm accumulator-head machine is used to set programming parameters. Published capillary viscosity curves for this specific grade are limited; converter evaluations should use slit-die rheometry at the intended melt temperature before final die design.

Melt Temperature and Oxidative Degradation Interact at the Die Head

Thermal stabilisation of HP076 is formulated for normal extrusion blow moulding residence times, but stagnation in poorly designed accumulator heads can consume antioxidants and generate gel particles. On machines with 120 mm accumulator heads and first-in-first-out flow channels, gel formation becomes visible after 12–24 h of continuous operation at 230 °C. If a colour change or material transition is required, purging with a lower-viscosity HDPE or a commercial purging compound is recommended because high-molecular-weight fractions can remain in dead spots and release later as melt defects. The maximum recommended melt temperature is 240 °C; prolonged hold-up above this value can reduce oxidative-induction time measured by ASTM D3895 to less than 15 min, indicating loss of active antioxidant protection. This is not a product defect but an operating boundary common to high-molecular-weight polyethylenes.

Large-part blow moulding applications for HP076 include monolayer and multilayer industrial containers, agricultural chemical packaging, fuel oil tanks, water storage vessels, and automotive fluid reservoirs. In automotive fuel tank trials on accumulator-head machines with 3 kg to 8 kg shot weights, the resin’s high melt strength allows monolayer tank walls to be formed without excessive thinning at the corners; however, homologation for fuel systems requires barrier-layer coextrusion with EVOH or surface sulfonation/fluorination because neat HDPE is permeable to hydrocarbons. The resin’s ASTM D1693 ESCR performance supports service life in contact with aggressive liquids, but the final part must pass customer-specific stack-load and drop-impact tests. For agricultural packaging, the grade is used in containers that must withstand outdoor UV exposure; adequate carbon black or hindered-amine light stabilizer masterbatch is required because the natural resin is not UV-stabilised. Published data for specific fuel permeation rates of containers moulded from HP076 are limited; designers should obtain permeation coefficients from barrier-layer suppliers for the specific wall-thickness distribution.

When HP076 Replaces Lower-Molecular-Weight Blow Moulding Resins

Substitution of HP076 for a conventional unimodal blow moulding HDPE with a density near 0.955 g/cm³ and a melt index above 0.5 g/10 min changes both the mechanical property balance and the processing economics. The comparative table summarises the directional differences.

The lower density and lower flexural modulus mean HP076 is not a direct substitute where top-load stiffness or creep modulus is the governing specification. Conversely, in applications where ESCR and sub-zero impact failure modes dominate, the HP076 property set provides a wider service window. The lower melt index increases extruder torque and can reduce throughput on the same machine compared with higher-flow grades; screw speed and head-tooling settings must be re-optimised to prevent melt temperature overshoot. On 80–100 mm grooved-feed extruders, throughput loss relative to higher-flow grades is commonly 10–20%. Accumulator heads with first-in-first-out flow paths are preferred because the resin’s high molecular weight can retain previous material in dead spots and generate gels after colour or material changes. Purge with a lower-viscosity HDPE or a commercial purging compound is required when transitioning from metallocene LLDPE or other lower-viscosity grades.

Blow moulding lines for HP076 do not require unusual clamp force; inflation pressures of 0.6–1.0 MPa are typical for large containers. For parts with projected areas above 0.5 m², machines with clamp forces of 150–500 tonnes are often required, but the limiting factor is usually parison drop time rather than clamp capacity. Blow pressure settings should be verified by wall-thickness mapping and pinch-off flash analysis.

For food-contact applications, unfilled natural HP076 may be specified to conform to FDA 21 CFR 177.1520 for olefin polymers and to European Union Regulation (EU) No 10/2011 when the final article meets migration limits. Compliance is formulation- and processing-dependent; colour concentrates, regrind streams, and processing aids must be evaluated separately. The resin is not supplied with a UV stabiliser package unless ordered as a UV-stabilised grade. Outdoor exposure requires 2.0–3.0 wt% carbon black concentrate or an equivalent hindered-amine light stabilizer masterbatch to achieve long-term weathering performance under ISO 4892-2 conditions. Regrind ratios for blow moulding are typically limited to 20–30% depending on part wall thickness and impact requirements; higher levels of hot regrind can shift the melt index upward and reduce ESCR. Drying is not required for resin from sealed bags at ambient relative humidity below 60% RH, but surface moisture must be removed before processing if condensation occurs. Chemical inventory status should be verified against the current REACH safety data sheet for the specific grade and region.