PCC (Iran) HDPE HB5510 is a high-molecular-weight, bimodal extrusion-blow-moulding high-density polyethylene supplied as cylindrical pellets without talc. The product specification is defined around a low melt flow index measured at 190 °C under a 2.16 kg load and a density near 0.955 g/cm³. These two figures place the grade in the large-part blow moulding segment rather than in thin-wall injection moulding or cast-film extrusion, because high melt viscosity and high melt strength are required for parison hang time and weld-line integrity. The material is specified on continuous-extrusion shuttle machines, reciprocating-screw blow moulders, accumulator-head machines, and rotary wheel systems producing containers from 5 L jerrycans to 1,000 L intermediate bulk containers. The primary application boundary is conversion of the pellet into hollow articles by intermittent or continuous parison discharge; the grade is not intended for blown film, monofilament, pipe, or high-speed injection moulding without verified recompounding.

What molecular architecture and specification indicators separate HB5510 from general-purpose unimodal HDPE?

The distinguishing structural feature in HB5510 is a bimodal molar mass distribution in which a high-molecular-weight fraction carries the short-chain comonomer distribution and a lower-molecular-weight fraction provides processability. This architecture is typical of cascaded dual-reactor polymerisation. The comonomer, generally butene-1 or hexene, is preferentially incorporated into the long-chain fraction. The result is a higher tie-molecule concentration at equivalent density compared with a unimodal copolymer, which increases environmental stress crack resistance without lowering flexural modulus to the same degree as a density reduction would. Under ISO 1133-1, the melt flow index is typically reported in the 0.30–0.40 g/10 min range at 190 °C and 2.16 kg. Density is typically 0.954–0.956 g/cm³ under ISO 1183-1. The combination of low melt flow index and moderate density means the grade behaves as a high-load melt-strength material, not as a high-flow injection resin. The practical consequence is a melt that supports long parison lengths in large moulds but retains limited spiral flow. The high-molecular-weight tail also contributes to high die swell; blow moulding die tooling must be sized accordingly. In comparative terms, a general-purpose unimodal HDPE at the same melt flow index would show lower die swell and lower environmental stress crack resistance because the longest chains would be present in smaller concentration and the comonomer distribution would be less segregated toward the longest chains.

When HB5510 is converted on a grooved-barrier extruder with L/D 25:1

On a grooved-barrier single-screw extruder with an L/D ratio of 25:1, the practical barrel profile begins at 160–170 °C in the feed section, rises to 180–190 °C in the compression section, and is held at 190–200 °C in the metering section. The extruder head and die are maintained at 195–205 °C. Below 180 °C, the frozen layer at the die lip becomes sufficiently stiff to generate sharkskin on the parison surface and cold-edged pinch-off welds. Above 210 °C, the melt loses parison integrity in long drop distances, and residence-time-dependent crosslinking can form black specks after 15–20 min of stagnation. The processing window is therefore tight; accumulative heat history must be monitored through melt temperature at the head rather than barrel set-point alone. A barrier flight in the compression zone reduces solid-bed pressure fluctuation when the pellet feed contains up to 30 % high-quality regrind. Regrind addition above this level, particularly after multiple heat histories, reduces the notched impact and ESCR of the container because the longest chains are progressively broken. Predrying is normally not required because HDPE is non-hygroscopic, but surface condensation in humid silos above 60 % relative humidity can produce splay; hopper drying at 70–80 °C for 1–2 h is applied when bulk-storage condensation is suspected. Continuous-extrusion shuttle machines should keep hydraulic clamp force sufficient for the mould pinch-off; under-clamping produces flash that quenches last and results in a weak weld line.

Accumulator-head machines producing containers above 60 L require a programmed parison die gap rather than a constant gap. The high die swell of HB5510, typically in the 50–80 % range at practical shear rates, means tooling must be undersized relative to final container diameter. Parison programming is set with a thicker bottom section for pinch-off feed and a thicker top section for the closure or handle zone; wall-thickness distribution is measured by sectioning and ultrasonic or magnetic gauges. The shear rate at the die lip under a 1.5–2.5 mm gap is low enough that melt fracture is not the main defect; parison sag and fold lines are the main process defects. If a melt temperature above 205 °C is required for surface gloss, a shorter drop distance or a lower melt draw ratio must be used to preserve wall uniformity.

In the production of UN-certified 220 L open-head drums, the parison is dropped at a melt temperature of 195–205 °C and closed in a mould with a pre-aged carbon steel or aluminium alloy construction. The pinched parison is inflated at blow pressures of 0.7–0.9 MPa against a mould temperature of 10–25 °C. The resulting drum wall is tested under internal hydraulic pressure and under drop impact after conditioning at -18 °C. For hazardous-liquid packagings, damage tolerance is confirmed by methods in the UN Manual of Tests and Criteria, Part III, section 6.1.5.3. HB5510 also appears in agricultural chemical packaging where long-term contact with emulsifiable concentrates and surfactants can accelerate environmental stress cracking; the high-molecular-weight fraction is selected to resist slow crack growth under top-load stress and stack creep. The resin’s limited melt flow prevents efficient filling of high-flow spirals, so thin-wall closures and injection-moulded spouts are usually produced in a higher-flow HDPE, not HB5510.

Nominal property ranges with final article test methods

The following values are compiled from commercial datasheet ranges for this resin class; batch-specific certificates of analysis should be used for final article qualification.

The ESCR measurement is a slow crack growth test, not an impact test. The F50 value should not be interpreted as a shelf-life guarantee; it is a comparative indicator of resistance to stress cracking in the presence of surface-active fluids. For final articles, the relevant test is container drop impact or internal pressure creep, because weld lines and thickness distribution dominate failure.

Comparative property signatures against injection moulding and film extrusion HDPE

HB5510 differs from high-flow HDPE grades primarily in melt viscosity and molecular weight. An injection moulding HDPE with an MFR in the 8–20 g/10 min range will fill thin-wall sprues and channels at lower injection pressures, but the resulting product will have lower ESCR and lower drop impact than a blow-moulded HB5510 container. In blow moulding, that high-flow resin cannot maintain a stable parison; parison sag and variable wall thickness occur. Conversely, HB5510 cannot match the cycle time of an injection moulding grade because its high viscosity requires lower melt flow and higher pressure. Compared with film-grade HDPE of density 0.946–0.950 g/cm³, HB5510 has a higher density and higher flexural modulus; the film grade has greater draw-down and lower parison hang stability. Compared with a unimodal blow moulding HDPE at the same 0.950–0.956 g/cm³ density and 0.30–0.40 g/10 min MFR, the bimodal architecture of HB5510 offers a higher ESCR at equal stiffness. This difference is observable in stacked agricultural chemical bottles where surface wetting and top load combine to produce slow crack propagation from the pinch-off weld. The main penalty is a more complex sensitivity to thermal history: bimodal resins with segregated comonomer require careful control of melt temperature because the longest molecules degrade first and reduce ESCR rapidly.

Weld line strength cannot be optimized without controlling pinch-off geometry and melt temperature

The pinch-off weld is formed when the mould closes on the hot parison. The local weld is strongest when melt temperature at the pinch zone is 190–205 °C, the mould closing speed is low enough to permit squeeze-out of flash, and the pinch land has a single-angle blade geometry with a land width adequate for the container wall. A thin land creates a knife-edge flash that cools before fusion; a broad land creates excessive flash and reduces residual wall section at the weld. The weld is not merely a geometric seam; it is a localized region of residual stress and oriented high-molecular-weight chains. Slow crack growth from the weld zone under chemical contact is the most common failure mode in large HDPE containers. For this reason, drop impact testing of a closed 220 L drum at -18 °C under a regulated drop height is a more discriminating quality gate than a tensile bar test. During extrusion, melt temperature variation of ±3 °C at the die lip is observable as wall thickness asymmetry; every 5 °C increase in melt temperature above 205 °C increases parison sag enough to require parison program correction.

In moulds with a side seam, the weld line is parallel to the axis and is loaded in hoop stress under internal pressure. In pinched-bottom containers, the weld is loaded in flexure and top-load creep. The latter is more sensitive to incomplete fusion because the outer layers of the pinched parison are quenched by the mould before chain interdiffusion completes. A mould temperature of 10–25 °C is standard for cycle time, but weld-line toughness is slightly improved by preheating the pinch area to 30–40 °C in heavy-wall applications. Published data for this specific grade under varied pinch-land geometries is limited; therefore, container trials should be conducted when the land angle or flash thickness is changed.

A further process boundary is oxidative stability. The oxidation induction time of virgin HB5510 at 200 °C is typically above 20 min under ISO 11357-6; however, multiple heat histories from regrind reduce OIT and broaden the molar mass distribution. Material with regrind content above 30 % should not be assigned to UN packaging without retesting, because loss of the high-molecular-weight tail preferentially degrades ESCR. When the container is recycled, industrial systems should use float-sink separation in water at density 0.93–0.97 g/cm³ to separate HDPE from polypropylene contamination.

For converters assessing food-contact status, HB5510 is an olefin polymer within the scope of FDA 21 CFR 177.1520 and may be assessed under Regulation (EU) No 10/2011 provided the final article meets the overall migration limits and specific migration requirements for the actual food simulant. No such migration limit is meaningful without specifying the simulant, contact time, and food type. The resin does not contain a built-in flame-retardant package, and a UL 94 classification is not applicable to the unfilled grade. It should be stored away from direct sunlight and strong oxidizing agents. Prolonged contact with concentrated nitric acid, chlorine gas, or liquid hydrocarbons above 60 °C can swell or chemically attack high-density polyethylene; the material is not a barrier to non-polar solvents without fluorination or barrier-layer coextrusion. For automotive fuel tanks, monolayer HDPE of this class requires fluorination or a polyamide barrier layer to meet evaporative emission limits; published data for the specific HB5510 configuration in barrier coextrusions is limited, so coextruded container qualification must be conducted on the converting line.