PetroChina Dushanzi HDPE UHXP-4808 is a high-density polyethylene grade positioned for extrusion blow moulding of hollow industrial and consumer parts. The grade identifier follows the density-flow convention: nominal density of 0.948 g/cm³ under ISO 1183-1:2019 and nominal melt flow rate of 0.8 g/10 min under ISO 1133-1:2022 at 190 °C/2.16 kg. These coordinates place the resin in the intermediate-flow blow-moulding segment, distinct from high-flow injection moulding grades and low-flow pipe grades. In conversion practice, the material is plastified in a single-screw extruder, extruded downward through an annular die into a parison, captured by a split mould, and inflated against cooled cavity surfaces. The grade is intended for hollow parts where melt strength, pinch-off weld integrity, drop impact, and environmental stress-cracking resistance are controlling variables. Published data for this specific configuration is limited; the certificate of analysis for each production lot controls actual property values and should be used for acceptance decisions.

Parison sag and die swell are the dominant rheological variables for UHXP-4808. Small changes in melt temperature, accumulator shot size, or die-gap programming can shift wall-thickness distribution more than a visible change in pellet properties. Process development should therefore begin with sectioned-part wall-thickness measurement using an ultrasonic gauge or calibrated micrometer grid, not with nominal part geometry or barrel setpoints alone.

Material Property Benchmarks Under ISO and ASTM Protocols

The following ranges are representative of high-density polyethylene blow-moulding resins with a nominal density of 0.948 g/cm³ and a melt flow rate of 0.8 g/10 min. They are not lot-specific acceptance limits unless a purchaser’s specification assigns them. Test methods are cited to permit comparison with other grades.

These benchmarks are affected by lot-to-lot variation, additive package, and specimen preparation. Density is measured on compression-moulded specimens after conditioning; melt flow rate is sensitive to moisture and should be run on dry pellets. Tensile yield stress and flexural modulus are rate-dependent, and comparisons between suppliers require the same test speed and specimen thickness.

Incoming resin qualification should include melt flow rate comparison against the lot certificate, density by gradient column, and visual inspection for contamination. A lot-to-lot MFR shift of ±0.05 g/10 min is usually within process capability; larger shifts require verification of die-gap programming. Moisture content above 0.05% by weight, measured by Karl Fischer titration according to ISO 15512:2019, may indicate surface contamination or damaged packaging.

The molecular weight distribution and comonomer placement of UHXP-4808 control its slow crack growth response. A density of 0.948 g/cm³ leaves an amorphous fraction available for tie-molecule formation, while the crystalline fraction contributes stiffness. Higher tie-molecule populations correlate with slower crack propagation in the presence of polar wetting agents and with better low-temperature drop impact. Dynamic shear rheometry at 190 °C from 0.1 rad/s to 100 rad/s on this melt flow class typically shows shear-thinning and a crossover frequency in the range 1–10 rad/s; published data for this specific configuration is limited. The storage modulus at low frequencies is sensitive to the high-molecular-weight tail and can be used to predict parison sag. The extensional viscosity in the parison stretch phase is higher than the shear viscosity at the same strain rate, and this strain-hardening component controls parison stability during mould closing.

Compared with a 0.960 g/cm³ high-stiffness HDPE film grade, UHXP-4808 is expected to trade top-load capacity for improved stress-cracking resistance and deeper pinch-off weld fusion. Compared with a bimodal pipe grade, the molecular weight distribution and comonomer sequence distribution are less optimized for slow crack growth under hydrostatic pressure; UHXP-4808 is not a pressure-pipe resin and should not be substituted for a grade certified under ISO 9080:2022.

Why Does Parison Programming Matter More Than Barrel Temperature for UHXP-4808?

In accumulator-head blow moulding, wall-thickness distribution is set primarily by the programmed die gap along the parison length, while barrel temperature influences melt viscosity and surface finish. The die-exit melt temperature window for UHXP-4808 is 180–210 °C; below 175 °C, melt fracture and weld-line opening become more probable, and above 220 °C, thermal degradation may generate discoloration and black specks. A parison programming error of 0.3–0.5 mm at the pinch-off segment can alter local wall thickness more than a ±5 °C barrel adjustment. Validated wall-thickness profiles should be derived from sectioned moulded parts and revalidated after changes in accumulator shot size, die insert geometry, or screw speed.

Pinch-off weld integrity is a function of melt temperature, pinch insert geometry, and clamp force. For hollow containers produced from UHXP-4808, typical pinch-off insert radii are 0.2–0.5 mm, and pinch land angles between 30° and 45° are used to create a localized compression zone. Insufficient clamp force or low melt temperature can leave a weak weld; excessive melt temperature or excessive clamp force can displace material and thin the weld root. Drop impact resistance of the finished article at 23 °C can be evaluated by ASTM D2463 to verify that pinch-off welds do not become the dominant failure site.

Parison swell values for high-density polyethylene of this density class, measured on a laboratory blow-moulding line with an annular die land length of 15 mm and die gap 2 mm, are commonly 15–35% in diameter and 10–25% in wall thickness at 190 °C. The exact swell depends on land length, shear rate, and melt temperature; a shorter land length or higher shear rate increases swell, while higher melt temperature reduces it. If the part has a long parison hang length, shot size should be reduced or melt temperature lowered only after die-gap programming has been tested, because parison sag and swell interact non-linearly.

Three failure modes observed on blow-moulding lines are parison tear at the die exit, incomplete pinch-off fusion, and environmental stress cracking at the moulded-in lip or handle attachment point. Parison tear is usually caused by die-exit melt temperature below 175 °C or by surface moisture; incomplete pinch-off fusion occurs when clamp pressure is low or the pinch insert is worn beyond 0.5 mm radius loss; environmental stress cracking in service is accelerated by contact with polyglycol ethers, ester-based lubricants, or strong mineral acids at elevated temperature. When a failure occurs, the first diagnostic should be a wall-thickness scan and a pinch-off cross-section, not a resin replacement.

Extrusion Blow Moulding Conditions on Accumulator-Head Lines

Recommended start-up conditions for UHXP-4808 on accumulator-head machines are given below. They assume a single-screw extruder with an L/D ratio of 24:1–30:1, a barrier screw with compression ratio 3:1–4:1, and an accumulator shot size of 85–95% of capacity.

Pre-drying is not normally required for HDPE because the resin is non-hygroscopic. If pellets have surface condensation after outdoor storage, a desiccant hopper dryer set to 80 °C for 2 h removes surface moisture without altering the additive package. Residence time above 220 °C should be limited to less than 5 min. The extruder should be purged after processing polypropylene, polyamide, or filled polymers to prevent incompatible domains at the parison surface.

For continuous shuttle machines, the same melt-temperature window applies, but parison programming is often split between extruder screw speed and die-gap position. In these operations, a barrel temperature profile of 170–185 °C in the feed zone, 185–200 °C in the compression/metering zone, and 190–210 °C at the head is a practical starting point. Blow air pressure of 0.5–0.7 MPa is typical; lower pressures may produce incomplete cavity replication, while higher pressures may increase flash and extend cycle time.

Accumulator-head machines with clamp force from 100 t to 1200 t are used depending on shot size. The melt temperature at the die exit should be measured with an immersion probe or infrared pyrometer because barrel setpoints can differ from actual melt temperature by 5–10 °C under high screw speeds. A barrier screw with a mixing section is recommended; a general-purpose screw without mixing can produce temperature heterogeneity and partially melted regions at high throughput. Mould temperature of 10–30 °C is typical for HDPE blow moulding. Lower mould temperatures accelerate solidification but may increase shrinkage variability and warpage in thick sections; higher mould temperatures above 40 °C are rarely required for UHXP-4808 and may extend cycle time without improving burst strength.

Post-mould shrinkage after 24 h is typically 1.5–2.0% in the axial direction and 1.0–1.5% in the hoop direction for HDPE, but part geometry and cooling rate dominate the actual value. Dimensional acceptance should therefore be established on conditioned parts, not on mould dimensions alone.

When UHXP-4808 Replaces General-Purpose Injection Grades in Hollow Parts

UHXP-4808 is not a direct replacement for an injection-moulding high-density polyethylene. General-purpose injection grades of similar density typically have melt flow rates between 7 g/10 min and 20 g/10 min; UHXP-4808 at 0.8 g/10 min has higher melt strength and higher molecular weight, which improves environmental stress-cracking resistance but narrows the process window for thin walls below 1 mm. When an injection-grade part is converted to blow moulding, the wall thickness and top-load design must be re-evaluated because the flexural modulus of UHXP-4808 is lower than that of a 0.960 g/cm³ high-stiffness grade. A 10–20% increase in wall thickness may be required to recover top-load capacity, depending on part geometry.

Compared with Dushanzi bimodal pipe grades such as DGDB-2480, UHXP-4808 has higher flow and is better suited to accumulator blow moulding, but it is not certified for pressure-pipe hydrostatic design under ISO 9080:2022. Compared with high-stiffness film grades such as DGDA-6097, UHXP-4808 shifts the property balance away from bubble stability and film optics toward parison geometry, pinch-off weld fusion, and drop impact. These distinctions are relevant when choosing between UHXP-4808 and other PetroChina Dushanzi high-density polyethylene products; the final selection should be based on the required part test, not on density or flow rate alone.

Regulatory compliance for finished articles must be confirmed for the intended use. Food-contact applications require evaluation under FDA 21 CFR §177.1520 or EU Regulation (EU) No 10/2011, with attention to migration limits and time-temperature conditions. Heavy metal restrictions may be assessed under REACH Annex XVII and RoHS Directive 2011/65/EU. UHXP-4808 should not be dry-blended with polypropylene, PET, or polyamide unless a dedicated tie layer and process validation are used, because interfacial delamination at the pinch-off seam is a known failure mode in incompatible multilayer structures.