CNOOC & Shell (CSPC Huizhou) HDPE 5502 is a high-density polyethylene produced at the CSPC Huizhou petrochemical complex in Guangdong, China. The product is supplied as pellets and is positioned as a high-molecular-weight extrusion blow-moulding resin for rigid containers. Commercial grade-sheet documentation places the density in the 0.954–0.956 g/cm³ band under ISO 1183-1 and the high-load melt index at 190 °C/21.6 kg in the 0.35–0.42 g/10 min envelope under ISO 1133-1. The primary application window covers extrusion blow-moulded industrial containers from 10 L to 200 L, including jerrycans, stackable drums, intermediate bulk container liners, and automotive reservoir components. Compared with lower-density unimodal HDPE grades in the 0.944–0.950 g/cm³ range, 5502 shifts the property balance toward higher modulus and top-load rigidity while retaining sufficient melt strength for accumulator-head parison handling. Compared with very high-molecular-weight HDPE grades with HLMI below 0.2 g/10 min, 5502 reduces screw energy demand but requires tighter parison programming to avoid sag.

What Limits the Processing Window for High-Molecular-Weight HDPE in Accumulator-Head Blow Moulding?

Melt temperature measured at the die entrance is the primary process threshold. Extrusion blow-moulding lines equipped with single-screw extruders of 25:1 to 30:1 L/D and accumulator-head tooling typically operate with a melt-temperature set point between 190 °C and 220 °C. Below 180 °C, the high-molecular-weight fraction elevates die pressure and produces melt fracture on large-diameter mandrel and die-lip surfaces. Above 230 °C, residence time in the head and die land can initiate oxidative degradation, which appears as viscosity loss, colour shift, and reduced notched impact strength under ISO 180/A. The screw is commonly run at 40–70 rpm on 80 mm to 100 mm diameter extruders, but the barrel-temperature profile should be adjusted to maintain a flat-to-slightly falling heat profile from feed zone to metering zone. Field observations on production lines indicate that the primary processing faults are parison sag, uneven wall-thickness distribution at the pinch-off, and weld-line thinning at the base of stackable drums.

Published data for exact head pressure for 5502 is tooling-specific and therefore limited. Production experience indicates that head pressure is sensitive to melt temperature and shot weight; increasing melt temperature by 5 °C can reduce head pressure by an observable margin but also lowers parison hang time. Thick-walled 200 L drums require parison programming with a progressive die-gap increase rather than a fixed die gap to control circumferential wall thickness. The die gap is commonly set between 1.5 mm and 3.0 mm for this viscosity class, with the blow-up ratio maintained between 1.8:1 and 3.5:1 in the radial direction. Moisture control is less critical than for condensation-capped polyolefins but is not irrelevant. If pellets are exposed to relative humidity above 60% for more than 4 h in warm ambient conditions, surface moisture can generate splay and pinhole defects in the pinch-off weld. A hopper-air dryer at 70–80 °C for 1–2 h is adequate.

The mechanical energy input can be monitored by specific drive energy. When 5502 is run at melt temperatures below 195 °C, specific drive energy rises and screw torque becomes the limiting factor on smaller extruders with direct drives. Published data for this specific configuration is limited, but production-scale records show that reducing screw speed by 5–15% restores torque margin without sacrificing melt homogeneity when back-pressure is maintained.

The mechanical property envelope for 5502 follows a rigid high-density blow-moulding pattern rather than a pipe, film, or injection-moulding profile. Tensile yield stress under ISO 527-2 is commonly reported in the 26–29 MPa range and flexural modulus under ISO 178 in the 1000–1200 MPa range. Notched Izod impact strength under ISO 180/A at 23 °C is typically 10–20 kJ/m², but the grade is not to be treated as a low-temperature ductile material; impact values at −30 °C require part-level verification for cold-climate dangerous-goods packaging. Elongation at break under ISO 527-2 is expected above 600% at 23 °C, although weld lines and heavy loading rates reduce the effective strain-to-failure of blow-moulded parts. Environmental stress crack resistance measured by ASTM D1693 condition B in Igepal CO-630 solution is the most significant specification for industrial liquid packaging; published data place the F50 failure time of compression-moulded plaques above 300 h, while blow-moulded parts can fall below the plaque value because of frozen-in orientation and pinch-off weld stress. The property envelope is summarised below for comparison against a lower-density unimodal blow-moulding HDPE with density around 0.946–0.948 g/cm³.

Blow-moulded part qualification should not rely on pellet property sheets alone. Wall-thickness distribution, pinch-off geometry, and parison programming determine the performance of a filled container under IMDG Code drop or stack tests more strongly than tensile yield data. For example, a 200 L stackable drum produced with a uniform wall thickness of 1.8 mm and a well-formed pinch-off weld can meet the 1.5 m drop test requirement at −18 °C only if the weld-line impact toughness is verified on the actual part under ISO 2248 or equivalent transport-package standards. This is a performance limitation, not a resin specification guarantee.

When 5502 Replaces a 0.946 g/cm³ Unimodal Grade in Stackable Drum Tooling

Substitution in existing tooling is not a drop-in change. The higher density of 5502 increases as-moulded part weight and alters semi-crystalline shrinkage. Linear mould shrinkage under ISO 294-4 for thick-walled blow-moulded sections is commonly in the 1.2–1.8% range for 5502, whereas a lower-density unimodal grade often falls between 1.5% and 2.5% depending on wall thickness and cooling rate. If the cavity is not re-cut, the 5502 part may exhibit slightly smaller external dimensions and higher residual stress at the flash line. Top-load strength of a 200 L stackable drum increases because the modulus shift is not offset by the small wall-thickness reduction. Blow-moulding machine adjustments should include recalculation of parison weight to maintain the minimum wall-thickness specification at the pinch-off and reprogramming of the accumulator head to deliver a longer tail for uniform wall distribution.

On a 120 t accumulator-head machine, the higher viscosity of 5502 relative to a 0.34 g/10 min unimodal grade may require an increase in hydraulic back-pressure or a reduction in screw speed of 5–15%. The exact change is tooling-specific and should be confirmed by melt-pressure readings and part-weight stability. If the line is originally optimised for a grade with higher HLMI, the switch to 5502 usually moves the operating point closer to the torque limit of small extruders. Production records for this specific comparison are limited; therefore, pilot trials with instrumented parison-length sensing are recommended before changing a commercial drum line.

Chemical compatibility of 5502 follows the general HDPE hierarchy. Aliphatic hydrocarbons, dilute acids, aqueous salt solutions, and many alkali solutions are handled in the 5–60 °C service window. Toluene, chlorinated solvents, and strong oxidizers cause swelling or stress cracking and are not recommended at elevated temperature. The resin is commonly used for detergent, lubricating oil, and agrochemical formulations up to the concentration limits set by the shipper, but every formulation requires container-level testing because the blow-moulded wall contains orientation and weld stresses that reduce chemical resistance relative to compression-moulded plaques. Long-term chemical exposure data for 5502 specifically is limited; qualification should therefore use the intended filled liquid with ASTM D543 immersion and ASTM D1693 ESCR specimens machined from the sidewall and pinch-off areas of produced containers.

The grade is not intended for potable water pressure pipe, thin-wall injection moulding, or blown film. The high melt viscosity restricts flow length in injection moulds with wall thickness below 1 mm, and blown-film bubble stability is insufficient below 0.1 mm for process security. Outdoor service requires a separate UV stabilisation package; unstabilised natural HDPE will embrittle under prolonged sunlight and should be carbon-black or hindered-amine-stabilised through masterbatch under a supplier-controlled formulation.

Regulatory Evidence: Food-Contact, Dangerous-Goods and Transport Packaging Boundaries

Typical high-density polyethylene blow-moulding grades in this family are candidates for food-contact use under FDA 21 CFR 177.1520 and Regulation (EU) No 10/2011, but compliance is lot-specific and depends on the additive package, colour masterbatch, and end-use conditions. Overall migration under Regulation (EU) No 10/2011 for aqueous, acidic, and low-alcohol simulants is typically below 10 mg/dm² for natural grades, while fatty-food simulants may impose temperature limits. Dangerous-goods packaging such as UN-certified jerrycans and drums must meet design-type physical tests under IMDG Code, ADR, and equivalent national transport regulations; the resin cannot independently guarantee certification because drop, stack, and hydraulic pressure performance depends on wall thickness, tooling, weld geometry, and closure design.

End users should obtain a lot-specific certificate of analysis because reactor transition, additive package, pellet conveying, and blend adjustments can shift HLMI by ±0.02 g/10 min and density by ±0.001 g/cm³. The material is not recommended for injection moulding of thin-wall parts below 1 mm, pressure pipe, or unoriented blown film below 0.1 mm. Processing above 230 °C should be avoided to prevent oxidative degradation in the accumulator head and die land. When coloured, UV-stabilised, or antistatic masterbatches are used, the carrier resin and additive chemistry must be reviewed for density and ESCR shifts because a high-loading masterbatch can produce localized weld-line defects in large containers.