ExxonMobil HDPE HSGC7260 is a high-molecular-weight, copolymer high-density polyethylene supplied for blow-moulded industrial containers, agricultural chemical packaging, large ducts and technical hollow parts. The grade is identified by a density of 0.956 g/cm³ measured to ISO 1183-1 and by a high-load melt mass-flow rate of 6.0 g/10 min at 190 °C/21.6 kg under ISO 1133-1. The low-load melt index at 190 °C/2.16 kg is typically below 0.10 g/10 min, which distinguishes the product from injection-moulding grades and indicates a broad molecular weight distribution. The polymer is designed to retain sufficient melt strength for large-part parison formation while maintaining a density low enough to preserve slow crack growth resistance.

How does the bimodal molecular structure alter ESCR and rigidity?

The bimodal distribution in HSGC7260 places short-chain branches preferentially along the high-molecular-weight fraction. This architecture increases the number of tie molecules that bridge adjacent crystalline lamellae after cooling. Tie-molecule density is a controlling variable for environmental stress crack resistance because it distributes external stress across the amorphous phase instead of concentrating it at a few intercrystalline links. Under ASTM D1693-15 Condition B with 100 % Igepal CO-630 at 50 °C, published F50 values for the grade exceed 1000 h; under Condition A the onset of brittle failure is also delayed relative to a conventional unimodal high-density polyethylene of similar density. Tensile yield stress is approximately 28 MPa when tested to ISO 527-2, and flexural modulus is in the range of 1200 MPa to 1300 MPa under ISO 178. Charpy notched impact at −40 °C remains above 10 kJ/m² for specimens prepared to ISO 179-1.

The stiffness–ESCR balance is not governed by density alone. Raising density above 0.960 g/cm³ would increase flexural modulus but reduce the amorphous tie-molecule population; lowering density below 0.950 g/cm³ would improve slow crack growth resistance but reduce top-load strength and creep resistance. HSGC7260 therefore occupies a narrow density window in which chemical containers can survive rough handling and prolonged stress-crack exposure without requiring crosslinking or a multilayer barrier.

Relative to a conventional unimodal chromium-catalysed HDPE blow-moulding resin of the same density, HSGC7260 produces higher melt strength and lower parison sag at the same die-head temperature. The practical consequence appears in large-part tooling: a unimodal resin may require a higher melt temperature to obtain an acceptable surface finish, but that temperature increase causes drawdown and forces a thicker parison. HSGC7260 retains dimensional stability at the lower end of the melt-temperature window, so wall-thickness distribution improves without increasing shot weight. The trade-off is die swell. The broad molecular weight distribution generates higher die swell at the die exit; tooling sized for a low-swell unimodal grade may need a modified die gap or additional parison programmer stroke. Compared with high-density polyethylene injection-moulding grades having MFR values above 1.0 g/10 min, HSGC7260 is unsuitable for thin-wall injection moulding because its low melt index at 2.16 kg limits cavity filling and increases orientation-induced warpage. Compared with pipe-grade HDPE, HSGC7260 has a higher flexural modulus but lower resistance to slow crack growth under hydrostatic pressure; it is not a substitute for PE100 pipe extrusion grades where long-term hydrostatic strength is controlled by ISO 9080.

Accumulator blow moulding parameters, tooling response and cycle boundaries

Processing on accumulator blow-moulding machines requires a grooved-barrel extruder with an L/D ratio between 24:1 and 30:1. Barrel temperature profiles typically start at 170 °C to 180 °C in the feed zone and increase to 200 °C to 215 °C at the metering zone. The melt temperature measured at the die entry should be held between 190 °C and 220 °C; excursions above 230 °C reduce melt strength and can generate oxidation by-products that appear as yellow discoloration in thick-walled sections. At 190 °C to 200 °C, annular dies with die-to-pin diameter ratios of 1.5:1 to 2.0:1 produce parison swell in the range of 35 % to 55 %. The resin’s high-molecular-weight tail provides sufficient hang-time for containers with shot weights above 10 kg; however, parison control remains critical for parts longer than 1.5 m because sag varies with die-head temperature and accumulator hold time.

The melt index ratio, calculated as high-load melt flow divided by low-load melt flow, is above 60. This high ratio indicates strong shear thinning: the resin retains high viscosity at low shear, stabilising the parison after die exit, but reduces viscosity under screw and die shear. It also means that standard low-shear melt index measurements at 2.16 kg are poor predictors of extrusion output and die pressure. Output should be established with a pressure transducer at the breaker plate; typical head pressures of 20 MPa to 30 MPa are acceptable. Screen packs of 20/40/20 mesh are commonly used to protect the die; excessive pressure drop across the screen indicates melt temperature is too low or the screen pack is blocked, not that the resin is outside specification. Melt residence time in the accumulator head should not exceed 10 min at 220 °C, because repeated heat history consumes antioxidant and may generate gels that disrupt wall-thickness control and drop-impact performance.

Sealed containers may be used as supplied. If silo storage or open Gaylord boxes are exposed to relative humidity above 60 % for more than 24 h, pre-drying at 80 °C for 2 h to 3 h is recommended. Regrind from uncontaminated flash and tails may be re-introduced at 20 wt% to 30 wt% without measurable loss of ESCR in most container geometries; higher regrind fractions narrow the high-shear processing window and may reduce weld-line integrity at pinch-off seams. For a 20 L container with 2 mm nominal wall thickness, cycle times are commonly 60 s to 90 s; thicker-walled parts above 5 mm require extended cooling to prevent post-mould shrinkage above 2 % to 3 % measured over 24 h. Mould surface temperatures are usually controlled between 10 °C and 20 °C; a differential greater than 5 °C between core and cavity can produce differential shrinkage and warpage in flat sidewalls or wide handle sections.

When chemical exposure and environmental stress cracking govern container life

Applications for HSGC7260 include blow-moulded industrial containers, agricultural chemical packaging, lubricant and oil bottles, and large automotive ducts. The resin resists hydrolysis, aqueous acids, alkalis and many polar solvents at ambient temperature. Continuous exposure to strong oxidizing acids above 50 % concentration, aromatic hydrocarbons, chlorinated solvents or ketones at temperatures above 40 °C is not recommended without specific chemical-resistance testing to ASTM D543. Environmental stress cracking is a physical failure mechanism rather than chemical degradation; it depends simultaneously on external stress, temperature, wetting agent concentration and the resin’s tie-molecule network. The pinched-off weld line is the usual initiation site because residual orientation and thickness variation create local strain amplification. Allowable strain in the pinched-off weld line should be kept below 2 % to 3 % for aggressive formulations; higher local strains reduce the time to brittle fracture even if the base resin has an F50 ESCR above 1000 h.

At low temperatures, HDPE retains impact resistance down to approximately −40 °C, but continuous load-bearing service is limited by creep modulus. For load-bearing parts, continuous service temperature is usually kept below 60 °C unless creep rupture data under ISO 899-1 are available for the specific geometry and stress state. Long-term exposure to ultraviolet light is a separate limit. HSGC7260 does not contain a high-dose UV stabilizer package for extended outdoor service, so containers intended for direct sunlight should be formulated with a UV-stabilised masterbatch or replaced by a weatherable grade. Outdoor weathering of the specific grade should be confirmed by ISO 4892-2 or ASTM G154 on the finished article; published data for this specific configuration is limited.

As an olefin polymer, the base resin may be considered for food-contact applications only when the specific grade, stabilizer package and colour masterbatch have been evaluated under FDA 21 CFR 177.1520(c) and, where applicable, EU 10/2011. Industrial chemical packaging does not automatically confer food-contact status. Lot-specific certificates of analysis report density, high-load melt flow, tensile yield and ESCR control values; conformity to REACH and RoHS requires evaluation of the finished article because additives, pigments and post-consumer recyclate may introduce restricted substances. The resin should not be blended with amine-based processing aids or certain phenolic compounds without compatibility testing, because polar additives can migrate to the surface and reduce weld-line strength or closure adhesion. Storage should be in unopened, moisture-protected packaging at ambient temperatures below 40 °C; outdoor storage can cause pellet surface oxidation and dust accumulation before processing. The controlling document remains the lot certificate of analysis together with the application-specific validation report.