Braskem HDPE ES6004 is a high-density polyethylene extrusion blow moulding resin specified with a melt flow rate of 0.40 g/10 min at 190 °C/2.16 kg according to ASTM D1238 and a density of 0.960 g/cm³ according to ASTM D1505. The grade occupies the low-melt-flow, high-density segment of HDPE, where parison hang strength and container top-load stiffness are more important than spiral-flow fill behaviour. In extrusion blow moulding, it is processed on shuttle lines, reciprocating-screw machines, and wheel machines using grooved-feed extruders. Melt temperature is maintained between 180 °C and 220 °C, and die head temperature is typically 190 °C to 210 °C. Because the melt flow rate is low, the resin produces stable parisons for wall sections above 1.5 mm, but die pressure at a given output is higher than that of blow moulding grades rated above 4 g/10 min. The material is not intended for thin-wall injection moulding because the high viscosity limits filling of narrow flow paths.

Data-driven die design for HDPE blow moulding uses the Carreau-Yasuda model because the power-law region does not extend into the low-shear-rate zone where parison hang strength is generated. Typical model parameters for a 0.960 g/cm³ HDPE would include zero-shear viscosity from 2 × 10⁴ Pa·s to 1 × 10⁵ Pa·s at 190 °C, but published parameters for this specific configuration are limited. The die land length should be at least 10 times the die gap to reduce swell variation; die gaps between 0.8 mm and 1.8 mm are common for bottle diameters from 20 mm to 80 mm. Die swell ratios for high-density polyethylene at 190 °C and shear rates of 500 s⁻¹ generally range from 1.4 to 1.8. Incorrect die swell compensation produces wall thickness deviations that cannot be fully corrected by parison programming.

Melt rheology and the extrusion blow moulding processing envelope

Capillary rheometry at 190 °C and shear rates from 100 s⁻¹ to 1,000 s⁻¹ is required for die sizing because the single-point melt flow rate does not describe shear-thinning behaviour. High-density polyethylene resins in this density class typically exhibit power-law index values between 0.35 and 0.45 over that shear rate range; published data for this specific configuration is limited. Grooved-feed extruders with 24:1 to 30:1 L/D ratio are preferred. A recommended barrel temperature profile is 170 °C feed, 190 °C compression, 200 °C metering, and 190 °C die. At output rates below 100 kg/h, screw cooling is not normally required. Above 100 kg/h, oil-cooled screw temperature control stabilises melt homogeneity and reduces gel formation. Accumulator-head machines with parison programming are specified when container length exceeds 300 mm because software-controlled die gap reduces wall-thickness variation from ±15 % to less than ±5 % in well-characterised tooling.

Parison sag is influenced by zero-shear viscosity and parison length. For HDPE with melt flow rate 0.40 g/10 min, sag length measured at 190 °C in a controlled oven is lower than for grades above 0.7 g/10 min. Wall-thickness distribution is improved by die gap programming; open-loop programmes with 20 to 40 interpolation points reduce top-load failure caused by thin sidewalls. Thickness measurement on cut bottle sections is performed with a Hall effect gauge at 6 to 12 circumferential positions. On shuttle machines, clamp force for 5 L moulds is typically 80 kN to 150 kN per cavity; insufficient clamp force causes flash and weight variation.

Processing failure modes observed on production-scale equipment include star-shaped die lines from contaminated regrind, surface melt fracture above 220 °C, and parison hooking when die centering is off by more than 0.2 mm. Melt fracture is managed by lowering die temperature to 190 °C and reducing extrusion rate below 50 kg/h on a 60 mm extruder. On production-scale shuttle lines, the most common extrusion failure mode is pressure fluctuation from worn grooved bushes. A pressure variation above 5 bar across the metering section creates wall thickness variation and lightweight containers. Barrel and screw wear should be monitored by measuring melt pressure at the die inlet; a gradual increase of 10 % for the same output indicates screw or barrel replacement. Auxiliary equipment specifications include a screen pack of 40/60/100 mesh to remove gels from regrind. Screen pack blinding increases melt temperature and can push the material above 230 °C; at that point oxidative chain scission becomes measurable by an increase in ASTM D1238 melt flow rate after processing.

Pre-drying is not required under normal silo storage. When surface moisture from silo condensation or wet regrind is present, pre-drying at 80 °C for 2 h in a desiccant hopper dryer reduces parison bubbles and surface streaking. Storage should avoid direct sunlight and sustained temperatures above 40 °C; long-term oxidative degradation raises melt flow rate and creates gel specks that appear as surface defects in blow moulded parts. Regrind addition is typically limited to 20 wt% to 30 wt% with virgin resin. Higher regrind fractions narrow the melt-pressure operating window and reduce environmental stress crack resistance under ASTM D1693 condition B because repeated shear history lowers the high-molecular-weight tail.

What separates ES6004 from high-melt-index injection moulding grades?

The main difference is the melt flow rate gap. An injection moulding HDPE with 20 g/10 min fills thin-wall injection tooling at lower pressure but lacks parison hang strength in blow moulding. ES6004 at 0.40 g/10 min retains higher melt tension during extrusion, enabling continuous parison lengths above 300 mm without sag. The trade-off is high melt pressure in injection moulding; therefore the grade is not specified for thin-wall injection moulding or spiral-flow-dominated filling. In comparison with lower-density HDPE copolymers of 0.940 g/cm³, ES6004 provides higher flexural modulus and top-load stiffness, but the higher density reduces ESCR failure time when tested under ASTM D1693 condition B.

Differences from other products in the same melt flow range are defined by molecular weight distribution. A broader distribution improves shear-thinning and die swell, while a narrower distribution reduces haze and improves surface finish. Lot-to-lot variation in ASTM D1238 melt flow rate of ±0.05 g/10 min can shift fill point on accumulator-head machines. Therefore process control should include upstream melt flow testing and adjustment of die gap. Published data for this specific configuration is limited for some lot-to-lot comparisons.

Extrusion blow moulding tools are usually designed for blow ratios of 2.0:1 to 3.5:1. For containers in the 1 L to 5 L range, parison programming with 20 to 40 points is used to control wall thickness. Cooling time is regulated by mould temperature; moulds are maintained at 10 °C to 20 °C to achieve cycle times below 20 s for 1 L bottles. At lower mould temperatures, surface gloss improves but weld-line strength at the pinch-off can decrease. Weld-line strength is assessed by burst testing under ASTM D1599 and drop testing under ASTM D2463.

Colour concentrates for blow moulding HDPE should be based on polyethylene carriers with melt flow rates below 4 g/10 min to prevent local viscosity dilution. Carbon black additions of 2 wt% to 4 wt% improve ultraviolet weathering resistance, but carbon black reduces weld-line strength and increases die pressure. Photodegradation is assessed under ASTM D2565 or ISO 4892-2. If outdoor service life exceeds 12 months, a hindered-amine light stabilizer package is required at 0.1 wt% to 0.3 wt%; the final selection must be validated by tensile property retention under ASTM D638 after accelerated weathering. Blow mould pinch-off design affects failure under drop impact. A compression zone with 0.5 mm to 1.0 mm land and 45 ° to 60 ° included angle reduces residual stress. If the pinch-off temperature is below 160 °C, weld-line strength drops because chain diffusion across the interface is incomplete. Post-mould cooling jigs are used for containers above 5 L to prevent panel bulging and to maintain dimensional stability. Shrinkage of 0.960 g/cm³ HDPE after blow moulding is typically 2.0 % to 2.5 % in the axial direction and 1.5 % to 2.0 % in the hoop direction; tooling dimensions must compensate for anisotropic shrinkage.

When the container contacts aggressive chemicals or fatty food simulants

At sustained temperatures of 60 °C to 80 °C, continuous contact with aromatic hydrocarbons, chlorinated solvents, and strong oxidising acids can soften the material and accelerate stress cracking. In these environments, the grade is not suitable without barrier modification; coextrusion with polyamide or EVOH layers or fluorination is required. For food contact, resin compliance with FDA 21 CFR 177.1520 and EU 10/2011 is only the starting point. The finished article must be tested for overall migration under EU 10/2011 using 3 % acetic acid, 10 % ethanol, and vegetable oil or food simulant D2 as specified in Commission Regulation (EU) No 10/2011. The end user must confirm that colourants, processing aids, and regrind do not alter migration. The material is typically compliant with RoHS Directive 2011/65/EU and REACH registration obligations, but suppliers should provide a lot-specific certificate of compliance.

Environmental stress cracking is evaluated under ASTM D1693 condition B at 50 °C in 10 % Igepal CO-630 solution. The failure mechanism involves slow crack growth from surface defects in the presence of polar surfactants and residual stress. Blow moulded parts with sharp corners, insufficient radii, or high orientation near the pinch-off are more prone to ESCR. Stress concentrators at the pinch-off should be radiused at least 0.5 mm. For agricultural chemical containers, ESCR performance under ASTM D1693 condition B should exceed 100 h; higher-risk formulations may require a hexene-modified HDPE copolymer with density below 0.955 g/cm³. Top-load strength is measured under ASTM D2659. The higher density of 0.960 g/cm³ increases top-load stiffness, but the property is also influenced by wall thickness distribution and cooling. A 1 L bottle with 1.2 mm uniform wall thickness and 0.960 g/cm³ density exhibits higher top-load strength than the same bottle in 0.940 g/cm³ MDPE at equivalent conditions; however, the MDPE container often survives longer under ESCR testing.

Typical end uses include household chemical bottles from 0.5 L to 20 L, agricultural chemical containers, personal care bottles, and light-duty industrial drums. In these applications, wall thickness is generally 1.0 mm to 2.5 mm, and drop impact is evaluated under ASTM D2463. For pharmaceutical or food packaging, lot-specific testing should include melt flow rate under ASTM D1238, density under ASTM D1505, and environmental stress crack resistance under ASTM D1693 condition B. Published data for this specific configuration is limited for some application categories; therefore end users should qualify each container design on production-scale equipment before commercial release.