Braskem HDPE BU004W is a high-density polyethylene blow moulding resin supplied in pellet form. The grade is specified with a melt flow rate of 0.4 g/10 min under ASTM D1238 at 190 °C with a 2.16 kg load and a density of 0.954 g/cm³ per ASTM D1505. These values place the material among low-MFR, high-molecular-weight HDPE grades used for extrusion blow moulding. The low MFR restricts parison sag during continuous extrusion and accumulator discharge, and the density contributes to container stiffness. The material is suited to rigid containers, industrial packaging, and technical blow moulded parts in which wall uniformity and environmental stress crack resistance are critical.

The grade’s reported mechanical properties place it among medium-stiffness HDPE blow moulding resins. Tensile yield strength is approximately 25 MPa per ASTM D638, elongation at break exceeds 600%, and flexural modulus is near 950 MPa per ASTM D790. Shore D hardness is reported as 64 under ASTM D2240, and Vicat softening temperature is approximately 127 °C according to ASTM D1525. The reported Vicat softening temperature positions BU004W below the softening point of polypropylene but above that of many low-density polyethylene grades. Continuous use above 80 °C in aggressive chemical environments requires creep and stress relaxation testing because stiffness drops as the polymer approaches its crystalline alpha transition. In top-load tests on blow moulded containers, wall buckling and sidewall paneling may occur before tensile failure; the flexural modulus value of 950 MPa indicates the contribution of density and crystallinity to panel stiffness. However, container geometry, wall thickness, and mould cooling rate produce final properties different from those measured on compression-moulded test plaques.

What separates BU004W from high-flow HDPE grades used in injection moulding?

High-flow HDPE injection grades are frequently specified at 8 g/10 min to 40 g/10 min. Those resins have lower melt viscosity and can fill thin walls under moderate injection pressure. BU004W, by contrast, is intended for extrusion where low MFR maintains a continuous parison under its own weight. If BU004W is injection moulded, the required melt temperature and injection pressure would rise, and the melt may degrade before complete filling occurs. Conversely, a high-flow injection grade used in blow moulding would exhibit severe parison sag, narrow die swell control, and insufficient melt strength for accumulator machines.

Molecular weight distribution also differs. High-flow injection HDPE grades may use narrow molecular weight distribution to reduce viscosity at high shear rates, whereas BU004W is characterized by a broader distribution that retains some low-shear viscosity and promotes die swell. On a single-screw extruder with L/D 30:1 and a smooth-bore feed section, BU004W generally requires higher specific energy input than high-flow HDPE. Screw speed, back pressure, and die gap must be adjusted to maintain a melt temperature of 200 °C to 210 °C at the die exit. The high molecular weight increases die swell; tooling designed for lower-viscosity HDPE may need a reduced die gap or a different mandrel-to-bushing ratio to achieve the target parison diameter and wall distribution.

Relative to HDPE grades intended for film or pipe extrusion, BU004W is not specified for pressure pipe or thin-gauge film. Pipe grades often use bimodal molecular weight distributions to achieve long-term hydrostatic strength under ISO 9080; BU004W does not carry PE100 or PE4710 pressure ratings. Film grades are often lower in density and higher in melt flow to improve tear resistance and processing line speed. The density of BU004W at 0.954 g/cm³ gives higher modulus but lower impact at low temperatures than medium-density polyethylene used in some large-part blow moulding applications.

Extrusion blow moulding of BU004W on shuttle and accumulator-head machines is typically performed with a melt temperature at the die exit between 180 °C and 210 °C. The feed throat is maintained below 80 °C to prevent pellet bridging, and barrel zone settings are ramped from 170 °C near the feed section to 200 °C at the die head. High-density polyethylene is not hydroscopic; pre-drying is generally unnecessary unless pellets show surface condensation after storage in high-humidity conditions. Surface moisture can be removed by drying at 80 °C for 2 h, but published data for this specific configuration is limited. Melt temperature above 230 °C should be avoided because chain scission and oxidation can lower molecular weight, reduce ESCR, and generate gel defects visible on the container surface.

Parison thickness programming should account for die swell and melt strength. A programming curve with a slower initial extension rate at the top of the container and faster extension near the bottom may be required to prevent thin corners and pinch-off defects. The pinch-off weld is a limiting mechanical zone: excessive melt temperature produces a weak weld, while insufficient temperature creates visible notch lines. Mould closing speed must be balanced to prevent air entrapment at the parting line.

When ESCR performance dictates material selection

Environmental stress crack resistance is the main differentiator for BU004W in packaging of surfactants, detergents, motor oil, and glycol-based coolants. The ASTM D1693 test uses a bent specimen immersed in a stressed-cracking agent at 50 °C; F50 values above 600 h indicate that the resin retains toughness under slow crack growth conditions. The high molecular weight fraction in BU004W increases tie-molecule density between crystalline lamellae, resisting craze propagation. However, actual service life is controlled by moulded-in residual stress, wall thickness distribution, closure torque, and the specific chemical formulation of the filled product. The F50 value should not be used as a direct service-life predictor.

In blow moulded containers, the top-load region below the neck and the pinch-off weld are frequent crack initiation sites. Residual stress from rapid cooling or an over-tightened die can concentrate stress in these zones. Processors should evaluate container performance with successive top-load tests such as ASTM D2659 or in-house creep-to-failure protocols that simulate stacked storage. Adjusting mould temperature and blowing pressure can shift crystallinity gradients and reduce stress concentration. Published data for BU004W under specific container geometries is limited; therefore, prototype testing on the production line is required.

BU004W follows the general chemical resistance profile of high-density polyethylene. It withstands dilute aqueous acids, bases, and many polar solvents at ambient or moderately elevated temperatures. It is not recommended for continuous exposure to strong oxidizing acids, chlorinated solvents, or aromatic hydrocarbons, which can swell or oxidize the wall. For packaging applications, compatibility is evaluated by ASTM D543 immersion tests or by direct container testing at the intended fill temperature, headspace composition, and storage duration. Permeation of non-polar chemicals may occur over long storage periods; barrier requirements must be derived from the application.

Regulatory compliance matrix and food-contact status

Food-contact and regulatory status must be confirmed through the supplier’s product stewardship documentation. HDPE grades of this type are commonly covered by olefin polymer provisions in food-contact regulations, but final articles require migration testing or end-use compliance statements. The following matrix summarizes the typical regulatory context for exploratory formulation work.

For blow moulding plants running shuttle machines with clamp forces from 50 kN to 300 kN, the resin can be processed at screw speeds appropriate for the extruder diameter, usually in the range of 20 min⁻¹ to 80 min⁻¹ on a 60 mm extruder. These values are equipment-dependent and are provided only as a starting point. The use of a barrier screw with a compression ratio of 2.5:1 to 3.5:1 is recommended to melt the high-viscosity polymer without excessive shear heating. Melt pumps are generally not required for blow moulding of BU004W unless the accumulator head demands precise shot-to-shot consistency. On accumulator-head machines, parison drop time is controlled by melt temperature and die gap. BU004W can be run with parison drop times of 0.5 s to 2 s for containers up to 5 L, but this depends on shot size and head geometry. When container capacity exceeds 10 L, pilot runs should measure parison sag by comparing parison length at fixed time intervals after discharge. If sag exceeds 10% of initial parison length before mould closing, die gap or melt temperature should be reduced, or a higher-molecular-weight grade should be considered. Published data for this specific configuration is limited.

Colouring with HDPE-compatible masterbatch is performed by dry blending or dosing at the feed throat. The recommended addition rate for standard colour concentrates is 2 wt% to 4 wt%, but dispersion must be verified by optical inspection of thin sections. High shear mixing at the die screen may be necessary for pigments with agglomerate potential. Incompatible additives, particularly amine-based stabilizers or metal stearates, should be evaluated for their effect on ESCR and melt stability before production use. Amine-based processing aids and some secondary antioxidants can interact with the resin’s stabilizer package and alter ESCR. Compatibility of such additives should be tested by ASTM D1693 and melt flow stability before production use. Halogenated flame retardants and certain metal stearates may have similar effects. Copper or copper-alloy components in the melt stream should be avoided because copper ions catalyze oxidative chain scission.

Storage of pellets should be in sealed containers or silos protected from UV radiation, as extended outdoor storage can cause surface oxidation and yellowing. The grade is not UV-stabilized unless explicitly specified. If prolonged outdoor exposure is required for the finished container, an adequate UV stabilizer package or a compounded concentrate should be added. The base resin should not be processed at melt temperatures above 230 °C for more than 10 min cumulative residence time. Purging after coloured or filled resins is required to avoid cross-contamination in the accumulator head.

Incoming resin lots should be checked for melt flow rate and density against the certificate of analysis. Batch-to-batch variation in MFR should be held within ±0.05 g/10 min if tight parison control is required. Larger variation can shift parison hang time and wall distribution. Moisture content, although low, can be checked by ASTM D6869 or Karl Fischer titration if surface condensation is suspected. Bulk railcar deliveries should sample from multiple compartments to detect segregation.