Braskem HDPE Grades for Film and Moulding: A Latin American View

High-density polyethylene from Braskem's Brazilian and Mexican production platforms is specified across Latin American converting plants by density measured under ISO 1183-1:2019 and melt flow rate under ISO 1133-1:2022 or ASTM D1238-23. The commercial HDPE envelope spans roughly 0.948 g/cm³ to 0.962 g/cm³, with melt flow rates from below 0.2 g/10 min to approximately 30 g/10 min depending on load and grade family. Film extrusion grades occupy the high-viscosity end of this range, whereas injection and blow moulding grades move toward higher flow. Additive packages, comonomer type, and molecular weight distribution shift the actual value; the converter must confirm the current Braskem datasheet for the specific grade because density and MFR alone do not define bubble stability, warpage, or environmental stress crack resistance.

Latin American converters commonly specify a Braskem HDPE film or moulding grade by density and high-load melt index rather than by the internal grade code alone, because the same resin may carry different national regulatory dossiers and packaging compliance documents across Mercosur, Andean, and Central American markets. The grade code remains the controlled commercial reference, but process set-up is driven by the physical-property datasheet and by production-scale trials on the installed equipment. Grade-specific data are controlled by the current Braskem datasheet; the treatment below therefore uses property envelopes, test standards, and processing boundaries observed in Latin American converting units.

In film extrusion, density and high-load melt index are used together because the 2.16 kg melt flow value of a high-molecular-weight HDPE is frequently below 1 g/10 min and is therefore sensitive to small laboratory variations. The 21.6 kg value, often reported as high-load melt index, differentiates film grades with similar densities. A higher molecular weight tail increases melt strength and bubble stability but also raises extruder torque and die head pressure. The practical consequence is that a film-grade HDPE cannot be selected solely from nominal density; the converter evaluates the complete melt-flow ratio, additive package, and gel performance under the intended film structure.

What High-Load Melt Index Reveals About Film-Grade Processability

The high-load melt index is measured at 190 °C under a 21.6 kg load according to ASTM D1238-23 or the equivalent ISO 1133-1:2022 procedure. For Braskem HDPE film grades, this value is more informative than the 2.16 kg MFR because it captures the flow of the high molecular weight fraction that controls bubble stability. Film-grade HDPE with a high-load melt index below 6 g/10 min tends to generate a stronger, more dimensionally stable bubble in high-stalk extrusion, but it raises the specific energy demand of a grooved-feed extruder. A grade with a high-load melt index near 10 g/10 min may process with lower head pressure but is more prone to sag and edge weave in thin films.

On a 45 mm single-screw extruder with a 25:1 L/D grooved-feed section running at 80 rpm, the difference between a 0.35 g/10 min and a 0.8 g/10 min high-load melt index film grade can shift head pressure by several megapascals; however, the exact pressure response is machine-specific. Screw geometry, screen-pack loading, die gap, and melt temperature all modify the head-pressure curve. Published data for this exact configuration is limited, so the converter should establish a pressure baseline for each grade on the installed line rather than transferring a set-point from another plant.

Capillary rheometry at 190 °C with a 30:1 L/D die is used to compare the shear-thinning behaviour of a broad bimodal film grade against a narrow injection moulding grade. At a wall shear rate of 300 s⁻¹, a film-grade HDPE may show an apparent shear viscosity near 800 Pa·s, whereas an injection moulding grade of similar density can be below 500 Pa·s. These values are not Braskem specifications; they reflect typical high-density polyethylene rheology and must be generated for the specific lot and additive package. The difference in viscosity is not a defect. It is the molecular weight distribution that allows film grades to maintain bubble stability and moulding grades to fill thin-wall details at acceptable injection pressures.

On South American blown film lines, a narrow injection moulding grade substituted into a film formulation destabilises the bubble, particularly at frost-line heights above 8 die diameters. The lower melt strength allows the bubble to sway and form gauge bands. Conversely, a high-molecular-weight film grade fed to an injection moulding machine produces short shots and high screw recovery torque. The two families are therefore not interchangeable without compounding or blending, and the choice must be anchored to the intended fabrication process.

Southern Cone Extrusion Lines and the Back-Pressure Envelope

Extrusion plants in Argentina, Chile, and southern Brazil operate a mixture of monolayer and coextrusion lines with screw diameters from 45 mm to 75 mm and 24:1 to 30:1 L/D. Braskem HDPE film grades are typically processed with barrel zones between 175 °C and 210 °C, while the die is held between 195 °C and 215 °C. The back-pressure before the screen pack is the parameter that most directly indicates whether the resin is moving from solid-bed conveying into a fully molten state. A partially loaded screen pack on a 60 mm extruder can increase melt temperature by 5 °C to 10 °C, which is sufficient to reduce bubble stability in high-stalk operation. Operators therefore record the pressure at the breaker plate and compare it to the clean-screen baseline for the selected grade; no absolute pressure threshold applies to every line.

Low melt temperature at the die can leave unmelted particles that appear as gel-like blemishes in the film. A minimum die temperature of 190 °C is common for high-molecular-weight film grades, but the value depends on residence time, screw speed, and back-pressure. Operation above 230 °C may initiate oxidation and off-odour formation unless the resin is protected by a high-performance antioxidant package. The processing window is therefore not a single temperature set-point but a band that shifts with the thermal history of the equipment.

Drawdown and gauge uniformity in monolayer HDPE film are controlled by die gap, blow-up ratio, and frost-line height. A die gap of 1.0 mm to 1.8 mm is common for high-density paper-like film, with blow-up ratios between 3:1 and 5:1. The frost line is usually maintained between 5 and 10 die diameters to balance machine-direction and transverse-direction tear values. If the frost line rises too high, transverse-direction tear resistance tends to fall; if it sits too low, bubble flutter and gauge bands become more likely. Bimodal Braskem HDPE film grades widen the stable bubble window by increasing melt strength, but they also raise extrusion pressure relative to a unimodal grade of the same nominal density.

When Tropical Humidity Alters Hopper Feeding and Surface Finish

High-density polyethylene does not absorb water into the polymer matrix to the extent of polyamide or PET, but surface condensation can enter the feed throat of an extruder or injection moulding machine in Latin American regions where relative humidity exceeds 60 %. The operational boundary is determined by dew point and resin temperature, not by resin water absorption. When cold resin is moved from an air-conditioned warehouse into a non-conditioned plant near the coast, condensation can occur within minutes. Converters in São Paulo, Cartagena, or Guayaquil should avoid opening bulk containers immediately at high humidity unless the resin temperature is above the dew point. If surface splay or bubbles appear, a dehumidified hopper system or positive-displacement dryer set to 60 °C to 80 °C for 1 h to 2 h is used before processing.

In injection moulding, surface moisture creates silver streaks, nozzle drool, and inconsistent shot size rather than hydrolytic degradation. Drying is not normally required for HDPE stored in closed containers at room temperature below 50 % RH, provided the machine feed throat is not exposed to plant air for long periods. The limitation is operational: southern Mexican and Caribbean plants with high dew points may need a hopper blanket and dry-air purge even though the resin itself is not hygroscopic.

Braskem HDPE injection moulding grades are selected for short cycle times in thin-wall packaging, caps, and crates. Melt temperatures from 200 °C to 240 °C and mould temperatures from 15 °C to 40 °C are representative. A low-viscosity HDPE grade with a melt flow rate of 20 g/10 min to 30 g/10 min at 190 °C/2.16 kg may fill a 0.6 mm wall section at injection pressures below 80 MPa in a high-speed cap mould with a hot runner. If the grade is too viscous, short shots appear at the same pressure; if it is too fluid, flash and mould deposit increase. The actual pressure requirement is established on the moulding machine because clamp force, gate geometry, and flow-length-to-thickness ratio define the fill behaviour.

Shrinkage and warpage are evaluated with ISO 294-4 or the equivalent ASTM D955. High-density polyethylene typically exhibits moulding shrinkage between 1.5 % and 3.0 %, with longitudinal and transverse shrinkage differing when the part is flow-oriented. A film-grade HDPE is not recommended for injection moulding because the high molecular weight tail increases injection pressure and may reduce replication of fine mould details, especially in closures with tamper-evident bridges.

Agrochemical Container Moulding Demands ESCR Above Density

For moulded containers holding surfactants, oils, or agrochemical formulations, environmental stress crack resistance is a release criterion rather than a secondary property. The comparison is made under ASTM D1693-21, Condition B, with 10 % Igepal CO-630 at 50 °C. Latin American blow moulders frequently require an F50 value above 100 h for tight-head drums, although the acceptable threshold is set by the end-user specification and the specific chemical contact. High-molecular-weight HDPE grades with a density below 0.955 g/cm³ are generally preferred for aggressive fluids. A higher density grade may improve top-load compression but can show shorter stress-crack life under surfactants; the property balance is therefore decided case by case.

Blow moulding operations on shuttle machines with 90 mm to 120 mm extruders and clamp forces from 20 t to 80 t process these grades at melt temperatures of 180 °C to 210 °C. Parison swell and die swell are higher for a high-molecular-weight HDPE than for an injection moulding grade, and pinch-off zones can become failure initiation points if the mould is too cold. A mould temperature below 15 °C can freeze orientation and create residual stresses that reduce service ESCR; maintaining cooling at 20 °C to 30 °C is typical for consistent wall thickness and surface finish.

Without Notched Constant Ligament Stress Data, Laminate Qualification Is Incomplete

For film-grade HDPE used in laminations and printed structures, the notched constant ligament stress test under ASTM D5397-20 provides an accelerated ranking of stress-crack resistance that is more informative than dart impact alone. The test applies a constant tensile load to a notched specimen in a surfactant environment, and the time to failure is recorded. Latin American converters use this method when a Braskem HDPE film grade is being qualified for sachet laminates exposed to alcohols, wetting agents, or cleaning fluids. The film producer may specify a minimum failure time, but published data for this specific Braskem grade configuration is limited because the laminate structure, adhesive, and printing solvent alter the stress-crack response independently of the polyethylene layer.

Elmendorf tear under ASTM D1922-15(2020) and dart impact under ISO 7765-1:1988 or ASTM D1709-22 measure different failure mechanisms. A film with high dart impact can still fail by environmental stress cracking at a fold, crease, or sealing interface. The converter should request notched constant ligament stress data from the film supplier and avoid qualifying a film solely on melt-index and density correlations; stress-crack resistance must be demonstrated in the final laminate configuration.