Braskem HDPE GM7746C is a high-density polyethylene blow molding grade supplied by Braskem for rigid packaging and small-to-medium hollow technical components. Its commercial identity derives from a nominal density of 0.944 g/cm³ and a melt flow rate of 0.45 g/10 min at 190 °C/2.16 kg. The density is determined under ASTM D792-20 or ISO 1183-1:2019; the melt flow rate is determined under ASTM D1238-13 or ISO 1133-1:2022. The low melt flow rate places GM7746C among high-molecular-weight extrusion blow molding resins rather than high-flow injection molding resins. In contrast to an injection molding HDPE with a melt flow rate of 20 g/10 min, GM7746C provides greater parison melt strength and improved environmental stress crack resistance, but it is not suitable for thin-wall injection mold filling.

The grade is typically supplied as cylindrical pellets stabilized with a phenolic/phosphite antioxidant package and an acid scavenger. The public datasheet does not identify the comonomer; the density below 0.950 g/cm³ indicates controlled short-chain branching, which interrupts the linear chain packing sufficiently to reduce crystalline density while retaining the high molecular weight needed for blow molding. This architecture differentiates GM7746C from high-density homopolymer grades with densities above 0.958 g/cm³, which have higher flexural modulus but lower resistance to environmental stress cracking in surfactant-containing liquids.

How Does Melt Rheology Constrain Blow Molding Cycle Limits?

Processing behavior is governed by the combined effect of high molecular weight and broad molecular weight distribution. At die shear rates in the range of 100–500 s⁻¹, the grade displays shear thinning; the viscosity at these shear rates is substantially lower than the zero-shear viscosity, which reduces melt pressure without destroying parison integrity. On continuous shuttle blow molding machines with screw diameters between 60 mm and 90 mm and 24:1 L/D barrier screws, the barrel set-point profile is typically 160–200 °C from the feed zone to the metering zone, with head and die temperatures of 190–210 °C. The recommended melt temperature is 185–215 °C. Below 180 °C, head pressure and screw torque rise, and the parison surface may exhibit melt fracture or sharkskin, especially at narrow die gaps below 0.8 mm. Above 225 °C, parison sag increases and additive decomposition may generate odor; the upper limit is therefore tighter than that for lower-viscosity grades.

Mold-side conditions are equally important because GM7746C has a relatively high freeze-off temperature. Mold coolant is generally set between 10 °C and 20 °C for thin-wall containers with wall thickness below 2 mm. Blow pressure is commonly 0.6–0.8 MPa. HDPE does not require desiccant drying under normal resin handling. If pellets are cold-soaked or stored at relative humidity above 60%, hopper drying at 70–80 °C for 2–3 h is used to prevent surface splay and die lip deposit. Published data for this specific configuration is limited; the appropriate set-points must be confirmed by measuring bottle top-load and drop impact under ASTM D2659-16 and ASTM D2463-15 rather than by melt temperature alone.

Density and modulus control top load and panel stiffness. A nominal density of 0.944 g/cm³ corresponds to a flexural modulus near 950 MPa under ISO 178 and a tensile yield stress near 24 MPa under ISO 527-2. These values are lower than those of high-density homopolymer HDPE but sufficient for household chemical bottles up to approximately 5 L. For a 500 mL bottle with a sidewall thickness of 2.0–2.2 mm, the material provides adequate top-load stiffness for palletized distribution; the pinch-off weld is typically the limiting region, and its strength is validated by cutting tensile specimens across the weld and comparing yield stress with the sidewall value. When the container is exposed to diluted bleach, quaternary ammonium disinfectant, or nonionic surfactant solutions, environmental stress crack resistance under ASTM D1693-21 is more predictive of service life than short-term tensile properties.

When GM7746C Replaces Lower-Density or Higher-Flow HDPE in Rigid Packaging

Material substitution of GM7746C into an existing tool is not a direct drop-in where the predecessor grade has a different molecular weight distribution. Replacing a lower-density HDPE or MDPE with density 0.938 g/cm³ increases top-load capacity and allows modest wall thickness reduction; conversely, replacing a high-density homopolymer with density 0.960 g/cm³ reduces flexural modulus and may require an increase in sidewall thickness, especially for rectangular bottles with large flat panels. The low melt flow rate of GM7746C also prevents it from being used in high-speed injection molding applications; it is intended for continuous extrusion blow molding, and attempts to run it in injection molds would require melt temperatures outside the stable degradation window.

The most significant comparative differences are environmental stress crack resistance, permeation, and processability. In applications where containers carry aggressive liquids, GM7746C is selected because its short-chain branching and high molecular weight delay the brittle crack that occurs under sustained hoop stress. The improvement is shown by longer failure time under ASTM D1693-21 in 100% Igepal at 50 °C compared with higher-density homopolymer HDPE. The trade-off is lower oxygen and water vapor barrier than higher-density HDPE; transmission rates are approximately 10–20% higher for oxygen and water vapor because the lower crystalline fraction increases free-volume transport. For products requiring low oxygen transfer, a coextruded barrier layer or fluorinated surface treatment is more effective than increasing density alone.

Values in the matrix are representative published datasheet values for material selection; the supplier certificate of analysis governs the actual lot.

For direct food contact, GM7746C is generally covered by FDA 21 CFR 177.1520, but the converter must verify that the finished container meets the associated migration testing requirements of 21 CFR 174.5 and, for fatty or aqueous applications, the relevant end-use test protocols. For non-food household chemical packaging, REACH and RoHS compliance are documented for the supplied pellets, but downstream additives, color concentrates, and processing aids must be assessed separately. The material is not marketed as a medical-grade or pharmaceutical-grade resin; those applications require additional biocompatibility and extractables testing according to ISO 10993-1 and USP ⟨661.1⟩.

In service, GM7746C is not suitable for continuous exposure to aromatic hydrocarbons such as toluene or xylene, chlorinated solvents, or strong oxidizing acids above 30% at temperatures above 40 °C. These fluids can produce softening, swelling, or environmental stress cracking that is not predicted by simple immersion testing. For hydrocarbon-based formulations, a fluorinated HDPE container or a coextruded polyamide/EVOH barrier is required; the monolayer HDPE grade alone is insufficient. In alkaline cleaners and aqueous acids below 10% concentration, the grade generally retains acceptable performance, but container qualification should include storage at 50 °C for 28 days followed by drop testing and visual inspection.

Thermal and Environmental Stress Crack Resistance Benchmarks

The Vicat softening point of GM7746C is approximately 124 °C under ISO 306 method A50, and the heat deflection temperature under 0.45 MPa is below 75 °C. These values define the upper temperature limit for empty or lightly loaded containers. Hot-fill operations above 75 °C are not recommended for thin-wall monolayer HDPE of this density because sidewall distortion and neck finish deformation can occur during cooling. For household chemical bottles stored in uncontrolled warehouses, thermal performance is less limiting than environmental stress cracking. Resistance to ESCR is evaluated using ASTM D1693-21 with 100% Igepal at 50 °C; the high molecular weight of GM7746C produces longer failure times than high-melt-index HDPE of identical density. This property is the primary reason for using GM7746C instead of a 0.950 g/cm³ high-flow HDPE in aggressive liquid packaging.

Impact resistance at low temperature is also relevant for e-commerce and winter distribution. The drop impact failure height under ASTM D2463-15 is typically higher for GM7746C than for homopolymer HDPE bottles at -20 °C because the lower crystalline fraction reduces brittle crack propagation. However, the exact failure height depends on bottle geometry, sidewall thickness distribution, pinch-off design, and conditioning time; it is not a single material property. Published data for this specific configuration is limited. For critical applications, instrumented puncture testing under ISO 6603-2 or drop testing on filled containers is recommended.

The grade also differs from fractional-melt HDPE blow molding resins with melt flow rate below 0.2 g/10 min. Compared with those resins, GM7746C has lower parison sag resistance because of its higher melt flow rate, but it offers lower head pressure, easier trimming, and faster cycle time on smaller containers. Compared with high-density homopolymer blow molding grades of density 0.960 g/cm³, GM7746C gives lower flexural modulus but better ESCR and better pinch-off weld toughness. Compared with metallocene MDPE of density 0.938 g/cm³, GM7746C gives higher stiffness and lower moisture vapor transmission, but it may have lower stress crack resistance in extreme surfactant solutions. The selection between these classes is made using top-load testing under ASTM D2659-16, ESCR testing under ASTM D1693-21, and permeation testing under ASTM F1249-20 or ASTM D3985-17.

During regrind use, the proportion of GM7746C regrind is typically limited to 20–30% with virgin pellets for critical chemical packaging, because repeated heat history reduces ESCR and increases gel formation. The grade is not designed for film extrusion or injection molding. In extrusion blow molding, die gap should be set to produce parison wall thickness 1–4 mm; if die gap is below 0.8 mm, melt fracture risk increases because of the high viscosity. Color dispersion with masterbatch requires a metering system capable of 2–4% addition without disturbing melt temperature; color concentrates with unsuitable carriers can cause delamination at the pinch-off and loss of ESCR.