Borealis HDPE MG9647B is a pelletised high-density polyethylene resin formulated for injection moulding of thin-wall packaging, caps and closures, housewares, and industrial containers. The grade is produced by a bimodal polymerisation route, which places a controlled high-molecular-weight fraction within a lower-molecular-weight matrix. That molecular architecture modifies the usual inverse relationship between melt flow and stiffness. The nominal density is 964 kg/m³ when determined by ISO 1183-1, and the nominal melt mass-flow rate is 7.0 g/10 min at 190 °C and 2.16 kg when determined by ISO 1133-1. These values place the resin in the high-flow, high-stiffness segment of the HDPE range. The pellet formulation includes antioxidant and acid scavenger stabilisation but does not include a flame-retardant additive. The grade is intended for applications where short cycle time, dimensional stability, and food-contact compliance are production requirements rather than optional benefits.

What Melt Flow Rate Governs Multi-Cavity Filling in This Grade?

The 7.0 g/10 min MFR is a nominal midpoint, not a lot-specific limit. In multi-cavity tools with flow-length-to-wall-thickness ratios above 150:1, this flow level reduces injection-pressure requirements relative to blow-moulding HDPE grades, but it does not eliminate the need for balanced runner geometry. The bimodal distribution creates a shear-thinning response stronger than a unimodal HDPE of equivalent MFR; at injection shear rates between 1000 s^-1 and 10 000 s^-1, apparent viscosity falls rapidly, while low-shear melt strength remains sufficient to limit melt drainage from hot-runner gates. The property set reported for this grade is summarised in Table 1.

Density and MFR together define the processing and end-use trade space. A density of 964 kg/m³ is above the 0.950 g/cm³ threshold marking general-purpose HDPE, so the resin shows a higher crystalline fraction. That higher crystalline fraction contributes to the tensile modulus and top-load stiffness, but it also reduces environmental stress crack resistance compared with a 0.950 g/cm³ grade. The MFR of 7.0 g/10 min is roughly one order of magnitude higher than that of a typical blow-moulding HDPE, which means shorter cooling-limited cycles but lower melt strength. The two values are therefore not independent; the grade is positioned for injection moulding, not extrusion.

The property set shows the expected inverse relationship between melt flow and impact resistance. The notched Charpy value at 23 °C is 5.0 kJ/m²; at -20 °C the value drops to 2.5 kJ/m², which is approximately 50 % lower. The Vicat softening temperature of 126 °C is a short-term heat-distortion characteristic, not a continuous-use limit. Continuous exposure above 60 °C requires creep and oxidation testing because polyethylene softens progressively with time and temperature.

In injection moulding, the barrel-temperature profile is normally set from 180 °C at the feed throat to 240 °C at the nozzle. Melt temperature measured by an air-shot probe is maintained between 220 °C and 260 °C. Mould wall temperature is controlled between 10 °C and 40 °C; the lower mould temperature shortens cooling time but can reduce weld-line strength and surface gloss. Back pressure is kept between 5 bar and 15 bar, and screw speed should remain below 150 rpm on a 50 mm screw to avoid shear heating above the melt-temperature ceiling. Holding pressure is typically 50 % to 70 % of the injection-pressure setpoint and must be maintained until gate freeze. For a 1.5 mm wall section with a 0.8 mm pin gate, gate freeze time is approximately 2 s to 4 s. Predrying is not mandatory when pellets have been stored below 60 % relative humidity. After condensation or outdoor storage, drying at 80 °C for 2 h in a desiccant-hopper dryer is sufficient to prevent surface splay.

The shear heating rule used in production is that screw rotation above 100 rpm on a 50 mm screw can raise melt temperature by 3 °C to 5 °C for every 100 rpm increase when back pressure is fixed at 10 bar. This is an operational approximation, not a material property, and it depends on screw design, screw wear, and heater band calibration. Frequent checks of the air-shot melt temperature are therefore required. The grade can be processed with a standard three-zone screw; a barrier screw is preferred for colour change and regrind because it reduces melt-temperature variation. Gate design should avoid abrupt land lengths below 0.5 mm because high shear rates near the gate can exceed the critical shear stress and generate melt-fracture defects in thick sections.

Shrinkage Anisotropy and Gate Freeze-Off in Thin-Wall Sections

Differential shrinkage between flow and cross-flow directions is a principal source of warpage in HDPE injection moulding. For MG9647B, mould shrinkage in the flow direction is typically 1.5 % to 2.0 % under ISO 294-4; cross-flow shrinkage can be 0.2 % to 0.5 % higher depending on orientation and packing. The high-molecular-weight fraction crystallises more slowly than the low-molecular-weight fraction, but rapid cooling at mould temperatures below 40 °C still produces anisotropic lamellar stacks in high-shear regions. Warpage is minimised when fill-time variation across cavities is held below 5 % and when packing pressure is sustained through gate freeze. Unbalanced hot-runner systems generate asymmetric orientation that can produce ovality greater than 0.5 mm on a 200 mm diameter lid. For precision parts, post-mould shrinkage should be measured after 48 h at 23 °C because demoulded articles can lose an additional 0.1 % to 0.3 % in linear dimensions during the first day of recrystallisation.

Because the grade contains a high-molecular-weight fraction, quiescent crystallisation under non-isothermal cooling has a bimodal lamellar thickness distribution. Differential scanning calorimetry at 10 °C/min typically shows a melt peak near 130 °C to 135 °C, but no grade-specific value is mandated. The practical consequence is that cavity-pressure decay is slower than in a unimodal grade of the same MFR, so gate freeze can be delayed by 0.5 s to 1.0 s in thick sections. Moulders should not reduce packing time based solely on the MFR; the packing phase must be confirmed using pressure transducers in the cavity.

In thin-wall packaging production, the grade is commonly used for containers from 0.5 L to 25 L on stack moulds with hydraulic clamp force between 3500 kN and 12 000 kN. The high MFR permits filling of side-wall sections below 1.2 mm, but the low-temperature impact limit restricts stacking of filled pails in cold storage below -20 °C. In multi-cavity cap tools, hot-runner tip temperatures below 220 °C increase melt-pressure requirements and can produce short shots in outer cavities. Tip temperatures above 280 °C accelerate molecular weight degradation and may generate odour precursors. The grade is not intended for extrusion blow moulding, rotational moulding, or pipe extrusion because the high melt flow reduces melt strength and long-term hydrostatic creep resistance. For food-contact thin-wall packaging, organoleptic neutrality is process-dependent: residence times above 10 min at 260 °C can create off-taste precursors even if the resin formulation is clean.

The grade is also used in tamper-evident closures where hinge life and strip torque are controlled by the final part design, not by the resin alone. In closure tools with 64 to 128 cavities, the injection fill time is usually below 0.5 s, which places a premium on repeatable hot-runner balance. Cavity-to-cavity weight variation above 1.5 % is typically traced to thermal imbalance in the hot runner, not to melt-flow-rate variation in the pellet batch. Process capability studies on closure dimensions should use control plans with a minimum of 30 consecutive shots to separate material lot variance from thermal drift.

When Low-Temperature Impact Becomes a Limiting Design Input

Design for freezer service requires a different resin-selection logic. The notched Charpy value of 2.5 kJ/m² at -20 °C under ISO 179-1/1eA is a material property, but the failure mode of a moulded part also depends on wall thickness, gate geometry, and packing quality. Thin sections below 1.0 mm can undergo a ductile-to-brittle transition at higher temperatures because plane-stress conditions near notches reduce the size of the plastic zone. For moulded containers, a free-fall drop test such as ASTM D5276 after 24 h at -18 °C is more predictive of field performance than a Charpy value alone. If the application requires impact resistance at -40 °C, published data for this specific configuration is limited; in practice, a lower-density HDPE or an LLDPE-rich blend is substituted at the expense of top-load stiffness. The grade should not be stored in contact with amine-based antistatic additives above 40 °C, because amine migration can accelerate yellowing of the polymer surface.

In addition to impact, slow crack growth under environmental stress is relevant for containers holding surfactants, oils, or alcohol-water mixtures. The high density and high MFR of MG9647B lower the resistance to stress cracking relative to lower-density, lower-MFR HDPE. Where ESCR is critical, ASTM D1693 or ISO 22088-3 tests should be performed on the final article because moulded-in orientation and residual stress can dominate the resin value. Published data for this specific configuration is limited, so converters should run bottle-notch or container-panel tests under the intended chemical environment rather than relying on a datasheet value.

Regulatory status is evaluated under three frameworks. In the European Union, the base material is assessed under Regulation (EU) No 10/2011 as amended; final articles must be tested for overall migration and, when applicable, specific migration using the assigned food simulants. In the United States, the olefin polymer falls under 21 CFR 177.1520, subject to the specified food types and conditions of use. The resin is registered under REACH (EC) No 1907/2006, and no substance of very high concern is present above 0.1 % w/w. Under Directive 2011/65/EU, the four restricted heavy metals and brominated flame retardants are not expected above the maximum concentration values because the grade is not flame-retarded and no restricted metal-based pigment is part of the standard formulation. These regulatory classifications are not a substitute for article-specific compliance testing, especially when colour concentrates or regrind are added by the converter.

Comparative Position Against Lower-MFR HDPE and Polypropylene Copolymers

Relative to blow-moulding HDPE grades with MFR between 0.2 g/10 min and 1.0 g/10 min, MG9647B reduces injection pressure and permits thinner nominal wall sections at equal clamp force. The penalty is a reduction in slow crack growth resistance. ESCR testing under ASTM D1693 condition A is not a strength of high-flow HDPE; published data for this specific configuration is limited, but the bimodal high-molecular-weight fraction partially offsets the ESCR loss typical of a unimodal 7 g/10 min grade. Compared with a 0.950 g/cm³ density HDPE, the 964 kg/m³ density of this grade increases tensile modulus and top-load capacity, but lowers environmental stress crack resistance and low-temperature impact. Compared with random copolymer polypropylene of similar MFR, the HDPE offers better environmental stress crack resistance and lower density, but usually lower flexural modulus and lower continuous-use temperature in hot-fill applications. The final selection in caps, closures, and thin-wall containers is therefore governed by compatibility with the closure liner, hinge fatigue, seal retention, and the specific filling temperature, not by a single tensile value.

For converters replacing a random copolymer PP in a closure, the lower density of HDPE gives a weight saving for the same part volume, but the lower modulus requires a thicker wall or added top-load ribs. The HDPE also has a lower melting point than PP, so hot-fill temperatures above 80 °C are outside the normal service window unless the container is retorted only under controlled conditions. For cold-food packaging, the HDPE impact performance is generally sufficient at 0 °C to -10 °C, but below -20 °C the design margin narrows. The difference from other Borealis HDPE grades is primarily the MFR/density combination; higher-density grades offer more stiffness but lower ESCR, while lower-MFR grades offer better ESCR and melt strength but demand higher injection pressures.

Storage before processing should be in clean, dry conditions below 50 °C. Post-industrial regrind can be added at up to 20 % by mass for non-food applications. In food-contact articles, regrind is acceptable only when the source is controlled and the finished article continues to meet migration limits. Regrind fractions above 20 % narrow the processing window because repeated heat history reduces melt viscosity and can increase gel formation. The material is incompatible with polyvinyl chloride, polycarbonate, and uncompatibilised polyamide in mixed recycle streams; contamination from these polymers can form delamination defects. Natural and white compounds should not be processed after carbon-black colour changes without thorough purging because the high melt flow carries residual pigment through the screw in fewer than 20 shots. Melt temperatures above 280 °C are outside the recommended processing window and can produce surface defects, odour, and yellowing.