Braskem HDPE IA58 is an injection-moulding-grade high-density polyethylene homopolymer supplied in pellet form. The nominal density is 0.958 g/cm³ when determined by ISO 1183-1 or ASTM D1505, and the melt flow rate is 5.8 g/10 min at 190 °C under 2.16 kg load according to ASTM D1238 / ISO 1133-1:2022. End-use segments include rigid packaging, caps, closures, thin-wall containers, housewares, toys and general-purpose technical injection mouldings. The polymer backbone is linear high-density polyethylene; published data for the specific antioxidant and acid-scavenger additive package in IA58 is limited. Processing and compliance performance are therefore described from nominal density, melt flow rate and the established envelope for HDPE homopolymer injection resins in this flow class. The grade is not intended for blown-film extrusion, rotomoulding or pipe extrusion.

Mechanical property values from published datasheets for HDPE injection-moulding homopolymer grades in the melt-flow interval 4.0–7.0 g/10 min and density interval 0.955–0.960 g/cm³ typically fall within tensile yield stress 22–30 MPa, flexural modulus 900–1400 MPa, notched Izod impact 20–80 J/m at 23 °C and Shore D hardness 64–70. These values are representative of the material class and should not be cited as IA58-specific unless confirmed by the supplier. Melt crystallization temperature for HDPE of this density typically occurs between 110 °C and 120 °C in differential scanning calorimetry. Vicat softening temperature for comparable density HDPE is usually between 120 °C and 130 °C.

When IA58 Replaces Fractional-Melt Injection Grades in High-Cavitation Tooling

The substitution threshold is governed by melt flow rate, molecular weight distribution and flow-path length in the mould. A melt flow rate of 5.8 g/10 min places IA58 in the medium-flow HDPE injection-moulding range, below high-flow grades above 20 g/10 min used for high-cavitation thin-wall lids, but above fractional-melt injection grades below 1.0 g/10 min used for thick-wall crates and pails. The higher flow relative to fractional-melt HDPE reduces injection pressure by approximately 15–25% in comparable flow-path geometries, based on capillary rheometry data for HDPE melts with similar density. However, the lower molecular weight associated with higher flow typically reduces environmental stress-cracking resistance and tensile elongation at break compared with lower-melt-flow injection grades. IA58 is selected when cycle time, thin-wall fill and dimensional uniformity dominate over long-term environmental stress-crack resistance.

Processing in injection moulding machines with a clamp force appropriate to the projected area uses standard HDPE screw profiles. A metering-section length-to-diameter ratio of at least 20:1 and compression ratio between 2.2:1 and 3.0:1 are commonly specified. Melt temperature measured at the nozzle should be held between 180 °C and 230 °C; barrel zones are typically profiled from 160 °C at the feed throat to 210–230 °C at the metering zone. Mould temperature is maintained between 10 °C and 40 °C; lower mould temperatures shorten cycle time but increase residual stress and in-mould shrinkage anisotropy. Injection pressure for a 2 mm wall section may range from 60 MPa to 100 MPa, with holding pressure at 50–70% of the injection pressure. Screw back pressure of 0.5–1.5 MPa is sufficient for melt homogeneity without excessive shear heating. Screw surface speed in small and medium machines is generally 0.2–0.5 m/s. Gate freeze time is established when shot-weight variation across consecutive shots stabilizes below 0.1%; cooling time for a 2 mm wall is typically 6–10 s, scaled by the square of wall thickness. Hot-runner systems are acceptable, but long residence times at temperatures above 240 °C increase discoloration and molecular degradation. Mould shrinkage according to ASTM D955 or ISO 294-4 is commonly reported in the range 0.015–0.040 mm/mm, with transverse shrinkage typically 10–20% lower than flow-direction shrinkage depending on orientation. Required clamp force can be estimated from a cavity pressure of 30–50 MPa at gate freeze; projected area calculations are mandatory for large moulds.

The shear viscosity of HDPE IA58 at processing temperatures ranges from 200 Pa·s to 400 Pa·s at a shear rate of 1000 s⁻¹ and 230 °C, based on published capillary data for HDPE with similar melt flow. At lower shear rates below 100 s⁻¹, viscosity may exceed 600 Pa·s, which favours melt cushion stability but requires sufficient gate geometry to avoid jetting. Spiral flow length at 230 °C, 80 MPa injection pressure and 2 mm flow depth is commonly 200–300 mm for this MFR class. These values should not be applied as IA58-specific without supplier confirmation.

The melt flow ratio at 21.6 kg load is a practical indicator of molecular weight distribution. For injection-moulding HDPE grades with MFR near 5.8 g/10 min, the flow rate at 21.6 kg load is typically 12–20 times the 2.16 kg MFR, corresponding to a molecular weight distribution that balances shear thinning with melt strength. A lower flow ratio in film or blow-moulding grades supports parison strength but increases melt viscosity. Published data for the specific melt flow ratio of IA58 is limited.

What Distinguishes IA58 from Blow-Moulding and Film Resins?

Blow-moulding HDPE grades are typically formulated with melt flow rates below 1.0 g/10 min and a broader molecular weight distribution to maintain parison sag resistance and die swell. Film grades often have melt flow rates below 1.2 g/10 min and are designed for bubble stability and draw-down. IA58 at 5.8 g/10 min would not provide the melt strength required for blown-film bubble formation or long parison hang time; its narrower-to-medium molecular weight distribution favours rapid relaxation, lower injection pressure and faster filling of thin wall sections. Compared with high-molecular-weight film resins, IA58 shows lower environmental stress-cracking resistance as measured by ASTM D1693 Condition A and lower impact at low temperature. In rigid injection moulding, these reductions are acceptable when the service temperature remains above −20 °C and the part is not under continuous environmental stress. The density of 0.958 g/cm³ is higher than many film grades, giving greater stiffness and lower moisture vapour transmission, but also higher shrinkage and a higher tendency to post-mould dimensional change.

In multi-cavity cap production with a 250-tonne clamp force machine and 24-cavity hot-runner tool, cycle time for a 1.5 mm wall is typically 8–12 s. Gate diameter is set by capillary balance; unbalanced runners produce cavity-to-cavity fill variation greater than 2%. Injection velocity should be profiled so that flow-front velocity remains between 150 mm/s and 300 mm/s. Screw decompression distance of 3–6 mm after plasticating is generally used to prevent nozzle drool. If the nozzle tip is incorrectly sized, shear heating at the nozzle may raise local melt temperature by 10–25 °C, shifting effective viscosity and causing cavity-to-cavity imbalance. In hot-runner systems, gate thermal controls should maintain gate temperature within ±5 °C of the process setpoint to prevent cold-slug formation and weld-line displacement.

Environmental stress-cracking resistance of HDPE injection grades in this density range is typically 2–20 h under ASTM D1693 Condition A, 10% Igepal at 50 °C; the exact IA58 value should be confirmed from the supplier datasheet. Lower-density and lower-MFR grades exhibit longer failure times, while IA58 may fail earlier in the presence of detergents, alcohols and surfactants. Continuous stress above 10 MPa reduces ESCR sharply. Use of regrind above 20% by weight may lower ESCR and increase melt-flow variability. In top-load comparisons, a 28 mm beverage cap made from 0.958 g/cm³ HDPE can show an increase of 10–20 N in top-load strength relative to 0.950 g/cm³ HDPE at equal wall thickness, but the higher-density material has lower environmental stress-crack resistance.

In production-scale injection moulding, IA58-class materials are susceptible to specific failure modes when process limits are exceeded. Overpacking of thin-wall caps with excessive hold pressure above 80 MPa often produces gate blush, diametral shrinkage variation and elevated residual hoop stress. When residual stresses exceed 12 MPa, stress-cracking under soap or detergent contact may occur within 24–72 h in ASTM D1693 screening tests. At melt temperatures below 180 °C, injection pressure rise and flow-front hesitation can create weld-line weakness; weld-line tensile strength in HDPE injection moulding is typically 60–85% of the uninterrupted material strength. At temperatures above 240 °C, thermal degradation increases the melt flow rate, reduces notched Izod impact and shifts the part colour from translucent white to yellow. In multi-cavity hot-runner moulds, melt residency exceeding 10–15 minutes at 220 °C may cause gate stringing and black specks. Published data for IA58-specific degradation kinetics is limited; the stated limits are derived from high-density polyethylene homopolymer processing literature and are not a substitute for supplier process capability studies.

Regulatory and Compliance Matrix for Rigid Packaging

Storage of Braskem HDPE IA58 should be in dry, ventilated conditions at or below 40 °C and below 50% relative humidity. Polyethylene is not hygroscopic; if regrind is introduced, surface moisture from outdoor storage may require drying at 80 °C for 2–3 hours in a dehumidifying dryer. The grade is incompatible with strong oxidizing agents, chlorinated solvents and certain amine-based additives when wet. Ultraviolet stabilization is not implied; published data for long-term outdoor weathering of IA58 is limited. In applications requiring prolonged contact with aggressive stress-cracking fluids, a lower-melt-flow, higher-molecular-weight HDPE should be evaluated.