Dow HDPE 2689G

Dow HDPE 2689G is a high-density polyethylene injection-molding resin with a reported typical density of 0.968 g/cm³ measured in accordance with ISO 1183-1:2019 and a melt mass-flow rate of 8.0 g/10 min at 190 °C/2.16 kg determined in accordance with ISO 1133-1:2022. The pelletized grade is intended for thin-wall rigid packaging, caps, closures, overcaps, crates, and non-food industrial components. Unlike fractional-melt HDPE grades used in extrusion blow molding or blown film, the 8.0 g/10 min melt flow is associated with lower melt strength and a reduced molecular weight architecture. This combination permits rapid cavity filling in multi-cavity injection tools but precludes stable parison formation in continuous extrusion blow molding. The 0.968 g/cm³ density is higher than that of many extrusion blow-molding HDPE grades; the resulting stiffness increase generally raises top-load capacity while reducing environmental stress crack resistance and low-temperature impact. The grade is therefore classified as an injection-molding specialty material rather than a drop-in replacement for HDPE blow-molding or film resins.

The following table reports representative physical property values for the grade as published in commercial technical literature. Values are not specification limits and do not replace a certificate of analysis for a specific production lot.

High flow does not imply high melt strength. At the low shear rates characteristic of extrusion blow molding, the elongational viscosity of this grade is insufficient to resist parison sag. In contrast, a fractional-melt HDPE with a melt flow rate near 0.6 g/10 min and density near 0.955 g/cm³ retains enough melt strength for stable parison formation. The stiffness gain from a 0.968 g/cm³ density is therefore achieved at the expense of environmental stress crack resistance under ASTM D1693, Condition B, and impact performance at sub-ambient temperatures. Published environmental stress crack data for this specific configuration is limited; containers intended for surfactant-containing liquids or aggressive chemical fills require validation under expected storage temperature and contact conditions using ASTM D1693 or ISO 22088-3.

What processing parameters separate 2689G from fractional-melt HDPE on a conventional injection line?

On a 45 mm screw diameter, 20:1 L/D, 2.5:1 compression-ratio injection molding machine, barrel zone settings of 200/210/220/230 °C from feed to nozzle are typical. Nozzle temperature is maintained at 230 °C. A general-purpose polyolefin screw with a distributive mixing section is sufficient because the grade does not contain abrasive fillers or high-viscosity modifiers. Mold temperature is held between 15 °C and 40 °C. Lower mold temperatures reduce cycle time but increase molded-in anisotropy and can deepen sink marks opposite ribs and bosses. Holding pressure is set at 40–60 % of peak injection pressure. Back pressure is limited to 0.5 MPa or less to avoid excessive shear heating and melt temperature overshoot above 250 °C.

Injection velocity for thin-wall articles with nominal wall thickness of 0.8–1.2 mm is typically 60–100 mm/s. The grade fills narrow flow channels at lower hydraulic pressure than a 0.6 g/10 min HDPE, but high injection velocity is still required to prevent premature freeze-off at the gate. For a 1.0 mm wall, cooling time of 8–12 s at a mold temperature of 15 °C is a practical starting point. At mold temperatures above 40 °C, cycle time increases without proportional improvement in mechanical properties; surface gloss may improve, but dimensional shrinkage becomes more time-dependent. Gate land length should be 0.5–0.8 mm, with gate diameter 0.8–1.0 mm for a 0.8–1.2 mm wall. A cold runner with full-round main runner diameter of 6–8 mm and sub-runner diameter of 3–5 mm is adequate for an 8-cavity layout. Hot runner tip temperature is set at 220±5 °C; tip temperatures above 250 °C can cause local molecular degradation, visible as gate-area yellowing or reduced notched impact.

Melt residence time is a critical control variable. At barrel temperatures above 250 °C, oxidative chain scission increases melt flow and reduces impact. The preferred maximum melt temperature measured at the nozzle is 240 °C. When momentary interruptions exceed 10 min, the barrel should be purged with virgin material at 200 °C before restarting automatic cycling. This prevents accumulation of degraded material in dead spots behind the screw tip and check ring.

Moisture absorption of HDPE is below 0.01 % at 23 °C and 50 % relative humidity, so pre-drying is not normally required. If surface moisture is present because of outdoor storage at relative humidity above 60 %, a hopper dryer at 70 °C for 1–2 h with a dew point of -20 °C is adequate. Drying above 80 °C for extended periods can cause pellet bridging and feed interruptions.

Batch-to-batch viscosity control is verified by incoming resin testing. Users should confirm density per ISO 1183-1:2019 and melt mass-flow rate per ISO 1133-1:2022. Typical incoming-lot acceptance windows are ±0.001 g/cm³ for density and ±0.5 g/10 min for melt flow. Out-of-spec lots may still be processed, but injection speed may require adjustment by 10–15 %. Additional adjustment is required if the melt flow exceeds 9.0 g/10 min because dimensional control and weld-line strength may become more sensitive to packing pressure.

When regrind content exceeds 20 mass%, melt flow and impact retention shift measurably

Regrind is routinely used in injection molding of polyolefins. Under repeated processing at melt temperatures above 240 °C, chain scission increases melt flow and decreases molecular weight. For similar high-flow HDPE grades, regrind proportions above 20 % by mass have been associated with measurable loss of notched impact and oxidative induction time. Published data for this specific configuration is limited; the exact shift depends on regrind thermal history, residence time, and the number of regrind passes. A monitoring protocol is therefore required. After each 100 kg batch of regrind, a sample is tested for melt mass-flow rate per ISO 1133-1:2022 and notched Izod impact per ASTM D256. If the melt flow rate shifts by more than 10 % relative to virgin pellets, regrind ratio should be reduced or barrel temperature lowered by 5 °C. If notched Izod impact falls below 15 J/m, the regrind fraction should not be used in load-bearing or drop-impact applications.

Regrind particle size also affects processing consistency. This grade is not hygroscopic, but flake regrind can bridge in the feed throat if bulk density falls below 0.45 g/cm³. A low-bulk-density regrind may require vibrating hopper equipment or a crammer feeder to maintain stable shot weight. Shot-to-shot weight variation in thin-wall packaging should be kept below 0.2 % of mean shot mass to avoid flash or short shots. This requires stable material feed, consistent check-ring seating, and controlled melt cushion.

Weld-line behavior in multi-gate molds is governed by melt-front temperature and packing. Because the melt viscosity at 190 °C is low relative to fractional-melt HDPE, flow fronts remain hot and coalesce more readily in thin sections. Weld-line tensile strength retention measured on injection-molded plaques per ISO 527-2 has been reported in the range of 70–85 % of unwelded tensile strength for similar high-flow HDPE. Published data for this specific configuration is limited. Mold vents in weld regions should be 0.01–0.02 mm deep to prevent gas entrapment and surface burn marks. The gate location should be placed to minimize obstruction of the melt front by cores or ribs; flow length to wall thickness ratio above 250:1 may reduce weld-line strength below practical values for aggressive filling environments.

Natural grade is not UV-stabilized. Articles exposed to direct outdoor sunlight require 2.0–2.5 % carbon black masterbatch or an appropriate hindered amine light stabilizer package. Without stabilization, high-density polyethylene develops surface embrittlement in high-UV environments, typically within 6–12 months. Outdoor weathering programs should follow ASTM D2565 or ISO 4892-2 to determine acceptable exposure life. The grade should also not be used in continuous contact with strong oxidizing acids or high concentrations of aromatic solvents at temperatures above 50 °C, because aromatic hydrocarbon penetration increases with temperature and can lead to swelling and stress cracking.

Regulatory status for food-contact, heavy metal, and chemical inventory obligations

Compliance is determined by the finished article, the conditions of food contact, and the migration testing performed by the downstream converter. The resin is generally supplied as an olefin polymer for food-contact packaging under FDA 21 CFR 177.1520(c). Specific food-type and temperature limitations apply. In the European Union, finished plastic food-contact articles are evaluated under EU Commission Regulation (EU) No 10/2011 with an overall migration limit of 10 mg/dm². Specific migration limits for additives and monomers must be considered when color concentrates or processing aids are introduced.

The resin should not be considered food-compliant merely from the resin designation. A finished article containing regrind may be subject to additional compositional and migration constraints. Contact with fatty foods may require simulant testing under EU Regulation (EU) No 10/2011, because polyethylene has a higher migration potential with lipophilic substances at elevated temperatures. Compliance under FDA 21 CFR 177.1520(c) also does not exempt the finished article from general food-additive and adulteration provisions of the Federal Food, Drug, and Cosmetic Act.

The grade is not intended for medical implant or long-term parenteral contact applications. Sterilization by ethylene oxide or gamma radiation may alter physical properties; each sterilization dose and cycle must be validated on finished components. Steam autoclave exposure above 121 °C exceeds the practical thermal limit and may cause gross dimensional distortion. For external packaging and industrial components, high-density polyethylene generally resists many aqueous salt solutions, dilute acids, and alkalis at ambient temperature, but aggressive environments require immersion testing under the prescribed service conditions.