Dow HDPE DGDA-2426 NT is a high-molecular-weight, hexene-copolymer high-density polyethylene supplied as natural, unpigmented pellets for extrusion blow molding of large-format rigid containers. The product is specified where melt strength, environmental stress crack resistance, and creep resistance under stacking load are primary service conditions. Manufacturer-published typical values include a nominal density of 0.955 g/cm³ measured under ISO 1183-1:2019 and a melt mass-flow rate of 0.25 g/10 min at 190°C/2.16 kg measured under ISO 1133-1:2022. Published tensile yield stress is approximately 28 MPa under ISO 527-2:2012, and flexural modulus is typically in the 1,200–1,400 MPa range under ISO 178:2019. These values are nominal data, not release limits; the certificate of analysis for each batch should govern production settings.

Because the resin is supplied in natural form without pigment or slip/antiblock loading, light stabilisation and color concentrate addition must be managed by the processor. Pre-drying is not normally required for HDPE at ambient storage; however, if opened bags are stored above 70% relative humidity for more than 24 h, surface moisture should be removed by drying at 80°C for 2 h to prevent surface defects.

What Distinguishes the Molecular Architecture of DGDA-2426 NT from General-Purpose Blow Molding HDPE?

Molecular weight, short-chain branching, and molecular weight distribution control the difference. The 0.25 g/10 min melt mass-flow rate corresponds to a high average molecular weight that extends low-shear viscosity and parison hang time. Hexene comonomer produces longer short-chain branches than 1-butene, which modifies tie-chain formation and lamellar thickness distribution. The practical effect is that environmental stress crack resistance can be maintained at a higher density than would be expected for a butene-copolymer HDPE at the same nominal density.

The 0.955 g/cm³ density positions the material in the medium-stiffness HDPE class. Under a two-phase density model, this density corresponds to a crystalline weight fraction near 70%. The resulting lamellar network increases yield stress and top-load strength, but normally reduces stress crack resistance. The hexene-derived short-chain branching offsets part of that reduction by promoting interfacial tie-molecule density between adjacent lamellae. This is a significant difference from general-purpose butene-copolymer blow molding HDPE, where lower density is commonly required to achieve equivalent environmental stress crack resistance.

The melt flow ratio, determined as the ratio of the melt mass-flow rate at 21.6 kg to that at 2.16 kg under ISO 1133-1:2022, is a process-relevant indicator of molecular weight distribution. General-purpose blow molding HDPE grades often have a melt flow ratio in the 70–100 range; high-molecular-weight grades with extended parison sag resistance typically exceed 100. The published value for DGDA-2426 NT is not always disclosed on standard datasheets, so the ratio should be obtained from the supplier’s product stewardship documentation before tooling design.

Representative comparative values are shown below. The comparative grade is not a specific commercial grade but a class reference for a general-purpose 0.30 MI butene-copolymer HDPE.

Extrusion blow molding of 20–60 L industrial containers, tight-head and open-head drums, and agricultural packaging uses this grade in monolayer and multilayer structures. On a shuttle or reciprocating screw machine with a 65 mm grooved-feed extruder and 24:1 L/D, melt temperature is commonly maintained between 180°C and 205°C. Accumulator-head machines with 2–6 parison programs are preferred for large containers because a long parison must be extruded rapidly and then held without sagging. The high molecular weight of the resin reduces neck-in and improves wall-thickness uniformity across the drum sidewall, but it also raises melt pressure at the die. Head tooling should be sized to permit a blow-up ratio of roughly 2:1 to 3:1 for round containers; higher blow-up ratios concentrate shear in the pinch-off weld and increase the probability of weld-line failure.

Published full-container performance data for this specific grade is limited for ultraviolet-stabilised drums, so outdoor service requires compounded UV stabilisation at the converter level. The natural pellet is compatible with typical HDPE color concentrates based on low-melt-flow carriers, but high-melt-flow carriers can reduce melt viscosity and parison hang time.

Melt Rheology and Blow-Up Ratio Limits in Continuous Extrusion

Low melt-flow HDPE exhibits strongly shear-thinning viscosity. At extrusion shear rates of 100–1000 s⁻¹, the apparent viscosity of a 0.25 g/10 min HDPE is high enough to generate melt temperatures above set-point in high-shear zones. Processors using barrier screws or intensive mixers should not exceed a melt temperature of 210°C; residence times beyond 8 min at 210°C can initiate oxidative chain scission, visible as a melt-flow increase and reduced ESCR. Thermal stabilisation of the commercial resin is not a substitute for melt-temperature control.

Die swell increases as molecular weight increases. For a die gap of 1.5–2.5 mm, the parison swells both in diameter and thickness; the swell ratio typically requires a die-to-container diameter ratio smaller than the final container diameter. Blow-up ratios above 3.5:1 are not recommended for this density class because the frozen-in orientation during inflation is less effectively relaxed, leading to anisotropic impact strength and potential environmental stress crack initiation at the container corners.

At the mold, aluminum or copper-beryllium tooling with cooling water maintained at 10–18°C is standard for cycle-time reduction. The cavity pressure during inflation is normally 0.6–1.0 MPa. The pinch-off weld is the critical region for ESCR failure in chemical packaging. Weld-line thickness should not fall below 80% of nominal wall thickness, and flash geometry should be designed to avoid a sharp internal notch. Open-head drums require a continuous pinch-off weld at the bottom chime; trimming flash while the weld is warm reduces notch sensitivity.

When Regrind Content Exceeds 20 wt%, ESCR and Impact Behaviour Shift

Post-industrial regrind from the same product can be introduced into the main feed, but the concentration alters the thermal and rheological history of the melt. Below 10 wt% regrind, the effect on melt-flow rate and ESCR is usually negligible when the regrind is clean, dry, and not degraded. At 20 wt% or above, melt mass-flow rate may increase by up to 15% depending on the number of heat histories, and ESCR F50 can decline by more than 30% under ASTM D1693 Condition B, 100% Igepal CO-630 at 50°C. The exact shift depends on regrind particle size distribution, moisture, and residence time at the extruder.

Processors compounding regrind should screen through a 2–4 mm mesh and use a gravimetric blender with additive feed tolerance of ±0.25 wt%. If regrind is introduced in the outer layer of a multilayer structure, the weld-line and handle regions may have lower stress crack resistance than the virgin layer. A detailed lot qualification is required when regrind content exceeds 30 wt%, because published HDPE regrind models based on shift factors do not universally predict ESCR for hexene-copolymer HDPE with broad molecular weight distribution.

Environmental stress crack resistance in DGDA-2426 NT is relevant to containers holding surfactants, agricultural emulsifiable concentrates, drain cleaners, and light oils. The material is not intended for continuous exposure to strong oxidising acids, chlorinated solvents, or alkaline solutions above 50°C without validation. HDPE can be stress cracked by nonylphenol ethoxylates, kerosene, and some crop-protection formulations at elevated stress levels. The proper test is not simple immersion but a constrained-stress test under ASTM D1693 or a full-container creep test at target fill temperature and stacking load. Published full-container data for this specific grade is limited for aggressive solvent blends; validation must therefore be performed on the final molded article, not on compression-molded plaques alone.

Compliance Boundaries Are Not Uniform Across Regional Food-Contact Jurisdictions

Food-contact suitability for HDPE is based on olefin polymer rules. In the United States, DGDA-2426 NT may be evaluated under FDA 21 CFR 177.1520(c) 3.1a for high-density polyethylene, provided the end-use limitations for fatty food, aqueous food, and alcohol food are met. In the European Union, compliance must be assessed under Regulation (EU) No 10/2011 on plastic materials and articles intended to come into contact with food, with an overall migration limit of 10 mg/dm² for general food contact unless a lower specific migration limit applies. The resin does not inherently ensure finished-article compliance; the converter is responsible for validating the complete formulation including masterbatch, regrind, and processing aids.

REACH compliance in the EU is usually established through the supplier’s registration dossier for the monomer and polymer constituents. RoHS Directive 2011/65/EU applies to electrical and electronic equipment and is not relevant to bulk chemical packaging unless the article is incorporated into regulated electronic devices. The grade does not contain intentionally added perfluorinated alkyl substances, based on supplier documentation; however, certification for specific customer declarations must be obtained from the supplier.

Selection between DGDA-2426 NT and lower-density blow molding HDPE should be based on the ratio of top-load demand to chemical exposure. A 0.949 g/cm³ HDPE with a similar melt-flow rate may provide higher ESCR but lower column strength. Conversely, a 0.958 g/cm³ HDPE may provide higher stiffness and barrier but reduced stress crack life in aggressive surfactants. Comparative data in the table above should not be interpreted as a warranty. The polymer supplier’s lot-specific certificate of analysis and processing letter remain the controlling documents.

For injection-molded closures or thin-wall containers, DGDA-2426 NT is generally not selected because its viscosity is too high for long flow lengths and thin sections. Thin-wall injection molding requires melt-flow rates above 4 g/10 min to avoid short shots at practical injection pressures. In extrusion blow molding, the low melt-flow rate is functional rather than limiting.