Dow HDPE DMDB-6400 NT 7 is a high-density polyethylene blow-moulding resin distributed as unpigmented natural pellets. The grade is defined by a nominal density of 0.964 g/cm³ measured under ISO 1183-1:2019 and a melt flow rate of 0.70 g/10 min recorded at 190°C under a 2.16 kg load according to ISO 1133-1:2022. These values place the material in the medium-molecular-weight HDPE segment, where top-load strength and parison hang time are balanced for industrial chemical packaging. The product is converted on extrusion blow-moulding lines producing containers in the 0.5 L to 25 L range. Typical end uses include household cleaner concentrates, agricultural adjuvant bottles, and mid-sized industrial intermediate bulk containers. The NT 7 code corresponds to a natural, unpigmented pellet form without a carbon-black UV-stabilizer package.

Why Does Parison Melt Strength Govern Tooling Selection for This Grade?

In extrusion blow moulding, the processing window is governed by the interaction between melt viscosity, die swell, and parison sag. For this resin, a melt temperature measured at the die exit of 190°C to 210°C is recommended. On a 60 mm grooved-barrel extruder with L/D 24:1, typical set points from feed throat to die run from 170°C to 200°C, with the die head maintained at 195°C to 205°C; screw speed is commonly 30 to 60 min⁻¹, producing melt pressure at the adapter of 250 to 400 bar depending on die gap. At die exit temperatures below 185°C, sharkskin can appear on the parison surface; above 220°C, parison sag becomes the dominant defect. Diverging die gaps of 1.0 mm to 1.4 mm are used for 1 L bottles, with blow-up ratios of 2.0:1 to 2.6:1 and parison programming that increases wall thickness by 20% to 40% at the pinch-off. The melt strength of the 0.70 g/10 min resin is lower than that of high-molecular-weight HDPE grades with MFR below 0.35 g/10 min, so accumulator-head machines are preferred for containers above 10 L to control wall-thickness distribution. Two-stage accumulator blow-moulding machines with first-in first-out heads are commonly used for 5 L to 25 L containers. Water-cooled aluminum tooling is held at 10°C to 15°C, and blow pressure is typically 6 to 10 bar. Cycle time for a 1 L bottle at 0.8 mm minimum wall thickness on a twin-station shuttle machine falls in the 10 to 14 s range, depending on parison programming and cooling efficiency. Flash trim thickness at the pinch-off must be monitored; flash above 0.5 mm can increase clamp force requirements and delay cooling.

Published typical property values are summarized below; these are representative data and not minimum specification limits. Finished-part properties depend on tooling geometry, cooling rate, regrind level, and pigmentation.

From a mechanical design standpoint, the 0.964 g/cm³ density places the part in the upper range of HDPE. This provides higher flexural modulus and top-load retention than lower-density HDPE copolymers in the 0.950–0.958 g/cm³ class; however, it also reduces the amorphous-phase mobility that contributes to slow-crack resistance. The >600 h ESCR value under ASTM D1693-15 condition B indicates that the material can withstand typical non-ionic surfactant solutions encountered in laundry and hard-surface cleaner packaging, but it does not provide universal resistance to aggressive solvents. The Vicat softening point of 128°C limits continuous service temperatures in hot-fill applications; containers filled above 60°C require process validation because hoop stress and chemical aggressiveness increase simultaneously. Tensile stress at yield of 29 MPa and elongation at break above 800% indicate a ductile failure mode in slow tensile loading. The flexural modulus of 1450 MPa supports high top-load in filled containers; in a 5 L jerry can with a 1.2 mm nominal wall, this modulus corresponds to greater top-load resistance than that of lower-density grades, but actual top-load depends on corrugation geometry and handle design. At -18°C, drop-impact resistance of the final article should be verified because impact toughness for HDPE decreases with temperature; the brittleness temperature below -75°C does not guarantee drop performance in a filled container. Bottle drop tests are typically conducted under ASTM D2463-15 at -18°C after 24 h conditioning, with pass criterion of no leak.

Comparative Positioning Against Lower-Density and Bimodal HDPE Resins

A comparison with lower-density HDPE blow-moulding grades clarifies the positioning of DMDB-6400 NT 7. Grades with density near 0.954 g/cm³ and MFR near 0.35 g/10 min often show lower flexural modulus, in the range of 1000–1300 MPa under ISO 178:2019, but can offer longer ESCR when catalyzed with comonomers. DMDB-6400 NT 7 moves toward a narrower molecular weight distribution than dual- or multi-modal high-melt-strength grades. The trade-off appears in parison hang time: the 0.70 g/10 min melt flow rate reduces shear heating and permits easier processing on continuous wheel lines, yet the parison melt strength is insufficient for very large containers unless accumulator-head tooling or higher head pressure is applied. Compared with UV-stabilized outdoor grades, the NT 7 natural form does not contain a hindered-amine light stabilizer or carbon-black package, so exposure beyond temporary outdoor storage requires compatibility testing under ASTM D2565-21 or ISO 4892-2:2013. The resin should not be substituted for injection-moulding HDPE grades in thin-wall parts without evaluating melt-flow ratio and weld-line strength. The ESCR performance is higher than many unimodal HDPE grades of similar density, but lower than bimodal grades specifically optimized for aggressive surfactant packaging. For containers requiring both high stiffness and ESCR above 1000 h, a bimodal counterpart may be preferable; however, published data for this specific configuration is limited.

Pre-drying of the resin is generally unnecessary when pellets are stored in dry silos at relative humidity below 60%. If surface condensation occurs, a desiccant hopper dryer set at 80°C for 2 h can be used; hopper temperatures above 95°C may cause pellet agglomeration and bridging at the feed throat. Clean post-industrial regrind may be added at up to 20 wt%, but closed-loop recycled content above this level can narrow the process window by increasing die swell variation and reducing melt strength. Color concentrates should be based on polyethylene carriers; incompatible low-molecular-weight carriers can form plate-out at the die lip after 4 to 6 h of continuous operation. When processing on a machine with a 20:1 to 24:1 L/D screw, screw speed should be limited so that melt temperature measured by an immersion thermocouple at the die exit remains below 220°C; higher temperatures lead to parison drawdown and can increase the formation of odorous low-molecular-weight species. A screw compression ratio of 2.6:1 to 3.0:1 with a barrier mixer is typical for this density class. If melt temperature drops below 190°C, extruder torque may rise and weld-line strength in the pinch-off can decrease.

If the Moulded Container Must Meet Regulatory Migration Limits Under EU 10/2011

Regulatory status is not a property of the resin pellet alone; the finished container must be tested under the conditions of use. The following matrix summarizes the typical compliance framework. It is not a substitute for a supplier letter or article-specific migration testing.

For EU food-contact articles, the overall migration limit of 10 mg/dm² applies under the intended simulant and time-temperature combination in Annex III of Regulation (EU) No 10/2011. A resin that meets 21 CFR 177.1520(c) may still fail on a finished container if colour concentrates or processing aids introduce non-listed substances. The processor must obtain a formulation disclosure and migration report before claiming compliance. REACH Article 33 applies to articles, not resin pellets, but suppliers often provide a declaration that the resin contains no SVHC above 0.1% w/w. The packaging directive 94/62/EC Article 11 limits the sum of heavy metals to 100 ppm by weight in packaging or packaging components; this is typically met by natural HDPE but must be confirmed when recycled material is used.

Chemical Compatibility Boundaries and Environmental Stress Crack Resistance in Field Trials

Environmental stress cracking in HDPE containers is a creep-assisted brittle failure that occurs under residual hoop stress and surface-active fluid contact. The >600 h ESCR result under ASTM D1693-15 condition B is a ranking indicator using 100% Igepal CO-630 at 50°C; it does not replicate all formulations. Containers for bleach, quaternary ammonium disinfectants, and agricultural emulsifiable concentrates should be evaluated by bottle stress-crack tests with a minimum wall thickness at the shoulder of 0.6 mm. Field experience from 1 L to 5 L extrusion blow-moulded containers indicates that local thinning below 0.6 mm in the shoulder can accelerate environmental stress cracking when nonylphenol ethoxylate-based adjuvants are stored at 40°C; however, published data for this specific configuration is limited. The grade is incompatible with strong oxidizing acids such as concentrated nitric acid and fuming sulfuric acid, and with chlorinated solvents at elevated temperatures. Immersion screening under ASTM D543-20 is recommended for new chemical formulations. Processing aids and antistatic additives containing low-molecular-weight esters can act as stress-cracking agents and should be avoided unless validated through ESCR testing.