NOVA Chemicals HDPE 2907 is a high-density polyethylene injection moulding grade supplied by NOVA Chemicals. The resin is positioned for thin-wall rigid packaging, closures, pails, housewares, caps, and material-handling components where melt flow rate, stiffness, cycle time, and dimensional recovery control part cost and mould productivity. At the technical data sheet level, the grade is specified with a melt flow rate of 7 g/10 min determined under ASTM D1238-23 or ISO 1133-1:2022 at 190 °C with a 2.16 kg load, and a density of 0.960 g/cm³ measured by ASTM D792-20 or ISO 1183-1:2019 at 23 °C. The density places the grade at the upper end of the HDPE density range, indicating a high crystalline fraction that governs shrinkage, tensile yield, oxygen transmission, and permeation resistance. The melt flow rate separates HDPE 2907 from fractional-melt blow moulding grades and film extrusion grades, which require greater melt strength to stabilise a parison or film bubble. In a reciprocating-screw injection moulding machine with a general-purpose screw of 20:1 to 24:1 L/D, the resin is normally processed in a melt-temperature range of 200 °C to 240 °C, with the lower end selected for thick-walled parts and the upper end selected for thin-wall closures with extended flow-length ratios.

What separates this grade from higher-molecular-weight blow moulding HDPE?

The primary distinction is rheological rather than compositional. Blow moulding HDPE grades are typically specified with a melt flow rate below 1 g/10 min under the same ASTM D1238 test condition. That low melt flow rate reflects a higher weight-average molecular weight and in many cases a controlled molecular weight distribution that provides the parison melt strength needed in accumulator-head or shuttle blow moulding. HDPE 2907 at 7 g/10 min does not sustain continuous parison drawdown in blow moulding tooling, but it provides lower melt viscosity at injection shear rates. The practical consequence is that filling pressure in a multicavity thin-wall injection tool is lower than for a fractional-melt blow moulding grade by approximately 30 % to 40 % at equivalent fill speed, gate geometry, and runner layout. This pressure difference is measurable on a screw-tip pressure transducer and on the hydraulic pressure trace of the injection unit. The 0.960 g/cm³ density also separates the grade from many blow moulding and extrusion HDPE grades that fall between 0.949 g/cm³ and 0.955 g/cm³. The higher density of HDPE 2907 increases flexural modulus and top-load strength in closures and pails but reduces environmental stress-cracking resistance under aggressive wetting-agent exposure. Tensile yield strength is generally specified in the 26 MPa to 28 MPa range under ASTM D638-14 or ISO 527-2:2012, while flexural modulus is between 1200 MPa and 1500 MPa under ASTM D790-17 or ISO 178:2019. These are engineering ranges; lot acceptance requires the specific certificate of analysis from the manufacturer.

To compare HDPE 2907 against lower-density HDPE copolymers or medium-molecular-weight distribution grades, the following representative values are used in part design and finite-element analysis. They are not intended as lot release limits; they are engineering approximations intended for shrinkage prediction, mould-flow simulation input, and mechanical design calculations.

The notched Izod range reflects sensitivity to specimen thickness, gate location, and moulding conditions; thin-wall closure designs with frozen-in orientation may fall at the higher end of the range, while coarser spherulitic structure from slow cooling lowers impact performance. Shrinkage values are influenced by melt temperature, holding pressure, holding time, and mould temperature. A decrease in holding pressure below the gate-seal requirement increases shrinkage toward the upper bound and raises the risk of sink marks over thick bosses or ribs.

Pressure-dependent melt viscosity and fill behaviour in stack-mould thin-wall closures

Thin-wall closure moulding imposes apparent shear rates above 1000 s⁻¹ during gate passage. At such shear rates, HDPE 2907 exhibits shear thinning that permits filling pressures in a stack mould with a 0.8 mm sidewall and a cold runner to be held between 70 MPa and 90 MPa at a melt temperature of 220 °C. The exact pressure depends on gate land length, runner diameter, cavity balance, and venting efficiency. Tooling engineers commonly calculate clamp force using a projected-area pressure of 3.5 kN/cm² to 4.5 kN/cm² for this grade when fill time is held at 0.8 s to 1.5 s. A toggle-clamp injection moulding machine of 1500 kN to 2500 kN is adequate for stack-mould tools producing 26 mm beverage closures at a total projected area of 350 cm² to 500 cm², provided the injection unit maintains a screw cushion of 3 mm to 5 mm after switch-over. The cushion is critical because compressibility of HDPE melt under holding pressure can consume 2 mm or more of stroke; loss of cushion below 2 mm produces cavity-to-cavity weight variation and short shots in the last cavities to fill.

Barrel zone settings from feed to nozzle are typically 170 °C, 190 °C, 210 °C, and 220 °C, with the nozzle held at 220 °C to reduce stringing. Mould temperature is commonly maintained at 10 °C to 30 °C. Lower mould temperatures reduce cycle time but increase shrinkage anisotropy and may reduce surface gloss; higher mould temperatures improve gloss and dimensional recovery but extend cooling time. Holding pressure is generally set at 50 % to 70 % of peak injection pressure and held for 0.5 s to 1.0 s per 0.1 mm of nominal wall thickness. The critical processing window lies between 200 °C and 240 °C. Below 200 °C, the melt viscosity increases sufficiently to require higher cavity pressure and can produce underfilled ribs or weld-line weakness. Above 245 °C, oxidative degradation begins to reduce molecular weight, lower notched impact, and create odour and yellowing. In high-volume closure production, a melt-temperature window of approximately ±5 °C around 220 °C is often maintained to stabilise part weight, seal ring dimensions, and cycle time.

Shrinkage in injection-moulded HDPE 2907 is governed by crystallinity development and pack pressure. In-plane mould shrinkage for a 2.0 mm plaque is generally 0.018 mm/mm to 0.025 mm/mm under ASTM D955-21, depending on melt temperature, mould temperature, and holding pressure. Thicker sections may show higher centreline shrinkage and lower surface shrinkage; unbalanced cooling produces warpage. For closure ring diameters, a tolerance of ±0.05 mm is commonly achievable only with stable packing and post-mould cooling. Without post-mould cooling, ejection should occur at a part surface temperature below 70 °C to prevent dimensional drift during stacking and palletising. Mould-flow simulation of HDPE 2907 requires capillary rheometry data rather than a single melt flow rate. A Cross-WLF viscosity model is usually fit from data at 200 °C, 220 °C, and 240 °C. The pressure-volume-temperature model should be a two-domain modified Tait representation with crystallisation transitions near 124 °C to 130 °C. Without the PVT model, predicted packing pressure and shrinkage can deviate from measured values by more than 15 % in thin-wall sections.

Regulatory acceptance for food-contact packaging is established through the olefin polymer controls of 21 CFR 177.1520(c) when the material is used in direct contact with food. Specific conditions of use determine end-test compliance. For European food-contact applications, the grade is assessed under Commission Regulation (EU) No 10/2011; the overall migration limit of 10 mg/dm² applies to the final article. The resin is normally managed under REACH Regulation (EC) No 1907/2006 with no intentionally added substances of very high concern. For electrical and electronic applications, the material is not expected to contain restricted substances above the maximum concentration values in RoHS Directive 2011/65/EU. The following checklist is used for lot qualification and document control.

If poor surface gloss or jetting occurs in cold-runner systems

When cold-runner multicavity tools are started after a material change from a fractional-melt HDPE to HDPE 2907, the observed gate blush, jetting, or irregular gloss is frequently traced to residual high-viscosity melt in the runner system rather than to the incoming resin. The corrective sequence is a purge with a polyolefin-rated purging compound, followed by three to five barrel capacities of HDPE 2907 at a melt temperature of 220 °C. In hot-runner systems, the gate temperature should be set 10 °C to 20 °C above the nozzle temperature to prevent cold-slug formation. Jetting is often eliminated by reducing injection speed to 60 % or 70 % of maximum setting and by increasing gate land length or enlarging the gate diameter slightly. The resin is not hygroscopic in the manner of polyamides or polycarbonate; however, surface moisture on pellets stored above 60 % relative humidity can produce splay and silver streaks in thick-walled parts. Predrying in a desiccant dryer for 2 hours at 80 °C is recommended only when visible condensation or splay is present. Drying above 95 °C may cause pellet agglomeration in the hopper and feed throat bridging.

At melt temperatures above 245 °C, molecular weight may decrease through oxidative chain scission. Residence time should not exceed 12 minutes at 230 °C to limit odour, yellowing, and loss of notched impact. HDPE 2907 should not be blended with propylene-based polymers above approximately 5 wt% because incompatible melt phases can produce delamination and embrittlement in living-hinge or thin-wall closure applications. Outdoor exposure of unpigmented HDPE 2907 leads to chain scission and loss of elongation at break within 6 to 12 months under temperate conditions when tested with ISO 4892-2 UV-A exposure; parts requiring outdoor resistance must use a UV stabiliser package or a carbon black concentrate above 2 wt%. Warehouse storage should avoid direct sunlight and sustained temperatures above 40 °C. The grade is not recommended for continuous service at 80 °C or above because creep modulus and notched Izod impact decline rapidly as the melting region is approached. In applications involving hot detergent contact or aggressive surfactants, environmental stress-cracking resistance should be validated on the actual moulded closure under ASTM D1693-15, and creep should be measured under ISO 899-1:2017 at the intended service temperature. Published data for moulded HDPE 2907 parts under low-temperature impact below -30 °C is limited; ductile-to-brittle transition behaviour should be evaluated on production tooling before product approval.