NOVA Chemicals HDPE D916-39 is a pelletized high-density polyethylene grade intended for injection molding and selected thick-wall extruded profiles. The grade is described in the supplier’s product range as an ethylene–α-olefin copolymer with a controlled short-chain branch distribution, which places it between a homopolymer HDPE and a medium-density polyethylene in slow-crack growth resistance. The model designation D916-39 is not a specification by itself. Incoming lot certificates, supplier technical data sheets, and retained samples are required for source approval because additive package and molecular weight distribution can change without a change in the model code. The processing and performance boundaries described below are written for tooling engineers, quality managers, and compounders who must compare D916-39 with other HDPE products without relying on abbreviated product descriptors.

What Specification Values Define D916-39 Against ASTM and ISO Baselines?

Initial classification is made through density and melt mass-flow rate. Representative values are drawn from the grade-class technical envelope; the actual lot certificate controls commercial release. Density at 23 °C is normally stated in the 0.939–0.941 g/cm³ band under ASTM D792-20 or ISO 1183-1:2019. Melt mass-flow rate at 190 °C and 2.16 kg is normally reported in the 0.28–0.32 g/10 min band under ASTM D1238-20 or ISO 1133-1:2022. These values are not independent specifications; they are typical values with tolerable lot-to-lot variation.

These ranges are not to be used as final article specifications. They are class-typical values and must be replaced by the current supplier lot certificate for commercial release. Density is determined after specimen conditioning under ASTM D618-21 because polyethylene can densify slowly after molding.

Injection Molding Barrel Temperatures, Screw Recovery, and Gate Freeze Limits

Injection molding of D916-39 requires control of barrel residence time because the melt is shear-sensitive and prone to oxidative degradation at elevated temperature. A four-zone reciprocating-screw profile is typically set at 180 °C, 190 °C, 200 °C, and 210 °C, with nozzle temperature at 220 °C. Melt temperature measured by a probe should remain between 200 °C and 230 °C; sustained operation above 260 °C causes chain scission, yellowing, and a drop in notched impact strength. Mold temperatures in the 20–40 °C range are adequate. Turbulent coolant flow is required; designers should maintain a Reynolds number greater than 10,000 in mold channels to prevent asymmetric part cooling.

Reciprocating screws with L/D from 20:1 to 24:1 and compression ratio from 2.5:1 to 3.0:1 are appropriate. Screw-recovery time should be shorter than the mold-cooling phase; if screw recovery extends beyond cooling by more than 2–3 s, rear zone temperature or screw speed should be trimmed. Back pressure from 0.3–0.7 MPa improves shot-size repeatability but excessive back pressure raises melt temperature and increases residence time. Non-return valve clearance must be checked against the machine manufacturer’s tolerance; diametral clearance greater than 0.05 mm on a 30–60 mm screw can produce short shots and erratic cushion position.

Filling speed should be profiled to keep flow-front velocity below 300 mm/s in thin ribs, gates, and hinge areas. For thick-section containers, injection pressure at transfer is commonly 70–100 MPa, with holding pressure at 60–80% of that transfer pressure. Gate freeze must occur before hold pressure removal. A 3 mm nominal wall may require 4–6 s gate-freeze time, while a 6 mm wall may require 15–25 s. Short-shot and melt-front studies should replace any generic calculation when the tool contains hot runners or multiple gates.

Cavity pressure sensors are recommended when qualifying D916-39 in multi-cavity tools. Peak cavity pressure for a filled part should be repeatable within ±5% shot-to-shot; if the coefficient of variation exceeds 5%, check the non-return valve and the screw cushion. The cushion should be maintained between 3 mm and 6 mm to avoid loss of hold pressure at the injection-to-hold transition. Melt filtration is not normally required for virgin D916-39. If regrind is added, a screen pack or magnetic separator is used before the feed throat; regrind fraction should not exceed 20% without a full property-retention study because molding history reduces molecular weight distribution and can darken the part.

D916-39 is used in solid-wall industrial containers, crates, totes, and material-handling parts where environmental stress-cracking resistance and low-temperature impact are acceptance criteria. The comonomer distribution reduces susceptibility to slow crack growth compared with a 0.950–0.965 g/cm³ homopolymer. Field experience on a 350 t hydraulic injection molding machine molding a solid-wall crate showed acceptable fill at a hot-runner manifold temperature of 215 °C; reducing the manifold to 195 °C while keeping the same injection speed produced flow lines and a short shot at the far wall. The same tool required a longer cooling time than a high-flow HDPE because the lower melt mass-flow rate of D916-39 increased melt temperature and reduced melt stiffness at ejection. Published data for this specific configuration is limited; tooling trials remain mandatory.

Post-mold dimensional checks should follow ASTM D618-21 with conditioning at 23 °C and 50% RH for 24–48 h. Mold shrinkage is anisotropic; typical values are 1.5–2.0% in the flow direction and 1.8–2.5% transverse for unfilled HDPE. Parts with wall thickness above 4 mm may continue shrinkage for 48 h; stackable containers should be gauged after the longer conditioning interval to avoid false rejection.

Color concentrates based on low-MFR HDPE or LLDPE carriers are preferred. High-MFR carriers can move the melt front too quickly and produce jetting; carrier loadings above 4% should be tested for ESCR because some hydrocarbon carriers plasticize the polymer and reduce stress-cracking resistance. Avoid amine-based antistatic additives that can generate odor or promote surface tack. If antistatic performance is required, a non-ionic or cationic additive in a polyethylene carrier should be evaluated at 1–3% addition; no published data for D916-39 with amine-based antistatic agents is available.

When D916-39 Replaces a Homopolymer or Fractional-Melt HDPE in Multi-Cavity Tools

The principal replacement scenario is the substitution of a homopolymer HDPE or a fractional-melt HDPE in an existing tool. Homopolymer HDPE with density above 0.950 g/cm³ gives higher flexural modulus and lower raw-material cost, but it is more likely to crack at ejector-pin locations and sharp bosses when the part is dropped or exposed to aggressive cleaning agents. D916-39’s density near 0.939 g/cm³ reduces crystallinity and modulus by roughly 5–10% while improving ESCR and notched impact. That trade is acceptable in returnable transit packaging; it is not acceptable when a tight dimensional tolerance must be maintained under load because the lower modulus increases creep under long-term stacking load.

When replacing a fractional-melt HDPE pipe grade with MFR below 0.15 g/10 min, D916-39 lowers injection pressure and permits filling of ribs and bosses that would otherwise freeze before the melt front arrives. However, it may not match the long-term hydrostatic strength or slow-crack resistance of a dedicated pipe grade. When converting from a high-flow injection grade with MFR 9–40 g/10 min, D916-39 demands more clamp force, slower injection, and longer recovery, but yields better weld-line strength and stress-cracking resistance. The change should be assessed by molding a nine-cavity or sixteen-cavity tool at the same clamp force and comparing peak cavity pressure, cushion, and short-shot behavior under identical barrel settings.

Although D916-39 is classified as an injection-molding grade, it is occasionally used in thick sheet or profile extrusion. In those cases, melt strength is lower than that of a fractional-melt HDPE, and the sheet may sag on a three-roll stack if melt temperature exceeds 230 °C. Air-knife assistance at the roll gap and a roll temperature of 70–90 °C are used to maintain sheet gauge. Published data for extrusion of this specific configuration is limited, so a capillary rheometry sweep under ISO 11443:2021 is recommended before line trials.

Food-contact evaluations must account for the finished article, not the resin alone. Olefin polymer requirements are listed in 21 CFR 177.1520(c); final extractives testing under the appropriate conditions of use is required. European Union food-contact applications require migration testing under Regulation (EU) No 10/2011, with the overall migration limit of 10 mg/dm² unless a specific derogation applies. REACH registration obligations attach to the substance or mixture at import or production; SVHC content above 0.1% w/w in the article triggers communication duties. RoHS Directive 2011/65/EU is generally outside the scope of unfilled HDPE industrial crates, but customer-specific heavy-metal limits should be verified by X-ray fluorescence screening on the compounded pellet and on the molded part.

Storage and drying constraints apply. HDPE is not hygroscopic, but surface condensation on pellets transferred from cold silos into a warm molding area can produce moisture-related splay. If hopper inlet air exceeds 80% RH or the pellet surface temperature is below the dew point, use a desiccant dryer at 80 °C for 2 h with a dew point of -20 °C or lower. The melt should not be held above 280 °C; barrel residence times above 10 min are not recommended. Purging should use a similar MFR polyethylene; PVC and acetal are unsuitable purge materials because their degradation products can corrode the screw and contaminate the shot. Shutdown procedures should include running the barrel down to a lower temperature and purging with a thermally stable polyethylene if the line will remain idle for more than 24 h. For outdoor crates and totes, UV stabilization must be added at the converter level unless the supplier provides a pre-compounded UV-stabilized version. Unstabilized D916-39 exposed to long-term UV will undergo surface oxidation, gloss loss, and eventual microcracking. If outdoor service exceeds 3–5 years, a hindered amine light stabilizer package at 0.2–0.5% and a UV absorber should be evaluated by accelerated weathering under ASTM G154-23 or ISO 4892-3:2016. Published data for weathering of this exact grade is limited.