PetroChina Fushun HDPE DMDA-8008 is supplied as an injection moulding grade of high-density polyethylene produced at the Fushun petrochemical complex. The pelletized resin has a nominal melt flow rate of 8.0 g/10 min when tested at 190 °C under 2.16 kg load in accordance with ISO 1133-1:2022, and a nominal density of 0.956 g/cm³ determined according to ISO 1183-1:2019. The grade designation DMDA-8008 is a commercial resin designation; the trailing digits identify the nominal melt flow rate class and should not be used as a specification. The product is intended for injection moulded articles such as thin-walled pails, dairy crates, caps, housewares, and industrial containers where rapid filling and a controlled balance of stiffness and impact strength are required.

The values listed are typical release data, not guaranteed specifications. Lot-specific certificates of analysis should be reviewed before production. Commercial injection moulding grades from the Fushun site are commonly controlled within ±0.2 g/10 min of the nominal melt flow rate and ±0.002 g/cm³ of the nominal density; however, actual process capability data are site-specific and should be confirmed with the resin producer.

What Distinguishes DMDA-8008 from Lower-Flow High-Density Polyethylene Grades?

The principal difference between DMDA-8008 and lower-flow HDPE grades is the relationship between molecular weight and processing behaviour. Lower-flow injection grades with melt flow rates near 4.0 g/10 min require higher injection pressure and often exhibit short-shot defects in thin sections, but they typically retain higher notched impact strength and improved environmental stress crack resistance. Blow-moulding grades with melt flow rates of 0.3–0.5 g/10 min develop sufficient melt strength for parison hang, but their high viscosity prevents reliable filling of complex, thin-wall injection moulds at commercial cycle times.

In DMDA-8008, the 8.0 g/10 min melt flow rate reduces hydraulic injection pressure requirements relative to a 4.0 g/10 min grade, often by 15–30% for equivalent part geometry. This reduction is design-dependent and should be verified with in-mould pressure transducers rather than inferred from melt flow rate alone. The lower molecular weight also reduces cycle time through faster plastication and shorter cooling requirements, but the trade-off is lower melt strength and reduced resistance to slow crack growth.

Because DMDA-8008 has a lower molecular weight than blow-moulding grades, environmental stress crack resistance is correspondingly lower. Converters evaluating pails or containers for detergent, oil, or aqueous surfactant solutions should test the finished article under ASTM D1693-15e1 or ISO 22088-3:2006. A 10% Igepal CO-630 solution at 50 °C is a common screening medium. No ESCR guarantee is included in the base resin datasheet, and the material may be unsuitable for aggressive liquid packaging without barrier or design modification.

Comparisons with isotactic polypropylene homopolymer are also encountered in cap and crate applications. Polypropylene homopolymer generally has lower density and higher heat deflection temperature, but many PP homopolymers exhibit lower notched impact strength at low temperature than HDPE. The quoted 4.0 kJ/m² Izod impact value for DMDA-8008 at 23 °C should not be extrapolated to freezer or sub-zero service. For articles used below 0 °C, the finished part must be impact-tested because HDPE impact strength decreases as temperature declines.

Melt Temperature, Screw Design, and Residence-Time Constraints

Injection moulding of DMDA-8008 requires control of melt temperature and shear history because the relatively high melt flow rate lowers melt viscosity and can allow excessive screw recovery speed. A melt temperature between 200 °C and 240 °C is normally suitable. Barrel settings from feed to nozzle are commonly programmed at 180 °C, 200 °C, 220 °C, and 220–230 °C. Mould temperature should be maintained at 15–40 °C for rapid cooling. Mould temperatures above 60 °C can improve surface gloss and weld-line strength but extend cycle time by increasing cooling demand.

General-purpose reciprocating-screw machines with screw L/D ratio of 20:1 to 24:1 and compression ratio of 2.5:1 are appropriate. Low-shear metering sections are preferable to high-shear barrier mixing elements because high shear can generate melt temperatures above the barrel set point. The check ring should be sized for free flow. If screw recovery time is longer than 5 s, plastication is not limiting; if recovery exceeds cooling time, the cycle is controlled by plastication. On a 2,500 kN clamp-force machine moulding 60 g pails, screw diameters of 70–90 mm are typical, with hydraulic injection pressures of 130–180 MPa and hold pressures of 60–100 MPa.

Residence time is a critical boundary. At melt temperatures above 240 °C, thermal-oxidative degradation can occur within 10–15 min. Degradation may be indicated by nozzle bubbling, yellowing of the purge, or an increasing melt flow rate. If a machine interruption exceeds 15 min, the barrel should be shifted to 150–160 °C standby. If purging is required, a general-purpose HDPE with a melt flow rate of 2–5 g/10 min can be used. Halogenated purging compounds or abrasive purging formulations should not be used unless approved by the manufacturer.

Drying is not normally required because HDPE is not hygroscopic. If regrind or pellet surfaces have been exposed to relative humidity above 60% RH, surface moisture can cause splay. A hopper dryer set to 80 °C for 2 h is adequate for regrind; fresh pellets are usually dry as supplied. Regrind addition should be limited to 20 wt% of the blend for visual and impact performance. Higher regrind levels can alter molecular weight distribution through repeated shear history, increasing the risk of brittle impact behaviour.

Fill speed should be maximized within the capability of the machine but not exceed the velocity at which gate blush or jetting occurs. For thin-walled mouldings, injection velocity at the screw plunger is typically set between 80 mm/s and 150 mm/s; actual linear melt velocity through the gate is geometry-dependent. In-mould pressure transducers can be used to maintain short-shot-free filling at a peak cavity pressure of 30–50 MPa while avoiding overpacking.

When DMDA-8008 Is Used in Thin-Walled Crates and Pails

Thin-walled dairy crates and pails represent the primary application field for DMDA-8008. The 0.956 g/cm³ density provides sufficient flexural modulus for stacking loads, while the 8.0 g/10 min melt flow rate permits filling of wall sections down to 1.2 mm at practical injection speeds. Typical mould shrinkage in the flow direction is 1.5–2.0%, with transverse shrinkage of 1.0–1.5%. These ranges depend on wall thickness, mould temperature, and packing pressure. Warpage in flat crate bottoms is minimized by uniform cooling and by maintaining core-to-cavity temperature differentials below 10 °C.

For high-speed pail moulds with 4 or 6 cavities, hot-runner manifold settings should not exceed 230 °C. Manifold dead spots can trap material for extended periods, creating black specks and localized degradation. Gate design should provide shear heating at the gate but not excessive viscous dissipation. A gate diameter of 0.8–1.2 mm is commonly used for side-gated pails of 1–3 L capacity, but gate dimensions must be confirmed by mould filling simulation and short-shot studies.

Mechanical testing of crates and pails produced from DMDA-8008 is typically performed under ISO 12048:1994 for stacking compression and GB/T 4857.3-2008 for vertical compression. Drop impact of filled pails should be assessed using ASTM D2463-15 or customer-defined drop-height protocols. Published data for specific crate geometries are limited, but the isotropic flexural modulus of 1,150 MPa predicts useful top-load capacity for a 30 L crate with a 3.0 mm wall. Actual compressive strength must be measured on the finished part because failure often initiates at corners, handles, or weld lines.

Food-contact suitability is a regulatory issue, not a property of the polymer alone. The base resin may be used in food-contact applications only if the finished article meets FDA 21 CFR 177.1520(c) for polyethylene, EU Regulation (EU) No 10/2011 with its overall migration limit of 10 mg/dm², and China’s GB 9685-2016 for food-contact additives. A converter must verify the additive package and production hygiene. Natural DMDA-8008 does not contain ultraviolet stabilizer; outdoor exposure requires a UV-stabilized grade or carbon black masterbatch at a level sufficient to meet the specified accelerated weathering rating under ISO 4892-2:2013.

Chemical compatibility boundaries should be established before container use. DMDA-8008 is resistant to many aqueous solutions, dilute acids, and alkalis, but aromatic hydrocarbons, chlorinated solvents, and strong oxidizing agents can cause swelling or stress cracking. Containers for oxygen-sensitive products should not rely on HDPE without a barrier layer because the oxygen transmission rate of HDPE at 23 °C and 0% RH is high relative to barrier polymers. A metallocene or ethylene-vinyl alcohol barrier layer is required for oxygen-sensitive contents. Industrial articles should also be checked for compliance with REACH and RoHS Directive 2011/65/EU at the finished-article stage, since restrictions apply to the final composition rather than the base resin alone.