PetroChina Dushanzi HDPE DMDA-8008H is a high-density polyethylene injection-moulding resin produced by gas-phase polymerisation and supplied as pellets for rigid packaging, materials-handling, and consumer-durables conversion. The grade’s published product data list a nominal melt flow rate of 8.0 g/10 min at 190 °C under 2.16 kg load per ISO 1133-1 and a nominal density of 0.956 g/cm³ per ISO 1183-1. The product is positioned between fractional-melt blow-moulding high-density polyethylene and high-flow thin-wall injection grades, allowing medium- to long-flow filling without sacrificing the toughness required for industrial containers. Primary uses reported in supplier literature include crates, trays, pails, caps and closures, housewares, and toys. The following values are reproduced from the product’s published typical property sheet and are not batch-release specifications; the certificate of analysis for each delivered lot governs the production batch.

On a 350 t hydraulic injection-moulding press equipped with a 22:1 L/D general-purpose HDPE screw, a starting barrel profile of 190 °C/200 °C/210 °C/220 °C from feed to nozzle is commonly used. Melt temperature is maintained at 200–230 °C; mould temperature is typically 15–40 °C. Injection pressure of 70–110 MPa and holding pressure of 40–70 MPa are applied, with back pressure at 0.5–1.5 MPa. Screw speed is limited to 80–150 rpm to avoid shear overheating. Shot size is kept between 30% and 70% of barrel capacity, and melt cushion is held at 3–6 mm. Pellets exposed to relative humidity above 60% or visible moisture require drying at 80 °C for 2 h in a desiccant dryer; moisture content above approximately 0.05% can produce splay and reduce impact consistency.

How does the hexene-based comonomer structure alter toughness relative to butene-copolymer HDPE?

The supplier product data identify DMDA-8008H as a hexene-copolymer high-density polyethylene. The longer 1-hexene side chains increase the tie-molecule concentration between crystalline lamellae at equivalent density, which raises resistance to slow crack growth and low-temperature fracture. Under ISO 180/A, the grade retains notched Izod impact energies of approximately 6.5 kJ/m² at 23 °C and 2.5 kJ/m² at -20 °C; butene-based HDPE of similar density commonly shows 10–20% lower low-temperature notched Izod values. Environmental stress-crack resistance determined by ASTM D1693-B in 100% Igepal CO-630 at 50 °C is shifted upward for hexene-based injection grades; published data for comparable resins typically fall between 30 h and 80 h F50, but grade-specific values for DMDA-8008H should be requested from the supplier. The same molecular architecture can produce slightly higher die swell and orientation relaxation; therefore, filling speed and hold-pressure profiling may require adjustment when switching from butene-based HDPE.

When hot-runner manifold temperatures exceed 230 °C for more than five minutes

Thermal degradation of HDPE under melt processing follows free-radical chain scission rather than crosslinking. With DMDA-8008H, hot-runner setpoints are normally 200–230 °C. If manifold or nozzle zones exceed 230 °C and heated residence time exceeds 5 min, melt flow rate can drift upward by 5–15% relative to virgin pellets, and low-temperature impact strength declines. At melt temperatures above 260 °C, oxidation accelerates rapidly; at 280 °C, visible yellowing and acrid odour develop in less than 10 min. The maximum melt temperature for unpigmented thin-wall parts should therefore be 220 °C with a heated residence limit of 5 min; heavily pigmented industrial crates may tolerate 250 °C for up to 8 min, but impact and colour shift must be monitored. Purging with general-purpose polypropylene or ABS is acceptable. Purging with PVC or acetal should be avoided because corrosive decomposition products can damage hot-runner components. These stabilizer packages are processing antioxidants and do not qualify the material for continuous service above 80 °C in structural loading.

On a 1,600 t injection-moulding machine producing pallets with 3 mm nominal wall thickness, DMDA-8008H at 220 °C melt temperature and 30 °C mould temperature has been processed with clamp force of 3–5 t per projected square metre to prevent flash. Melt cushion is maintained at 5–8 mm, and holding pressure is set to 50–70% of filling pressure for 4–8 s. Gate freeze for 3 mm walls occurs at approximately 8–12 s; hold time beyond 15 s adds cycle time without meaningful weight gain. Gate lands below 1.0 mm can freeze before 10 s, causing sink marks over bosses. These observations are general HDPE injection-moulding practice and may vary with tool geometry and hot-runner balance.

Injection moulding screw and barrel temperature profile for DMDA-8008H

A three-zone general-purpose screw with compression ratio 2.5:1 and L/D of 20:1–25:1 is sufficient for unfilled DMDA-8008H. A barrier screw is recommended when clean regrind content exceeds 20% of the blend. The feed zone is set to 180–200 °C, compression zone to 200–220 °C, metering zone to 210–230 °C, and nozzle to 210–230 °C. For hot-runner tools, manifold and drop temperatures follow the same 210–230 °C band. Back pressure of 0.5–1.0 MPa is adequate for homogenisation; back pressure above 2.0 MPa raises melt temperature without improving part weight stability. Screw speed above 150 rpm can generate local melt temperatures above 240 °C and initiate chain scission, visible as silver streaks near the gate. Injection speed is profiled so that the flow front reaches the end of fill in 0.5–1.5 s for 2 mm walls; fill times below 0.3 s in thick bosses can cause jetting and internal voids.

Capillary rheometry data for comparable 8 g/10 min HDPE injection grades indicate shear-thinning behaviour over the reciprocal-seconds range encountered in injection moulding. At low shear rates the melt is more viscous than high-flow 20 g/10 min grades, but at gate shear rates above 10,000 s⁻¹ the difference narrows. Thin-wall filling is therefore better improved by raising injection velocity rather than melt temperature. Excess temperature increases cooling time and cycle time without a proportional reduction in filling pressure. For hot-runner valve-gated tools, the valve stem should close after pack pressure has decayed, not at high pressure, to avoid strings and gate vestiges.

For materials-handling crates and trays, stacked-load creep is a more restrictive design criterion than short-term tensile yield. Creep is evaluated according to ISO 899-1 or ISO 899-2, and stack tests for HDPE crates are commonly conducted at 40 °C for 28 days. The flexural modulus of 1,150 MPa supports thinner grid ribs and corner bosses, but the typical mould shrinkage of 1.6–2.2% requires compensation in the tool cooling layout and gate geometry. Crate tools with 2.5 mm nominal wall thickness usually require gate lands of 1.0–1.5 mm and cold-runner diameters of 6–8 mm for multi-cavity filling. If melt temperature falls below 190 °C, viscosity rises and peripheral cavities may short-fill; if melt temperature exceeds 230 °C, shrinkage and warpage increase because of slower crystallisation under residual heat.

Differentiation from lower-flow and higher-flow HDPE grades appears in the property-to-flow envelope

DMDA-8008H is separated from blow-moulding and sheet-extrusion HDPE grades by its higher melt flow rate, which reduces injection energy and increases cavity count. It is separated from high-flow injection grades by lower melt flow rate and higher notched impact and stress-crack resistance. Table 2 presents a generic comparison based on published industry data for representative lower-flow, mid-flow, and higher-flow HDPE injection grades. The lower-flow and higher-flow values are not batch certificates for any specific product and should be confirmed by the alternate supplier before substitution.

When replacing a lower-flow HDPE with DMDA-8008H, cavity-to-cavity imbalance often improves because the lower melt viscosity reduces pressure loss in hot-runner drops. However, gate freeze may occur later, requiring an increase in hold time of 1–3 s to avoid sink marks. When replacing a higher-flow HDPE with DMDA-8008H, clamp force and injection pressure may increase for the same part because the level of shear thinning is lower; process simulation using the grade’s viscosity curve should be run before tool transfer. For moulds with flow length-to-wall thickness ratios above 200:1, melt temperature should be shifted to the upper end of the permitted range and injection speed increased rather than adding excessive pack pressure.

Clean regrind generated from sprues, runners, and rejected parts is normally blended with virgin DMDA-8008H at 20–30% by weight for non-food and non-child-contact articles. Each regrind pass raises melt flow rate by approximately 5–10% because of chain scission and reduces low-temperature impact slightly. When regrind exceeds 30%, the melt flow rate of the blend should be measured before production start-up, and the mould holding pressure may require a 3–5% reduction to prevent flashing. Sifting of fines and metal separation are required to protect check rings and hot-runner tips. In food-contact articles, regrind use is governed by the same migration limits as virgin material under EU Regulation 10/2011 if the regrind is uncontaminated and obtained from the same production line.

In food-contact conversion, grade-specific compliance must be obtained from the supplier because polymerisation aids, neutralisers, and antioxidants vary by production line. High-density polyethylene olefin polymers are referenced in 21 CFR 177.1520 with extractable limits in 177.1520(c). In the European Union, overall migration is limited to 10 mg/dm² under EU Regulation 10/2011 using the migration test conditions appropriate for the intended food simulant and contact time. For caps and closures, organoleptic carryover and hydrocarbon permeation should be evaluated according to EN 1622 or equivalent methods. DMDA-8008H is not a polypropylene and should not be specified for repeated autoclave cycles above 121 °C because the crystalline melting range of HDPE is approximately 130–135 °C.

In caps and closures, the melt flow rate of 8.0 g/10 min permits high-speed injection with cycle times of 6–12 s in multi-cavity tools. The grade’s flexural modulus allows reduced thread deformation during demoulding, but ejection should be verified because HDPE can stick to polished cores. Surface lubrication is not required for simple cap profiles; if external lubricants are used, they should be selected to avoid stress cracking in the hinge area. Closure performance tests normally include torque retention and seal integrity under ASTM D2063 or ASTM D3198 depending on the finish and liner system.