Product designation Sinopec Fujian HDPE DMDB8916 identifies a high-density polyethylene blow moulding grade produced by Sinopec Fujian Refining & Chemical Company Limited. The resin is a bimodal ethylene-hexene-1 copolymer in which a high molecular weight fraction supplies melt strength and a lower molecular weight fraction contributes shear thinning during plastication. Commercial documentation lists a nominal melt flow rate of 0.8 g/10 min at 190 °C under 2.16 kg load when tested to ISO 1133-1:2022 and a nominal density of 0.956 g/cm³ when measured by ISO 1183-1:2019. The primary application envelope is extrusion blow moulding of containers between approximately 5 L and 220 L, including jerry cans, open-top pail bodies, drum liners, and industrial tight-head drums. The resin is not a pressure pipe grade and is not supplied with a hydrostatic design basis claim for buried service.

Rotational rheometry in nitrogen atmosphere at 190 °C shows a zero-shear viscosity in the range of 2.5 × 10⁴ Pa·s to 4.0 × 10⁴ Pa·s, with a pronounced reduction in complex viscosity at angular frequencies above 1 rad/s. This shear-thinning response is relevant to accumulator discharge and die lip pressure. Differential scanning calorimetry at 10 K/min reveals a crystalline melting peak near 132 °C and a crystallinity of approximately 60% to 65% estimated from heat of fusion. The broad relaxation time spectrum distinguishes DMDB8916 from single-reactor unimodal grades with the same density and melt flow rate.

Screw configurations with a barrier flight and a shear mixing section are preferred for DMDB8916. Grooved-feed sections with cooling jackets maintain solids conveying and prevent premature melting in the feed throat. Extruders with L/D ratios below 20:1 may produce incomplete plastication, appearing as star-pattern surface defects on the container sidewall. Extruders with L/D ratios above 30:1 increase residence time and may reduce molecular weight retention at melt temperatures above 210 °C. The grade is not hygroscopic, but when ambient relative humidity exceeds 60%, surface condensation on pellet surfaces can generate pinholes in thin-wall sections. Pre-drying for 2 h at 80 °C is recommended when condensation is visible.

How Does DMDB8916 Differ from Conventional Unimodal HDPE Blow Moulding Resins?

Unimodal chromium-catalysed HDPE resins typically require a reduction in density or a shift to lower melt flow rate to raise environmental stress cracking resistance. These adjustments increase cycle time and soften the finished container wall. DMDB8916 uses a bimodal molecular weight distribution to place comonomer-rich lower molecular weight molecules in tie-chain populations while retaining a high molecular weight fraction for load-bearing crystal networks. The resultant F50 environmental stress cracking resistance under ASTM D1693-B exceeds 600 h, whereas conventional unimodal blow moulding grades with a density near 0.956 g/cm³ and melt flow rate near 0.8 g/10 min frequently fall below 100 h. This difference is the principal reason the grade is selected for aggressive liquid packaging, including agricultural chemical containers and industrial solvent jerry cans.

A second distinction is shear response. Dynamic frequency sweep data from parallel-plate rheometry reveal that the crossover frequency for elastic and viscous moduli shifts to higher values than in unimodal grades, indicating a more shear-thinning melt during extrusion. On blow moulding lines equipped with 25:1 L/D grooved-feed extruders, this lowers motor current at equivalent throughput and permits lower head pressures at the die. However, the high molecular weight fraction also increases die swell. Tooling designed for unimodal HDPE may require parison programming adjustment to avoid excessive flash in the pinch-off zone.

DMDB8916 should not be confused with high-flow HDPE injection grades such as DMDA-8920 or DMDA-8007. Those products have melt flow rates under the same test condition of 8 g/10 min to 20 g/10 min and are designed for rapid cavity filling in thin-wall injection moulds. DMDB8916 is optimised for large parison blow moulding; its low flow index is necessary to maintain parison integrity and pinch weld strength. Use of an injection grade in blow moulding reduces parison hang time and produces excessive sidewall thinning under the preform weight.

Extrusion blow moulding equipment used for DMDB8916 typically consists of a grooved-feed extruder with a 20:1 to 30:1 L/D barrier screw and a parison programmer. Recommended melt temperature at the die exit is 180 °C to 200 °C; higher temperatures reduce melt viscosity but increase parison sag on large tools. Die gaps from 2.0 mm to 3.0 mm and blow pin pressures of 0.5 MPa to 0.8 MPa are typical starting conditions for 25 L to 60 L jerry cans. Mould temperature should be held between 10 °C and 20 °C to maximise surface gloss and shorten demould time. For thin-wall bottles below 2 L, DMDB8916 is generally not recommended because the high molecular weight fraction resists the rapid parison extrusion rates needed on high-cavity shuttle lines. The lower practical size boundary is around 5 L to 10 L, below which cycle time penalties and uneven wall distribution can appear.

When DMDB8916 is Processed on Accumulator-Head Machines for 200 L Industrial Drums

Accumulator-head blow moulding of 200 L tight-head drums imposes a requirement for dimensional stability during accumulator discharge and preform transfer. The parison for a 200 L drum body can exceed 900 mm in length and weigh 12 kg to 15 kg depending on wall thickness specification. The high molecular weight fraction in DMDB8916 reduces sagging during this transfer. Industrial processing guidelines include a die head temperature of 185 °C, an accumulator capacity of 25 L to 35 L, and a preform profiler set to increase wall thickness at the top and bottom chime sections to 4.5 mm to 5.5 mm while thinning the sidewall to 2.5 mm to 3.5 mm. Blow-in pressure of 0.6 MPa to 0.8 MPa and mould temperature of 15 °C are typical. The pinch weld line remains the critical flaw location; DMDB8916’s slow crack growth resistance reduces weld-line failure in drop testing when compared with higher-flow injection grades.

For dangerous goods packaging, drum performance is assessed under UN 1H2 criteria, including drop, leakproofness, hydraulic pressure, and stacking tests. DMDB8916 is used in drum bodies that must pass drop impacts at -18 °C and 1.8 m height, although final certification depends on drum design, closure, and wall thickness.

Food-contact status for DMDB8916 is based on the olefin polymer provisions of 21 CFR 177.1520 for high-density polyethylene. Compliance is also stated under EU 10/2011 with an overall migration limit below 10 mg/dm² for aqueous and acidic simulants at contact conditions appropriate to long-term ambient storage. The resin is not formulated with phthalates, bisphenol A, or heavy metal stabilisers. REACH candidate list SVHC content is below 0.1% w/w per article. Electrical and electronic applications are outside the primary use range, but the grade can satisfy RoHS 2011/65/EU restricted substance thresholds when processed without contaminated regrind.

Environmental Stress Cracking Resistance and Chemical Exposure Boundaries

The critical mechanical weakness of HDPE is environmental stress cracking in the presence of polar liquids, surfactants, and certain lubricants. DMDB8916 is characterised by a bimodal distribution that increases tie-molecule density. The F50 value under ASTM D1693-B in 100% Igepal CO-630 at 50 °C is reported above 600 h. This supports use in containers for agrochemical emulsifiable concentrates, non-ionic wetting agents, and mild oxidiser formulations. The chemical compatibility envelope remains that of high-density polyethylene: continuous exposure to strong oxidising acids, halogens, aromatic hydrocarbons, and higher aliphatic solvents is not recommended above 40 °C. Published permeation data for DMDB8916 in specific solvent systems are limited; qualification testing under ASTM D543 or EN 14477 is required for aggressive formulations.

Regrind addition must be controlled when thin-wall containers are specified for drop impact. Industrial evaluations indicate that up to 30 wt% clean in-house regrind from the same production lot can be incorporated without violating ASTM D2463 drop impact requirements for 5 L to 20 L bottles, provided the regrind is dried and screened through a 2 mm mesh. Higher regrind fractions reduce parison extensibility and increase gel counts in the sidewall. Black containers exposed to outdoor ultraviolet radiation should include a carbon black masterbatch at 2.0 wt% to 2.5 wt% carbon black content in the final wall because natural DMDB8916 has limited UV stabilisation. The grade should not be dry blended or compounded with high levels of acidic fillers at processing temperatures above 210 °C, as acidic species accelerate polymer degradation and reduce molecular weight retention.