High-density polyethylene grade DSM HDPE SB21 is a high-molecular-weight extrusion blow molding resin used for large closed-head and open-head containers, industrial drums, jerry cans, and intermediate bulk container liners. The product is defined in commercial technical literature by a density of 0.954 g/cm³ (ISO 1183-1), a melt flow rate at 190°C/5 kg of 1.9 g/10 min (ISO 1133-1), and a high-load melt index at 190°C/21.6 kg of 21 g/10 min. The low-load melt index at 190°C/2.16 kg is approximately 0.30 g/10 min; the ratio of high-load to low-load melt index is approximately 70, indicating broad molar mass distribution and strong shear thinning. In extrusion blow molding that rheological character reduces parison sag and permits larger shot sizes on accumulator-head machines without loss of wall-thickness uniformity.

Typical large-part blow molding lines use barrel temperatures of 180°C to 220°C and a die head temperature of 190°C to 210°C. The melt temperature at the head should be held between 190°C and 230°C; exposure above 240°C for extended residence time accelerates oxidative chain scission and reduces environmental stress crack resistance. Mold temperatures are normally set from 10°C to 30°C, with cooling circuits concentrated near the pinched-off neck and handle areas. HDPE is not hygroscopic and pre-drying is not normally required; regrind containing external moisture should be dried at 80°C for 2 h before use.

Accumulator-head equipment for 20 L to 1000 L containers is typically configured with screw diameters of 80 mm to 120 mm, length-to-diameter ratios of 24:1 to 30:1, and a barrier or pin mixer to minimize melt-temperature variation. Head pressure in the accumulator is commonly 20 MPa to 35 MPa. The die gap is set between 1.5 mm and 4 mm for finished walls of 1.5 mm to 5 mm. Parison die swell is typically 25% to 45%; axial thickness programming increments of 0.2 mm to 0.6 mm are used to compensate for swell and sag. Blow air pressure of 0.6 MPa to 0.8 MPa and mold venting at the bottom pinch-off are standard. Shot sizing should use melt density rather than solid density. At 190°C to 230°C, HDPE melt density is approximately 0.75 g/cm³; a container designed with a solid-wall mass of 2.0 kg therefore occupies about 2.7 L of melt volume. These parameters are not batch-specific for SB21 and should be verified on the conversion line because accumulator volume and screw configuration alter residence time.

What Distinguishes SB21 from High-Flow Injection HDPE at the Melt Level?

High-flow injection molding HDPE grades are formulated with low-load melt indices at 190°C/2.16 kg from 4 g/10 min to 20 g/10 min and lower melt strength. By contrast, SB21’s low-load value of approximately 0.30 g/10 min is not appropriate for thin-wall injection melt filling. The high-load value of 21 g/10 min at 190°C/21.6 kg indicates that the material becomes sufficiently fluid only at the high shear rates common in blow molding. The resulting flow rate ratio of about 70 is much higher than that of typical injection HDPE and correlates with elevated zero-shear viscosity, longer terminal relaxation time, and greater extensional viscosity. These are the properties that stabilize a hanging parison. In capillary rheometry at 190°C, the melt shows shear thinning across apparent shear rates from 10 s⁻¹ to 1000 s⁻¹; no public capillary curve is provided for SB21, and published data for this specific configuration is limited. A direct substitution into injection molding would require higher hold pressure, higher melt temperature, and shorter flow length.

Environmental stress cracking resistance and chemical service boundaries. Under ASTM D1693 condition B with 100% Igepal CO-630, supplier technical literature reports F50 values for SB21 in the range of 40 h to 80 h. High-flow HDPE injection grades often fail below 5 h under the same test, but the comparison is only qualitative. ASTM D1693 uses a bent notched strip under constant strain and does not predict service life in a formulated product. For aggressive fluids, full-scale testing according to UN 6.1.5.2 is required. Hot filling or continuous storage above 60°C reduces ESCR and increases creep; wall thickness and corner geometry must be evaluated accordingly. HDPE is not suitable for prolonged contact with strong oxidizing acids, aromatic hydrocarbons, or halogenated solvents. These fluids can plasticize or swell the surface and reduce the hydraulic failure limit. In such service, fluorination or a multilayer barrier structure is required; SB21 alone is not sufficient. Clean in-house regrind may be added up to 30 wt%, but higher levels lower notched impact and ESCR. Contamination with polypropylene or EVOH should be prevented because it produces delamination and weld-line defects.

Representative physical property values for DSM HDPE SB21 are shown below. They are not batch release specifications and should be confirmed against the active certificate of analysis.

Quality control on incoming resin should monitor melt flow rate, density, and contamination. A temperature-controlled melt indexer with calibrated die dimensions per ISO 1133-1 is sufficient to detect gross viscosity shifts. Density is checked by gradient column or gas pycnometer according to ISO 1183-1. In production, the most frequent defect associated with high-molecular-weight HDPE grades is a weak pinch-off weld. The pinch-off land should be 3 mm to 6 mm wide, with mold compression of 2 MPa to 4 MPa at the flash tail; a sharp pinch induces notch-like stress concentration that reduces ESCR. Accumulator short-shot instability can appear when hydraulic shot volume is below 1.1 to 1.3 times the part volume, causing wall-thickness oscillation. These conditions are corrected by increasing shot size, adjusting parison programmer curve, and verifying accumulator head fill pressure.

Thermal-oxidative stability and regrind survival. The stabilizer package is designed for multiple-pass extrusion, but the exact number of acceptable regrind cycles is not provided in public technical literature. Melt flow rate shift after five passes of a typical HDPE blow molding grade can exceed 20%; for SB21, no published multipass dataset is available. Plant trials with 30 wt% clean in-house regrind are usually possible without loss of container drop performance. Above 30 wt%, lower ESCR and gel accumulation become measurable. The accumulator head should be purged when melt temperature overshoots 240°C or when color change is required; stagnant melt in dead zones can form degraded flecks that appear in the pinch-off weld. For thick-wall parts, cooling time for a 5 mm HDPE wall is often 60 s to 90 s depending on mold temperature and air pressure. The part should be ejected below 80°C at the pinch-off area to avoid post-mold deformation.

Container Design, Testing, and Regulatory Compliance Checklist

Compliance status of a converted container depends on the complete formulation and processing history, not only the base resin. The base polymer is typically assessed against FDA 21 CFR 177.1520(c) for olefin polymers and European Union food-contact Regulation (EU) No 10/2011. For food-contact articles, the overall migration limit is 10 mg/dm² under the intended food-simulant conditions. EU 10/2011 uses simulant A (10% ethanol), simulant B (3% acetic acid), simulant D2 for fatty foods, and simulant E for dry foods; not all articles are tested in all simulants. Dangerous goods containers require the applicable UN performance tests for plastic drums or jerricans, commonly 3H1 or 3H2 designs, including hydraulic pressure, drop, stacking, and leakproofness. Outdoor grades must be UV-stabilized with carbon black masterbatch at 2 wt% to 2.5 wt% or a suitable hindered amine light stabilizer package; accelerated weathering can be evaluated under ISO 4892-2. If the container is used in electrical or electronic equipment, RoHS restrictions apply only to added colorants and stabilizers; heavy-metal pigments are not automatically excluded by the base HDPE.

The material is not intended for pressure piping. PE100 HDPE grades are qualified against ISO 9080 and carry a minimum required strength of 10 MPa at 50 years; SB21 has no published pipe-grade hydrostatic classification. Rotomolding is also outside the intended use because SB21 is supplied as pellets with a melt index and particle morphology unsuitable for low-shear powder sintering. These limitations define the application envelope and avoid substitution errors in multi-product plants.

The comparative position of SB21 against other HDPE product classes is summarized below using typical commercial ranges. Values are not batch specifications for the compared grades.

These differences mean that SB21 cannot be treated as a drop-in replacement for injection grades. It has the melt strength to hold a 20 L to 1000 L parison, but it requires the high-load melt index to keep extrusion back pressure manageable. A lower-viscosity blow HDPE has lower ESCR and may require higher wall thickness to pass chemical stress cracking tests. The choice of SB21 over a general-purpose blow HDPE is driven by regulatory drop tests, chemical resistance, and large-part wall uniformity, not by tensile strength alone.

For continuous outdoor use, UV stabilization and antioxidant levels must be selected for the intended climate. Containers made from SB21 should not be exposed to constant hydrostatic pressure at temperatures above 60°C without creep testing. The practical upper service limit is determined by accumulated creep strain, chemical attack, and UV embrittlement rather than a single Vicat temperature.