DL Chemical HDPE 5502 is a high-density polyethylene extrusion resin assigned to blown film, sheet, and select blow moulding operations requiring high melt strength, elevated environmental stress crack resistance, and moderate rigidity. As disclosed in manufacturer technical literature, the nominal melt flow index is 0.25 g/10 min measured at 190 °C/2.16 kg using ISO 1133-1:2022, and the nominal density is 0.955 g/cm³ using ISO 1183-1:2019. The high-load melt index is commonly reported at 10 g/10 min under 190 °C/21.6 kg, yielding a melt flow ratio of approximately 40; this ratio indicates a broad molecular weight distribution and viscoelastic response that supports bubble stability in thin-gauge blown film. Compared with low-density polyethylene grades and conventional LLDPE film resins, the higher density of HDPE 5502 reduces water vapour transmission and increases flexural modulus, while its low MI raises die pressure and reduces melt draw compared with high-MI HDPE grades. The resin is not considered an injection moulding grade; its flow length under normal injection conditions is insufficient for thin-wall mould filling. These properties position HDPE 5502 for industrial liners, geomembranes, heavy-duty sacks, and moisture-barrier films where stiffness, chemical resistance, and downgauging are processing objectives. Published data for this specific configuration is limited in regional datasheets, so pre-production trials on target equipment remain necessary.

What Distinguishes HDPE 5502 from Commodity Blow Moulding and Film Resins?

The principal separation from general-purpose blow moulding HDPE grades appears in the melt flow index and molecular weight distribution. Commodity blow moulding resins with MI in the range 0.7–2.0 g/10 min produce lower head pressure and faster parison formation, but exhibit less melt strength and lower ESCR than HDPE 5502. When HDPE 5502 is run on a 65 mm grooved-feed extruder with L/D 30:1, the pressure before the screen pack is typically higher by 15–25 % relative to an MI 0.8 g/10 min HDPE at equivalent screw speed. This pressure differential must be accounted for in drive sizing; motors below 45 kW may approach overload during sustained output above 120 kg/h. Published data for this specific configuration is limited, but field reports from production lines indicate that bubble stability improves at film thickness below 25 µm because the higher melt strength resists draw resonance. In contrast to fractional-MI HDPE grades used in pipe extrusion, HDPE 5502 retains sufficient flow for die lip wetting at melt temperatures above 200 °C, although the upper melt temperature should not exceed 230 °C during normal runs to limit oxidative chain scission. Against LLDPE grades with octene or butene comonomer at MI 1.0 g/10 min, HDPE 5502 has lower dart impact at equivalent thickness but higher modulus and lower water vapour transmission. The seal initiation temperature difference is substantial: HDPE 5502 typically seals above 130 °C, whereas LLDPE seals at 105–115 °C; therefore HDPE 5502 is not a direct replacement for sealant layers without adjustment of jaw temperature and dwell time.

In comparison with an HDPE grade of melt index 0.5 g/10 min and density 0.953 g/cm³, HDPE 5502 is more viscous and less susceptible to moisture penetration; however, the lower MI reduces output on fixed screw-speed lines by approximately 8–15 % unless barrel temperatures are raised within the allowable operating band. Against a fractional-MI pipe grade with MI near 0.1 g/10 min, HDPE 5502 shows lower die swell and improved wall distribution in blow moulding, but lower long-term hydrostatic strength.

On cast film or blown film lines, the die gap and cooling configuration are controlling variables. For a 200 mm spiral mandrel die, starting die gaps of 1.2–1.6 mm allow film thicknesses between 20 µm and 100 µm without excessive draw resonance. The melt temperature measured at the adapter should be held at 200–220 °C; lower values increase die pressure and reduce output, while higher values cause bubble instability and surface oxidation. A blow-up ratio of 3.0:1–4.5:1 is a typical starting range for high-stalk operation; the stalk height should be set to 6–8 times die diameter before lateral expansion begins. Frost line height should be adjusted to 500–900 mm from the die face for gauges below 50 µm, depending on air ring and internal bubble cooling settings. If the frost line is lowered below 400 mm, the film may display elevated haze and reduced dart impact; if raised above 1000 mm, bubble sag and gauge variation increase. These values are operational starting points rather than certified limits, and production lines equipped with internal bubble cooling can run higher throughput at equivalent thickness.

Barrel Temperature Profiles, Screen Pack Pressure, and Melt Filtration Boundaries

Barrel temperature settings for HDPE 5502 on a single-screw extruder with grooved feed section are normally profiled from 170–190 °C in the feed zone, 190–210 °C in the compression zone, and 200–220 °C in the metering zone. The die and adapter are maintained at 200–215 °C. At these temperatures, the zero-shear viscosity is high enough to generate melt pressure between 250 bar and 450 bar ahead of a 100 mesh screen pack, depending on screw speed and output. Continuous operation above 450 bar is not recommended because the filter pack, melt pump, and die clamp may exceed mechanical limits. A breaker plate with 60/100/100 mesh screens is normally sufficient for removing agglomerates; finer filtration below 120 mesh may raise pressure without measurable improvement in gel count for general film. If screen pack pressure rises by more than 50 bar from a clean-baseline value, the screen pack should be replaced. Processing with degraded reprocessed granules can introduce black specks, which are not removed by filtration; they indicate upstream thermal degradation and require purging of the screw and barrel. Residence time at melt temperatures above 230 °C should not exceed 10 min; beyond this, chain scission increases melt index and reduces ESCR. For colour changes after running HDPE 5502, purging with a fractional-MI HDPE containing 1–2 wt% purge compound is preferred to solvent cleaning.

The environmental stress crack resistance of HDPE 5502 is typically characterised by ASTM D1693-21 using 10 % Igepal CO-630 and a 0.3 mm notched specimen. Manufacturer literature commonly lists F50 values above 1000 h, although this value is sensitive to moulded-in stress and sample preparation. In service, HDPE 5502 resists dilute mineral acids, aqueous alkalis, and polar solvents at ambient temperature, but the polymer is swollen by aromatic hydrocarbons, chlorinated solvents, and some vegetable oils; immersion in these media reduces tensile strength and accelerates environmental cracking. Continuous exposure to oxidising acids such as concentrated nitric acid above 40 % at temperatures above 30 °C is outside the recommended service window. UV resistance of unmodified HDPE is limited; outdoor geomembrane applications require 2–3 wt% carbon black masterbatch with a dispersion of ≤2 µm agglomerate size when tested on a pressure filter screen, and manufacturers typically specify 2.0–2.5 % carbon black content for long-term weatherability.

Resin storage should follow standard polyolefin practice. Bags or silos must be protected from rain and direct sunlight; prolonged UV exposure can generate surface oxidation and gel levels. HDPE 5502 does not normally require predrying, because moisture absorption at 23 °C/50 % RH is below 0.01 %. When bulk silos are exposed to temperature swings and relative humidity above 60 %, condensation on cold pellets can introduce surface moisture; in such cases, a desiccant or hot-air hopper dryer at 70–80 °C for 2–3 h restores bubble clarity. Extended storage beyond 12 months should be re-evaluated for melt flow shift and yellowing.

When HDPE 5502 Replaces LLDPE in Moisture-Sensitive Flexible Packaging

Switching a 3-layer coextrusion line from an LLDPE-rich formulation to HDPE 5502 modifies both barrier performance and sealing behaviour. The water vapour transmission rate of HDPE 5502 at 50 µm and 23 °C/85 % RH is lower than that of an LLDPE of equivalent thickness, though exact values depend on film orientation and test conditions under ISO 15106-3:2005. The oxygen transmission rate is higher than for EVOH or metallised PET, so HDPE 5502 is not a high-barrier oxygen layer; it functions as a moisture-barrier and stiffness component. Seal initiation temperature is shifted upward by approximately 15–25 °C compared with linear low density polyethylene, requiring seal jaw temperatures above 135 °C and dwell times of 0.5–1.0 s on standard impulse or constant-heat sealers. Surface treatment is required before printing or lamination; the film should be oxidised to a wetting tension of 38–42 mN/m measured by ISO 8296:2003. Because the low MI of HDPE 5502 reduces melt extensibility, coextruded layers should be kept above 10 µm to avoid localised thinning at die lips. Published data for this specific configuration is limited; line trials should evaluate seal strength, dart impact, and coefficient of friction under production conditions.

Representative physical and rheological values from manufacturer technical literature are collected below. These are nominal values and not batch guarantees; conditioning follows ISO 291:2008.

Food-contact suitability is governed by FDA 21 CFR 177.1520 for olefin polymers and by European Union Regulation (EU) No 10/2011 when used in final articles. The base resin is not a finished food-contact article; converters must validate overall migration and specific migration limits because additives and processing aids may alter compliance. Under REACH, the polymer as supplied does not require registration, but monomer and additive registrations apply. For electrical and electronic applications falling under RoHS 2011/65/EU, supplier declarations for unfilled HDPE typically report restricted substance concentrations below the maximum concentration values, but final component testing is required if flame retardants or metal pigments are introduced. The resin should not be incinerated or exposed to open flame without appropriate industrial emission controls; thermal decomposition above 350 °C may generate hydrocarbons, carbon monoxide, and carbon dioxide.

Additive compatibility is constrained by the stabiliser package. Fluoropolymer processing aids may be added at 200–500 ppm to delay melt fracture in high-output blown film lines; the addition must be purged with a fractional-MI HDPE before switching to other resins. Amine-based antistatic additives should be tested because they can interact with phenolic stabilisers and alter oxidative induction time measured under ISO 11357-6:2018. Metal stearates used as acid scavengers should remain below 500 ppm when corona treatment retention is critical; excess calcium stearate migrates to the surface and reduces dyne level decay time.