Marlex HHM 5502BN vs HXM 50100: Which HDPE Blow Grade for Which Bottle

In extrusion blow moulding of high-density polyethylene containers, the comparison Marlex HHM 5502BN vs HXM 50100: Which HDPE Blow Grade for Which Bottle is resolved through a small set of material variables: melt flow rate, density, flexural modulus, environmental stress crack resistance, and parison melt strength. Neither resin occupies a universal position. HHM 5502BN is specified where short parisons, fast cycles, and wall-thickness reduction are dominant constraints. HXM 50100 is specified where continuous chemical exposure, tight closure torque, and pallet load require slow crack growth resistance. The following sections define the boundaries between those two application classes.

What separates the two grades at the molecular and rheological level?

Typical published datasheet values place HHM 5502BN at a density of 0.955 g/cm³ and a melt flow rate of 0.35 g/10 min under ASTM D1238 at 190 °C/2.16 kg. HXM 50100 is typically reported at 0.950 g/cm³ and 0.10 g/10 min under the same load. The lower density of HXM 50100 reflects a higher comonomer content designed to increase tie-molecule density and resistance to slow crack growth. The lower melt flow rate corresponds to a higher viscosity average molecular weight, which increases parison sag resistance on large machines but also raises head pressure and can reduce output if the extruder lacks torque capacity.

Environmental stress crack growth in HDPE is a slow craze-crack propagation process accelerated by surface wetting agents, residual moulded-in stress, and crystallinity. Higher molecular weight and comonomer distribution in HXM 50100 increase tie-molecule density. HHM 5502BN has a higher density and modulus but fewer tie molecules, so it can pass short-term top-load tests yet fail after 30–90 days of stressed contact with aggressive fluids.

The mechanical consequence is directional: HHM 5502BN shows higher stiffness, with published flexural modulus values near 1,380 MPa (ASTM D790) and tensile yield near 29 MPa (ASTM D638). HXM 50100 exhibits lower stiffness, typically near 1,240 MPa and tensile yield near 26 MPa, but its ESCR is reported at >600 h under ASTM D1693 Condition B, 100% Igepal, against a much lower value of 40–50 h for HHM 5502BN. That difference is the critical transition: the higher-modulus grade is not the automatic choice when the bottle is subjected to clamping force, closure torque, and aggressive liquid contact.

On a reciprocating-screw blow moulder with a 24:1 L/D screw and 45 mm diameter, HHM 5502BN is commonly processed at melt temperatures of 176–204 °C. The shorter parison length permits cycle times determined mainly by cooling rather than sag resistance. For HXM 50100, the same machine may require melt temperatures of 190–226 °C and an accumulator or grooved-feed section to maintain throughput at the lower melt flow rate. Published capillary rheometry data for HXM 50100 at 230 °C and apparent shear rates above 1,000 s⁻¹ are limited in open datasheets; processing trials therefore rely on parison sag measurement and die lip adjustment rather than on a single viscosity curve.

Die gap and blow pressure separate the two grades on the shop floor. HHM 5502BN typically runs with die gaps of 0.5–1.5 mm depending on bottle wall thickness, while HXM 50100 large-part tooling frequently uses die gaps of 1.5–3.0 mm to manage heavy parison swell and prevent melt fracture. Blow pressure on production equipment is usually 0.6–0.9 MPa, with mould temperatures held at 10–25 °C. Surface splay from condensation is avoided by pre-drying at 70–80 °C for 2 h when storage humidity exceeds 60 % RH. On production-scale grooved-feed extruders, the die-entry pressure differential is typically measured as 18–28 MPa for HHM 5502BN and 28–38 MPa for HXM 50100 in identical tooling, reflecting the difference in viscous heat generation and shear stress.

Parison programming is used to compensate for die swell and sag. HXM 50100, with a heavier parison, requires axial programming with 10–25 points for cylindrical large containers; the die gap is opened at the top and bottom to control pinch-off weld thickness. HHM 5502BN runs with fewer programming points because the parison length is shorter and sag is less critical. In both cases, the programming curve is validated by section-weight analysis of a cut preform, not by visual wall thickness alone.

Small-bottle top-load, wall thickness, and lightweighting trade-offs

Where the cavity is below 2 L and the filling line requires top-load resistance in unfilled bottles, HHM 5502BN is selected because its higher flexural modulus allows a thinner sidewall to carry the same vertical load. For a cylindrical bottle, the critical top-load force is proportional to the effective hoop and axial modulus multiplied by the square of wall thickness at constant radius. The modulus differential between 1,380 MPa and 1,240 MPa permits a wall-thickness reduction of roughly 8–12% while maintaining equivalent buckling resistance. That reduction translates directly into part mass and cycle time, but only when the chemical fill does not require high ESCR.

Typical package examples include household cleaners with low surfactant aggressiveness, certain cosmetic and personal-care bottles, and non-aggressive industrial liquids where the bottle is not exposed to continuous stress at the pinch-off seam. In these applications, HHM 5502BN is processed with a neat or lightly re-ground feedstock; the faster crystallisation associated with higher density and lower molecular weight shortens cycle time, but moulds must be cooled uniformly to avoid warpage at the base and handle pinch-off. Titanium dioxide at 2–4 wt% is often added for opacity and can nucleate HDPE, changing shrinkage by a few tenths of a percent; tooling dimensions must be adjusted accordingly.

Thread and closure performance also follows the modulus difference. HHM 5502BN retains cap torque better at 2–3 N·m on a 28-mm neck, but may crack if the cap is overwound against a plug seal. HXM 50100, with its lower modulus, can exhibit thread yielding under the same torque unless the neck wall is thickened or an insert is used. These are secondary considerations to ESCR, but they determine whether a lightweighted package survives distribution.

At volumes above 10 L, and particularly in jerrycans and tight-head containers, parison sag becomes the first process limit. HXM 50100 is used because its higher melt strength supports a heavier parison over a longer shot without thinning at the top of the mould. The blow ratio and part length impose different stress states than a small bottle: the pinch-off tail, handle weld, and closure neck become stress concentrators where slow crack growth can initiate. Under ASTM D1693 Condition B, HHM 5502BN reaches failure at 40–50 h, while HXM 50100 exceeds 600 h; this is the reason bleach, agricultural emulsifiable concentrates, and solvent-based cleaners are directed away from HHM 5502BN when container volume and closure torque increase.

Real-world failures in this class often present as environmental stress cracking at the neck or bottom pinch-off after filling, not as a burst during blow moulding. Closure torques of 2.5 N·m on a 28-mm neck and pallet loads of 400 N on lower tiers are sufficient to sustain constant tensile stress in the bottle wall. HXM 50100 is formulated to resist the resulting slow crack propagation. The trade-off is a softer part: if a 5-L jerrycan requires a specific top-load specification, the wall thickness or sidewall geometry must be increased relative to HHM 5502BN, adding mass. For a 20-L jerrycan with 2.0 mm average wall thickness, a top-load of 500 N is often a pass/fail criterion. HXM 50100’s lower modulus requires a wall increase of roughly 0.2 mm to match the stiffness of HHM 5502BN at the same geometry.

When the closure torque and pallet load make ESCR non-negotiable

This section addresses the decision path for containers that combine moderate volume, aggressive filling liquids, and high stacking load. HXM 50100 is specified when the container must survive a 14-day stressed-immersion test or bottle ESCR evaluation under ASTM D2561 at the neck and pinch-off areas. The higher molecular weight and lower density reduce crack propagation, but they also require verification of top-load after filling because stiffness decreases as density drops from 0.955 to 0.950 g/cm³. When a bottle is designed with snap-on caps, high-integrity tamper-evident necks, or post-consumer recycled content above 10–15%, additional lot-to-lot ESCR testing is required, because the stress-crack performance of HXM 50100 can shift with molecular weight distribution and regrind content.

On the filling line, HXM 50100 containers are more tolerant of line stoppages and hot filling up to 60 °C in some configurations, but they are not universally approved for all solvent mixtures: aromatics and ketones can still swell HDPE and reduce the retained ESCR. Published data for this specific resin combination in high-aromatic solvent contact is limited, so compatibility testing follows the final package, not the resin alone. In automated filling, superficial damage from guide rails and clamping jaws can reduce the practical ESCR below the resin datasheet value; line trials should therefore include stressed crack testing of filled bottles after three-axis compression and cap torque.

Color concentrates and UV stabilizers also interact with the molecular weight distribution. Carbon black at 2–3 wt% in HXM 50100 is common for agricultural containers stored outdoors; it provides UV protection but may reduce weld-line integrity if the concentrate carrier has a lower melt flow index. The processor should pre-disperse the concentrate at the feed throat and avoid allowing the melt temperature to fall below 190 °C at the die, because undispersed pigment agglomerates can initiate slow crack growth.

Table 1. Published typical datasheet values for the two blow-moulding grades.

Values are published typical values; they are not specification limits and should be confirmed against the producer’s certificate of analysis for each lot.

Regulatory compliance for both grades is generally established under FDA 21 CFR 177.1520 as olefin polymers, but the final article must be tested for end-use extraction because pigments, processing aids, and regrind alter migration. EU Regulation (EU) No 10/2011 requires article-specific migration testing; resin-level compliance does not transfer automatically. REACH and RoHS declarations are supplied by the resin manufacturer. No data supports selecting one grade over the other purely on regulatory grounds; the selection is governed by mechanical and chemical constraints.

In a 20-L agricultural chemical container with a 2.0-mm nominal wall, fluorinated surface treatment may be added for solvent permeation control; the base resin remains HXM 50100 because post-treatment surface crosslinking does not restore ESCR lost to lower molecular weight. When a 500-mL personal-care bottle is filled with a low-surfactant emulsion, HHM 5502BN is retained and the tooling is cut for a thinner wall to meet an empty-bottle top-load of 180 N.