LyondellBasell HDPE ALATHON M5370 is a high-density polyethylene copolymer intended for heavy-gauge sheet extrusion, industrial thermoforming, and large-part blow molding. The grade is specified with a nominal density of 0.953 g/cm³ when tested to ASTM D1505 or ISO 1183-1:2019 and a melt flow rate of 0.70 g/10 min at 190 °C under a 2.16 kg load when tested to ASTM D1238 or ISO 1133-1:2022. These two values place the product in a relatively high-molecular-weight HDPE processing band; the flow rate is lower than typical injection-molding HDPE but higher than fractional-melt extrusion grades. Consequently, the material is selected where a converter must hold a large parison or wide sheet without excessive sag while avoiding the high head pressure and melt fracture limitations of grades with flow rates below 0.30 g/10 min.

Mechanical property data published for this grade cluster around a tensile yield strength of 28 MPa as measured by ASTM D638-14 and a secant flexural modulus of approximately 1,200 MPa when tested according to ASTM D790. These stiffness values make the grade suitable for rigid industrial panels, pallet sheets, and chemical containment structures that require creep resistance under static load. The copolymer nature of the resin, inferred from its density below 0.960 g/cm³, contributes to slow crack growth resistance compared with density-equivalent homopolymers. An environmental stress-crack resistance value above 600 h under ASTM D1693 Condition B is often reported for this resin class; specific lot data must be confirmed from the certificate of analysis.

These values are typical lot averages and should not be interpreted as specification minima. For critical barrier or structural applications, a converter should request a product specification sheet and establish incoming inspection limits using the same specimen preparation and conditioning procedures referenced in the standard methods.

What Distinguishes Alathon M5370 from Lower-Melt-Index HDPE Grades in Sheet and Blow Molding?

Compared with HDPE grades having a melt flow rate near 0.30 g/10 min, ALATHON M5370 produces lower die pressure at equal screw speed and reduces start-up torque on 60 mm to 75 mm single-screw extruders. This is a direct consequence of the higher melt flow rate; however, the resin retains a broad molecular weight distribution that maintains shear-thinning behavior and melt strength during sag-sensitive operations. In blow molding, the practical difference appears as a longer allowable parison hang time before draw-down tears, while in sheet extrusion it appears as a wider processing window between melt fracture and excessive drawdown. Compared with high-MFR injection-molding grades above 10 g/10 min, the lower flow rate of ALATHON M5370 gives better hot-melt coherence, lower short-shot tendency in thick sections, and improved stress-crack resistance because of a higher entanglement density.

The melt flow ratio between standard 2.16 kg and 21.6 kg loads, an indirect indicator of molecular weight distribution breadth, should be obtained from the supplier for this grade. For similar broad-MWD HDPE copolymers, values in the range of 50 to 80 are not unusual; published data for this exact product is limited, and the melt flow ratio alone does not replace rheological testing on a capillary rheometer or a parallel-plate oscillatory rheometer. Rheologically, the zero-shear viscosity of high-molecular-weight HDPE such as ALATHON M5370 is high enough to maintain parison integrity, but the broad molecular weight distribution lowers high-shear viscosity. Capillary rheometer tests at 190 °C and apparent shear rates from 100 s⁻¹ to 1,000 s⁻¹ are more useful than MFR alone for die design.

Compared with linear low-density polyethylene sheet of melt index 1.0 g/10 min, ALATHON M5370 provides higher flexural modulus and better high-temperature load resistance, but lower impact toughness at sub-zero temperatures. The notched Izod impact transition is not as flat as an LLDPE; therefore, applications requiring ductile impact below -20 °C should verify low-temperature impact behavior according to ASTM D256 or ISO 180.

On a production 75 mm barrier-screw extruder with a 30:1 L/D and a 60/100/60 mesh screen pack, head pressure for this melt-flow class can remain below 24 MPa at outputs near 200 kg/h. If head pressure rises above 24 MPa, the first diagnostic step is to check the screen pack differential pressure and the melt thermocouple rather than increasing barrel temperature uniformly. Local overheating above 240 °C can initiate oxidative chain scission and produce gel particles in the sheet. Residence time at temperatures above 240 °C should not exceed 5 min; longer residence times can create carbonized specks and gel defects that are visible in thin-gauge thermoformed parts.

Die lip settings for heavy-gauge sheet are commonly held 10% to 15% above the target sheet thickness to accommodate drawdown. Excessive drawdown can orient the sheet in the machine direction, producing anisotropic shrinkage; converters should verify shrinkage according to ASTM D2732 or ISO 11501. On a three-roll stack, the middle roll is usually operated at 80–100 °C and the lower roll at 70–90 °C; roll pressure and surface finish then control sheet curl and gloss. Regrind addition above 30 wt% may lower ESCR and increase gel count, so extruders running high regrind ratios must monitor melt pressure stability and screen-pack lifetime at intervals shorter than 8 h.

When Die Head Pressure Rises Above 24 MPa

The condition is most frequently observed when screens become partially blinded, when the die gap is too narrow, or when melt temperature falls below 195 °C. The corrective sequence begins with a 5 °C increase in the metering zone and die zones, followed by a throughput reduction of 5% to 10% while observing the pressure trend. If the pressure remains above 24 MPa at reduced throughput, the screen pack should be replaced and the screen mesh sequence reviewed. A gear pump can decouple die pressure from screw speed, but it must be operated with a suction-side pressure of 5–10 MPa; lower suction pressure may cause cavitation and surge, while higher suction pressure may overload the pump seals. Die land lengths shorter than 10 times the final sheet thickness can raise shear rate and induce sharkskin melt fracture on sheet surfaces. In that case, increasing die width in combination with a higher melt temperature inside the allowed window is preferred over raising temperature alone.

ALATHON M5370 is not inherently UV stabilized. For outdoor sheet, geomembrane, or white-bodied industrial parts, a carbon black masterbatch at 2.0–2.5 wt% is the usual starting point; dispersion quality should be assessed according to ISO 18553 or ASTM D5596. Poor carbon black dispersion creates surface specks and can reduce weathering performance even when the average carbon black content is within specification. In combination with carbon black, a hindered amine light stabilizer package may be required for long-term outdoor exposure; the stabilizer selection must be validated by accelerated weathering according to ASTM D2565 or ISO 4892-2 and correlated with outdoor exposure data.

Avoid prolonged contact with strong oxidizing acids such as concentrated nitric acid, chlorinated hydrocarbons at elevated temperature, and aromatic solvents under load because these agents can swell the amorphous phase of the HDPE and accelerate environmental stress cracking. For chemical containment applications, a specific chemical resistance assessment should be conducted under the intended service temperature and stress. The standard gravity and melt flow rate of this grade do not constitute a chemical resistance rating; the converter must verify compatibility using the chemical exposure protocol relevant to the end use.

Sheet produced from ALATHON M5370 is typically thermoformed at sheet-surface temperatures between 160 °C and 180 °C. A surface-temperature spread greater than ±3 °C across the forming area produces uneven draw and corner thinning; therefore, tunnel ovens with independently controlled zones are preferred. At temperatures below 150 °C, deep-draw parts may crack at the corner radii; above 190 °C, the sheet may sag and stick to the oven mesh. Cavity vacuum in the range of 500–700 mbar with plug-assisted pre-stretch is common for heavy-gauge HDPE; plug materials and plug temperature interact with the sheet's yield stress and can alter wall-thickness distribution more than vacuum level alone.

In accumulation-head blow molding of large containers, the die temperature is typically maintained at 200–220 °C while the mold is held at 10–20 °C. Parison programming with a diverging die gap of 1.2–1.5 times the initial gap is used to account for swell. Blow pressure of 0.6–0.8 MPa is common for HDPE containers with wall thickness above 4 mm; lower pressure can result in poor replication of the mold surface and excessive weld-line visibility.

Compliance Matrix for Food-Contact and Industrial Converters

Food-contact authorization is not automatic from the resin supplier; the converter must consider the entire formulation, including regrind, masterbatch, processing aids, and surface treatment residues. LyondellBasell product stewardship bulletins should be requested for the specific grade and production location because additive packages may vary by plant.

For extrusion operations, the barrel and die should be purged before processing ALATHON M5370 if the previous material was a lower-density polyethylene or a polar copolymer. A 5–10 kg purge with a viscous HDPE transition grade followed by a 30 min run at stable melt temperature reduces cross-contamination. The screw should not be left idle with the barrel heated above 200 °C for more than 15 min because stagnant melt can undergo thermal oxidation and create black specks in the next start-up. These operational limits are widely used on sheet and blow-molding lines but should be adapted to the specific extruder design and residence time characteristics.