LLDPE M500026 and M200024: Decoding the Newer Multi-Digit Grade System

Linear low-density polyethylene continues to be ordered through producer-specific designation systems, but the migration to longer multi-digit identifiers has changed the data that can and cannot be read from a grade code. In M500026 and M200024, the alpha prefix identifies the linear polyethylene platform, while the numeric sequence carries flow and density information in a producer-defined arrangement. The structure is not an ISO classification and does not replace certificate-of-analysis evaluation under ISO 1133-1:2022 or density determination under ISO 1183-1:2019. The leading numeric digit usually corresponds to the nominal melt mass-flow rate decade, the middle two-digit block is generally assigned to stabilizer or processing-package variation, and the trailing 3-digit block is commonly a density-related code expressed in kilograms per cubic metre above 900 kg/m³. Because different producers can assign different meanings to the same positional block, incoming resin control must verify the code rather than assume equivalence.

Published technical bulletins for these grades describe M200024 as a blown film resin with a nominal melt mass-flow rate of 2.0 g/10 min at 190°C under 2.16 kg and density near 0.924 g/cm³. M500026 is positioned at a nominal 5.0 g/10 min and density near 0.926 g/cm³. These values are typical nominal figures, not specification limits; lot-to-lot variation within the producer’s published ranges requires confirmation against the incoming certificate of analysis. The processing discussion below demonstrates why the lower-flow M200024 and higher-flow M500026 are not interchangeable in applications where melt strength or injection pressure defines the operating window.

How Should the Multi-Digit Code Be Read Without Legacy Short-Code Assumptions?

Legacy LLDPE short codes frequently compressed melt flow rate and density into two or three characters. The newer designations represented by M200024 and M500026 introduce an additional positional block between the flow indicator and the density indicator. In the producer nomenclature, the leading numeric digit is not an absolute melt index; it is a nominal decade indicator that must be confirmed by ISO 1133-1:2022 at 190°C and 2.16 kg. The middle 00 block should not be interpreted as zero functionality. In this system, it commonly identifies a base stabilizer and processing package variant rather than a comonomer change. The trailing 024 and 026 blocks are density-directional codes, not direct substitutes for density measurement by ISO 1183-1:2019 or ASTM D1505.

Comonomer type cannot be inferred reliably from the grade number alone. Butene, hexene, and octene copolymers can all be produced within the same nominal density envelope, but their branch lengths differ and affect tear resistance, sealing behaviour, and stiffness. Verification requires supplier polymerization data supported by differential scanning calorimetry, ASTM D792 density, or infrared compositional analysis. Table 1 summarizes the positional interpretation of the two multi-digit codes as manufacturer-specific ordering logic, not as public specification values.

Incoming resin verification should therefore separate code logic from physical property measurement. A release certificate may list the grade code and the measured melt mass-flow rate, density, and additive package. Without that document, the multi-digit identifier is insufficient for lot qualification because the coding system is not harmonized across producers or across different polyolefin families within the same producer.

On a 55–75 mm single-screw extruder with a 30:1 L/D groove-fed barrel and a die gap of 0.8–1.2 mm, M200024 can be processed with melt temperature between 185°C and 210°C. Blow-up ratio is typically held at 2.2–2.8, with frost line height controlled between 300 mm and 450 mm above the die. Under these conditions, the lower nominal melt mass-flow rate of 2.0 g/10 min supports bubble stability in monolayer film above 35 µm. Dart impact is evaluated according to ASTM D1709-15 Method A, and tear propagation is determined by ASTM D1922-15. Production-scale observations on grooved-feed lines show that increasing internal bubble pressure above 0.5 kPa without adjusting the frost line can generate width oscillation, while die land temperature below 175°C can raise melt pressure and promote gel formation. Pre-drying is not normally required at ambient relative humidity below 60%; above 75% RH, surface moisture should be removed by hopper drying at 45–55°C for 2 h. Excessive melt temperature above 240°C should be avoided because it can oxidize the polymer and increase taste-and-odour risks in food-film applications.

The main process conflict for M200024 is the balance between frost line height and tear anisotropy. A high frost line above 500 mm can raise machine-direction orientation and reduce Elmendorf tear in the transverse direction, while a frost line below 250 mm can reduce bubble cooling and create blocking in wound film. Coefficient of friction should be monitored by ASTM D1894 when slip and antiblock additives are present. Published data for this specific resin configuration is limited for ultra-wide lines above 1.2 m die diameter, and pilot trials are required before committing to full production.

If M500026 Is Selected for High-Speed Thin-Wall Injection Moulding

Where cycle time reduction outweighs melt strength retention, M500026 with a nominal 5.0 g/10 min melt mass-flow rate is used in thin-wall injection moulding of caps, closures, and technical articles. On an injection moulding machine with clamp force of 100–150 tonnes and a 20:1 L/D general-purpose screw, barrel temperature zones are normally set from 180°C at the feed throat to 230°C at the nozzle. Holding pressure between 30 MPa and 50 MPa, backpressure below 10 bar, and screw rotation speed of 80–120 min⁻¹ are used to avoid excessive shear heating. The higher flow path reduces injection pressure in multi-cavity tools with wall thickness below 1.5 mm, but tensile elongation measured by ISO 527-2:2012 is typically lower than that of M200024, and the material should not be specified where ASTM D1709 impact resistance below -20°C is required.

Mould shrinkage measured by ASTM D955-08 is normally below 2.5%, but shrinkage differs in flow and transverse directions and must be validated on the intended tool geometry. Mould release agents based on zinc stearate are generally acceptable, but amine-containing purging compounds should be avoided because they can discolour polyolefins and interfere with downstream organoleptic acceptance. For food-contact and pharmaceutical closures, compliance must be confirmed under FDA 21 CFR 177.1520 or EU Regulation 10/2011, and the grade code alone does not establish specific migration limits.

Rheological differentiation between M500026 and M200024 is not limited to melt flow rate. Capillary rheometry at 190°C over shear rates from 100 s⁻¹ to 1000 s⁻¹ shows that the higher-flow M500026 exhibits a steeper viscosity decrease under shear, whereas M200024 retains a broader Newtonian plateau. In coextruded structures, the melt viscosity mismatch at 230°C can cause interfacial instability when the M500026 layer exceeds 30% by mass. Published data for this specific interface is limited, and pilot trials should be conducted on the intended layer structure before full production.

For packaging applications, compliance must be confirmed on the specific grade and lot under EU Regulation 10/2011 with migration testing per EN 1186-1:2002. A multi-digit grade code does not itself establish global migration or specific migration limits. Additive depletion and organoleptic thresholds should be evaluated with the supplier’s compliance statement, not inferred from the numeric designation. In multilayer blown film and injection-moulded barrier systems, the grade code is a starting point for material selection; the processing window, additive limits, and regulatory conformity must be confirmed independently before release to production.