LDPE Grade Codes You Meet in Trade: 20 Codes and Where Each Goes

Low-density polyethylene (LDPE) is a branched polyolefin produced by high-pressure radical polymerization; its density normally falls between 0.910 g/cm³ and 0.935 g/cm³ when tested by ISO 1183-1:2019 or ASTM D1505. The trade codes encountered in distributor paperwork, purchase orders, and resin warehouse systems are not harmonized, but they commonly identify melt flow rate at 190 °C/2.16 kg and a density class. A converter that selects an LDPE grade by code alone without checking producer-specific melt flow rate, density, and additive package may encounter bubble instability, excessive backpressure, or seal-temperature defects. The reference below identifies 20 LDPE grade codes regularly met in trade and the downstream process to which each is normally routed.

What Does the Four-Digit Nomenclature Actually Encode?

European LDPE designations such as 2420D, 2426H, and 3020H use a producer-specific shorthand. In the LyondellBasell Lupolen system, the first digit typically classifies density, the following digits approximate melt flow class, and the terminal letter identifies a sub-grade or additive variant. No ISO or ASTM standard defines the decoding of commercial LDPE grade codes. A 2420D and a 3020D may both have an MFR class near 0.2–0.5 g/10 min, yet the 3020D has a higher density and is generally used for higher-stiffness industrial film. Similarly, a code ending in K usually indicates a higher-flow extrusion coating grade, but only the synthesis route and molecular architecture determine neck-in and draw-down behavior. Melt flow rate is measured by ISO 1133-1:2022 or ASTM D1238, but it does not quantify long-chain branching, molecular weight distribution, or melt strength.

Table 1 compares nominal MFR and density classes for 20 commonly traded LDPE designations. MFR is measured at 190 °C/2.16 kg. The values are producer-bulletin typicals, not specification limits; certificates of analysis control at lot level.

The table shows a pattern: low-MFR grades with nominal melt flow not more than 0.5 g/10 min are heavily skewed toward heavy-duty film and sacks, while grades at 3.5–4.5 g/10 min are skewed toward extrusion coating. Density shifts from 0.915 g/cm³ in high-clarity shrink film toward 0.928 g/cm³ in industrial liners produce measurably higher modulus but lower optical clarity and higher seal initiation temperature.

Blown Film Grade Selection and the Property Window

Low-MFR film grades 2420D, 3020D, 955, and HP0323NN are typically processed on monolayer blown film lines with die diameter 200–400 mm, die gap 0.8–2.2 mm, and blow-up ratio 2.0:1–3.0:1. The low MFR class of 0.2–0.5 g/10 min yields high melt strength but raises backpressure and requires screw L/D 24:1–30:1. Melt temperature is usually maintained at 170–190 °C; above 200 °C, oxidative gel formation can reduce dart impact as measured by ISO 7765-1:2019 or ASTM D1709. Heavy-duty sacks produced from 2420D and 3020D commonly target thicknesses of 80–150 µm and require tear and puncture values controlled by ISO 6383-2 and ASTM D5748.

Medium-flow film grades 2420H, 2426H, 3020H, 722, 748, HP2023J, and LD 100AC are selected for high-output packaging lines. On a 90 mm single-screw extruder with L/D 24:1, melt temperature is typically set at 160–180 °C and frost line height at 1.5–2.0 die diameters. These settings balance haze, measured by ISO 14782 or ASTM D1003, against dart impact. Thin-gauge liners from 748 with an MFR class of 2.5–3.5 g/10 min generate lower head pressure but may exhibit bubble flutter if air-ring velocity is poorly controlled.

Shrink grades 2420H, 4016, 959, and LD 150BW are processed with lower melt temperatures and controlled cooling. A grade such as 4016 with MFR class 1.5–2.0 g/10 min is run at 160–180 °C and BUR 2.0:1–2.5:1, then passed through shrink tunnels at 120–150 °C. Shrink force and percentage are characterized by ISO 14616 or producer-specific methods. Long-chain branching supplies strain-hardening and melt strength; regrind addition above 20% may degrade the branching network and reduce shrink force.

Extrusion coating lines specify LDPE 2426K, 3020K, and HP4023W where thin-gauge draw-down, heat seal, and low neck-in are required. The polymer is extruded through a slot die onto paperboard, foil, or oriented film at 280–320 °C to generate adhesion through surface oxidation; many lines add ozone dosing in the air gap. Chill roll temperature is held at 15–25 °C. For a 1,000 mm die and coat weight 15–25 g/m², neck-in below 50 mm per side is typical for these MFR classes. Coating weight uniformity is tested by ISO 3892 or producer-specific beta-gauge procedures. Paperboard moisture above 6% can create blisters and lower adhesion; preheating is used when line speed exceeds 200 m/min.

Injection molding uses LDPE 1800S and 501I for overcaps, closures, housewares, and masterbatch carriers. LDPE is not specified for hot-fill or structural parts because the heat deflection temperature under 0.45 MPa is below 50 °C according to ASTM D648. These grades process on machines with clamp force 500–1,500 kN, melt temperature 180–220 °C, and mold temperature 20–40 °C. The high-flow 1800S fills thin walls but has lower environmental stress crack resistance than low-MFR film grades. Linear mold shrinkage is commonly reported from 1.5% to 3.0% and should be measured by ISO 294-4 or producer-specific methods.

When Melt Flow Index Alone Cannot Specify a Grade

ISO 1133-1:2022 and ASTM D1238 measure melt mass-flow rate under a fixed load, but they do not measure molecular weight distribution or long-chain branching. Two LDPE lots with the same MFR class can differ in extruder amperage, die swell, neck-in, and melt strength. In extrusion coating, a broader molecular weight distribution may draw to 10–15 µm coat weight without edge tearing, while a narrower distribution may require higher melt temperature or die gap adjustment. Oscillatory shear rheometry—storage modulus, loss modulus, and crossover frequency—provides more useful process characterization than MFR alone. Gel permeation chromatography is rarely available in converting plants, so capillary viscosity and Rheotens melt strength data are used for grade substitution decisions.

This practical limitation explains why resin distributors separate film, extrusion coating, and injection molding grades even when nominal MFR values overlap. It also explains why processing trials remain necessary after any supplier change, despite a code match.

Food-contact use of film and extrusion coating grades in Table 1 requires lot-specific compliance with FDA 21 CFR 177.1520 and EU Regulation 10/2011. Overall migration for plastic food-contact articles under EU 10/2011 is limited to 10 mg/dm²; specific migration limits depend on the slip, antioxidant, and processing aid package. Industrial LDPE grades may not carry food-contact certification. Converters must obtain supplier declarations for REACH and RoHS when products are exported. No grade code alone establishes compliance; certificates of analysis and conformity statements must accompany each lot.