Low-density polyethylene grade 2426H is designated in converter specifications as LDPE 2426H: The Film Grade Behind Everyday Packaging. The resin is produced by high-pressure free-radical polymerization, which introduces short-chain and long-chain branching; the resultant molecular architecture provides the extensional strain hardening required for bubble stability in blown film extrusion. Melt flow index measured according to ISO 1133-1:2022 at 190 °C with a 2.16 kg load is reported as 1.9 g/10 min. Density measured according to ISO 1183-1:2019 is 0.924 g/cm³. The combination of a low melt flow index and a density below 0.925 g/cm³ places 2426H in the film extrusion envelope used for general-purpose packaging, heavy-duty sacks, carrier bags, and collation shrink film. The grade is also used in lamination film where a low seal initiation temperature is required. These applications depend on the capacity of the melt to form a stable bubble at high blow-up ratios while retaining dart impact resistance and tear propagation resistance in the final film.

What Melt Rheology Establishes the 2426H Processing Window?

Blown film processing of 2426H depends on shear-thinning behavior in the die and extensional viscosity in the bubble. Capillary rheometry at 190 °C with a 1.0 mm die and 20:1 L/D ratio shows that apparent shear viscosity for this melt-flow class falls from approximately 900–1,500 Pa·s at 100 s⁻¹ to 250–450 Pa·s at 1000 s⁻¹. The broad molecular weight distribution typical of high-pressure LDPE produces a power-law index in the shear-thinning region of 0.35–0.45. That index is not a data sheet value but is calculated from the logarithmic shear stress versus shear rate curve. High extensional viscosity is essential for maintaining bubble geometry between the die exit and the frost line. Insufficient strain hardening at high draw speeds manifests as bubble breathing, gauge bands, or complete bubble collapse on lines producing film thinner than 25 µm.

In production-scale extrusion, 2426H is processed on single-screw extruders with a smooth-barrel feed section, screw L/D ratio of 24:1 to 30:1, and barrier mixing sections. Melt temperature measured by an immersion thermocouple at the die entrance is maintained between 160 °C and 200 °C. Reduced temperatures below 150 °C cause unmelts and torque fluctuations, while elevated temperatures above 220 °C accelerate thermal-oxidative chain scission and gel formation. Die gap settings of 1.2 mm to 2.0 mm and blow-up ratios between 2.0:1 and 3.5:1 are reported across monolayer and coextruded lines. Frost line height is adjusted between 2 and 6 die diameters to control orientation balance. A high frost line promotes transverse direction orientation and improves dart impact retention, while a low frost line stabilizes the bubble but may increase film gauge variation. On a 90 mm single-screw extrusion line with L/D 30:1 running at 250 kg/h, melt pressure fluctuations above ±2% typically correspond to film thickness variation exceeding ±5%. Operators then reduce screw speed until die pressure stabilizes, which lowers throughput below the nameplate capacity of the line.

Heavy-duty sack film made from 2426H at 120 µm gauge is processed with lower bubble stability but higher retained dart impact than thinner carrier bag film. Converters commonly blend 10–20 wt% linear low-density polyethylene into the core layer to raise dart impact at the expense of optical clarity. The blend is fed by separate gravimetric dosing units and mixed in the extruder rather than dry-blended in the hopper. Gravimetric feeding accuracy of ±0.5% is necessary to keep melt flow index and gauge distribution within the specification window. Batch-to-batch variance in 2426H is typically low; however, converters report that different production campaigns vary in slip-additive response because the resin is supplied without a fully formulated additive package. Therefore, downstream masterbatch addition must be validated for each silo lot on a laboratory blown film line before full-scale production.

When High-Slip Formulations Shift Coefficient of Friction in Multilayer Structures

Surface friction for 2426H packaging film is not an intrinsic resin property; it is controlled by migrating slip additives and mineral antiblock particles compounded by the converter at masterbatch dilution ratios between 2% and 5%. The kinetic coefficient of friction for a 50 µm film measured after 24 h ageing per ASTM D1894-24 typically targets 0.10–0.30. Erucamide and oleamide are the primary amides used. Migration rate follows concentration-dependent diffusion through the film cross-section. At 500 ppm erucamide in the film, the coefficient of friction reaches equilibrium within 24–72 h at 23 °C. At 1000 ppm the time is shortened, but haze may increase above 10% as the amide crystallizes on the surface. Addition of 5–10 wt% silica antiblock masterbatch with a 2 µm median particle size reduces blocking, but it lowers coefficient of friction only when slip is present. Excess antiblock above 15% masterbatch loading is associated with visible die buildup and local thickness defects caused by plate-out on the die lips.

In multilayer coextrusion, the slip package for 2426H is usually confined to the sealant layer, not the core or outer layer. The outer layer is often corona treated and printed; high slip levels in the outer layer can reduce ink adhesion. Corona treatment level is measured per ASTM D2578-23 and maintained above 38 dyn/cm for water-based flexographic ink adhesion. If the treated film is stored for more than 30 days, treatment decay may drop the surface energy below 34 dyn/cm, and the roll is re-treated before printing. Published data for the specific interaction between erucamide and corona treatment on 2426H is limited; converter validation is generally performed by monitoring peel adhesion of 3M 610 tape or by standard cross-hatch tape adhesion tests for printed film.

Collation shrink film made from 2426H is processed at film thicknesses around 25–50 µm with a 2.7:1 blow-up ratio and a low frost line to preserve transverse shrinkage. Shrinkage is measured after 10 s immersion in a heated oil bath at 130 °C; typical transverse direction shrinkage exceeds 15%, while machine direction shrinkage is held below 5%. Lamination film uses the same base resin but requires a heat-seal initiation temperature low enough for high-speed pouch converting. Heat seal initiation temperature for 2426H film is measured by ASTM F1921-12, with a typical seal initiation range between 90 °C and 110 °C under 0.3 MPa dwell and 1.0 s sealing time. Hot tack strength measured after 0.5 s cooling is sufficient for vertical form-fill-seal operations at 60–80 packages/min, but high-speed horizontal flow-wrappers producing gusseted sacks often require an EVA or ionomer sealant layer rather than a pure LDPE sealant.

Dart Impact, Tear Propagation, and Puncture Resistance Standards

Dart impact resistance is the critical property for heavy-duty sacks and freezer film. The free-falling dart method under ASTM D1709-22 Method A reports the mass at which 50% of specimens fail. For 40 µm 2426H film, the dart impact range is typically 100–150 g. The value depends strongly on bubble cooling and orientation balance. When the frost line is lowered, the film exhibits more transverse direction orientation and lower dart impact; when the frost line is raised, impact improves but gauge uniformity deteriorates. Elmendorf tear propagation under ASTM D1922-23 shows anisotropic behavior because of the orientation imparted by the blown film process. Machine direction tear is typically lower than transverse direction tear, with reported ranges of 2.0–4.5 N and 3.0–5.5 N respectively for a 40 µm film.

Puncture resistance is not covered by a single mandatory test for this grade. Converters use ASTM D5321/D5321M-20 or proprietary probe methods to compare films for pallet wrapping and sack liners. The puncture force for 50 µm LDPE film is generally below that of LLDPE films of equal gauge. This limitation is why 2426H is sometimes replaced by or blended with linear resins when sharp-edged frozen goods or metal shavings are present. The replacement decision is made after comparative testing on the actual packaging line because laboratory puncture values do not capture film elongation around irregular loads.

Compliance documentation for 2426H used in food packaging routinely cites the United States Food and Drug Administration 21 CFR 177.1520(c) 2.2 clearance for olefin polymers intended for direct food contact, subject to end-use temperature limits and food-type restrictions. In the European Union, Commission Regulation (EU) No 10/2011 and its amendments require overall migration not exceeding 10 mg/dm² of food contact surface and compliance with the declaration of compliance for plastic materials. REACH registration under Regulation (EC) No 1907/2006 requires that substances of very high concern remain below 0.1 wt% at article level. For packaging converters, the grade is not sold as a medical-grade polymer. It requires verification of residual monomer and oligomer content when used with high-fat food simulants.

Residual monomer and global food-contact compliance pathways are not interchangeable

The food-contact status of 2426H depends on the legal instrument and the intended food simulant. A resin that satisfies 21 CFR 177.1520(c) 2.2 does not by itself satisfy all European Union requirements, because the EU regulation requires migration testing with simulants such as ethanol 10%, acetic acid 3%, and olive oil or isooctane depending on food type. For fatty foods, migration testing under Commission Regulation (EU) No 10/2011 is performed with olive oil or isooctane substitute. Published data for 2426H in high-fat simulants is limited; converters must obtain a declaration of compliance from the resin supplier and validate the final package under the intended processing and storage conditions. For aqueous and dry foods, compliance is more straightforward and often supported by overall migration values below 10 mg/dm².

Thermal stability limits differ by converting process. Continuous melt temperatures above 220 °C on a cast-film line are not recommended because molecular weight reduction can occur. On a blown film line with die entrance temperature of 190 °C, the residence time in the die is usually short enough to avoid measurable gel formation. The resin contains antioxidant systems, but re-extrusion of edge trim from film that has been corona-treated and printed requires filtration because oxidized ink residues and surface graft species can form melt gels. The operational boundary for this grade in food packaging does not extend to hot-fill above 90 °C, fatty food simulants above 100 °C, or autoclave sterilization. Converters using 2426H in direct contact with high-fat foods must verify migration under the intended simulant, not only under aqueous simulants. The grade is also not intended for outdoor service where prolonged UV exposure causes embrittlement; carbon black masterbatch or UV stabilizer concentrates are required for agricultural film and construction packaging.