Dow LDPE 150E, 310E and 312E: Film Grades Compared

Selection among Dow LDPE 150E, 310E and 312E for blown film production depends on melt viscosity, bubble stability, heat removal, and the mechanical and optical performance required by the converted web. In a conventional blown film line, resin is plastified in a single-screw extruder with an L/D ratio between 24:1 and 30:1, metered through an annular die with a die gap between 0.8 mm and 1.2 mm, and expanded to a blow-up ratio between 2.0:1 and 3.0:1. The three grades span a melt index range from 0.25 g/10 min to 1.0 g/10 min under ASTM D1238 conditions of 190 °C with 2.16 kg. Density values of 0.921 g/cm³ for 150E and 0.923 g/cm³ for 310E and 312E are determined under ASTM D1505. These values influence crystallinity, modulus, and permeability. The following sections establish processing boundaries, property trade-offs, and application constraints for each grade without assigning a universal replacement.

Which Rheological Parameters Differentiate 150E from 310E and 312E?

Melt index measured by ASTM D1238 is an inverse indicator of average molecular weight but does not capture molecular weight distribution or long-chain branching. Low-density polyethylene produced in high-pressure autoclave or tubular reactors contains long-chain branches that lower zero-shear viscosity and increase shear thinning. A resin with 0.25 g/10 min melt index, such as 150E, exhibits higher zero-shear viscosity and lower melt flow than a resin with 1.0 g/10 min, such as 312E. At blown film shear rates between 200 s⁻¹ and 500 s⁻¹, shear thinning reduces the viscosity difference, but the high-viscosity grade still generates higher extruder head pressure and screw torque. On a 60 mm extruder with 24:1 L/D, barrel zones set from 150 °C to 190 °C, 150E typically requires more motor load than 312E at equal screw speed. Production-scale failure modes for 150E include pressure-limited melt filtration, more frequent screen pack changes, and localised temperature rise at the screw tip if barrel override is not controlled. For 312E, the failure mode shifts to bubble instability because the lower melt strength cannot restrain circumferential stress at high blow-up ratios. Melt strength is not measured by ASTM D1238; converter trials typically combine melt index with bubble stability observations at a die gap of 1.0 mm and a blow-up ratio of 2.5:1.

Because both 310E and 312E share a density of 0.923 g/cm³, their differentiation in film production is governed almost entirely by melt index and the resulting extrusion pressure and bubble stability. The increase from 0.75 g/10 min to 1.0 g/10 min between 310E and 312E is sufficient to reduce back pressure and melt temperature at the die, but it also lowers bubble tension and can increase gauge variation unless internal bubble cooling and air-ring geometry are adjusted. A processor moving from 310E to 312E without rebalancing frost line height may observe thickness variation measured by ISO 4593 exceed ±10% and a reduction in machine-direction tear resistance measured by ASTM D1922. These changes are not attributable to density but to the reduction in molecular weight and melt strength.

Blown Film Operating Windows and Converted Web Property Trade-Offs

Process stability for the three grades is defined by die gap, blow-up ratio, frost line height, and melt temperature. A die gap between 0.8 mm and 1.2 mm is typical for low-density polyethylene; the lower-melt-index 150E generally operates more consistently at the upper end of this range because a wider gap reduces die entry pressure and delays melt fracture. Melt temperatures between 160 °C and 190 °C are common, with the higher-viscosity 150E requiring higher temperature set points at the die head to maintain volumetric output without exceeding the extruder pressure limit. Melt temperature excursions above 200 °C accelerate oxidative chain scission; film producers monitor yellowness index under ASTM E313 to detect early degradation. Bubble stability for 150E can be maintained up to blow-up ratios of approximately 3.0:1 on lines with dual-lip air rings. For 312E, the stable upper limit is usually between 2.2:1 and 2.5:1 unless internal bubble cooling is used, because the lower melt strength produces less resistance to ambient air turbulence and die non-uniformity. On a 150 mm die with dual-lip air ring and cooling air at 5 °C, frost line height and gauge profile differ from those on a 250 mm die with ambient air. For 150E, higher melt strength allows a shorter frost line and lower total air volume, which can improve optics but may increase blocking if the web is wound above 35 °C. For 312E, higher air volume and an elevated frost line reduce bubble sag, but excessive cooling air can introduce chill-induced orientation and raise haze under ASTM D1003. Orientation balance is assessed by shrinkage after 10 min at 100 °C under ASTM D2732 or by tensile strength ratio in machine and transverse directions under ASTM D882. Films produced from 150E at high draw ratios typically display higher machine-direction tensile strength and lower transverse-direction elongation, whereas films from 312E display lower modulus and higher elongation. These differences are not solely resin-dependent; they are governed by the same line parameters that determine gauge uniformity.

Is Higher Melt Index Always Detrimental to LDPE Film Toughness?

At equivalent film gauge, lower melt index grades generally exhibit higher dart impact energy and tear resistance, but the relationship is not linear. Dart impact measured by ASTM D1709 Method A at 50 µm gauge depends on film orientation, gauge uniformity, and molecular weight. Film tensile strength at break measured by ASTM D882 is influenced by draw ratio and frost line height; for 50 µm LDPE films of the density range represented by these grades, machine-direction values commonly fall between 15 MPa and 25 MPa, and transverse-direction values between 12 MPa and 20 MPa. Higher melt index grades typically occupy the lower portion of this range when orientation is not intentionally increased. Elongation at break under ASTM D882 commonly ranges from 300% to 650%, with lower values in the machine direction at high take-up ratios. Dart impact by ASTM D1709 Method A for 50 µm LDPE film may range from 80 g to 250 g, with higher values associated with lower melt index and higher blow-up ratio. Elmendorf tear under ASTM D1922 may range from 50 gf to 300 gf depending on orientation and additive package. The higher molecular weight of 150E increases chain entanglements and tie-molecule concentration, which resists crack growth and contributes to higher puncture resistance in heavy-duty shrink film and frozen-food overwrap. 310E provides intermediate impact energy with a lower melt viscosity that supports higher line speed without excessive melt pressure. 312E yields lower impact energy but improved drawdown and less shear heating in the extruder. Haze measured by ASTM D1003 and gloss at 45° under ASTM D2457 are influenced by surface roughness, melt uniformity, and additive package. The intermediate melt index of 310E often supports a smoother melt surface and better optics than 150E at the same film thickness, but the difference is sensitive to die gap and cooling rate. Slip and antiblock concentrates at addition levels between 1% and 3% by weight modify surface coefficient of friction under ASTM D1894 and blocking force after stacking. Published numerical values for identical laboratory film preparation among the three Dow grades are limited; converter-scale film evaluations under controlled blow-up ratio and frost line height remain the only reliable basis for specification limits.

In heavy-duty shrink bundling at film thickness between 75 µm and 125 µm, 150E is selected because its higher molecular weight provides retained shrink force after orientation. Shrink force measured under ASTM D2732 after conditioning at 70 °C for 20 s is governed by orientation, long-chain branching, and molecular weight; lower melt index grades generally maintain higher shrink tension under load. However, the viscosity of 150E limits output on older extruders with L/D ratios below 24:1. Operators may compensate by raising barrel zone temperatures to 175 °C or 180 °C, which can initiate gel formation if antioxidant reserves are depleted. In contrast, 310E and 312E are used in films from 25 µm to 50 µm where optical clarity and line speed outweigh extreme puncture resistance. Replacing 150E with 312E on the same die typically lowers head pressure and melt temperature at equal screw speed; the bubble must be rebalanced by reducing internal air volume and lowering the frost line. If the frost line is not lowered to compensate for lower melt strength, thickness variation measured by ISO 4593 can deteriorate beyond ±10%, and dart impact under ASTM D1709 can fall below the minimum required for the package. Published data for this specific substitution on a given extruder is limited; production trials are required to establish the new operating window.

When 310E Replaces 150E in High-Output Thin-Gauge Packaging Lines

In high-output thin-gauge packaging lines running film below 40 µm, 310E is often used as a bridge between the toughness of 150E and the processability of 312E. On a 75 mm extruder with 30:1 L/D and a barrier screw, 150E may exceed the pressure interlock of the melt filtration unit at target throughput, while 310E remains below the safety limit. The replacement requires a reduction in melt temperature set points from approximately 180 °C to 170 °C, a higher frost line position, and a slight reduction in blow-up ratio to keep bubble chatter below the threshold that produces gauge bands. If the same settings are retained, the lower melt strength of 310E can produce bubble flutter and a 5% to 10% loss in transverse-direction tensile elongation measured by ASTM D882. The lower viscosity of 310E also reduces motor load and allows either higher screw speed or lower melt temperature, which limits oxidation. In applications requiring low seal initiation temperature, 310E and 312E generally seal at lower heat-seal jaw temperatures than 150E because the lower molecular weight permits faster chain interdiffusion at the interface; heat seal strength is measured by ASTM F2029 with a dwell time of 0.5 s and pressure set to the equipment manufacturer's specification. The seal plateau of 150E may be narrower at high line speed, but its bond strength above the plateau is often higher due to greater entanglement density.

Vicat Softening, Seal Initiation, and Regulatory Compliance Boundaries

Vicat softening point under ASTM D1525 for these resins typically lies between 90 °C and 96 °C; grade-specific datasheets should be consulted because additive package and density can shift the value by several kelvin. The higher density grades 310E and 312E generally show a slightly higher Vicat value than 150E due to increased crystallinity from a density of 0.923 g/cm³. Heat seal initiation measured by ASTM F2029 is governed primarily by melting range and molecular mobility; LDPE of 0.921 g/cm³ to 0.923 g/cm³ density typically shows seal initiation between 95 °C and 110 °C. Lower melt index grades may require a higher seal bar temperature to reach a given bond strength, while 312E seals faster at lower temperature but may produce lower ultimate hot-tack strength. Hot tack measured by ASTM F1921 is critical for vertical form-fill-seal operations where the seal is loaded immediately after sealing. On high-speed vertical form-fill-seal machines with seal dwell below 0.2 s, the faster chain interdiffusion of 312E reduces leaker rates; 150E may require higher sealing temperature or longer dwell to achieve equivalent hot tack. For food-contact applications, the resins may be used in compliance with FDA 21 CFR 177.1520 for olefin polymers, provided end-use packaging is tested for migration limits under 21 CFR 177.1520(c). REACH registration and specific migration limits under EU No 10/2011 must be confirmed for additive packages and downstream coatings. The unmodified LDPE chemistry generally provides compliance with RoHS 2011/65/EU only when no prohibited flame-retardant additives are introduced during compounding.

Frozen food packaging operating at -20 °C to -40 °C often demands low-temperature puncture resistance that is not fully captured by ambient dart impact testing. Films made from 150E at 75 µm are frequently selected because the higher molecular weight resists brittle failure at sub-zero temperatures, as evaluated by instrumented puncture energy retention after conditioning at -20 °C for 24 h. Ambient ASTM D1709 impact is not a substitute for low-temperature toughness testing; converters utilise in-house instrumented puncture tests with hemispherical probes at test temperatures from -20 °C to -40 °C. Films from 310E and 312E can be modified with 20% to 30% LLDPE or metallocene plastomer to improve low-temperature impact, but blending raises density and may shift the seal plateau. Such blends may also change food-contact status under FDA 21 CFR 177.1520 and EU No 10/2011, requiring new migration documentation for the specific blend ratio. The comparison of Dow LDPE 150E, 310E, and 312E therefore cannot be reduced to melt index and density alone; the full formulation, film gauge, frost line height, and downstream conversion conditions control final film performance. Published data for the specific configuration of all three grades under identical sub-zero test conditions is limited; pilot-line validation under actual air ring and cooling conditions remains the standard method before commercial specification.