Borealis LDPE NAV101 is a low-density polyethylene produced by the high-pressure free-radical polymerization route. It is supplied as a natural pellet and is intended primarily for blown-film extrusion and for lamination structures in which autoclave-type long-chain branched architecture is required. Under ISO 1133-1:2022, the melt flow rate at 190 °C/2.16 kg is nominally reported near 0.70 g/10 min, while density under ISO 1183-1:2019 is nominally reported at 0.922 g cm^-3. These values are representative nominal data for the NAV-series film grade; published data for this specific NAV101 configuration is limited, and the certificate of analysis controls lot-specific values. The product is differentiated from high-flow LDPE extrusion-coating grades by its lower melt flow rate and its stronger emphasis on bubble stability, optical quality, and balanced film mechanics rather than high drawdown at low coating weight.

Borealis LDPE NAV101: melt rheology and extrusion profile

The melt rheology of NAV101 follows the expected pattern for high-pressure LDPE: strong shear thinning at die-lip shear rates above 100 s^-1 arises from the long-chain branching distribution. On single-screw extruders with a 24:1 to 30:1 L/D ratio and a compression ratio of 2.8:1 to 3.2:1, the melt temperature is typically maintained between 160 °C and 195 °C. Barrel set points from feed to metering can be profiled from 150 °C to 180 °C, with adapter and die zones held at 180 °C to 190 °C. Die gaps of 0.8 mm to 1.2 mm are common for films up to 80 µm, while heavier structures above 100 µm may use 1.6 mm to 2.0 mm gaps to reduce melt fracture. Blow-up ratios from 2.0:1 to 2.8:1 provide practical transverse-direction toughness without excessive bubble sway on conventional air-cooled towers.

Capillary rheometry at 180 °C demonstrates the non-Newtonian response: apparent shear viscosity is commonly above 2000 Pa s at 10 s^-1 and falls below 150 Pa s at 1000 s^-1. The resulting power-law index is observed in the range of 0.35 to 0.45. These values are generic for film-grade high-pressure LDPE and are not a substitute for a lot-specific certificate of analysis. Molecular weight distribution and long-chain branching also affect melt relaxation. During film blowing, the lower melt relaxation rate of NAV101 relative to LLDPE can increase machine-direction orientation and reduce transverse-direction tear. This is why converters often use a higher blow-up ratio of 2.5:1 to 2.8:1 to balance the property profile. At a die gap of 1.0 mm and haul-off speed of 15 m min^-1, the frost-line height normally lies between 280 mm and 400 mm for a 150 mm die. These values are equipment-dependent and should be established by line trials.

On production-scale blown-film lines, bubble instability appears when the frost-line height is set below 4 die diameters or above 8 die diameters, because the long-chain branched network requires sufficient residence time for orientation. Film made from NAV101 at 40 µm gauge typically shows haze below 10 % when measured according to ISO 14782, tensile strength at break in the machine direction near 36 MPa according to ISO 527-3, and dart impact F50 values near 150 g according to ISO 7765-1. Elmendorf tear strength is anisotropic, with machine-direction values generally lower than transverse-direction values in high-blow-ratio film by 20 % to 40 %. These figures are typical for a film-grade LDPE and should not be read as guaranteed specification limits.

The mechanical response of NAV101 follows from its high-pressure synthesis. Long-chain branches increase the melt relaxation time and produce a higher molecular weight tail, while short-chain branches lower crystallinity relative to HDPE. In film form, this architecture yields a tensile yield stress near 11 MPa and elongation at break above 500 % under ISO 527-3. The secant modulus in the machine direction is typically near 260 MPa. Because the density remains below 0.925 g cm^-3, the film retains flexibility and adequate dart impact without the addition of plastomers.

How does NAV101 differ from linear-low-density and high-flow LDPE grades?

NAV101 differs from a butene-based LLDPE of similar density in several measurable ways. In blown-film equipment, NAV101 reaches lower extrusion head pressure at equivalent output because high-pressure LDPE long-chain branching produces more pronounced shear thinning. For a 50 mm grooved-feed extruder at a screw speed of 100 min^-1, a melt flow rate of 0.70 g/10 min LDPE may show die-head pressure in the range of 18 MPa to 24 MPa, while an LLDPE with a similar melt flow rate typically shows higher motor load at the same screw speed. The penalty is lower solid-state toughness: LLDPE films of equivalent gauge may exhibit dart impact values above 300 g, whereas NAV101 films generally fall below 200 g, because the short-chain branching distribution in LLDPE forms more tie molecules and higher elongation at break. Compared with high-flow LDPE extrusion-coating grades with melt flow rates near 7.5 g/10 min, NAV101 produces better bubble stability in vertical film extrusion but is not optimised for high-drawdown coating at low coating weights. Relative to a high-molecular-weight LDPE film grade such as FA6220 with a melt flow rate near 0.25 g/10 min, NAV101 offers lower melt viscosity and easier drawdown at medium film thicknesses but lower dart impact and tear resistance.

In multilayer structures, NAV101 is used as a carrier for masterbatch because its broad molecular weight distribution aids distributive mixing. It can be used in outer layers to deliver gloss and surface smoothness, while a core LLDPE layer provides tear resistance. The die swell of NAV101 is generally lower than that of a broad-MWD HDPE but higher than that of a metallocene LLDPE, so die gap adjustments are required when changing the skin-layer resin. For coextrusion feedblocks, the viscosity ratio between skin and core layers should be kept between 0.7:1 and 1.3:1 to avoid interfacial instability.

The standard stabilisation package for NAV101 is designed to withstand multiple extrusion passes up to 200 °C; exposure to melt temperatures above 220 °C for more than 10 minutes can raise gel counts and reduce film dart impact. The grade can be supplied in natural form or with slip and antiblock packages; exact additive levels are suffix-specific and must be confirmed against the grade datasheet. For food-contact applications, compliance depends on the complete formulation and the convertor’s manufacturing conditions. Under EU Regulation (EU) No 10/2011, the overall migration limit is 10 mg dm^-2 when tested according to EN 1186. Under FDA 21 CFR 177.1520, the base olefin polymer may be acceptable for direct food contact if the finished article meets extraction limits for the intended food type. The grade is not recommended for use with amine-based antifog masterbatches if the final structure is destined for high-temperature retortable packaging, because interactions between additives can alter organoleptic performance.

Although LDPE is not hygroscopic enough to require drying for moisture removal, storing pellets at relative humidity above 60 % may introduce surface moisture that causes bubble defects. Silo residence times should be kept below 24 h at temperatures above 30 °C to minimise additive bloom. Regrind content should be limited to 20 % by mass for high-speed film lines unless the line is equipped with an inert-gas purge and a resin dryer.

When melt temperature exceeds 195 °C on high-output film towers

When the melt temperature exceeds 195 °C on a high-output tower, bubble diameter often becomes unstable because the long-chain branched fraction is susceptible to thermal-oxidative chain scission at the inner bubble surface. Operators may observe a decrease in melt strength and an increase in dart impact variation from reel to reel. In a three-layer coextrusion line with a 250 mm die and a melt-fed die gap of 1.2 mm, reductions in melt temperature from 210 °C to 185 °C have been reported to reduce gel counts and stabilise bubble diameter. The processing window is not unusually narrow, but the stabilisation system should not be asked to protect the polymer over repeated regrind loops at high melt temperatures. Air-ring pressures of 20 Pa to 40 Pa are typical, and frost-line height should be controlled within 10 mm by adjusting blower speed rather than by changing melt temperature. A gauge variation of ±5 % at a 50 µm target can reduce dart impact F50 by as much as 15 % relative to uniform film, because the long-chain branched LDPE network cannot redistribute local stress as effectively as an LLDPE. The most common processing defect with NAV101 on high-output lines is drooping bubble instability caused by insufficient melt strength when the melt temperature is raised above 195 °C to increase output. The corrective action is to increase the blow-up ratio or lower the frost line rather than to continue raising melt temperature. Conversely, at melt temperatures below 160 °C, unmelted pellets can produce specks in the film. A flat temperature profile with a die-temperature set point of 180 °C is preferred.

In practice, NAV101 is used for general-purpose packaging films, surface-protection films, carrier bags, and lamination webs where consistent bubble stability and moderate optics are more important than maximum dart impact. Converters running blown-film lines with a 2.5:1 blow-up ratio and a 1.0 mm die gap can use NAV101 as a direct replacement for higher-molecular-weight film LDPE grades in applications below 50 µm gauge. It is less suitable for puncture-dominated applications or for stretched films where linear-low-density grades supply the required tear and dart performance. In coextruded structures, NAV101 is commonly placed in the core or skin layers to supply melt strength and optical quality, while LLDPE or metallocene grades carry the abuse-resistance requirements.