Asrene LLDPE UF1820S1 is a butene-comonomer linear low-density polyethylene supplied in pellet form for blown-film extrusion. The manufacturer identifies a nominal melt flow rate of 2.0 g/10 min at 190 °C/2.16 kg according to ASTM D1238/ISO 1133-1 and a nominal density of 0.918 g/cm³ according to ISO 1183-1/ASTM D792. The grade carries a formulated slip and antiblock system; exact slip-agent and antiblock loadings are lot-specific and are recorded on the certificate of analysis rather than in the standard datasheet. Typical values should not be construed as specification limits; the lot certificate governs.

The values are representative of C4 LLDPE film of this melt index and density. Published data for this specific product configuration are limited to the supplier datasheet; production lots may differ. The certificate of analysis governs.

What Are the Melt-State Flow and Screw-Drive Parameters That Control Output Stability?

The melt flow rate of 2.0 g/10 min places UF1820S1 in the medium-molecular-weight C4 LLDPE class. At extrusion shear rates, the linear structure generates less extensional viscosity than high-pressure LDPE, so the bubble is less self-healing under air-ring fluctuations. The practical melt-temperature window on high-output lines is 190–210 °C; below 175 °C, melt pressure rises sharply and sharkskin may appear on the film surface. Above 230 °C, oxidative gel formation accelerates, particularly in the presence of residual oxygen from poorly purged hoppers.

Extruders with grooved feed sections and 24:1 to 30:1 L/D should run a barrel profile from 170–180 °C in the feed zone to 190–210 °C in the metering zone. Compression ratio is set between 2.8:1 and 3.5:1. A screen pack of 60/100 mesh is common; finer filtration increases head pressure and melt temperature. Die gap is usually 1.0–2.0 mm. At the 1.0 mm lower boundary, shear heating can add 5–10 °C to the melt temperature; extruder speed must be reduced if the melt approaches 220 °C. At the 2.0 mm upper boundary, the melt web is thicker, which can reduce gauge uniformity when combined with high blow-up ratios.

Blow-up ratio is controlled between 2.0:1 and 3.0:1, and frost line height is set to maintain bubble diameter within ±25 mm. Excessive cooling air creates a concave bubble neck and increases transverse shrinkage; insufficient cooling air raises the frost line and can destabilize the bubble at high screw speed. The lack of long-chain branching limits the self-stabilizing extensional hardening seen in LDPE, so automatic bubble guides are recommended for gauge control beyond 100 kg/h output on a 65 mm extruder.

At 190 °C and 100 s⁻¹, the apparent viscosity of this melt index class is lower than an MI 1.0 C4 LLDPE by approximately 20–30%, depending on molecular weight distribution. The critical shear rate for sharkskin in spiral mandrel dies is typically in the 500–1000 s⁻¹ range. Exceeding that rate without raising melt temperature produces visible surface roughness. Die-lip build-up from slip additives can accumulate over extended runs; periodic purging or fluoropolymer processing aids at 200–500 ppm is used on high-output lines to reduce the frequency of cleaning.

Pellets do not require pre-drying if stored sealed. At ambient relative humidity above 60%, condensation on cold pellets can cause bubble defects; a desiccant or hot-air hopper dryer at 60–70 °C for 2 h removes surface moisture. Blending with up to 20 wt% high-pressure LDPE improves bubble stability and melt strength, but reduces the dart impact advantage of the LLDPE. Blending with HDPE or polypropylene is not recommended because incompatible melts generate visible gels. Converters who compound their own slip or antiblock masterbatch should verify dispersion by measuring haze on 40 µm film and film-to-film coefficient of friction after 48 h.

When a Slip-Antiblock Package Interacts with Corona Treating and Lamination

The slip additive is a long-chain primary amide dispersed in the amorphous regions of the polyethylene. Migration to the film surface follows a concentration gradient and is strongly temperature-dependent. Immediately after extrusion, kinetic coefficient of friction measured by ASTM D1894 can exceed 0.50. After 24 h at 23 °C, the surface concentration rises enough to reduce COF below 0.35; after 72 h, it usually plateaus in the 0.15–0.30 range. Storage at 30–40 °C shortens the plateau time; storage below 5 °C slows migration and can leave film with high COF and blocking tendency. The inorganic antiblock, typically a synthetic silica with median particle size in the 3–5 µm range, creates microroughness that reduces film-to-film contact area.

Corona treatment raises surface energy to 38–42 mN/m for ink adhesion but oxidizes the surface amide layer, raising the measured coefficient of friction. Dyne solution checks are performed according to ASTM D2578; a reconditioning period of 24 h may be required before the slip bloom equilibrates after corona. In lamination-grade film, excessive slip can reduce bond strength to solventless polyurethane adhesives. The corona dose, adhesive chemistry, and maturation time should be evaluated on the treated surface rather than on untreated film. If the film is metallized, the slip package may outgas under vacuum; published data for this specific configuration is limited.

Blocking resistance in wound rolls is a function of contact pressure, temperature, and slip maturation. At roll pressures above 0.5 MPa, film-to-film adhesion increases if the slip bloom is incomplete. Rolls should be aged for 24 h before slitting at high tensions. Hot-climate storage above 40 °C accelerates slip migration but also softens the film; blocking may become worse if rolls are compressed. A two-stage winding profile with lower initial tension and step-up after 24 h reduces blocking defects.

Blocking Resistance and Seal-Initiation Temperature Boundaries

Seal initiation for this butene LLDPE is not a fixed property; it depends on jaw pressure, dwell time, and film thickness. Under 0.5 s dwell and 0.3 MPa jaw pressure, initiation is typically 105–115 °C, which is 10–20 °C lower than a high-pressure LDPE of similar melt index. The hot-tack window measured by ASTM F1921 is broad enough for vertical form-fill-seal equipment; seal strength measured by ASTM F88 should be verified after 48 h of maturation because surface slip amides can act as a weak boundary layer before equilibration. The plateau seal temperature is usually below 160 °C; above this, the film thins excessively at the seal interface and loses burst strength.

The grade is not designed for solvent-based lamination requiring high-polarity anchor coatings without corona pretreatment. Aromatic solvents and strong oxidizers should be avoided because they can swell the polyethylene and extract surface additives. For food-contact use, the final film structure must be assessed under the intended simulant and contact ratio; the base polymer is typically covered by FDA 21 CFR §177.1520 and EU No 10/2011, but specific migration limits for the slip and antiblock additives must be confirmed with the supplier.

Butene Branching Sets the Ultimate Dart Impact and Tee-Tear Ceiling

The butene comonomer introduces ethyl branches that are less efficient than hexene or octene branches at distributing short-chain branching. This lowers tie-chain concentration and reduces ultimate dart impact and tear resistance relative to hexene metallocene LLDPE of the same 0.918 g/cm³ density and 2.0 g/10 min melt index. In 40 µm film, dart impact measured by ASTM D1709 is typically lower by 15–30%, and Elmendorf tear measured by ASTM D1922 is lower in the machine direction. The optical haze is higher because of the additive package and the less regular crystallite structure.

Against high-pressure LDPE, the linear backbone gives higher tensile stress at break and higher puncture resistance at equal gauge. The lack of long-chain branching reduces melt strength; extrusion coating and cast-film drawing should be adjusted for greater neck-in and lower draw resonance. Against a C4 LLDPE of 1.0 g/10 min and the same density, UF1820S1 runs at lower head pressure and torque; the trade-off is slightly lower bubble stability and lower dart impact at high blow-up ratios. A converter whose line is torque-limited may prefer UF1820S1; a converter whose film must pass a high cold-drop impact specification may need the lower-MI or hexene grade.

Film property comparisons are meaningful only at equivalent blow-up ratio, frost line height, and gauge. Increasing blow-up ratio increases transverse orientation and can partially compensate for TD tear; decreasing blow-up ratio increases MD orientation and improves tensile strength but reduces dart impact. The orientation balance is also influenced by die gap; a narrower die gap at constant output increases shear and MD orientation.

The water-vapour transmission rate is moderate and thickness-dependent; it should be measured on the final structure according to ISO 15106-2 or ASTM F1249 because coextruded layers, pigmentation, and surface additives affect permeability. Polyethylene is not an oxygen or flavour barrier; oxygen-sensitive products require coextruded EVOH or polyamide layers. Published data for this specific configuration is limited, so end-use barrier specifications must be verified by measurement rather than by inference from density or melt index.

For direct food-contact packaging, the following compliance checks are normally requested from the resin supplier and downstream converters. The base polymer may comply with FDA 21 CFR §177.1520 and Commission Regulation (EU) No 10/2011, but the final film structure, inks, adhesives, and lamination layers must be evaluated separately. REACH and RoHS declarations are lot-specific and should be maintained in the technical file.

For less demanding dry blending or pellet handling, conventional hopper loaders and vacuum conveying systems suffice. No special pre-heating is required. Pellet dust is low, but long vacuum conveying distances can abrade pellets and generate fines that carry slip additive to the die lip; conveying velocity should be controlled below 25 m/s where possible.

On a 65 mm grooved-feed extruder with a 150 mm spiral mandrel die, a stable operating envelope is established with a die gap of 1.5 mm, blow-up ratio of 2.5:1, and frost line height of 250–350 mm. At 25–60 µm gauge, this geometry yields a balanced MD/TD orientation. High-speed form-fill-seal trials show that a kinetic coefficient of friction below 0.30 after 48 h of maturation is sufficient for reliable film path control; however, if the film is later corona treated for lamination, the coefficient of friction should be re-measured. For heavy-duty sacks, the resin can be used in coextruded structures where the core layer carries the mechanical load and the skin layer supplies slip and seal performance. The practical upper gauge limit is governed by the cooling rate of the bubble, not by the resin itself.