Sinopec Yangzi Petrochemical mPE-L F181F is characterised as a metallocene-catalysed linear low density polyethylene resin intended for monolayer and coextruded film structures. In pellet form, the material is processed on standard single-screw lines; when trialled on a 30:1 L/D barrier-screw extruder with a 90 mm cylinder, melt-pressure stability of ±0.5 MPa was maintained up to 120 kg/h output. The nominal melt flow rate is 1.0 g/10 min at 190 °C under a 2.16 kg load per ISO 1133-1:2022, and the density is 0.918 g/cm³ per ISO 1183-1:2019. Differential scanning calorimetry according to ISO 11357-3:2018 places the peak melting endotherm between 118 °C and 122 °C. Pellets are typically supplied with a bulk density of 0.54 g/cm³–0.58 g/cm³. These baseline values place F181F in the low-density branch of LLDPE film grades, where metallocene catalysis is used to reduce the broad comonomer-distribution drift characteristic of Ziegler-Natta systems.

What Distinguishes Metallocene Linear Low Density Polyethylene from Conventional C4 Ziegler-Natta LLDPE?

The principal structural distinction is the narrow molecular weight distribution and the more uniform inter-molecular comonomer distribution. Gel permeation chromatography on converted film gives a polydispersity index of approximately 2.0–2.5, against 3.5–4.5 for conventional C4 Ziegler-Natta LLDPE of equivalent density and melt index. This shift reduces the high-molar-mass fraction that contributes to melt elasticity but also removes a portion of the low-molar-mass fraction responsible for extractable species. The consequence is a measurable increase in dart impact and a lower seal-initiation temperature without a loss of stiffness. On 50 µm monolayer blown film, comparison runs at a 2.5:1 blow-up ratio show dart impact values in the range 350 g–450 g for F181F under ASTM D1709A-21, while similarly formulated C4 Ziegler-Natta LLDPE typically records 150 g–200 g. Published data for this specific configuration is limited to converter trials; absolute values vary with die gap, frostline height, and cooling-air velocity.

Rheologically, the melt retains sufficient shear thinning for film extrusion but does not display the strain-hardening response of low-density polyethylene or high-pressure LDPE blends. At 190 °C, capillary rheometry under ISO 11443:2021 gives apparent shear viscosity of roughly 350 Pa·s–450 Pa·s at 100 s⁻¹ and 120 Pa·s–160 Pa·s at 1000 s⁻¹. In blown film, this translates into lower die swell than conventional C4 LLDPE and permits use of 1.6 mm–2.0 mm die gaps in packages designed for down-gauging. However, the same low melt elasticity reduces bubble stability when the frostline height is placed beyond approximately 8 die diameters; the bubble enters a low-stress ruffling mode that cannot be corrected by increasing extruder speed alone.

Process stability is bounded by melt temperature and die-gap selection

On high-output single-screw blown film extrusion, F181F is processed using a barrel profile from 40 °C–60 °C in the feed throat, 170 °C–180 °C in zone 1, and 185 °C–205 °C across the remaining zones, with a die temperature of 200 °C–215 °C. Melt temperature is normally held at 205 °C–220 °C; excursions above 230 °C increase the rate of thermo-oxidative branching and raise gel counts. The preferred die gap is 2.0 mm–2.5 mm for film thicknesses between 25 µm and 80 µm. At 120 kg/h output on a 90 mm extruder, back pressure typically remains within 25 MPa–35 MPa. When the die gap is reduced below 1.2 mm to force molecular mixing, melt fracture occurs earlier than with C4 LLDPE because the narrow molecular weight distribution offers lower extensional stress damping. Bubble stabilisation is further improved by maintaining the external cooling-air velocity at 3 m/s–6 m/s and the frostline height at 4–8 die diameters. Pre-drying is not normally required unless pellet surface moisture exceeds 0.05 wt%, in which case desiccant drying at 75 °C–80 °C for 2 h is sufficient.

Seal initiation on laboratory heat sealing under ASTM F88/F88M-21 is observed at 97 °C–103 °C for a 30 µm monolayer film at 0.5 s dwell and 0.6 N/mm² bar pressure. Hot tack according to ASTM F1921-18 remains above 1.5 N/25 mm through the 110 °C–130 °C interval. This window is sufficiently broad for vertical form-fill-seal lines cycling at 60–80 packs per minute. In contaminated-seal testing with 0.05 g/m² skim milk powder dispersed on the seal region, seal strength retention exceeds 70% of the uncontaminated value at 115 °C; the low extractable fraction limits the formation of an oily interfacial layer. Converters should note that this contamination tolerance is not equivalent to sterilisation resistance and does not replace barrier films in retort pouches. Published data for this specific configuration is limited to converter trials.

Film optical properties, haze development, and gel particle thresholds

Optical measurements on 50 µm blown film produce haze of 6%–9% under ASTM D1003-21, with 45° gloss of 70–85 under ASTM D2457-21. By comparison, conventional C4 Ziegler-Natta LLDPE at the same thickness typically yields haze of 12%–16%. Haze is sensitive to die-face oxidation and additive agglomeration; gel particle analysis on 100 µm cast film often shows fewer than 5 gels per m² above 0.7 mm diameter when the screw is purged with LDPE between grades. Accumulation of oxidised resin at the die lip can raise haze by 2–3 percentage points within 4 h if no fluoropolymer processing aid is used. Addition of 0.02 wt%–0.06 wt% fluoropolymer processing aid reduces die-lip build-up and permits longer continuous runs.

Tensile strength at break on 50 µm blown film measured by ISO 527-3:2018 is typically 40 MPa–50 MPa in the machine direction and 35 MPa–45 MPa in the transverse direction. Elongation at break exceeds 500% in both orientations. Elmendorf tear resistance per ASTM D1922-21 is approximately 80 N/mm–110 N/mm in the machine direction and 120 N/mm–160 N/mm in the transverse direction. Puncture resistance on a 19 mm probe under ASTM D5748-19 falls between 2.0 J and 3.0 J at 50 µm. At low temperature, ASTM D746-20 brittle point shows no failure above -40 °C; below this temperature, impact performance becomes thickness- and rate-dependent. These values are directional on blown film because of frozen-in molecular orientation; cast film exhibits a more balanced machine/transverse profile but lower absolute puncture energy at equal thickness.

Compared with a conventional C8 Ziegler-Natta LLDPE of the same density, F181F delivers a comparable dart impact but with lower haze and lower seal initiation. The C8 Ziegler-Natta grade may show a broader processing window and higher melt strength, although its extractable fraction from the broader comonomer distribution is higher. Compared with high-pressure LDPE, F181F has lower melt strength and cannot be used as the sole resin for shrink film where biaxial orientation stability is required; blending with LDPE is necessary for those applications.

When F181F is substituted into multilayer lamination film at inner sealant layers

In three-layer blown structures with a 20/60/20 layer ratio, F181F is placed in the outer and inner skin layers while a high-density polyethylene or conventional LLDPE core provides bubble stiffness. Because seal initiation drops by 8 °C–12 °C relative to conventional C4 LLDPE skins, packaging machines can run at lower jaw temperatures; however, the film surface must be formulated with slip and antiblock to prevent blocking after corona treatment. Typical additive loadings are 0.05 wt%–0.10 wt% erucamide and 0.10 wt%–0.20 wt% synthetic silica. In adhesive lamination to biaxially oriented polypropylene or polyester, corona treatment at 40 mN/m–42 mN/m is required, because metallocene PE has lower extractable surface species and therefore reaches acceptable wetting tension more slowly than oxidised LDPE. For extrusion lamination of aluminium foil, the resin is used as a sealant layer only; it is not intended as the high-temperature extrusion adhesive itself.

Blending with 5 wt%–15 wt% autoclave LDPE of density 0.923 g/cm³ and melt flow rate 0.25 g/10 min increases bubble stability by introducing long-chain branching that raises extensional strain hardening. The resulting haze penalty is generally less than 2 percentage points. When the LDPE fraction exceeds 20 wt%, dart impact decreases and the seal-initiation advantage narrows. Blends with more than 30 wt% conventional C4 LLDPE shift the seal-initiation temperature toward the Ziegler-Natta value and raise haze in proportion to the Ziegler-Natta fraction; such blends are used only when cost reduction overrides optical and sealing performance.

Why is the processing window narrower than conventional C4 LLDPE?

The narrow molecular weight distribution lowers the elastic stress that stabilises the molten bubble against small air-current perturbations. Stable operation therefore requires closer control of frostline height and external air flow. On a 200 mm die, frostline height is typically 450 mm–650 mm; movement of more than 50 mm in 5 min can initiate bubble instability. Internal bubble cooling is beneficial above 150 kg/h but must be commissioned gradually because the melt has lower strain hardening than LDPE. The melt temperature window is bounded at the lower end by 185 °C; below this, unmelts appear as clear gel flecks. Above 230 °C, the stabiliser package can be depleted during long runs, and gel counts rise. This narrow window is the principal trade-off for the lower seal temperature and higher dart impact. Converters transferring from C4 LLDPE should begin with a 2.0 mm die gap rather than the 1.5 mm gap common to conventional LLDPE. Published data for this specific configuration is limited; the operating range should be determined on the actual production line.

Without slip and antiblock additives, the low extractable surface generates coefficient of friction values above 0.6 and blocking tendency increases after corona treatment. Addition of 0.03 wt%–0.06 wt% of a silicone-based or erucamide-based slip package reduces kinetic coefficient of friction to 0.10–0.25 within 24 h of migration at 23 °C. The migration half-life is temperature-dependent; at 40 °C, the coefficient of friction reaches equilibrium in 8 h–12 h.

Storage below 40 °C and 60% RH in sealed original packaging avoids moisture pickup and additive migration. If bags are opened, inventory rotation within 12 months is recommended. The resin is stabilised with a phenolic primary antioxidant and a phosphite secondary antioxidant; exposure to hot-air drying above 100 °C for more than 4 h should be avoided because it can consume the phosphite stabiliser and shift oxidation onset temperature lower. The material is not compatible with intentional peroxide modification unless an additional stabiliser package is added.

Comparative data set for film converters

Table 1 presents typical values from monolayer 50 µm blown film except where indicated. The values are not specification limits and are compiled from converter trials and internal laboratory methods. The table is comparative only; final product performance depends on film construction, additive masterbatches, and cooling conditions.

The regulatory status of F181F is documented under the following frameworks. Final compliance of a converted article must be verified on the finished package because printing inks, laminating adhesives, and recycled layers may change migration behaviour. REACH Article 33 documentation confirms no substance of very high concern above 0.1 wt%. Under EU No 10/2011, overall migration must be below 10 mg/dm² on the final film; converters should test specific simulants for fatty, acidic, or aqueous food types according to Annex V. Under FDA 21 CFR 177.1520, olefin polymer status is available for film-grade LLDPE; condition-of-use declarations should be obtained from the manufacturer. The resin is also evaluated against RoHS 2011/65/EU Annex II and EU 94/62/EC Article 11 for heavy metals.