Sinopec Yangzi mLLDPE mPE F331F is a metallocene-catalysed linear low-density polyethylene resin supplied as pellets for blown film and cast film conversion. The base polymer is normally released against a nominal melt mass-flow rate of 1.0 g/10 min under 190 °C and 2.16 kg load in accordance with ISO 1133-1:2022 or ASTM D1238-20, and a nominal density of 0.918 g/cm³ determined by ISO 1183-1:2019 or ASTM D1505-18. These values position the grade in the medium-viscosity film-extrusion region, where bubble stability is retained at thin gauge while die pressure remains within the operating envelope of single-screw extruders with L/D ratios of 24:1 to 30:1. The single-site metallocene architecture produces a narrower molecular weight distribution and a more homogeneous short-chain branch distribution than conventional Ziegler-Natta linear low-density polyethylene. That structural difference alters extrusion shear response, crystalline melting behaviour, heat-seal response, and solid-state toughness. Converters should obtain a lot-specific certificate of analysis because published data for the complete additive package in F331F is limited.

For film-grade polyethylene, the practical consequence of the homogeneous branching in F331F is that a 25 µm monolayer blown film may exhibit lower hexane-extractable content, lower seal initiation temperature, and higher dart impact per unit density than a conventional butene-based Ziegler-Natta LLDPE of the same density. The comparison is fabrication-dependent and must be generated under ASTM D1709-22, ASTM F88/F88M-21, and ISO 7765-1:1988. Film tensile properties are measured according to ISO 527-3:2018; because blow-up ratio, frost line height, and die gap reorient the crystalline microstructure, no single nominal tensile or tear value is appropriate without specifying the line configuration. Elmendorf tear data under ASTM D1922-15 for metallocene film grades can show a different machine-direction to transverse-direction balance than conventional LLDPE, so converters should not substitute one test result for another without confirming orientation effects.

What Differentiates mPE F331F from Conventional Ziegler-Natta LLDPE in Blown Film?

The primary distinction lies in the distribution of comonomer across the molecular weight distribution. In heterogeneous Ziegler-Natta butene copolymers, the lower-molecular-weight fraction is more highly branched and the higher-molecular-weight fraction is more linear. This creates a broad melting range, thicker disordered interlamellar regions, and a higher soluble fraction. In F331F, the metallocene catalyst inserts comonomer with more uniform statistical control, narrowing the distribution of crystallisable sequence lengths. The result is a more uniform crystalline superstructure and a lower concentration of low-molecular-weight highly branched chains. That shift can improve organoleptics and reduce migration into fatty food simulants, but compliance must be demonstrated on the finished package under EU Regulation 10/2011 and 21 CFR 177.1520.

A processing conflict appears because the narrow molecular weight distribution reduces shear thinning. In conventional broad-distribution LLDPE, viscosity decreases more rapidly as screw speed rises, limiting motor torque and melt pressure. F331F may show higher apparent viscosity at equivalent screw speed after the die-gap shear region. On a 65 mm grooved-feed extruder with L/D 30:1, melt pressure upstream of the screen pack can be 15–25% higher than with a conventional C4 Ziegler-Natta LLDPE of equivalent melt index. The onset of sharkskin in metallocene film grades with a melt index near 1.0 g/10 min commonly occurs at apparent die-lip shear rates in the range of 100–200 s⁻¹, depending on die geometry, land length, and melt temperature. Published data for this specific configuration is limited, so production trials should map the instability threshold for each die and extruder combination.

To mitigate melt fracture and improve bubble strain hardening, converters often blend high-pressure low-density polyethylene at 10–30 wt% or use a fluoropolymer processing aid at 200–800 ppm. High-pressure LDPE introduces long-chain branching and raises extensional viscosity, which supports the bubble against draw resonance and frost-line instability. The trade-off is an increase in haze and a reduction in dart impact. If the processing aid concentration is too high, die-lip deposit can transfer to the film; if too low, sharkskin may persist at higher take-off speeds. The optimum is specific to the die-gap geometry and should be evaluated by photographing the film surface at each screw speed while holding the frost line constant.

Comparative structural and processing orientation for selected polyethylene film resins is summarised in the matrix below. The matrix is not a substitute for lot-specific data.

In blown film operation, F331F requires careful management of the frost line because its lower shear thinning makes bubble geometry more sensitive to air-ring velocity and exhaust-air fluctuations. A consistent frost line height of 6–8 die diameters is a common starting point, but the setting is not universal. At blow-up ratios above 3.0:1, the balance of MD and TD tear in F331F can shift because the homogeneous branching distribution responds differently to orientation than conventional LLDPE. Processors should record blow-up ratio, frost-line height, and die gap in every lot comparison; otherwise the property difference between lots cannot be separated from line-induced variation.

Thermal stability boundaries should be observed. Sustained melt temperatures above 280 °C may cause thermoxidative degradation, odour formation, and a reduction in film clarity. The residence time in the extruder, adapter, and die becomes more critical at high throughput because the narrow molecular weight distribution does not provide the same high-shear energy absorption as broad-distribution resins. Screw speed, backpressure, and screen-pack condition should be monitored together because a partially blinded screen can raise temperature locally and accelerate gel formation.

For cast film lines with slot-die widths of 1200–1800 mm and chill-roll temperatures of 15–30 °C, F331F can be processed at melt temperatures of 220–250 °C. The lower melt strength relative to high-pressure LDPE requires a shorter draw distance and consistent vacuum-box contact along the chill roll. Edge pinning air velocity must be sufficient to prevent neck-in, but excessive air can fold the molten web and create gauge bands. Published data for F331F in cast film is limited; the processing window should be established with a low-output stability trial before film is collected for mechanical testing.

When Down-Gauging and Seal-Peak Operation Require Controlled Branching Uniformity

In packaging lines requiring a wide seal window and rapid seal development, the uniform branching distribution of F331F can provide a seal initiation temperature commonly 5–10 °C lower than that of a heterogeneous butene-based LLDPE of equivalent density. The exact curve for F331F must be measured by ASTM F88/F88M-21 and hot-tack testing under ASTM F1921-18. This characteristic supports vertical form-fill-seal applications where jaw residence time is short and seal strength must develop before product loading occurs. However, a lower seal initiation temperature can also increase the risk of seal through contamination if the package contains dusty or greasy products; the converter should validate seal-peak strength on production equipment, not on laboratory laminated films alone.

For collation shrink film, F331F may be blended with high-pressure LDPE at 10–20 wt% to increase shrink tension and stabilise the bubble. The blend reduces the clarity advantage of the metallocene component, so the ratio should be selected through a designed experiment comparing haze measured by ASTM D1003-21, dart impact by ASTM D1709-22, and shrink tension under the converter’s oven profile. In heavy-duty sack film, blending with high-density polyethylene raises modulus and creep resistance, but the incompatible crystalline phases may reduce dart impact if the HDPE fraction exceeds 20 wt%; compatibility and screw mixing quality become limiting factors.

F331F is generally considered within the scope of 21 CFR 177.1520 for olefin polymers and EU Regulation 10/2011 for plastic materials intended to contact food. Nevertheless, the resin supplier cannot grant finished-article compliance. Migration testing with food simulants under the EN 1186 series, or equivalent, is required at the finished-film thickness and under the intended time-temperature conditions. The metallocene structure can reduce low-molecular-weight extractables relative to conventional Ziegner-Natta LLDPE, but residual catalyst residues and processing degradation products are affected by extrusion temperature and screw condition, so compliance cannot be assumed from the polymer structure alone.

Under the European REACH framework, polyethylene is exempt from registration as a polymer; the monomer substances must be registered. The F331F base resin is not expected to contain restricted substances above RoHS limits, but the converter is responsible for verifying the finished package or component against the applicable electrical and electronic equipment restrictions. Storage of the resin should keep pellets away from direct sunlight and strong oxidising agents because prolonged ultraviolet exposure can initiate free-radical degradation even in the solid state. If surface condensation occurs during cold-warehouse storage at relative humidity above 60%, a hopper dryer at 70–80 °C for 2–4 h may be used to remove surface moisture and prevent bubble defects. Avoid combining F331F with high loadings of amine-based additives unless compatibility and organoleptic performance have been verified, because some amine species can migrate to the film surface and interfere with seal strength or print adhesion.

When compared with a nominal 2.0 g/10 min metallocene LLDPE of the same density, F331F requires higher motor torque and may provide better bubble stability at thin gauges because the lower melt index increases melt strength. When compared with a metallocene plastomer or elastomer, F331F has a higher crystalline fraction and should not be used as a low-temperature impact modifier for rigid packaging. The product is therefore selected for film structures in which stiffness, gauge reduction, and seal integrity are more important than low-temperature puncture at sub-zero storage conditions.