Sinopec Qilu mLLDPE F3306S is a hexene-based metallocene linear low-density polyethylene blown-film resin with a supplier-declared nominal melt flow rate of 2.0 g/10 min at 190 °C/2.16 kg (ISO 1133-1:2022) and nominal density of 0.918 g/cm³ at 23 °C (ISO 1183-1:2019). The polymer is produced by a metallocene catalytic route and is characterized by a narrow molecular weight distribution and a more uniform short-chain branching distribution than conventional Ziegler-Natta qLLDPE. These structural features affect optical haze, dart impact strength, seal initiation temperature, and melt rheology in blown-film extrusion. Because the product is supplied in pellet form, lot-specific values should be confirmed against the certificate of analysis issued by Sinopec Qilu Petrochemical.

The uniform comonomer distribution in F3306S reduces the breadth of the crystalline lamellae population. This narrows the melting endotherm measured by ISO 11357-3, lowers film haze, and improves dart impact resistance at equivalent film gauge relative to Ziegler-Natta resins of the same density and melt flow rate. The same molecular architecture also produces lower melt tension and reduced shear thinning, which are the two primary reasons that processing behavior differs from conventional qLLDPE and from high-pressure LDPE. Capillary rheometry under ISO 11443 can quantify the shear-thinning difference. At equal melt flow rate and density, a Ziegler-Natta qLLDPE typically has a broader molecular weight distribution and therefore a larger viscosity decrease between 100 s⁻¹ and 1000 s⁻¹. The metallocene grade retains a higher apparent viscosity at high shear rates such as those encountered at a blown-film die lip, while its low-shear viscosity may be insufficient to generate the melt tension required for very large blow-up ratios.

What Limits the Processing Window of mLLDPE F3306S in Single-Lip Air Ring Blown Film Lines?

On monolayer blown-film lines, mLLDPE F3306S is typically extruded through a die gap of 1.5–2.5 mm with a melt temperature between 180 °C and 220 °C. The wider die gap is used to lower die-lip shear stress and postpone sharkskin melt fracture. Production-scale equipment with a 30:1 L/D barrier screw and Maddock mixing section is generally required for stable melt quality; shorter screws may generate melt temperature non-uniformity and reduce output stability. At a given screw speed, head pressure and torque are higher than those observed with Ziegler-Natta qLLDPE of identical melt index and density because the metallocene resin has a narrower molecular weight distribution and weakens the typical shear-thinning response.

Bubble stability is the principal restriction. The low melt tension of mLLDPE F3306S makes the frost line sensitive to air-ring turbulence, ambient drafts, and high blow-up ratios. In single-lip air-ring lines, bubble instability often appears when the blow-up ratio exceeds 2.5:1; dual-lip air rings or internal bubble cooling can extend this limit. Frost line height is normally held between 300 mm and 600 mm. A lower frost line improves clarity, while a higher frost line can improve gauge distribution but reduces bubble stability. When higher melt tension is required, plant practice is to blend 10–20 wt% high-pressure LDPE into the extruder feed. That addition improves bubble stability but increases haze and raises seal initiation temperature relative to the unblended resin.

Melt temperature control is also critical. If the melt temperature falls below approximately 190 °C, die-lip shear stress can rise toward the melt-fracture threshold on high-output lines. If it exceeds 230 °C, oxidative degradation may increase gel content. The exact thermal window depends on the antioxidant package, residence time distribution, and extruder screw design; the supplier’s processing recommendation should be used for commissioning.

Reported plant failure modes for metallocene LLDPE film grades include amber-tone gel streaks from melt-temperature excursions, sharkskin at the film edges from die-lip fouling, and bubble oscillation when ambient air velocity fluctuates. In F3306S conversion, the absence of long-chain branching increases sensitivity to these failures. The usual remedy is not primarily an antioxidant change but a reduction in screw speed, an increase in die gap, or a lowering of blow-up ratio. On a high-output line, the melt-fracture threshold may be reached if the die gap remains below 1.2 mm while melt temperature is below 200 °C; increasing the die temperature to approximately 215 °C or widening the gap to 1.8–2.0 mm is a common intervention.

Intended application fields include thin-gauge monolayer and coextruded blown film for food contact packaging, frozen food bags, heavy-duty sacks, agricultural film, and laminating film. In these uses, the resin is selected for low sealing temperature, high dart impact relative to density, and optical clarity. For printing or lamination, corona treatment is normally applied and surface energy should be checked with ISO 8296 test inks. The decay rate of corona treatment is lot-dependent and must be monitored in high-speed converting lines, particularly at relative humidity above 60%.

Seal Initiation, Hot Tack, and Hexene-Comonomer Architecture

Compared with Ziegler-Natta qLLDPE of equivalent density and melt flow rate, the hexene-based metallocene architecture of mLLDPE F3306S lowers heat-seal initiation temperature and often broadens the hot-tack plateau. Seal strength is tested according to ASTM F88/F88M and hot tack according to ASTM F1921-18. The lower seal initiation allows higher jaw temperatures to be replaced by faster line speeds on vertical form-fill-seal equipment, provided that jaw temperature uniformity is controlled within ±5 °C. Typical seal tests use a dwell time of 0.3–1.0 s and seal pressure of 0.2–0.4 MPa. The precise seal initiation temperature is film-gauge and thermal-history dependent; it must be established on the converter’s sealing equipment because laboratory values under ASTM F88/F88M do not directly predict machine performance.

The resin’s narrower short-chain branching distribution also reduces xylene solubles and hexane extractables relative to conventional qLLDPE. These factors are relevant for food contact compliance, but the finished article must be evaluated against 21 CFR 177.1520 and (EU) No 10/2011 under the intended conditions of use. For food contact film, the converter must verify overall migration and specific migration limits for all additives present in the complete formulation, not solely the base resin.

The table defines the test methods commonly used for film characterisation. It does not replace the lot certificate of analysis, nor does it establish specification limits because film properties are strongly dependent on film gauge, blow-up ratio, frost line height, cooling rate, and additive package.

When F3306S Replaces Ziegler-Natta qLLDPE in Thin-Gauge Blown Film

Reformulation from a Ziegler-Natta qLLDPE to mLLDPE F3306S typically requires adjustment of the extrusion profile, not simply a material swap. At equal melt index and density, F3306S can generate higher head pressure, lower melt temperature tolerance, and a narrower bubble-stability envelope. The benefit is film with lower haze and higher dart impact resistance at equivalent gauge. In thin-gauge applications below 25 µm, the metallocene resin may allow downgauging because of improved puncture and impact toughness, but the conversion must be validated against target package integrity tests such as ASTM D1709 dart drop and ISO 6383-2 tear resistance. Published data for this specific grade in all film gauges is limited; therefore, plant trials remain necessary.

Compared with high-pressure LDPE, F3306S has higher tensile strength and higher elongation at break, but lower melt tension and less strain hardening. It is therefore less suited to shrink-film applications where high free shrink and bubble stability are controlled by long-chain branching. Compared with octene-based metallocene LLDPE, hexene-based grades such as F3306S may have somewhat lower toughness at equivalent density, but are often easier to source and process. The selection among hexene, octene, and conventional Ziegler-Natta grades should be based on the full property envelope rather than any single film parameter.

Within the metallocene LLDPE family, grades with higher melt flow rates and similar density may be better suited to cast film because they show lower extruder torque; grades with lower melt flow rates may provide higher melt strength for large-bubble blown film. The F3306S designation is therefore a film-grade position, not a universal polyolefin substitution. Published data for injection molding, blow molding of hollow articles, or foam extrusion with this grade is limited; it should not be specified outside blown-film or cast-film extrusion without plant validation.

In coextruded structures, mLLDPE F3306S is used as a sealant web in polyolefin laminates. The sealant layer is not necessarily corona-treated; if the structure is reverse-printed or adhesive-laminated, the sealant side remains untreated to maintain coefficient of friction and seal performance. Film blocking at high winding tension has been observed when slip and antiblock additive levels are insufficient. Converters must set rewind tension based on roll hardness rather than shaft torque alone, particularly in high-humidity storage environments where film surface moisture can affect coefficient of friction.

F3306S may be supplied with an antioxidant, slip, and antiblock additive package. The type and level of slip and antiblock directly affect coefficient of friction and haze; converters should confirm the additive formulation with the lot certificate because additive-free or differently formulated variants behave differently in high-speed packaging lines.