PetroChina Dushanzi PME-18 mLLDPE mLL2010 is indexed in the metallocene linear low-density polyethylene film family as a narrow-molecular-weight-distribution ethylene/α-olefin copolymer produced at the Dushanzi petrochemical complex. The grade designation mLL2010 is commonly associated with a nominal melt flow rate of 1.0 g/10 min when measured at 190°C under 2.16 kg load according to ISO 1133-1:2022, and a nominal density of 0.918 g/cm³ when measured by ISO 1183-1:2019. These are lot-release reference values rather than guaranteed specification limits, and the producer’s certificate of analysis governs each batch. The resin is a gas-phase metallocene-catalyzed copolymer; its homogeneous short-chain branch distribution reduces crystalline melting point to a class-typical 115–122°C under ISO 11357-3:2018 at 10 K/min, while the narrow molecular weight distribution lowers low-shear melt strength relative to high-pressure low-density polyethylene and raises shear viscosity relative to a Ziegler-Natta LLDPE of equivalent melt index.

The PME-18 prefix identifies the production platform and the mLL designation indicates metallocene catalysis, while the trailing numeric code differentiates melt flow rate and density from adjacent grades in the Dushanzi mLLDPE slate. In procurement and specification documentation, the resin is often listed as a metallocene linear low-density polyethylene film resin rather than a conventional LLDPE or a high-pressure LDPE. This distinction has consequences for equipment sizing, additive selection, and final film property claims. Unlike a general-purpose butene LLDPE, mLL2010 is optimized for converter lines that can exploit its downgauging potential; it is not a drop-in replacement on extrusion equipment that lacks torque margin or temperature control.

In monolayer and coextruded blown film, mLL2010 is typically directed to applications that require puncture, tear, and optical clarity rather than high melt strength. Specific uses include heavy-duty sacks, agricultural greenhouse film, lamination film for liquid packaging, collation shrink film, and high-clarity sealant webs. Because of the narrow molecular weight distribution, extrusion lines must provide sufficient screw torque and pressure capability; melt temperatures at the die are normally set from 190°C to 215°C, with die gap settings between 1.5 mm and 2.0 mm to suppress shark-skin melt fracture. A wider die gap is common when a conventional C4 LLDPE line is converted to mLLDPE without changing the air ring or screw cooling profile. Published data for this specific configuration is limited, so line qualification must include torque, pressure, and gauge uniformity trials.

What Places mLL2010 Apart from Ziegler-Natta Butene LLDPE in Blown Film?

The structural distinction is not melt index or density but the interchain distribution of comonomer. In a conventional Ziegler-Natta butene LLDPE of 0.918 g/cm³ and 1.0 g/10 min, the active-site heterogeneity concentrates ethylene-rich, high-crystallinity fractions and comonomer-rich, low-melting fractions within the same resin. This broad composition distribution widens the melting endotherm and leaves extractable or soft domains that can raise haze and reduce hot tack. In a metallocene resin such as mLL2010, the single-site catalyst architecture distributes short-chain branches more uniformly across the molecular weight range. The practical consequence in blown film is a lower haze and higher dart impact at equal gauge, together with a lower seal initiation temperature. Class-typical comparative data for 25 µm films are summarized in the following table; the values are not producer guarantees for mLL2010 but are reference ranges from lab and pilot-line evaluations of 0.918 g/cm³ metallocene hexene films against equivalent Ziegler-Natta butene LLDPE.

The relative differences are process-relevant because they permit downgauging without equivalent loss of impact strength. If a converter reduces thickness from 50 µm to 35 µm, a broad-composition butene LLDPE may fall below the required dart impact threshold, while a metallocene grade of the mLL2010 class may retain sufficient impact because the crack-initiation and crack-propagation resistance are less tied to crystalline lamellae size distribution. In addition to impact and optical data, the class-typical tensile yield strength of 0.918 g/cm³ metallocene LLDPE film is 10–12 MPa in the machine direction and 9–11 MPa in the transverse direction under ASTM D882, with elongation at break above 500%. Tensile strength at break is commonly 25–35 MPa. These values are class-typical for 25 µm blown film; the mLL2010-specific lot data may fall outside these ranges, but the envelope is useful for selecting equipment and setting initial film property targets. The absolute film performance depends on cooling air temperature, frost line height, die gap, and blow-up ratio. In coextruded structures, LDPE is still required in the outer layers for bubble stability and melt strength; replacing all layers with mLL2010-class resin is generally not recommended on conventional lines with single-lip air rings because the bubble may show low stalk stability above a blow-up ratio of 2.5:1.

In multilayer cast and blown film structures, mLL2010-class resins are frequently placed in the sealant layer because the homogeneous branching architecture imparts a broader hot-tack plateau and lower initiation temperature than conventional LLDPE. Class-typical seal initiation for 0.918 g/cm³ metallocene LLDPE films runs from 100°C to 110°C under ASTM F2029/F88 with 0.5 N/mm² seal bar pressure, 0.5 s dwell, and 25 mm seal width, while conventional C4 Z-N LLDPE grades typically initiate 8–15°C higher under identical conditions. Hot tack strength in the 110–130°C interval is commonly 2–4 N/25 mm when evaluated by ASTM F1921. These properties make the grade suitable for form-fill-seal packaging lines where seal-through-contamination resistance and short dwell-time sealing are required. However, slip and antiblock additive packages alter hot tack and coefficient of friction; the converter must qualify the formulated film rather than rely on resin-only values.

Higher Low-Shear Viscosity in mLL2010 Increases Extruder Head Pressure

The low-shear viscosity of mLLDPE is higher than that of a broad-molecular-weight-distribution Z-N LLDPE of the same 1.0 g/10 min melt index, because there are fewer very-low-molecular-weight chains to act as internal lubricants. On a 45 mm single-screw blown film line with an L/D of 28:1 and a barrier screw designed for LLDPE, replacing a conventional butene LLDPE with a metallocene hexene resin of equivalent melt index has been reported to increase die pressure by 10–18% at constant screw speed and melt temperature, while motor load rises 5–12%. The actual increment depends on die gap, blow-up ratio, screw wear, and discharge temperature. Extruders without adequate torque or feed-section cooling may require output reduction. The melt fracture point is also reached at lower screw speeds than with broad-MWD resins; increasing the die gap from 1.0 mm to 1.8 mm and raising melt temperature to 205–215°C are standard corrective actions. When these adjustments are insufficient, purging with a melt-index-matched LDPE or processing aid masterbatch may be necessary to control polymer-metal friction and eliminate surface defects.

The pressure and torque behavior becomes more pronounced at high outputs because the resin’s viscosity curve is less shear-thinning. On an extrusion line with a 60 mm barrier screw and a 250 mm annular die, melt temperature may need to be increased by 5–10°C compared with a conventional C4 LLDPE to maintain output, but pellet softening in the feed section can cause feed throat plugging if the temperature exceeds the melting onset. Therefore, feed-section cooling capacity must be confirmed before raising discharge temperatures. In practice, converters using mLLDPE often select a screw with a deeper feed channel or add a grooved-feed section to increase solids conveying and reduce the tendency for pellet clumping.

When a C6 mLLDPE Replaces a C8 mLLDPE in Sealant Layers

If mLL2010 is supplied as a hexene-based metallocene LLDPE, its position relative to octene-based metallocene grades is defined by tear and toughness. Octene comonomer generally gives higher Elmendorf tear and puncture resistance at equivalent density because the longer branch more effectively ties adjacent chains across lamellar boundaries, while hexene comonomer provides a comparatively higher tensile yield and lower resin cost. In sealant applications, the difference is less pronounced at seal initiation but becomes important in cold-temperature abuse resistance and in film layers that must survive sharp package corners. Class-typical 25 µm films from 0.918 g/cm³ metallocene hexene resin show Elmendorf tear values of 6–9 N in the machine direction and 10–14 N in the transverse direction under ASTM D1922; comparable octene grades may exhibit 15–25% higher transverse tear. The trade-off is often a lower modulus and potentially higher extractables. Published data for mLL2010-specific tear performance is limited, so the converter must measure on the target line and, if necessary, blend with an octene metallocene or use thicker sealant layers.

This replacement decision also affects film blocking and coefficient of friction. Metallocene resins with homogeneous branching usually have lower surface crystallinity and can show higher blocking tendency unless antiblock and slip are added. In a C8-to-C6 substitution, the sealant layer may develop higher blocking at the same additive loading because the surface morphology differs. The maximum additive concentration is bounded by seal strength and haze; therefore, a formulated package for a C8 mLLDPE is not automatically transferable to a C6 mLLDPE such as mLL2010 without rebalancing.

Food-contact qualification is article-specific. PetroChina Dushanzi mLLDPE grades of the PME-18 family are generally supplied with conformity statements for China GB 9685 and, when produced under appropriate hygiene controls, may support FDA 21 CFR 177.1520 for olefin polymers and EU Regulation 10/2011, Annex I and Annex II, with limits on overall migration and specific migration of any additives or residual monomers. For EU industrial use, REACH Regulation 1907/2006 Annex XVII is also relevant, and the legal entity placing the resin on the market must ensure Safety Data Sheet conformity with Article 31. The converter must validate final films under the intended food simulant, contact time, and temperature; a resin certification alone does not establish finished-article compliance. Additive constraints apply particularly to organic slip agents and antioxidants, which can migrate and influence seal strength, haze, or organoleptic performance. Avoid combination with amine-based additives if the package is exposed to secondary disinfection or high-humidity storage, because reaction products may increase organoleptic risk. Published mLL2010-specific migration data is limited; full extraction testing is recommended before commercial use.

Blown Film Die and Air Ring Conditions for the 0.918 g/cm³ Class

Stable bubble operation for mLL2010-class resins is obtained when the die pressure stays within the extruder’s maximum continuous rating, typically 350–550 bar for single-screw film extruders in the 45–90 mm size range, and when the air ring maintains annular air velocity between 15 m/s and 30 m/s. Blow-up ratio is normally set between 2.0:1 and 3.0:1, with frost line heights of 4–8 die diameters. Lower frost lines improve optical clarity but may reduce impact strength due to faster quenching; higher frost lines improve bubble stability and orient the film, but can increase slip and alter shrink properties. Dual-lip air rings with standard venturi design are generally sufficient; internal bubble cooling can be used to raise output when the line has adequate chilled-air supply and the die has an IBC channel. Film gauge control should be tied to a closed-loop system, as melt temperature changes of ±3°C can shift local thickness variance in narrow-molecular-weight resins.

Coefficient of friction and blocking should be monitored because mLL2010-class films can be difficult to separate on winders when slip agents have not migrated to the surface. In high-clarity structures, the addition of silica-based antiblock may be limited to 500–1,000 ppm to preserve haze. Organic slip agents such as erucamide are typically added at 500–1,000 ppm, but migration to the surface can take 24–72 h at ambient temperature; immediate film-to-film blocking tests may therefore overstate the tendency. On slitting and bag-making equipment, the film may require longer conditioning time than conventional LLDPE because the narrow-MWD resin has higher residual stresses after winding.

Storage and handling of mLL2010 follow standard polyolefin practice. The resin is supplied as pelletized material and should be stored in dry, covered conditions at ambient temperature; pre-drying is not normally required unless the silo or bag has been exposed to condensation or relative humidity above 60%. Regrind from start-up film can be incorporated in monolayer structures at levels up to 10–20% by weight, but the exact limit depends on film optics, seal performance, and gel formation. Higher regrind ratios are possible in non-critical films if the material is clean and the extruder has adequate melt filtration with screens of 60–100 mesh. Avoid blending regrind with polar barrier polymers unless a compatibilizer is present, because gross phase separation will increase gel counts and reduce seal integrity. Published data for mLL2010-specific storage and regrind tolerance is limited.