Sinopec Maoming mLLDPE F181ZR is a metallocene-catalyzed linear low-density polyethylene produced by Sinopec Maoming Petrochemical Company. The product designation identifies a film-grade resin with a nominal density of 0.918 g/cm³ and a nominal melt mass-flow rate of 1.0 g/10 min at 190 °C and 2.16 kg. The resin is used in cast stretch film, food packaging, agricultural wrap, lamination film, and industrial overwrap where downgauging, puncture resistance, and optical clarity are specified. The metallocene catalyst system yields a narrow molecular weight distribution and a more uniform short-chain branching distribution than conventional Ziegler-Natta linear low-density polyethylene. The grade is supplied as free-flowing pellets and is normally processed without pre-drying unless storage conditions expose the pellets to liquid water or high humidity.

Specification Boundaries and Certified Property Ranges

Producer technical documentation lists the density and melt flow anchors as nominal values; mechanical and optical values are lot-specific and appear on the certificate of analysis. The density test method is ISO 1183-1:2019 and the melt flow test method is ISO 1133-1:2022. A density of 0.918 g/cm³ positions the grade in the lower-density region of the linear polyethylene family, which reduces crystalline content and contributes to lower secant modulus than 0.930 g/cm³ LLDPE. The melt index of 1.0 g/10 min is appropriate for cast film lines with moderate extruder motor capacity and permits a melt temperature window of 230 °C to 260 °C. The producer certificate of analysis typically includes tensile stress and elongation after processing into 25 µm film, dart impact resistance according to ASTM D1709-16a, and Elmendorf tear resistance according to ASTM D1922-15; these values are not fixed specification limits because they are affected by die gap, chill roll temperature, and film thickness. The grade is not a high-melt-strength blown film resin; its use in blown film requires bubble stabilization measures or blending with LDPE.

On cast film extrusion lines, the resin is processed through a single-screw extruder with an L/D ratio of 30:1 to 36:1 and a barrier screw or Maddock mixing section. Screw diameters from 65 mm to 120 mm are typical, with output capacities between 300 kg/h and 800 kg/h depending on die width and line speed. A screen pack of 40/60/80 mesh is common. Barrel temperature profiles typically begin at 180 °C in the feed section and increase to 240 °C at the adapter. Die temperatures are maintained between 240 °C and 260 °C. Die gaps for cast film range from 0.6 mm to 1.2 mm; narrower gaps reduce web thickness variation but raise melt pressure and can promote die lip buildup. The cast film process uses a chill roll with surface temperatures between 15 °C and 30 °C. An air knife and a vacuum box are used to pin the melt web to the chill roll and to reduce haze and gauge variation. Production lines running this resin at line speeds below 300 m/min typically achieve stable gauge control if the die bolt adjustment and automatic profile control are calibrated to the resin’s viscosity. At higher outputs, the melt curtain length and the air knife pressure become critical because the narrow molecular weight distribution reduces melt strength and allows web flutter if the curtain is too long.

What Differentiates F181ZR from Conventional Ziegler-Natta LLDPE in Cast Stretch Film?

The primary difference is molecular architecture. Metallocene catalysis produces a narrow molecular weight distribution and a uniform short-chain branching distribution along the polymer backbone. Conventional Ziegler-Natta LLDPE typically contains a broad distribution of molecular weights and comonomer sequences, creating higher-molecular-weight fractions that increase melt strength but also generate more heterogeneous crystalline regions. In cast stretch film, F181ZR has lower melt strength than Ziegler-Natta LLDPE of the same melt index, which reduces bubble stability in blown film but is less restrictive in cast film because the melt web is supported by the chill roll. The uniform comonomer distribution lowers the seal initiation temperature and improves hot tack at low sealing temperatures compared with conventional LLDPE. The narrow molecular weight distribution also reduces the high-molecular-weight tail content, which can lower hexane extractables and improve organoleptic properties in food packaging. However, the same narrow distribution reduces shear sensitivity, so extruder head pressure and torque may respond differently to screw speed changes than broad-MWD LLDPE grades.

In comparison with the conventional Ziegler-Natta film resin DFDA-7042, which has a nominal density of 0.918 g/cm³ and a nominal melt mass-flow rate of 2.0 g/10 min, F181ZR has a lower melt flow index that supports higher melt strength and higher extensional viscosity at low shear, but its metallocene architecture still produces lower melt strength than a broad-MWD resin of the same melt index would. The lower MFR of F181ZR contributes to better dart impact and tear resistance at equivalent gauge, while DFDA-7042 processes with lower head pressure and higher output on some cast film lines. The difference in catalyst chemistry is more significant than the MFR difference: uniform comonomer distribution in F181ZR reduces crystalline heterogeneity and improves optical and sealing properties relative to DFDA-7042.

The use of F181ZR in machine stretch film typically targets film thicknesses between 12 µm and 25 µm. In hand wrap, thicknesses of 15–20 µm are common; in high-performance machine wrap, 12–15 µm film can be produced when gauge uniformity remains within ±1.5%. The resin’s uniform comonomer distribution supports puncture resistance and dart impact values that are typically higher than those of conventional LLDPE film of the same thickness, but the absolute values are influenced by film density, cast roll temperature, and additive package. Stretch film processors evaluate the finished film using elongation at break measured by ASTM D882-18, dart impact measured by ASTM D1709-16a, and Elmendorf tear measured by ASTM D1922-15. Pre-stretch ratios of 200–300% are commercially common for machine stretch film; film produced from F181ZR is generally specified for applications requiring consistent extensional recovery and high puncture resistance at these ratios. Because the resin has a lower melt index than DFDA-7042, torque may be higher on the extruder, but the resulting film often tolerates increased pre-stretch without immediate film break if the film edges are trimmed cleanly and the winder tension is controlled.

When Line Speeds Exceed 500 m/min

At web speeds above 500 m/min, the cast film process imposes sharper demands on melt elasticity and die lip cleanliness. The narrow molecular weight distribution of F181ZR supports low melt memory and rapid relaxation, but it also reduces resistance to draw resonance at high draw ratios. Draw resonance appears as periodic thickness bands in the machine direction and becomes more probable when the draw ratio exceeds 15:1 and the melt temperature falls below 240 °C. To suppress draw resonance, the die gap is typically widened to 0.8–1.0 mm and the melt curtain is shortened. Air knife pressure and vacuum box suction must be increased relative to lower-speed operation to maintain web contact before the cooling surface. Converter data indicates that melt temperature variation at the die lip should be held within ±2 °C for stable gauge at speeds above 500 m/min. Die lip buildup from oxidized low-molecular-weight species can initiate edge streaks and film breaks; purging with HDPE or a commercial purge compound after 8–12 h of continuous operation reduces such defects. Published data for this specific configuration is limited, and line trials are required to establish the maximum stable speed for a given die and winder.

The resin is normally blended with cling additives, such as polyisobutylene or metallocene-compatible tackifier masterbatches, at concentrations below 2 wt% to generate film-to-film cling for stretch wrapping. High levels of low-molecular-weight tackifier can migrate to the film surface and may reduce printable surface energy or interfere with heat sealing. Processors using high-speed cast stretch lines have reported that increasing tackifier loading above 1.5 wt% can increase coefficient of friction and reduce line speed due to blocking at the winder. Published data for this specific resin and tackifier combination is limited; therefore, the final loading should be established by film blocking tests and coefficient of friction measurements according to ASTM D1894.

Food-contact compliance is conditioned on the final formulation and converting conditions. The base polymer can be evaluated against FDA 21 CFR 177.1520(c) 3.1a for olefin polymers and against EU Regulation 10/2011 with an overall migration limit of 10 mg/dm². For the China market, GB 4806.6-2016 applies to food-contact plastic resins. The resin is not a formulation containing heavy metals above the thresholds of Directive 2011/65/EU Annex II when tested as supplied, but final articles must be assessed. REACH SVHC declarations should be verified with the producer’s current safety data sheet; the standard threshold for declarable SVHCs is 0.1% w/w per candidate list entry.

Because the resin has low melt strength relative to LDPE, blown film applications requiring a blow-up ratio above 2.5:1 often require blending with 10–30 wt% LDPE or a polymer processing aid to stabilize the bubble. The resin is not hygroscopic, but if stored under ambient relative humidity above 60% and surface moisture is observed, pre-drying at 70–80 °C for 2–4 h is recommended before processing. Melt temperatures above 260 °C should be avoided because oxidative degradation can increase gel formation and reduce film toughness. Migratory slip and antiblock masterbatches can alter seal initiation and hot tack; converters should limit total additive masterbatch loading and validate seal performance using ASTM F88 or a hot-tack method before production. The combination with certain amine-based stabilizer packages or high-acid tie resins may shift color or increase extractables, but published data for these additive interactions with F181ZR is limited.

Unlike EVA-based stretch film formulations, F181ZR contains no vinyl acetate comonomer and therefore has no inherent polar surface tack. Cling must be generated by adding a tackifier masterbatch at controlled levels. This distinction is relevant for food packaging operations where vinyl acetate odour or migration may be undesirable; the polyethylene base can offer lower extractables and better organoleptic neutrality when formulated without migratory plasticizers. The grade is not intended for injection molding or rotational molding because the low melt strength and narrow molecular weight distribution can cause short shots, warpage, and poor mold surface replication. Its use in blown film is possible only with bubble stabilization.

At startup, the extruder is purged with a lower-viscosity polyethylene, such as an MI 2.0 LDPE or a purge compound, to displace degraded material from the barrel and die lips. The screw should be rotated at low speed until the melt temperature stabilizes, then increased to the target output. When switching from a higher-MFR resin to F181ZR, the lower melt flow index can require longer purging because the narrower molecular weight distribution may not displace broad-MWD residues uniformly from dead zones. A purge time of 30–45 min at production speed is often sufficient, but die lip inspection after purging is necessary to remove oxidized specks.

The resin can be reprocessed in closed-loop edge trim systems on cast film lines. Edge trim and start-up waste can be reintroduced at levels up to 20 wt% without exceeding typical film gel or optical specifications, but the exact level depends on trim cleanliness and thermal history. Higher regrind levels may shift dart impact and haze values, so validation is required.