Sinopec Maoming mLLDPE F331F is a metallocene-catalysed linear low-density polyethylene film resin produced by Sinopec Maoming Petrochemical Company for cast film and blown film conversion. The standard incoming-polymer reference values include a melt mass-flow rate of 1.0 g/10 min measured at 190 °C under 2.16 kg load using ISO 1133-1:2022 or ASTM D1238-20, and a density of 0.918 g/cm³ determined by ISO 1183-1:2019 or ASTM D1505-18. As a metallocene-catalysed medium-flow film grade, F331F exhibits a narrower molecular weight distribution and a more uniform short-chain branching distribution than conventional butene-based Ziegler-Natta LLDPE of the same nominal density. Those structural features influence low-temperature seal performance, dart impact, and the distribution of extractable fractions in the finished film. The values in this paragraph are reference values, not an entire specification; the supplier’s certificate of analysis for each lot is the controlling document for the exact melt index, density, and additive content.

Rheologically, the narrow molecular weight distribution of F331F typically produces a lower shear viscosity at a given low-density polyethylene melt index than a broad-distribution Ziegler-Natta resin, while melt strength is lower than that of high-pressure LDPE. Capillary rheometry on the raw pellet can be performed under ASTM D3835-16 or ISO 11443:2021 to establish the shear-viscosity curve. In film processing, this may reduce head pressure or allow a lower melt temperature, but it also requires closer control of the frost line and the blow-up ratio because the bubble retains less strain-hardening stress during inflation. The onset of melt fracture in mLLDPE can be different from that of Ziegler-Natta material; the condition should be mapped on the specific die before specifying a maximum screw speed.

What Should Be Checked on the Incoming Resin Before Blown Film Production?

Incoming inspection should include at minimum melt flow rate, density, and visual contamination. The batch certificate values should be compared with the purchase specification. A representative sample should be taken downstream of the resin dryer or hopper loader, because fines generated during dilute-phase conveying can segregate and change apparent bulk density. Moisture is not normally a controlling variable for well-stored polyolefin pellets, but if storage or conveying occurs under relative humidity above 60 % or in a temperature-cycled warehouse, surface condensation can be introduced into the extruder feed. A desiccant drier set at 70–80 °C for 2–4 h can remove surface moisture. The required drying time depends on the silo or hopper geometry and the initial pellet temperature.

The visual and moisture rows are plant controls, not resin-grade specifications. If pellet contamination is observed, the lot should be quarantined and the supplier’s batch record reviewed before feeding a production extruder.

Extruder Temperature Gradients, Die Gap, and Bubble Geometry for Monolayer Lines

On a grooved-feed single-screw extruder with 25:1 to 30:1 L/D and a low-shear barrier screw, the following starting profile is commonly used for F331F: feed throat 50–70 °C; cylinder zones 160 °C, 170 °C, 180 °C, 190 °C, 200 °C; adapter and die body 200 ± 10 °C. The melt temperature at the die should be held below 240 °C, because extended exposure above 230 °C can increase oxidative gel formation and shift the film’s taste and odour profile. A die gap of 1.2–2.0 mm is preferred for unfilled monolayer blown film; a gap below 1.0 mm may increase specific die pressure and reduce bubble stability. The typical blow-up ratio is 2.0:1 to 3.0:1. Frost line height should be set between 3 and 8 die diameters, with the lower value used for higher-density or lower-melt-strength structures and the upper value for heavier-gauge film requiring lower molecular orientation.

Because F331F is a metallocene LLDPE, it does not exhibit the long-chain branching and strain hardening typical of high-pressure LDPE. On an air-cooled monolayer film line without internal bubble cooling, thin-gauge film below 12 µm may require blending with 10–20 wt% LDPE or a higher-melt-strength HDPE component to maintain bubble geometry. The cooling air and IBC settings should be adjusted to avoid a frost line that oscillates more than ±25 mm, because thickness variation measured by a capacitance gauge may exceed ±5 % when the bubble is unstable. A dual-lip air ring with a moderate venturi setting is preferred over a single-lip ring for this grade at high output rates.

Melt fracture onset should be mapped on the specific die and resin combination. Surface defects can be assessed by film roughness measurement with contact profilometry or by visual inspection under polarised light. If sharkskin appears, increasing the die temperature or adjusting the die gap is generally preferable to raising the melt temperature above 240 °C.

In heavy-duty sack, agricultural, and logistics packaging, F331F is typically evaluated by dart drop impact, Elmendorf tear, tensile, seal, and hot-tack tests. Dart impact is tested per ASTM D1709-15e1 or ISO 7765-1; the value must be normalised for gauge, BUR, and cooling rate. A 25 µm blown film produced at 2.5:1 BUR and a low frost line is not directly comparable to a 50 µm cast film. Elmendorf tear is tested per ASTM D1922-15 or ISO 6383-2; the metallocene narrow distribution can shift the MD/TD tear balance relative to a broad Ziegler-Natta resin, so tear performance should be mapped over a range of BURs before finalising the film structure. Tensile yield and break values are measured by ASTM D882-18 or ISO 527-3:2018; elongation at break is strongly affected by draw ratio and die geometry. Seal initiation temperature and seal strength are best generated on a gradient heat-seal instrument according to ASTM F2029-16 and ASTM F88/F88M-21, using the target dwell time and jaw pressure. The absolute seal initiation temperature of F331F is not a fixed resin constant, because it is dominated by the thermal history, coextruded sealant dilution, and seal-bar design.

Optical transmittance and haze are measured by ASTM D1003-13 or ISO 14782:2008. In blown film, surface die lines and frost-line-induced roughness can overshadow the intrinsic optical advantage of metallocene resin; therefore, the total haze of a production film may be higher than laboratory-cast film values.

Published data for all end-use property values of this specific resin are limited in the open literature. The batch certificate, supplier technical data sheet, and pilot-scale conversion results are the only reliable sources for product-specific values. Generic metallocene-LLDPE studies may be used as a guide, but they do not replace a structured trial on the intended production line.

When F331F Replaces a Butene-Based Ziegler-Natta LLDPE in Multilayer Sealant Films

The substitution is most relevant in the sealant layer. In a coextruded structure where the sealant layer is a butene-based Ziegler-Natta LLDPE of 0.918 g/cm³ density and 1.0 g/10 min melt index, direct replacement with F331F may lower the heat-seal temperature. The reduction arises because the metallocene catalyst produces a narrower distribution of interchain short-chain branching, reducing the fraction of high-melting material that must be softened or melted before a seal forms. Hot-tack strength at short dwell times may also improve, but the actual difference should be measured with ASTM F1921/F1921M-18 or the relevant seal platform.

The same substitution can change extruder pressure and output. Because the high-molecular-weight tail is less pronounced than in a broad-distribution Ziegler-Natta grade, head pressure at constant screw speed may fall. This can lower specific energy consumption but may reduce the shear heating available to melt the resin, requiring a higher barrel setpoint. In addition, the lower melt strength of F331F may make the bubble more sensitive to air turbulence; therefore, the frost line height and cooling air should be retuned after the material change.

Compared with high-pressure LDPE, F331F cannot replicate the same melt tension or extrusion-coating neck-in behaviour. High-pressure LDPE contains long-chain branching that produces strain-hardening under extension; F331F does not contain the same long-chain branch population. In a 20 µm monolayer film produced on a 2.0:1 BUR, changing from 100 % LDPE to 100 % F331F may create bubble sag or unstable frost line movement. The correction is not to increase blow-up ratio further, but to adjust die gap, adjust the air ring, or blend in a suitable LDPE fraction.

Within the metallocene LLDPE range, F331F at 1.0 g/10 min melt flow rate has a lower melt index than typical high-flow mLLDPE grades specified at 2.0 g/10 min or above. The lower melt index is associated with higher average molecular weight, which can improve dart impact and puncture resistance but may increase melt viscosity at low shear and may require more careful purging when changing between resins. For a converter considering a switch from a 2.0 g/10 min mLLDPE to F331F, a pilot-scale evaluation is required to determine whether the chosen extruder drive and die pressure can tolerate the viscosity increase. Published data for this specific configuration is limited, so experimental verification is preferred.

Regulatory compliance for the raw resin is assessed under olefin polymer monographs. In the United States, the finished food-contact article may be evaluated against FDA 21 CFR 177.1520(c) when the article meets the specified extractive limits and use conditions. In the European Union, EU Regulation 10/2011 applies, with an overall migration limit of 10 mg/dm² for most food contact surfaces or 60 mg/kg for certain packaging configurations, depending on the food simulant and surface-to-volume ratio. The base resin must be REACH-registered or covered by a registration exemption for the intended market; the converter carries the obligation for finished article documentation. RoHS Directive 2011/65/EU restricts lead, mercury, cadmium, hexavalent chromium, PBB, and PBDE; these are not intentional components of the polymer, but converters must verify downstream masterbatch and ink compliance. For outdoor exposure, the unstabilised resin must be compounded with an appropriate UV stabilizer package; 0.5–1.0 wt% carbon black or an equivalent HALS/UV absorber system is common in agricultural film, but the exact dosage must be selected by accelerated weathering tests under ASTM G154-16 or ISO 4892-2:2013. Contact with strong oxidizers, chlorinated hydrocarbons, or aromatic solvents is outside the design envelope.