SABIC LLDPE Grades: A Buyer's Map of Film, Moulding and Rotomoulding Families

Linear low-density polyethylene (LLDPE) is a copolymer of ethylene with an α-olefin—butene-1, hexene-1 or octene-1—produced in gas-phase, solution or slurry polymerisation reactors. The short-chain branching distribution controls crystalline morphology, density, tensile yield stress, tear resistance and environmental stress-cracking resistance. Within the SABIC LLDPE portfolio, the film, injection moulding and rotational moulding families are separated primarily by melt flow rate at 190 °C and 2.16 kg load under ISO 1133-1:2022, density under ISO 1183-1:2019, comonomer type, molecular weight distribution and additive package. A buyer’s map therefore requires cross-referencing application-specific tests such as dart drop, tear propagation, flexural modulus and low-temperature puncture against extrusion or moulding machine capability.

The SABIC LLDPE film family includes designations such as 118W, 119Z, 121W, 218W, 318B and 518N. Moulding selections include M200024 and M500026, while rotational moulding selections include R40036E and R50035E. These designations are not interchangeable across the three conversion routes. Melt flow rate and density alone do not define suitability; the polymer architecture, additive loading, powder particle size for rotomoulding and gel level for film must be evaluated against the specific production line.

How Comonomer Type Shifts the Film-to-Rotomoulding Property Balance

Butene-1, hexene-1 and octene-1 comonomers introduce short-chain branches of different lengths. At equivalent density and melt flow rate, hexene-1 and octene-1 copolymers generally provide higher dart impact and Elmendorf tear values because longer branches are more effective in increasing tie-chain probability during crystallisation. The difference is measurable under ASTM D1709-16a dart drop for film and ASTM D1922-15 for tear propagation. For a 25 µm blown film, a hexene-1 grade may show a substantial dart impact advantage over a butene-1 grade of the same nominal density, although published grade-specific datasheets remain the controlling reference for exact values.

Rotational moulding grades are often positioned at density 0.932–0.939 g/cm³ and melt flow rate 3.5–6.0 g/10 min under ISO 1133-1:2022. This balance permits adequate flow during the oven residence window while retaining low-temperature impact and environmental stress-cracking resistance. The latter is commonly assessed using ASTM D1693-15 in 100% Igepal CO-630 at 50 °C; a high-toughness tank or chemical vessel grade may be specified with an F50 failure time exceeding 1000 h, but the exact value must be confirmed on the individual grade certification.

For blown-film conversion, the practical consequence of comonomer choice is not limited to mechanical properties. Hexene-1 grades can allow a lower film gauge while maintaining dart impact, but bubble stability, film blocking and seal initiation temperature must be revalidated when switching from butene-1 to hexene-1 or octene-1 platforms. Seal initiation temperature measured on a laboratory heat sealer according to ASTM F1921-18 is a key control for form-fill-seal packaging lines.

For blown-film lines with an 80 mm grooved-feed extruder and L/D ratio 24:1 to 30:1, die gap 1.8–2.5 mm, blow-up ratio 2.0:1–3.0:1 and frost line height 250–600 mm, a film-grade melt flow rate below 1.0 g/10 min can raise melt pressure and reduce throughput on older lines with limited motor torque. Field records from high-output lines show that bubble instability and blocking faults occur more frequently when the frost line is positioned above 600 mm or when air-ring cooling is uneven. A low-gel film grade with a controlled antioxidants package is required to avoid screen-pack pressure rise above 0.5 MPa per shift during long runs.

Film Extrusion Through Die Gap, Blow-Up Ratio and Bubble Stability

Die gap selection interacts with melt strength and draw ratio. A die gap below 1.8 mm on a conventional single-lip air ring increases shear stress at the die lip and can initiate melt fracture in high-molecular-weight film grades. A die gap above 2.5 mm lowers orientation and may reduce machine-direction tensile strength. Film converters using internal bubble cooling systems typically run lower frost line heights and higher output rates, but the frost line must remain below the collapsing frame to prevent film blocking on the nip rolls.

Dart drop resistance for 25 µm film is assessed under ASTM D1709-16a Method A with a 38 mm diameter dart. Elmendorf tear is measured under ASTM D1922-15 in both machine and transverse directions. Puncture resistance is measured under ISO 7765-1. These values depend on film gauge, blow-up ratio, frost line height and chill-roll temperature, not solely on grade selection. A grade datasheet value obtained on a 25 µm film at a 2.5:1 blow-up ratio cannot be directly applied to a 12 µm film on a high-stalk bubble.

The ranges in the table are commercial family windows, not single-grade specifications. Individual SABIC LLDPE grade certificates and technical datasheets provide the mandatory minimum and typical values for each designation.

On cast-film lines, chill-roll temperature below 18 °C may create non-uniform quench and increase haze, while chill-roll temperature above 25 °C can reduce gloss and promote blocking under tension. Corona treatment is typically applied at 38–42 mN/m wetting tension for lamination or print adhesion. Surface treatment decay with time, slip additive migration and coefficient of friction measured under ISO 8295 must be revalidated after any formulation change.

When Injection Moulding Grades Require Higher Melt Flow and Rapid Set-Up

Injection moulding LLDPE grades such as M200024 and M500026 are specified for thin-wall closures, caps, houseware and containers where high flow permits short filling time and low injection pressure. Melt flow rates in the 20–50 g/10 min range under ISO 1133-1:2022 reduce pressure drop and permit filling of long flow paths. The trade-off is reduced tensile strength and environmental stress-cracking resistance compared with lower-melt-flow rotomoulding grades.

On reciprocating-screw machines with screw L/D 20:1 and compression ratio 2.5:1, melt temperature is held at 190–230 °C and mould wall temperature at 10–30 °C. Specific injection pressures of 80–120 MPa are common for high-flow LLDPE in multi-cavity tools. Clamp force requirements depend on projected area and cavity count; a 1000 kN clamp may process a 4-cavity thin-wall closure tool with hot runner diameters optimised for LLDPE viscosity. In overcooled shallow parts, warpage is controlled by gate location, packing pressure decay and part ejection temperature rather than by a single resin variable.

Spiral flow length testing under ASTM D3123-09 is used to compare flow at fixed barrel temperature and injection pressure. A 50 g/10 min MFR grade fills a longer spiral than a 20 g/10 min grade at the same injection pressure, but the higher-flow material may exhibit lower environmental stress-cracking resistance. Notched impact strength is measured under ISO 179-1; heat deflection temperature under ISO 75-2 at 0.45 MPa is commonly reported for moulded parts. Published data for the specific SABIC moulding grade configuration should be requested from the supplier certification.

Rotational moulding converts powdered LLDPE into hollow tanks, agricultural storage vessels, road barriers and specialised liners. The process is limited by the oven residence window and the thermal stability of the polymer powder. A melt flow rate of 3.5–6.0 g/10 min and density 0.932–0.939 g/cm³ are typical for high-toughness rotomoulding grades. The powder is usually 35 mesh (500 µm) for general tanks, with finer fractions used where surface finish or thinner walls are required.

Rotomoulding Demands Fine Powder, Low Pigment Scorch and Long Oven Residence

Rotational moulding powders produced by ambient grinding exhibit differences in bulk density, dry flow and particle size distribution. A 35 mesh (500 µm) powder is standard for large parts, while an 80 mesh (180 µm) fraction may be used for foamable or detailed-surface applications but increases thermal degradation risk during long cycles. Oven temperatures of 260–300 °C and rotational ratios near 4:1 are common, but the exact peak internal air temperature must be matched to the grade. Pigment systems should be evaluated for scorch at the maximum cycle temperature; excessive residence above 30 min at peak temperature can produce yellowing and a measurable loss of impact strength.

Moisture pickup above 0.02% by weight in powdered rotomoulding grades can generate steam pinholes and surface porosity. Pre-drying at 50 °C for 2 h is recommended when the powder has been stored at relative humidity above 60%. The use of regrind in rotomoulding should be controlled by melt flow retention and low-temperature puncture testing under ISO 6603-2; regrind fractions above 25% can alter powder flow and part impact performance. Metal stearates and other acid-neutralising additives should be matched to the grade chemistry to avoid plate-out on the mould surface.

Compliance documentation for food-contact and industrial LLDPE shipments is part of the buyer’s map. Not all SABIC LLDPE grades carry every food-contact approval, and the approval status depends on food type, contact temperature and intended article use. Grade selection for potable water tanks, fuel tanks and food packaging must be cross-checked against the current grade certificate.

At the receiving warehouse, LLDPE pellets or powder should be stored below 50 °C and protected from direct sunlight. Continuous moisture absorption at relative humidity above 60% alters melt flow, surface finish and moulded or film impact. Before release to production, any lot with a melt flow deviation greater than 10% from the certification value or with visible contamination should be quarantined and retested against the grade specification.