SABIC LLDPE 218WJA is a butene-comonomer linear low-density polyethylene resin supplied as nominally translucent pellets for general-purpose film conversion. The grade is specified by a melt flow rate of 2.0 g/10 min at 190 °C and 2.16 kg load when tested in accordance with ISO 1133-1:2022 or ASTM D1238, and by a solid-state density of 0.918 g/cm³ at 23 °C when tested in accordance with ISO 1183-1:2019 or ASTM D1505. The numerical designation 218 identifies this density–melt-flow combination within the SABIC LLDPE film platform; the letters WJ designate the film-processing family, and the A suffix denotes an antioxidant-stabilised formulation in the standard grade-sheet nomenclature. The polymer backbone is produced by a low-pressure gas-phase polymerisation route with butene as the short-chain branching comonomer. The resulting molecule contains predominantly linear chains with a controlled distribution of ethyl branches, which lowers the crystalline density relative to high-pressure LDPE and imparts a balance of low-temperature sealability and tear resistance that is not obtained with a homopolymer at the same density. The resin is supplied in pellet form with a nominal bulk density of 480 kg/m³ and is conventionally extruded on single-screw film lines with a general-purpose polyolefin barrier screw. Because the grade is designed for thin-gauge blown and cast film, its property envelope is normally reported on 25 µm to 50 µm monolayer structures after conditioning for 40 h at 23 °C and 50 % relative humidity in accordance with ISO 291 or ASTM D618. End-use mechanical values are highly dependent on frost-line height, blow-up ratio, die gap, and take-off speed, so the manufacturer’s datasheet values should be read as lot-average targets rather than guarantees for a specific line configuration.

Resin Property Envelope and Compliance Matrix

Table 1 reports typical values from SABIC grade sheets and general film-conversion data for the 0.918 g/cm³ butene class. Values marked as film properties are configuration-sensitive and are not lot-release specifications.

The resin is not moisture sensitive in pellet form; equilibrium moisture uptake at 23 °C and 50 % relative humidity is below 0.01 % by mass. Pre-drying is therefore not a normal production requirement unless the material has been stored in conditions allowing surface condensation or the regrind fraction exceeds 30 % in blends with hygroscopic additives. Thermal decomposition begins to release measurable volatiles only above 300 °C under inert atmosphere; oxidative degradation under melt-processing conditions is controlled by the stabiliser package supplied in the A formulation. For food-contact use, the base olefin polymer may be assessed under Commission Regulation (EU) No 10/2011 and FDA 21 CFR 177.1520 olefin polymer clearance, provided the final article is tested for overall migration and specific migration limits for the additive package. Converters must not infer food-contact approval from the resin grade name alone; the final film structure, printing inks, adhesives, and coating layers all contribute to the compliance status.

What governs the choice between blown-film bubble stability and cast-film throughput?

Because SABIC does not publish complete rheological curves for 218WJA in the standard grade sheet, the processing ranges in this section are based on the broader butene LLDPE density class and on production-scale film line settings. Converters should obtain the lot-specific certificate of analysis and, where available, the supplier’s extrusion technical bulletin before locking process parameters.

In blown-film extrusion on a 90 mm single-screw extruder with a 30:1 L/D ratio and a 150 mm spiral mandrel die, the melt temperature at the die lip is commonly set in the range 190 °C to 220 °C. At a die gap of 2.0 mm, a blow-up ratio of 2.5:1 to 3.5:1, and a frost-line height of 5 to 8 die diameters, the 2.0 g/10 min melt flow allows drawdown to gauges below 20 µm without the high melt-extensional failure observed with comparable high-pressure LDPE at the same die temperature. The same melt flow that improves spiral-mandrel flow distribution reduces bubble stability relative to a 1.0 g/10 min butene grade such as SABIC LLDPE 118WJ. Converters running tall-bubble high-stalk geometries may therefore require additional air-ring cooling or an internal bubble cooling system to maintain a stable neck height above the die. At blow-up ratios above 3.0:1, bubble instability may present as a wandering neck rather than complete collapse, and the melt pressure at the screen changer should be monitored for excursions that indicate screen blinding from degraded polymer or contamination.

At the feed throat, pellet temperature should remain below 50 °C to prevent bridging; hopper magnets and drawer magnets should be checked for metal contamination. Screw cooling in the feed section is often operated at 40 °C to 50 °C to maintain solids conveying. A compression ratio between 2.5:1 and 3.5:1 is typical for LLDPE film screws. Melt pressure excursions above 35 MPa on a 75 mm extruder indicate screen blinding or excessive shear heating. In cast-film line configurations with a flat die and chill roll, the resin can be processed at melt temperatures of 230 °C to 260 °C and line speeds above 150 m/min, but the exact limit is set by the polymer’s relaxation spectrum and the quench rate of the primary chill roll. Die-lip deposit formation has been observed on long production runs above 260 °C with excessive residence time; converters should therefore match barrel-temperature profiles to screw recovery time and avoid over-shearing in the feed-compression zone.

Film properties in monolayer structures are routinely measured after conditioning according to ISO 291 at 23 °C and 50 % relative humidity. Tensile properties are commonly determined by ISO 527-3:2018 on 15 mm wide specimens cut from 25 µm film; the balance of machine-direction and transverse-direction elongation is sensitive to blow-up ratio and frost-line height. A 25 µm film produced at a 2.5:1 blow-up ratio and 5 die-diameter frost-line height generally exhibits a machine-direction tensile strength at break above 30 MPa and a transverse-direction tensile strength at break above 20 MPa; the corresponding elongation at break exceeds 500 % in both directions. Dart impact under ASTM D1709, Method A, is normally in the range 100 g to 150 g for 25 µm film, but the specific value varies with additive loading, die gap, and film conditioning history. Elmendorf tear values measured under ASTM D1922 or ISO 6383-2 are typically lower in the machine direction than in the transverse direction for blown film, consistent with orientation effects in the bubble. Published data for this specific configuration is limited; converters are required to generate line-specific capability data before commercial qualification.

When High-Speed Form-Fill-Seal Demands Narrow the Hot-Tack Window

The seal initiation temperature of butene LLDPE in this density class is commonly observed in the range 100 °C to 110 °C on a laboratory heat sealer using 1 s dwell and 0.3 MPa jaw pressure. The hot-tack window extends above the melt point of 121 °C but is narrower than metallocene-catalysed octene LLDPE. Converters running vertical form-fill-seal machines with seal-cycle residence times below 0.5 s should verify the seal strength under production conditions because SABIC LLDPE 218WJA is a conventional Ziegler-Natta grade with broad molecular weight distribution; hot-tack performance is governed by crystallisation rate and can be reduced by excessive film orientation or surface slip additives. The grade is often blended with 10 % to 20 % LDPE to improve bubble stability and seal-through-contamination behaviour, but the addition of LDPE raises the seal initiation temperature and reduces dart impact compared with the neat resin.

Relative to SABIC LLDPE 118WJ in the same 0.918 g/cm³ density class, the 218WJA grade has a higher melt flow rate, which reduces screw torque and melt pressure at equivalent output on a 65 mm extruder. The higher MFR also narrows the stable blown-film operating window at blow-up ratios above 3.5:1 because melt strength is lower. In cast-film applications, 218WJA permits thinner gauge targets and faster line speeds than 118WJ. Relative to SABIC LLDPE 318WJ, a nominal 3.0 g/10 min grade in the same family, 218WJA retains a slightly broader operating window in low-shear bubble formation but has a higher specific energy demand in high-screw-speed extrusion. Against a metallocene-catalysed octene LLDPE of equivalent density and melt flow, 218WJA typically gives lower dart impact and Elmendorf tear at 25 µm, but offers less shear sensitivity in conventional film extrusion. Direct blending with high levels of uncompatibilised polypropylene creates discrete PP domains that lower dart impact and create anisotropic tear because of immiscibility. Amine-based antifog concentrates at elevated addition levels can interact with the antioxidant package and generate colour shifts in unstabilised film edges; compatibility tests are required before large-scale use.

Storage temperature should remain below 50 °C to avoid oxidation of the stabiliser package before extrusion. Regrind levels up to 20 % are generally tolerated in monolayer film without significant loss of optical or mechanical properties, but edge-trim regrind from corona-treated film can raise melt viscosity unevenly because polar surface oxidation modifies local rheology. When regrind is used, the film should be evaluated for gel count, dart impact, and Elmendorf tear under the same conditioning protocol described above. The grade is not intended for medical implant applications; converters requiring USP Class VI or ISO 10993 testing must qualify the finished device independently because the resin supplier’s standard documentation does not cover implantable end-use pathways.