SABIC LLDPE 218BE is a pelletized butene-comonomer linear low density polyethylene blown-film resin. The grade is positioned for monolayer and coextruded film applications where processability, abuse resistance, and sealing response are specified in film specifications. The nominal density is 0.918 g/cm³ measured by ISO 1183-1:2019; the melt mass-flow rate is 2.0 g/10 min at 190 °C under 2.16 kg load measured by ISO 1133-1:2022. The resin is used in heavy-duty sacks, agricultural films, carrier bags, liners, and lamination films. Its additive package is standard polyolefin stabilisation for blown-film conversion, not injection moulding. Because the material is a butene-based linear low density polyethylene, its tear and dart impact performance are lower than those of octene-based grades at equivalent density and melt index but higher than those of low density polyethylene at equivalent film gauge.

In industrial sack lines producing 50 kg woven-polypropylene laminated sacks or heavy-duty polyethylene liners, 218BE is coextruded or laminated at 25 µm to 40 µm gauge. The film is frequently drawn through a gap-fed laminator with a chill roll at 15–20 °C; surface oxidation is managed by maintaining melt temperature below 220 °C to preserve seal strength measured by ASTM F88. On a 90 mm extruder with 28:1 L/D feeding a 350 mm die, edge trim rates above 12% may indicate insufficient melt homogeneity or die pin misalignment, and gauge variation measured by a beta gauge should be held within ±5% of target.

In greenhouse and silage film applications, 218BE is dry-blended with hindered amine light stabilizer and UV absorber masterbatches at let-down ratios specified by the masterbatch supplier. Film thickness is commonly 100 µm to 180 µm for greenhouse covers and 25 µm to 50 µm for mulch applications; tensile properties after weathering are evaluated by ISO 527-3 and ASTM D882, while resistance to UV degradation is assessed by ASTM D4329 or ISO 4892-3. The butene-comonomer structure provides adequate dart impact for season-long film, but the absence of a high-loading UV package in the base resin requires converter discipline in masterbatch dispersion. Poor dispersion appears as localised embrittlement after 1000 h of artificial weathering, when some agricultural films exhibit brittle failure in areas of masterbatch agglomeration.

How Does the Melt Flow Ratio of 218BE Influence Film Extrusion Stability?

The melt flow rate of 2.0 g/10 min does not define shear-thinning behaviour. The melt flow ratio between high-load melt flow rate at 21.6 kg and standard melt flow rate is more informative for die design and bubble stability. For butene-based LLDPE grades in this melt index range, melt flow ratios commonly fall between 24 and 28; this moderately broad molecular weight distribution permits stable bubble formation at blow-up ratios of 2.0:1 to 3.0:1 on spiral mandrel dies. The value for 218BE should be confirmed from the certificate of analysis because comonomer distribution and catalyst type shift this parameter across production lots. Narrow-bubble instability is less likely than with metallocene grades of the same melt index, but the attainable draw-down is lower than that of high melt strength LDPE. On a production line with a 45 mm grooved-feed extruder and 24:1 L/D, melt pressure response to screw speed changes is relatively flat compared with a 0.8 g/10 min grade, meaning that thickness corrections require longer stabilisation times after a speed adjustment.

At the die lip, shear viscosity of 218BE is lower than that of 1.0 g/10 min LLDPE, reducing extruder motor load on 25:1 to 30:1 L/D machines. A 65 mm grooved-feed extruder coupled to a 150 mm spiral mandrel die with 1.2 mm die gap operates with die melt pressure below the limit for barrier screws, and screen pack replacement is driven by gel accumulation rather than pressure. Filter screens of 60–80 mesh are common; finer screens can reduce visible gel particles in 12 µm film but increase shear heating and melt temperature. The die pressure differential between the centre and edge die zones must be held within ±10% to avoid uneven gauge bands, particularly when the die diameter exceeds 150 mm. Processing lot-to-lot variation is controlled by the supplier through melt flow rate and density specifications; a deviation of more than 0.05 g/10 min in melt flow rate or 0.001 g/cm³ in density from the reference lot may shift frost line height and gauge profile, requiring a die gap or blow-up ratio adjustment.

Gauge Uniformity Requires Controlled Draw-Down Below 25 µm

At nominal thickness below 25 µm, the film enters a draw-down regime where butene-comonomer LLDPE can develop machine-direction orientation. A die gap of 0.8 mm increases draw ratio and tensile strength measured by ASTM D882; a die gap of 1.2 mm to 1.6 mm reduces molecular orientation and preserves Elmendorf tear values measured by ASTM D1922. The optimum blow-up ratio on standard die configurations is between 2.2:1 and 3.0:1 for most film widths; higher blow-up ratios reduce machine-direction tensile strength and increase transverse-direction shrinkage, while lower ratios reduce bubble stability under plant air turbulence. Capacitive gauge measurement across the layflat should remain within ±5% of the target; excursions beyond ±8% compromise dart impact performance measured by ASTM D1709 Method A. On high-speed lines, edge-trim breakage and folded-edge splitting are observed when frost line height is raised above 1.5 times the die diameter, because the film loses bubble support before crystallisation is complete.

Film conditioning before mechanical testing follows ISO 291 at 23 °C and 50% RH for 40 h. Tensile properties are thickness-dependent and must be measured on nominal-gauge film rather than on resin plaques. Seal strength measured by ASTM F88 depends on jaw temperature, dwell time, and sealing pressure; for a 25 µm film, heat seal initiation temperature is a function of comonomer content and surface additive bloom. Users should not compare seal data across laboratories unless the sealing jaw profile and film conditioning history are identical. In extrusion lamination and extrusion coating, 218BE is usually blended with LDPE to increase draw-down and melt strength. The blend ratio is typically 70:30 to 80:20 LDPE:LLDPE by weight; the addition of LLDPE increases hot tack and heat seal strength measured by ASTM F1921 but raises melt pressure at the die. For a 2.0 g/10 min LLDPE, a blend ratio above 20 wt% may require a reduction in die gap or an increase in melt temperature of 5–10 °C to maintain neck-in below acceptable limits.

When Barrel Temperatures Approach 240 °C, Residence Time Becomes the Controlling Variable

At melt temperatures above 240 °C, oxidative stability of 218BE is finite. Extended hold-up in extruder dead zones, screen packs, or transfer lines leads to gel particles and film specks. On a 30:1 L/D grooved-feed extruder, melt temperature at the die should be kept below 230 °C; short transients to 240 °C are tolerated during purging but should not exceed 10 minutes. Degradation appears as reduced bubble transparency and amplifying backpressure fluctuation. If gel counts exceed the converter's optical inspection threshold, corrective action is a reduction of die setpoint by 5–10 °C and a screw speed decrease rather than an increase in screen pack density. Purging after the run should use a low-viscosity polyolefin purge compound or a higher-MFR LDPE to remove carbonized residues from dead spots.

218BE is not compatible with polar barrier resins such as ethylene vinyl alcohol and polyamide in direct coextrusion; a maleic anhydride grafted tie-layer is required between the polyolefin and the polar layer. Dry blending with recycled ionomer or heavily contaminated post-consumer material is not recommended at levels above 5 wt% without melt filtration of 40 mesh or finer, because incompatible domains reduce Elmendorf tear values measured by ASTM D1922 and create visible gels. No pre-drying is required under normal sealed storage; surface moisture condensation at relative humidity above 60% should be removed by using dry-air hopper blankets or silo ventilation.

Extrusion Backpressure and Melt Elasticity

218BE belongs to the butene-copolymer class of LLDPE. Compared with LDPE homopolymer, the linear backbone of 218BE provides higher tensile strength and dart impact at equal film gauge, but lower melt elasticity and more demanding bubble control. Compared with metallocene-catalyzed LLDPE of similar density, 218BE has a broader molecular weight distribution, lower melt pressure at the die, and lower film clarity, but it is less likely to develop melt fracture at high output. Compared with octene-copolymer LLDPE, the butene comonomer yields lower Elmendorf tear and dart impact under heavy abuse loads, but it provides adequate performance for many industrial films at lower resin cost. These differences are resolvable with ASTM D1709, ASTM D1922, and ASTM D882 on films of identical gauge and processing history.

Confirm the Regulatory Status Before Food Contact Use

The base polyolefin is within the scope of olefin polymers referenced in 21 CFR 177.1520. For food contact in the United States, 21 CFR 177.1520(c) specifies conditions of use A through H, with extractable fractions in n-hexane and xylene subject to upper limits depending on olefin polymer type. A converter must verify that the finished article meets the end-use condition appropriate for the food type and temperature/time profile. For European food contact, the finished article must comply with Commission Regulation (EU) No 10/2011 and its amendments; the overall migration limit of 10 mg/dm² applies for food contact films unless a specific food type or temperature condition requires a lower limit. The converter is responsible for verifying specific migration of additives and for ensuring that production aids such as slip and antiblock concentrates meet the applicable positive lists. REACH registration is maintained by the supplier according to applicable tonnage bands; no substance of very high concern is intentionally added above the reporting threshold. Users requiring medical or pharmaceutical film compliance must confirm that the grade meets USP Class VI or ISO 10993-5 requirements, because standard polyethylene film grades are not automatically certified for such applications.

The resin is not recommended for rotational moulding, injection moulding of thick-walled parts, or compression moulding, because the melt flow rate and additive package are not designed for long residence times at low shear. In multi-layer structures, the grade is normally used in the skin or core layers rather than as a sealant layer where very low seal initiation is required; sealant performance is determined by ASTM F88 on the final film structure. Storage should be below 50 °C in a dry environment; prolonged exposure to ultraviolet radiation should be avoided because the base grade does not contain high-loading UV stabilisers. If higher ultraviolet resistance is required, the converter must add a UV masterbatch at the recommended let-down ratio and verify film performance by ASTM D4329 or ISO 4892-3 weathering exposure.