Blown-film converters evaluating linear low-density polyethylene feedstocks for thin-gauge flexible packaging can specify SABIC LLDPE 6218BE as a butene-comonomer resin with a nominal melt flow rate of 2.0 g/10 min determined at 190°C/2.16 kg according to ISO 1133-1 and a nominal density of 0.918 g/cm³ according to ISO 1183-1. The product is supplied in pellet form for conventional single-screw blown-film conversion and is positioned in the 0.915–0.925 g/cm³ density band as a general-purpose film grade rather than a high-clarity or high-strength metallocene grade. The 0.918 g/cm³ density corresponds to a semicrystalline morphology with a lower crystalline weight fraction than HDPE and a reduced secant modulus measured by ISO 527-3 or ASTM D882. The 2.0 g/10 min melt flow rate provides sufficient melt fluidity to limit high-shear heating on lines from 45 mm to 65 mm extruder diameter. The resin does not require predrying below 60% relative humidity; above this threshold, hopper drying at 60–70°C for 2–4 h is applied to reduce surface moisture and prevent bubble defects.

Common film applications for this grade are general-purpose packaging, liner film, carrier bags, lamination film, and overwrap structures where stiffness requirements are moderate. The density and melt-flow combination supports thin films down to 20 µm on adequately sized dies, but gauge variation below 20 µm becomes a limiting factor on older air-ring systems. Film thickness variation should be measured by ISO 4593 or capacitive scanning and controlled within ±5% to avoid seal and print registration defects.

Why Does Butene Comonomer Architecture Constrain Dart Impact and Tear Propagation Relative to Hexene and Metallocene Grades?

The butene comonomer inserts a two-carbon short-chain branch into the polyethylene backbone, while hexene and octene insert four-carbon and six-carbon branches respectively. During crystallization, longer comonomer branches create tie-molecules that bridge adjacent lamellae and resist crack propagation under impact or tear loading; shorter butene branches are less likely to anchor in multiple crystalline regions. The resulting film from SABIC LLDPE 6218BE therefore displays lower dart impact F50 values and reduced machine-direction Elmendorf tear resistance when compared at equal thickness with a hexene-copolymer LLDPE or a metallocene LLDPE of the same 0.918 g/cm³ density and 2.0 g/10 min melt flow rate. This is a constitutive limitation of the comonomer architecture, not a processing defect.

Converters should measure dart impact according to ISO 7765-1 or ASTM D1709 and Elmendorf tear according to ISO 6383-2 or ASTM D1922 at the exact film gauge and blow-up ratio used in production. Values obtained at 50 µm cannot be scaled linearly to 25 µm because orientation and thickness-dependent failure mechanisms change the failure mode from ductile to brittle.

Melt Pressure, Shear Thinning, and Torque Response on Standard PE Barrier Screws

At the nominal melt flow rate of 2.0 g/10 min, SABIC LLDPE 6218BE exhibits lower viscosity than fractional-melt-index LLDPE grades and generally produces lower extruder discharge pressure. The shear-thinning response of conventional butene-copolymer LLDPE is pseudoplastic; apparent viscosity decreases with increasing shear rate in the die lip region. Processors should generate capillary viscosity data according to ISO 11443 at three temperatures such as 190°C, 210°C, and 230°C to calculate the shear-rate dependence and activation energy for the specific production lot, because molecular weight distribution variations can alter the curve. A single point of melt flow rate is insufficient for die design and output prediction.

Compared with a metallocene LLDPE of equivalent melt index and density, the broader molecular weight distribution of a Ziegler-Natta butene grade often lowers viscosity at high die shear rates. This reduces torque on standard PE barrier screws with L/D ratios from 24:1 to 30:1. The trade-off is a wider relaxation time spectrum that can delay sharkskin onset but increase die swell; die gap, melt temperature, and air-ring pressure require coordinated adjustment. Extruders with worn barriers or damaged screw coatings may present higher melt-temperature variability with this grade because low-viscosity melt can generate recirculation zones at the barrier flight.

On a 45 mm single-screw blown-film line with a 24:1 L/D barrier screw, a 1.8 mm die gap, and a 200 mm die diameter, the grade is initially processed with melt temperatures between 190°C and 230°C. Blow-up ratios from 2.0 to 3.0 and frost line heights of 8 to 12 die diameters are used as starting conditions. These values are process settings, not product specifications, and require adjustment for die size, air-ring capability, winder tension, and ambient humidity. Operation below 180°C raises the risk of melt fracture and poor homogenization, while melt temperatures above 250°C accelerate oxidative degradation and may form gels if residence time exceeds 5 min. Bubble stability is maintained with dual-lip air-ring chilled air at 8–15°C or internal bubble cooling where available. The 2.0 g/10 min melt flow rate lowers extruder motor load relative to fractional-melt-index film grades but also reduces melt strength at high stalk heights, so bubble oscillation must be controlled by frost line height and external air pressure rather than by increasing melt temperature alone.

Optical properties are controlled by the base resin crystalline morphology, frost line, and stalk height. Haze measurements per ISO 14782 are sensitive to bubble stability and internal die surface quality. The butene comonomer environment does not intrinsically create high clarity compared with metallocene grades but often remains acceptable for non-premium packaging. Gloss at 45° measured by ASTM D2457 decreases as frost line height increases because longer cooling time produces larger spherulites and surface roughness. For applications requiring high clarity, a metallocene LLDPE or an LDPE blend component may be necessary. Blending with LDPE is used to improve melt strength and bubble stability. Additions of 10–20 wt% LDPE at 0.918–0.924 g/cm³ density broaden the bubble stability window and increase draw-down ratio but reduce dart impact and tear resistance. Fluoropolymer processing aids are added at 200–500 ppm to delay melt fracture and reduce die-lip build-up. The exact loading depends on die gap and shear rate; excessive processing aid can reduce film surface energy and affect printing. Die-lip build-up should be monitored by visual inspection and adhesion testing after extrusion.

In high-speed horizontal or vertical form-fill-seal conversion, the seal initiation temperature of SABIC LLDPE 6218BE is typically higher than that of a metallocene LLDPE of equivalent density, and hot-tack force at seal bar release is generally lower. Seal strength should be measured according to ASTM F88 and hot-tack according to ASTM F1921 over a seal temperature range of 120–150°C and a dwell time appropriate to the machine. If the film contains no slip or antiblock, the coefficient of friction may exceed 0.40. Addition of a slip/antiblock masterbatch to achieve static coefficient of friction below 0.20 measured by ISO 8295 is required for high-speed packaging lines but can reduce corona treatment durability and lamination bond strength. Corona treatment levels of 38–42 mN/m according to ASTM D2578 are used for solventless lamination; retreatment is required after 72 h if migratory slip agents are present because surface energy decays through additive migration to the surface.

When Converters Substitute SABIC LLDPE 6218BE for Metallocene-LLDPE in High-Integrity Lamination Structures

Direct replacement of metallocene-LLDPE with SABIC LLDPE 6218BE in a high-integrity lamination structure should be validated against dart impact, seal initiation, and machine-direction tear. The butene grade may show lower puncture propagation resistance at sub-25 µm thickness. In a three-layer coex film with an HDPE core and LLDPE skins, the grade can be placed as a skin layer to provide sealability while the core supplies stiffness; film stiffness should be measured by ISO 527-3 or ASTM D882. Blending 20–30 wt% metallocene LLDPE into the skin layer is common for recovering dart impact and tear, but haze must be monitored according to ISO 14782 or ASTM D1003 because the blend can increase visible haze compared with the neat metallocene.

For extrusion-lamination applications where the polymer is applied at 290–320°C melt temperature, oxidative stability and gel formation should be evaluated. The lower melt strength of 2.0 g/10 min butene resin may produce greater edge neck-in than a hexene copolymer with lower melt flow. Edge neck-in should be measured on the actual coating line because published data for this specific configuration is limited.

Regulatory Boundary Conditions and Documentation Requirements for Food-Contact Structures

SABIC LLDPE 6218BE is represented as suitable for food-contact applications under 21 CFR 177.1520 in the United States and Commission Regulation (EU) 10/2011 in the European Union when the finished article meets the applicable conditions of use and the overall migration limit of 10 mg/dm². Specific migration limits for additives must be checked against the certificate of analysis and the full formulation, because the base resin alone does not define the migration profile of a finished film containing slip, antiblock, polymer processing aids, or solvent-based laminating adhesives.

Converters must maintain documentation for organoleptic testing, residual volatile content, and migration testing according to EN 1186 or ASTM D3642 where required. The resin should not be combined with amine-based additives without evaluating interaction with residual peroxides generated during extrusion; amine chemistry can lead to yellowing or crosslinking in polyethylene formulations. This boundary condition is particularly relevant in lamination inks and adhesives used downstream. Under REACH, the Safety Data Sheet status and SVHC candidate list status should be verified in the European SDS. Where masterbatches are added, the converter must re-evaluate heavy metal limits under applicable packaging regulations such as 94/62/EC.

Storage in original sealed containers at 20–30°C and below 60% relative humidity minimizes moisture regain and additive migration. Bags opened longer than 24 h should be re-closed and kept in a clean, dry area. The product should not be exposed to direct sunlight for extended intervals because UV-induced degradation can shift the molecular weight distribution and reduce film toughness; the base resin is not formulated with a long-term UV stabilization package. For heavy-duty shipping sacks and agricultural stretch-wrap applications requiring enhanced tear propagation resistance, the performance limits of butene-copolymer LLDPE should be compared with hexene or metallocene alternatives through measured dart impact according to ISO 7765-1, puncture resistance according to ASTM D5748, and tensile elongation according to ISO 527-3 or ASTM D882. Published data for this specific configuration is limited; converter trials remain the definitive validation method.