SABIC LLDPE 118NJA is a butene-comonomer linear low-density polyethylene supplied as free-flowing pellets for blown film extrusion. The nominal density is 918 kg/m³ when tested in accordance with ISO 1183-1:2019, and the nominal melt flow rate is 1.0 g/10 min at 190 °C/2.16 kg when tested in accordance with ISO 1133-1:2011. These melt-state and solid-state parameters place the grade in the low-density, low-melt-flow segment used for monolayer and coextruded packaging films, produce bags, carrier bags, lamination substrates, and general-purpose liners. The stabilization package protects molecular weight during standard screw plastication, but UV resistance must be supplied by a separate additive if the film is intended for extended outdoor exposure.

Because the comonomer is butene, the short-chain branch architecture differs from SABIC high-alpha-olefin grades and from metallocene-catalyzed LLDPE. Butene produces a more heterogeneous short-chain branch distribution than octene-modified resins of similar density. This influences tie-chain formation, tear resistance, dart impact, and certain optical properties in film form. The additive package in 118NJA includes a primary antioxidant and acid scavenger to maintain color and melt stability. The package is not designed for long-term outdoor exposure without additional stabilizer masterbatch.

What Processing Boundaries Are Imposed by a 1.0 g/10 min Melt Flow Rate?

On a conventional smooth-bore blown film line with an extruder screw L/D of 25:1 to 30:1, the resin normally enters the feed throat at ambient temperature and begins plastication in the compression zone. A barrel profile of 160 °C to 190 °C in the rear zones and 190 °C to 210 °C at the die adapter is commonly used. Melt temperatures below 170 °C can create high head pressure and reduce melt-temperature uniformity. Temperatures above 230 °C can cause oxidative chain scission, visible gel formation, and reduced dart impact in the finished film.

For narrow die gaps between 1.5 mm and 2.0 mm, thin-film production can be increased at the expense of tear anisotropy. A die gap of 2.0 mm to 2.5 mm is often selected to provide more uniform melt temperature and reduced die lip fouling. Blow-up ratios are typically set between 2.0:1 and 3.0:1. Below 2.0:1, transverse-direction orientation is limited and dart impact may decline. Above 3.0:1, bubble stability becomes more sensitive to ambient air turbulence. Frost line height is commonly maintained at 4 to 8 die diameters, depending on film thickness and air-ring design.

The low melt flow rate increases viscous heating in high-speed screws. If the resin remains above 200 °C for more than 5 min, oxidative gel formation may become visible as fisheyes. A specific energy input of 0.25 kWh/kg to 0.35 kWh/kg is typical for LLDPE blown film extrusion. Above 0.40 kWh/kg, melt-temperature control becomes difficult on small extruders. Screen packs and high-shear mixers are permissible, but the resulting melt-temperature rise should be offset by lowering rear barrel setpoints.

Melt fracture in 118NJA may be observed at high output rates when the wall shear stress exceeds the critical value for the polymer. Published studies on butene LLDPE place the critical shear stress for sharkskin between 0.1 MPa and 0.2 MPa. The condition appears as regular surface roughness at the die lip and can be controlled by raising melt temperature, increasing die gap, reducing output, or blending with LDPE. Sharkskin is more likely in films below 25 µm thickness at high line speeds.

Although polyethylene is not hygroscopic, condensation on cold pellets is a process risk. In plants with silo temperatures below 20 °C and high ambient humidity, surface moisture can create micro-bubbles at the die exit. Dry-air conveying or hopper heating to 40 °C to 60 °C can reduce this risk. Pre-drying at 80 °C for 2 h may be used when hopper residence time is short, but most blown film lines do not require it.

When SABIC LLDPE 118NJA is compared with LDPE of the same melt flow rate, the LLDPE resin generally displays higher dart impact and Elmendorf tear resistance when film specimens are tested under ISO 7765-1 and ISO 6383-2. However, LDPE has greater melt strength and higher clarity. In collation shrink and clarity films, LDPE is often blended with 118NJA to improve optical quality and bubble support. The addition of LDPE at levels above 20 wt% may reduce haze but also decreases tear resistance.

Compared with octene LLDPE of similar density, 118NJA generally exhibits lower dart impact and lower tear strength because the butene comonomer is less efficient at forming tie chains in the amorphous phase. The processing advantage of 118NJA is typically lower head pressure and less pronounced melt-fracture sensitivity. Published data for this specific comparison in monolayer 25 µm films is limited; grade selection must therefore be confirmed by pilot trials on the intended line.

Relative to metallocene LLDPE of similar melt index and density, 118NJA is usually described as having a broader molecular weight distribution and higher shear thinning. This favors extrusion stability but can reduce puncture resistance and clarity. The difference is caused by catalyst type and the resulting comonomer distribution rather than by density alone.

Film Property Evaluation Under ISO and ASTM Methods

Conditioning and specimen preparation dominate film test data. Film samples are typically conditioned at 23 °C and 50 % relative humidity for at least 40 h before testing per ISO 527-3 or ASTM D882. Because blown film is anisotropic, machine-direction and transverse-direction values are reported separately rather than as a single isotropic property. Dart impact is determined under ISO 7765-1 or ASTM D1709; tear resistance is determined under ISO 6383-2 or ASTM D1922; haze is evaluated under ASTM D1003 or ISO 14782. Laboratory cast-film data may not predict blown film performance because of differences in cooling rate and orientation.

For blown film, orientation is biaxial but unbalanced. Machine-direction tear resistance under ISO 6383-2 is often lower than transverse-direction tear resistance because of preferential machine-direction orientation. In a film produced at a blow-up ratio of 2.5:1, the ratio of transverse-direction to machine-direction tear strength may be as high as 3:1. This anisotropy is a result of molecular orientation rather than a material defect. Dart impact values are gauge-dependent and cannot be compared across laboratories unless specimen thickness, conditioning, and test method are identical.

Qualitative property ranking for monolayer 25 µm blown film can be summarized as follows when all resins are compared at similar melt flow and density.

For food-contact applications, the product must be evaluated against the applicable regulatory framework. In the United States, olefin polymers may fall under FDA 21 CFR 177.1520, which establishes olefin polymer specifications and end-use limitations. In the European Union, materials intended for food contact must comply with Regulation (EU) 10/2011 and its amendments, including overall migration limits and specific migration limits for additives. A supplier-issued compliance statement is required to confirm that the specific additive package in 118NJA meets the intended food-contact conditions.

Regulatory compliance for food contact is not a single property; it is a function of resin composition, additive package, conversion temperature, and food simulant. Under Regulation (EU) 10/2011, compliance requires verification of overall migration and specific migration limits. The converter is responsible for ensuring that final packaging does not exceed 10 mg/dm² overall migration for most food simulants unless a higher limit is specified for a specific simulant. The grade is not intended for medical implants or pharmaceutical packaging requiring ISO 10993 biological evaluation.

For heat-seal applications, the lower density of 918 kg/m³ reduces seal initiation temperature relative to higher-density LLDPE grades. Actual seal initiation must be measured under ASTM F2029 with specified seal pressure, dwell time, and film thickness. Seal strength is evaluated under ASTM F88; the result is influenced by seal-bar temperature, film gauge, and seal-bar configuration. A short dwell time on high-speed packaging machines may require an increase in seal temperature to achieve adequate seal strength.

When Coextrusion Layer Ratios Exceed 30 % in High-Stiffness Structures

In coextruded films with HDPE or polyamide tie layers, SABIC LLDPE 118NJA can be allocated to the seal layer or bulk layer. The 918 kg/m³ density produces lower seal initiation temperatures than LDPE and provides adequate seal strength. When the layer ratio exceeds 30 % of the total structure in an HDPE-dominated film, the mechanical contribution of 118NJA can reduce modulus; converter specifications may require a density adjustment. Interfacial instability is observed when adjacent layers have different melt elasticity, but 118NJA is generally regarded as moderately elastic. Die design with matched spiral channel lengths reduces layer waviness.

For the seal layer, LDPE or metallocene LLDPE may be blended to lower seal initiation or improve seal-through-contamination behavior. Blending with EVA or ionomer is possible but requires verification of thermal stability and seal strength. The melt flow rate of 1.0 g/10 min may be too low for very high-speed thin-gauge packaging lines that prefer 1.5 g/10 min to 2.0 g/10 min grades; in those cases, die temperature must be increased to maintain adequate flow.

Plant-specific failure modes observed with this category of butene LLDPE include gauge bands from uneven die lip temperatures, sharkskin in die gaps below 1.5 mm, and roll blocking in high-clarity thin films if slip additive is insufficient. The use of a chilled air ring and internal bubble cooling can expand the output envelope but may reduce dart impact if the frost line is set too low. Batch-to-batch variability of the base resin is controlled by the supplier, but converters should still monitor melt flow rate and density on incoming resin. Published data for this specific configuration is limited when processors use internal bubble cooling with die diameters above 400 mm; pilot-scale validation is required.