SABIC LLDPE 6821NJ is a pelletized linear low-density polyethylene supplied for blown-film and thin-gauge cast-film conversion. The resin is produced by low-pressure gas-phase copolymerisation of ethylene with a short-chain α-olefin; the short-chain branching concentration is controlled to yield a nominal density of 0.918 g/cm³ when determined by ISO 1183-1:2019. The nominal melt flow rate is 1.0 g/10 min at 190 °C under a 2.16 kg load when measured according to ISO 1133-1:2022. The grade is supplied as a natural resin without slip/antiblock additives; this is the principal distinction from additive-containing SABIC LLDPE film grades such as 118WJ. The absence of migratory surface additives is intended to preserve corona treatment, lamination bond strength, and print adhesion after film aging, but it shifts coefficient-of-friction control and blocking resistance to the converter.

Typical end-uses include heavy-duty sacks, lamination film, industrial liners, carrier bags, and agricultural film. In heavy-duty sacks, the resin is used in monolayer or coextruded structures where high dart impact and tear resistance are required. In lamination applications, the absence of amide bloom is often more important than melt flow rate alone. The grade is not designed for injection-moulded closures, refrigerator containers, or high-stiffness blow-moulded bottles.

Table 1. Representative property profile for SABIC LLDPE 6821NJ. These values are typical and are not specification limits; lot-specific certificates of analysis should be obtained for formal compliance.

The combination of melt flow rate and density places the grade in the general-purpose high-dart LLDPE film segment. The moderate melt flow rate and density balance melt strength against drawdown; the resin is not optimised for processes requiring high melt flow, such as thin-wall injection moulding. Its melt rheology and crystallinity profile also mean that screw design, die geometry, and temperature profile have a measurable effect on gel formation, bubble stability, and odour in the finished film.

What Separates 6821NJ from Additive-Containing LLDPE Film Grades?

The primary separation is surface chemistry of the finished film over time. Additive-containing LLDPE film grades rely on erucamide or oleamide migration to reduce the static coefficient of friction from initial values above 0.5 to values near 0.1–0.2. With 6821NJ, no migratory slip package is present, so the static coefficient of friction remains above 0.4 on untreated film unless an external slip masterbatch is added. This is advantageous in extrusion lamination and printing because secondary adhesion failures from amide bloom are eliminated. The trade-off is operational: wound rolls may block if winding tension is not reduced and if roll storage temperature exceeds 30 °C or relative humidity exceeds 60 %.

Compared with conventional butene LLDPE film grades, the difference is not primarily density or melt flow rate but the additive formulation and molecular architecture. Compared with metallocene-catalysed hexene LLDPE grades, 6821NJ may have lower dart impact at equivalent density but greater tolerance on older single-lip air-ring blown-film lines because the broader molecular weight distribution and more shear-thinning melt reduce melt pressure fluctuation. Compared with high-pressure LDPE, 6821NJ lacks strain-hardening behaviour, so bubble stability is more dependent on air-ring geometry and frost-line control. Direct comparative data across SABIC LLDPE grades should be taken from current technical data sheets and not from single-point property tables alone.

Rheological characterisation of the melt is central to its processing behaviour. At shear rates relevant to blown-film die land flow, the melt is pseudoplastic; the power-law index derived from capillary rheometry is typically below 0.5 at 190 °C. Melt strength is sufficient for stable bubble formation at blow-up ratios of 2.0:1 to 3.0:1, but the resin does not provide the strain-hardening response of LDPE. Conventional air-ring cooling is therefore preferred over high-stalk bubble configurations; high-stalk processing may produce bubble instability and gauge variation unless an internal bubble stabiliser is used. Published data for this specific configuration is limited, but the trend is consistent with the capillary rheology of linear low-density polyethylene of this density class.

In blown-film extrusion, the resin is typically run on single-screw extruders with smooth-bore or grooved-feed barrels. A barrier screw with length-to-diameter ratio between 24:1 and 30:1 provides adequate melting; grooved-feed extruders deliver more stable output at low melt temperatures. Start-up temperature profiles begin at 170–180 °C in the feed zone, increase to 200–210 °C in the metering zone, and hold adapter and die zones at 210–230 °C. Melt temperature at the die lip should be maintained between 195 °C and 220 °C; operation above 230 °C increases oxidative gel formation and carbonyl degradation products. A die gap of 1.8–2.4 mm is preferred for film thicknesses from 20 µm to 80 µm. Blow-up ratio is usually held between 2.0:1 and 3.0:1; higher ratios reduce machine-direction tear performance and destabilise the bubble on shallow air-ring geometries. Frost line height is controlled at 6–8 die diameters to balance quench rate and bubble stability. Because the resin is slip-free, winding tension should be set 15–25 % lower than with slip-additive grades, and contact rollers should have matte surfaces to reduce blocking.

Table 2. Blown-film start-up window used in production-scale trials for SABIC LLDPE 6821NJ.

Output rates are limited by extruder torque, melt pressure, and air-ring cooling capacity rather than by screw feeding alone. In a 90 mm grooved-feed line, stable bubble operation is commonly reached in the 120–160 kg/h range, but the actual limiting factor is often cooling geometry and frost-line control. Reducing die gap or raising melt temperature can increase output but may lower melt strength and increase gel risk. Published data for this specific configuration is limited; converter-scale trials are required to establish the upper throughput boundary.

When Low Gel Levels and Drawdown Govern Thin-Gauge Blown Film Economics

Processors selecting 6821NJ for thin-gauge applications typically balance two constraints: the need to maintain dart impact and tear resistance after downgauging, and the need to preserve bubble stability when the melt is drawn from a 1.8 mm die gap to final thickness below 25 µm. The resin exhibits the shear-thinning response expected of linear low-density polyethylene; melt viscosity decreases with increasing shear rate, but the critical shear rate for sharkskin surface melt fracture limits throughput on narrow die gaps. Production-scale observations on grooved-feed blown-film lines show that melt fracture is controlled more effectively by raising die temperature than by increasing melt temperature alone; die lip heaters set 10–15 °C above the adapter set point reduce melt fracture at a given output. Published data for this specific configuration is limited; however, the shear-thinning trend is consistent with capillary rheometry for the same density class.

To reduce gel generation in thin-gauge film, screen packs of 60/80/100 mesh are used to trap crosslinked particles; nickel mesh is preferred over stainless steel to limit pressure drop. The absence of amide slip additives in the resin means that thin film cannot rely on bloom to reduce blocking; corona treatment levels above 42 mN/m should be avoided unless an inline backside treatment system is installed. In downgauged film, dart impact failure mode shifts from ductile puncture to brittle shatter as thickness decreases or as processing temperature is reduced below the recommended melt temperature. The converter must therefore maintain the lower melt temperature boundary at 195 °C to avoid orientational brittleness in the finished web.

Coextrusion compatibility is acceptable on three-layer blown-film lines, typically with 6821NJ in the core or sealant layer. The outer skin layers are often additive-containing LLDPE or LDPE; this arrangement provides slip properties at the surface while retaining a lamination-friendly core. When 6821NJ is used as the sealant layer, the seal initiation temperature is governed by the low-density amorphous phase and is generally below that of HDPE-rich layers but above that of high-pressure LDPE. Exact seal data should be obtained from the supplier because seal performance is influenced by film thickness, jaw geometry, and dwell time.

Cast Film, Extrusion Lamination, and Surface Treatment Retention

On cast film lines, the resin can be run at lower melt temperatures than blown film because rapid quench on a chill roll preserves low crystallinity and improves optical properties. Typical melt temperatures are 210–230 °C with chill roll temperatures of 15–25 °C for thin-gauge lidstock and lamination webs. The natural, no-slip formulation is selected when corona treatment must remain above a critical dyne level after winding and storage. Treated film made from additive-containing LLDPE often decays from an initial 40 mN/m to 34–36 mN/m within days as amide migration covers the oxidised surface; with 6821NJ the decay is slower because the low-molecular-weight surface species are not present. Specific dyne retention depends on storage humidity, film crystallinity, and anti-block masterbatch; converters must verify adhesion with the actual lamination adhesive and coating system.

The grade is also used as a backing or sealant layer in extrusion lamination where melt stability above 220 °C is necessary to prevent edge neck-in. Neck-in at the die exit is affected by melt elasticity and die gap; a coat-hanger die with internal deckle is preferred for widths above 1200 mm. However, published data for this specific configuration is limited, and the die geometry must be validated on the target line to maintain gauge uniformity.

Blending with LDPE or HDPE is practised to modify stiffness, bubble stability, or seal initiation temperature. With LDPE-rich blends, 6821NJ increases dart impact and tear properties; addition rates are typically 20–40 wt% of LLDPE in the blend. Above 50 wt% LLDPE, bubble stability on conventional air-ring equipment becomes sensitive to frost line position and may require an internal bubble stabiliser. With HDPE, blends of 10–20 wt% HDPE raise modulus but reduce dart impact; phase separation can generate visible flow defects in films above 20 µm if the HDPE melt index differs by more than about one order of magnitude. Comparative data for the exact blend system should be generated on the target production line, because blow-up ratio, frost line height, and screw recovery time interact with blend viscosity.

Storage and handling requirements follow standard polyolefin practice. SABIC LLDPE 6821NJ is supplied in 25 kg bags or in bulk silo trucks depending on plant logistics. Pellets should be kept in closed containers at ambient temperature below 50 °C and away from direct sunlight to prevent oxidative degradation. Pre-drying is not required under normal conditions; if condensation occurs after cold storage below 10 °C, the pellets should be allowed to reach ambient temperature before conveying to the extruder hopper. The resin is intended for food-contact packaging applications when processed in accordance with good manufacturing practice; the relevant resin compliance statement is typically based on FDA 21 CFR 177.1520 and European Union food-contact legislation for polyolefins. The product is not designed for medical implant use or for prolonged service in contact with strong oxidizing acids. Processing at temperatures above 230 °C should be limited because thermal degradation increases gel level and odour in the finished film.