SABIC LLDPE 726NE is a narrow-molecular-weight-distribution linear low-density polyethylene supplied as natural granules for blown film and cast film extrusion. The grade is a butene-comonomer LLDPE with a nominal density of 0.926 g/cm³ determined under ISO 1183-1:2019 and a nominal melt flow rate of 2.8 g/10 min at 190 °C and 2.16 kg load measured according to ISO 1133-1:2022. These values place the material in the higher-density segment of the SABIC LLDPE film range, between conventional lower-density butene film grades and high-density polyethylene. The molecular architecture is predominantly linear with short-chain branching from the butene comonomer; long-chain branching is not intentionally introduced.

The grade is not hygroscopic in normal warehouse conditions. However, condensation on granules can occur when bulk material is transferred from cold storage into a humid production hall at relative humidity above 60%. In such cases a dry-air hopper purge at 70 °C for 2 h is the usual corrective measure before extrusion. For unopened packaging stored below 50 °C, a shelf life of 12 months is commonly applied for SABIC polyethylene grades. Beyond that period, entry checks by melt flow rate and oxidation induction time are recommended. Direct sunlight exposure should be avoided because ultraviolet radiation can partially consume the phenolic antioxidant package even in the solid state.

Compared with a broad-distribution autoclave LDPE of the same melt flow rate, SABIC LLDPE 726NE exhibits lower die swell, reduced freeze-line stability, and higher melt viscosity at low shear rates. The narrow molecular weight distribution also produces a wider Newtonian plateau in shear rheology; the viscosity remains nearly constant below 100 s⁻¹ and enters the strongly shear-thinning regime above 1000 s⁻¹ when measured by ISO 11443 capillary rheometry. This response increases die pressure at a fixed mass throughput relative to an LDPE of equivalent melt index, but it improves film thickness uniformity and reduces melt elasticity-related surface defects.

Blending with LDPE at 10 wt% to 30 wt% is common in blown film to improve bubble stability and optical appearance. The blend reduces some of the modulus advantage of the LLDPE and may shift the seal initiation temperature by several degrees Celsius. Because 726NE has a higher density than typical seal-layer LLDPE grades, it is generally not selected as the sealant layer when low-temperature seal initiation is critical.

What limits the melt processing window in high-output blown film lines?

The processing window is constrained more by melt temperature than by screw torque. On monolayer blown film lines with screw diameters from 45 mm to 75 mm and L/D ratios from 24:1 to 30:1, the melt temperature is maintained between 180 °C and 210 °C. Operation below 170 °C can produce insufficient melt homogeneity and visible flow lines in thin film. Operation above 220 °C accelerates thermo-oxidative chain scission and may generate gel particles that appear as fisheyes. The stabiliser package is formulated for a barrel residence time up to 5 min at the upper end of this range. Longer residence times at elevated temperature require a nitrogen blanket or an additional processing stabiliser masterbatch.

Die pressure and melt fracture are controlled by die gap and die temperature. A die gap of 1.4 mm to 2.0 mm and a die temperature 10 °C to 15 °C above the melt temperature allow specific output from approximately 0.7 kg/h to 1.2 kg/h per millimetre of die circumference. Reducing the die gap below 0.8 mm raises wall shear stress and can initiate sharkskin melt fracture at the die lip, particularly at high screw speed. In coextrusion, the melt-viscosity ratio between 726NE and lower-density seal-layer grades at the relevant channel shear rate should be kept below 3:1 to prevent interfacial instability and layer nonuniformity.

Frost line height controls molecular orientation and the balance between machine-direction and transverse-direction properties. A frost line height of 2D to 4D, where D is the die diameter, is typical for balanced film. A shorter frost line increases transverse direction shrinkage and reduces machine-direction tear resistance. A longer frost line increases machine-direction tensile strength and can improve dart impact but may reduce transverse-direction tear. These directional shifts are measurable with ISO 527-3 tensile testing and ASTM D1922-22 Elmendorf tear.

Film property measurements on 25 μm monolayer film blown at a blow-up ratio of 2.5:1 and die gap 1.6 mm typically produce tensile yield strength between 10 MPa and 12 MPa in both machine and transverse directions under ISO 527-3. Secant modulus at 1% elongation falls between 200 MPa and 280 MPa in the machine direction, while elongation at break exceeds 700%. Exact values are line-specific and depend on film gauge profile, frost line position, and die temperature. The grade is not normally selected for applications requiring very low haze; films based on higher-density LLDPE tend to show greater surface haze than metallocene LLDPE or LDPE-rich blends because of increased spherulitic scattering from the higher-density crystal fraction.

A stiffness layer in three-layer coextrusion for form-fill-seal packaging

In three-layer coextrusion lines with 60 mm barrier screws and L/D 30:1 extruders, SABIC LLDPE 726NE is used as a stiffness component at addition levels of 30 wt% to 50 wt% in the core or skin layers. The higher density raises film modulus without increasing total gauge. This permits downgauging of the total film structure by approximately 5% to 10% when compared with an all-0.918 g/cm³ LLDPE structure, provided that dart impact and tear resistance remain inside the end-use specification. The grade is also processed in cast film lines where its higher density reduces neck-in at draw ratios from 20:1 to 40:1 and improves web stability at the chill roll.

In form-fill-seal packaging, the elevated sealing initiation temperature is a design factor. Differential scanning calorimetry under ISO 11357-3 places the peak melting endotherm of a 0.926 g/cm³ LLDPE between 122 °C and 125 °C. A 0.918 g/cm³ butene grade typically peaks between 108 °C and 112 °C. Seal initiation therefore shifts upward by approximately 5 °C to 12 °C. If low-temperature sealing is required, a lower-density LLDPE or metallocene sealant layer must be coextruded. This shift also affects hot-tack behaviour, so packaging lines with narrow sealing jaws should validate seal strength and hot-tack through ASTM F1921-20 and ASTM F2029-16.

The difference from lower-density LLDPE film grades is not limited to stiffness. The higher density reduces the tie-chain population in the amorphous regions because of thicker lamellae. This mechanism raises tensile yield strength and secant modulus while lowering slow crack growth resistance and dart impact at equal film gauge. Compared with metallocene-catalysed hexene LLDPE grades of similar density, SABIC LLDPE 726NE may exhibit lower dart impact and lower tear because the shorter butene branch is generally less effective at tie-chain formation than hexene branching. Exact property gaps are grade-specific and must be verified with ASTM D1709-22 and ASTM D1922-22 on the same film line.

When downgauging reaches the dart impact threshold in heavy-duty sacks

The main operational boundary appears in heavy-duty sacks where film thickness is reduced below 40 μm. Increasing density from 0.918 g/cm³ to 0.926 g/cm³ increases film stiffness but lowers dart impact and Elmendorf tear at equal gauge. The magnitude is strongly dependent on orientation and die gap. A thicker die gap and lower blow-up ratio can partially compensate for the loss in transverse-direction tear. ASTM D1709-22 dart drop and ASTM D1922-22 tear tests should be conducted on production film because laboratory values from generic LLDPE films do not capture the line-specific orientation state. Published data for this exact grade under all die and blow-up ratio combinations is limited; the converter should therefore qualify the final structure on the production line.

Thermal stability at high shear is acceptable within the standard blown film window, but extrusion coating and flame lamination are outside the intended envelope. Melt temperatures at 230 °C or higher reduce oxidation induction time and may produce odour and gel formation. Oxidation induction time measured under ISO 11357-6 at 200 °C is a useful incoming quality-control indicator; a value below 20 min suggests partial antioxidant depletion. The resin is not compatible with long-chain branched LDPE at high addition levels above 50 wt% when maximum film clarity and melt strength are required, because the different branching architectures can increase surface haze and reduce gloss.