ExxonMobil LDPE vs SABIC LDPE: Substitution Check Before Switching

For a converter evaluating a direct replacement in blown film, extrusion coating, blow moulding, or injection moulding, the transition from an ExxonMobil LDPE to a SABIC LDPE is not a drop-in change unless the framework ExxonMobil LDPE vs SABIC LDPE: Substitution Check Before Switching is applied at the resin specification stage. Low-density polyethylene is defined by a density between 0.910 g/cm³ and 0.940 g/cm³ per ISO 1183-1, but this range conceals differences in molecular weight distribution, long-chain branching density, antioxidant chemistry, and slip/antiblock additive packages that control extrusion pressure, bubble stability, blocking behaviour, and seal response. A resin with a nominal density of 0.923 g/cm³ and a melt mass-flow rate of 2.0 g/10 min at 190 °C/2.16 kg by ISO 1133-1 may still diverge from another resin carrying the same published values when shear viscosity at 100 s^-1 or extensional viscosity at 1 s^-1 is compared on a twin-bore capillary rheometer. The first substitution gate is therefore not brand interchangeability, but the alignment of melt flow rate, density, molecular weight distribution, melt strength, and additive package against the specific die geometry, draw ratio, cooling configuration, and converting line operating discipline.

The comparison must begin with a rheological fingerprint rather than a single-point melt index. Capillary rheometry across shear rates from 10 s^-1 to 1000 s^-1 at 190 °C should be generated for both the incumbent ExxonMobil LDPE and the candidate SABIC LDPE. Melt mass-flow rate alone does not capture the power-law index or the shear-thinning transition that governs pressure consumption in a spiral mandrel die or a flat coathanger die. In blown-film lines operating with die gaps of 1.2 mm to 2.0 mm, a higher melt viscosity at 100 s^-1 will increase die pressure, elevate melt temperature through viscous dissipation, and may force a reduction in screw speed to maintain a barrel temperature range of 160 °C to 210 °C. On grooved-feed extruders with L/D 30, a change in melt flow rate of only 0.3 g/10 min can shift the stable frost-line height by 50 mm or more when the same blow-up ratio is retained. Extensional viscosity is equally significant because LDPE long-chain branching controls strain hardening and hence bubble stability under high-stalk and pocket configurations. A substitution that lowers melt strength below the line-specific threshold produces bubble sag, film gauge variation, and periodic frost-line oscillation even when tensile properties of the finished film remain within specification.

Why Is Melt Flow Ratio Not Sufficient to Qualify a SABIC LDPE on a Blown-Film Line?

The melt flow ratio, commonly determined from high-load and low-load melt flow rates, provides a limited indication of molecular weight distribution but not of long-chain branching architecture. For LDPE, two resins with equivalent ISO 1133-1 values at 2.16 kg may differ in melt strength by 15 % to 30 % when measured as extensional strain hardening on a Sentmanat extensional rheometer. This difference becomes visible during bubble inflation at a blow-up ratio of 2.0 to 3.0 when the frost-line height is fixed below 300 mm. A production-scale blown-film line equipped with a 350 mm spiral mandrel die and a 1.5 mm die gap may show no pressure deviation below 3 % yet exhibit heavier edge-web gauge bands because the SABIC LDPE relaxes differently in the draw-down region. Gauge control should be evaluated by scanning the layflat across 10 equally spaced points with a non-contacting capacitance thickness gauge; a coefficient of variation above 6 % indicates that the substitution requires adjustment of inner and outer cooling air, die gap, or blow-up ratio before mechanical testing proceeds.

For extrusion coating and laminating, the substitution check must include neck-in measured on a pilot or production coater with a 0.7 mm slot die and an air gap of 120 mm to 180 mm. Neck-in is controlled by the polymer’s high-shear viscosity, melt elasticity, and oxidation-induced edge stabilisation, not by the low-shear melt flow rate alone. A SABIC LDPE with equivalent ISO 1133-1 melt flow rate but lower extensional viscosity can draw down to a thinner coating weight but may also initiate draw resonance at lower line speeds. Draw resonance onset is likely when melt tension falls below the critical draw ratio for the specific coating line configuration. On a 90 mm extruder delivering 300 kg/h to a 1.2 m wide coating die, substituting resins without adjusting temperature setpoints may alter edge bead formation and adhesion to kraft paper or aluminium foil. If the SABIC LDPE contains a different antioxidant or slip package, odour and organoleptic properties must be re-qualified under the intended food-contact conditions. Published data for the exact comparative neck-in of ExxonMobil LDPE and SABIC LDPE under identical coater settings is limited; therefore the substitution decision requires a controlled head-to-head trial on the target line rather than reliance on supplier datasheet equivalence.

Mechanical Property Compliance, Dart Impact, and Tear Resistance

Table 1 values should not be interpreted as substitution approval. Tensile strength at break measured on 25 µm blown film is only one component of the converter’s risk profile. Dart impact and Elmendorf tear are direction-sensitive and depend on frost-line cooling rate, die gap, and blow-up ratio. A difference of 10 g in dart impact may be acceptable for heavy-duty sacks but not for freezer-grade packaging. The SABIC LDPE must be processed on the target line at the same blow-up ratio, normally 2.0 to 3.0, before comparative statements are made. Films with a higher gel count or a different slip/antiblock additive package can show changed coefficient of friction and blocking force despite equivalent haze values. Coefficient of friction should be measured by ISO 8295, and blocking force by ASTM D3354. When the application involves heat sealing, the seal initiation temperature should be compared using a laboratory sealer at 0.5 N/mm² and 0.5 s dwell; a shift of 3 °C in seal initiation is operationally significant on vertical form-fill-seal lines.

An injection-moulding plant evaluating a switch for closures or laboratory ware must first determine whether the SABIC LDPE grade is an extrusion grade or an injection-moulding grade. LDPE injection grades typically have melt flow rates from 20 g/10 min to 70 g/10 min at 190 °C/2.16 kg, while film grades below 4 g/10 min will produce short shots or require excessive injection pressure in thin-wall cavities. The comparison must include not only melt flow rate but also the softening point and mould shrinkage. Mould shrinkage for LDPE can range from 0.020 mm/mm to 0.035 mm/mm, and a difference of 0.005 mm/mm can move a closure outside dimensional tolerance if the tool was dimensioned for the incumbent ExxonMobil LDPE part. Processors running a 120-tonne clamp moulding machine with a 24-cavity cap mould may observe a change in part mass and cycle time when the SABIC LDPE has different crystallisation kinetics. Differential scanning calorimetry by ISO 11357-3 should be used to compare peak melting temperature and cooling crystallisation onset, because these values influence ejection temperature and post-mould dimensional stability. If the candidate SABIC LDPE has a lower cooling crystallisation temperature, the cycle may need an increase in mould cooling time of 0.5 s to 1.5 s to prevent sink marks.

Once Regulatory and Food-Contact Boundaries Are Applied, the Comparison Depends on Additive Chemistry

The regulatory text alone does not eliminate organoleptic and total migration testing. A SABIC LDPE may use a different catalyst neutraliser or antioxidant, which can increase non-volatile extractables in a fatty-food simulant. Under EU 10/2011, overall migration must not exceed 10 mg/dm² in simulant D2 for fatty foods when tested for 10 days at 40 °C. Under FDA 21 CFR 177.1520, the polymer is covered by the olefin polymer clearance when the density is between 0.85 g/cm³ and 1.00 g/cm³, but the specific additive package must be separately cleared. A converter cannot assume that one producer’s food-contact declaration transfers to another supplier’s grade. The certificate of conformity should list the specific grade, production plant, and authorised food-contact status. For pharmaceutical blow-fill-seal applications, the candidate resin should be evaluated against USP <661.1> for plastic packaging systems and the extractables profile under the drug product’s worst-case pH and organic solvent conditions.

At the onset of a substitution trial on a three-layer coextrusion line, the transition procedure must be written as a purge protocol. A 60 mm primary extruder with L/D 28 and a 75 mm coextruder will hold a significant melt inventory. A viscosity mismatch between the incumbent ExxonMobil LDPE and the incoming SABIC LDPE can leave gel tails or haze bands if the purge is truncated. The purge should use a high-viscosity purging compound at 10 kg to 15 kg per screw diameter until the melt temperature and die pressure stabilise. Sampling points for density and melt flow rate should be taken every 15 min over a 2 h run. If the melt pressure at the die is outside the incumbent’s established control range by more than 5 %, the temperature setpoints and screw speed must be rebalanced before film samples are collected. Only after stable gauge control with a coefficient of variation below 5 % across 10 points is achieved should comparative mechanical and optical specimens be cut.