Borouge FB2230 is a linear low-density polyethylene produced through Borstar bimodal technology for film; it belongs to the Borouge LLDPE range and is positioned for blown film structures. Nominal published datasheet values include a density of 0.922 g/cm³ and a melt mass-flow rate of 0.20 g/10 min at 190 °C/2.16 kg according to ISO 1133-1; density is determined by ISO 1183-1. In the Borstar cascade, a loop slurry reactor operating with supercritical propane as diluent is paired with a gas-phase reactor. This configuration generates two molecular populations: a low-molecular-mass fraction with limited comonomer incorporation and a high-molecular-mass fraction carrying comonomer-rich segments. The placement of comonomer on higher-molecular-weight chains increases tie-chain concentration and dart impact resistance under ASTM D1709-22, while the low-molecular fraction reduces melt viscosity at die-lip shear rates. Among Borstar grades, FB2230 occupies the 0.920 g/cm³ to 0.925 g/cm³ blown film density window. The wider Borstar film grade platform spans higher and lower density–MFR combinations, but the same bimodal reactor sequence governs the molecular architecture.

Gel permeation chromatography of Borstar bimodal film grades produces a broad molecular weight distribution with a distinct high-molecular-weight shoulder; the polydispersity index is typically above 6, compared with 3.5 to 4.5 for unimodal Ziegler-Natta LLDPE. The high-Mw shoulder corresponds to chains above 10⁵ g/mol that contribute to melt strength. Differential scanning calorimetry per ISO 11357-3 shows a broad melting endotherm for 0.922 g/cm³ LLDPE with a peak between 122 °C and 126 °C. The low-molecular and high-molecular fractions co-crystallize; the lower-Mw portion permits faster crystal packing and reduces haze, while the higher-Mw portion creates tie chains between lamellae. These structural features are directly relevant to film performance, but they cannot substitute for converter film testing because cooling rate, blow-up ratio, and layer structure alter the solid-state morphology.

What Limits Melt Fracture Onset in Borstar LLDPE Film Lines?

Critical wall shear stress at the die lip is the dominant constraint. For LLDPE melts, sharkskin initiates when wall shear stress exceeds approximately 0.1 MPa to 0.3 MPa, depending on temperature and molecular weight distribution. Wall shear stress is calculated from die pressure drop and lip geometry; in a spiral mandrel die with a die gap of 1.6 mm and melt temperature of 210 °C, the broader molecular weight distribution of FB2230 raises the critical shear rate for melt fracture compared with unimodal C8-LLDPE of equivalent 0.920 g/cm³ density. Capillary rheometry according to ISO 11443 records the transition from smooth extrudate to sharkskin as surface roughness increases. The low-Mw fraction lowers viscosity at the die wall, while the high-Mw fraction increases melt strength in the bubble; this combination permits stable operation at higher output before melt fracture onset. Die temperatures above 230 °C can degrade the comonomer-rich high-Mw fraction and generate gel particles, which appear as undispersed specks in the film. Therefore adapter and die zones are held at 190 °C to 220 °C, while screw sections are limited to 160 °C to 190 °C to avoid premature shearing and gel formation.

On production-scale blown film equipment, typically a 24:1 to 30:1 L/D single-screw extruder with a barrier screw and Maddock mixer, FB2230 does not require pre-drying when pellet surface moisture is below 0.05 wt%. If silo storage relative humidity exceeds 60% RH, pre-drying in a desiccant hopper at 70 °C to 80 °C for 2 h to 4 h is applied. For 25 µm to 80 µm film, the die gap is set at 1.2 mm to 2.0 mm and the blow-up ratio is held between 2.2:1 and 2.8:1. Internal bubble cooling stabilizes the frost line at 0.8 m to 1.2 m above the die face. Barrel profiles are reverse-set: feed zone 150 °C to 170 °C, compression zone 170 °C to 185 °C, metering zone 185 °C to 195 °C, adapter and die zones 195 °C to 210 °C. Use of a melt pump between extruder and die reduces pressure fluctuation to less than ±0.5 MPa and improves gauge uniformity.

Cooling rate and frost-line geometry directly affect crystallinity and film optics. On a 250 mm die with dual-lip air ring and internal bubble cooling, frost-line residence times of 5 s to 15 s produce smaller spherulites and lower haze; longer residence time increases crystallinity and stiffness but can reduce dart impact. The high-Mw fraction in FB2230 delays stress relaxation, so rapid cooling at high draw-down conditions freezes orientation before lamellar growth completes. This mechanism is measured by DSC cooling scans at 10 °C/min per ISO 11357-3 and by film shrinkage tests at 100 °C for 60 min per ASTM D2732. Raising the frost line unnecessarily to improve clarity reduces lateral bubble stability.

Mechanical, Optical, and Seal-Integrity Testing of FB2230 Films

Conditioning is performed for at least 40 h at 23 °C ± 2 °C and 50% ± 10% RH per ISO 291. Tensile testing at 500 mm/min under ASTM D882-18 or ISO 527-3 gives secant modulus, yield stress, and elongation at break; thickness normalization is mandatory because gauge variation alters the stress calculation. Dart impact is tested with Method A using a 38 mm dart and 660 mm drop height; reported values depend on frost-line cooling and blow-up ratio. Haze and gloss are measured on a single film surface; the gloss angle is 60°. Seal initiation is evaluated by ASTM F88 or ASTM F1921; hot-tack and seal-strength curves of FB2230-containing structures are determined by the skin-layer resin and slip additive migration. Published data for FB2230-specific tensile and dart values are grade-datasheet dependent and must be read together with the exact film gauge and processing history.

Regulatory declarations for FB2230 in food packaging rest on FDA 21 CFR 177.1520(c) and EU Regulation 10/2011, including the overall migration limit of 10 mg/dm² of food contact area. The grade is manufactured under ISO 9001-registered site quality systems; REACH registration covers the polymer as a substance under the EU monomer/polymer exemption. For end-use articles, RoHS 2011/65/EU as amended by EU 2015/863 is relevant only when electrical and electronic equipment components are manufactured from the film. Specific migration testing must account for additives, printing inks, and lamination adhesives; a final film may require testing with food simulants assigned under EU 10/2011 Annex III. The resin is not supplied for implantable medical use; ISO 10993 biocompatibility evaluation would be required for any medical-device application.

When a Three-Layer Line Shifts from Standard LLDPE to Borouge FB2230 in the Core Layer

Die pressure and motor load typically decrease when FB2230 replaces a narrow-molecular-weight LLDPE of similar 1.0 g/10 min melt index, because the bimodal distribution increases shear-thinning at die-lip shear rates. Field measurements on a 250 mm three-layer die with a 1.6 mm die gap show a pressure reduction of 10% to 20% at constant screw speed and melt temperature; this reduction is not an indication of lower molecular weight. Bubble stability can improve due to the higher extensional viscosity of the high-Mw fraction, but if the core layer exceeds 60 wt% of the total film, the frost line may become overly sensitive to air-ring turbulence. Operators should adjust internal bubble cooling rather than raise die temperature. Increasing die temperature above 220 °C with slip-containing skins can cause blocking on the collapsing frame; maintaining the die below this threshold is recommended for films with erucamide at 800 ppm to 1200 ppm. Processors should verify layer ratio by thickness profiling before adjusting output; abrupt pressure drops above 20% may indicate feed-bridge or screw wear rather than a resin effect. Published data for this specific three-layer configuration is limited, so pilot-line trials are required to establish pressure and frost-line setpoints.

Slip and antiblock concentrates are incorporated in the skins at 2 wt% to 5 wt%. Erucamide migrates to the surface over 24 h to 72 h at 23 °C; addition above 1200 ppm in the skin can depress seal initiation temperature by 3 °C to 5 °C but also produces variable coefficient of friction and may fog optics. Synthetic silica antiblock is typically used at 2500 ppm to 4000 ppm; loadings above 5000 ppm increase haze and can wear die lips over extended campaigns. Fluoropolymer process aids at 300 ppm to 800 ppm clear melt fracture during start-up, but incompatible acid scavenger or metal stearate packages may form die-lip deposits. Halogenated flame retardants should be excluded from FB2230 food films because such additives compromise food-contact declarations and can generate corrosive species during extrusion.

Coextrusion Layer Ratios Alter the Tear–Impact Balance

Tear and dart impact do not track linearly with core-layer thickness. In a three-layer film with FB2230 in the core and lower-melting metallocene skins, increasing core share from 30 wt% to 60 wt% generally increases dart impact and stiffness, but transverse tear may decrease if the frost line is held too high. Draw-down ratio, defined as die gap divided by final thickness and blow-up ratio, controls machine-direction orientation. For a 1.6 mm die gap and 50 µm film at 2.5:1 BUR, the approximate draw-down ratio is 12.8. At high draw-down ratio, the high-Mw fraction in FB2230 resists bubble necking, allowing thinner gauges without bubble rupture; however, extrusion pressure and melt temperature must be rebalanced. Dart impact is measured per ASTM D1709-22 and tear per ASTM D1922-15; evaluation should include 25 µm, 40 µm, and 70 µm gauge points to detect nonlinear shifts. Published data for this specific configuration is limited, and pilot-line characterization is required because coextrusion die residence time and cooling rate interact with the bimodal molecular architecture.

Receiving inspection for FB2230 includes melt mass-flow rate by ISO 1133-1 and density by ISO 1183-1. Silos are not nitrogen-blanketed; storage below 40 °C away from direct sunlight limits oxidative stability drift. Changeover from other polyolefins uses a higher-MFR purge resin until die lines and die-lip deposits are cleared; degraded process aid can accumulate at the upper die lip and should be monitored by visual inspection. Extrusion above 250 °C in long-residence-time screw geometries is not recommended because gel formation increases and film appearance degrades.