In blown film operations, the nominal density of 0.918 g/cm³ determined in accordance with ISO 1183-1 and a melt flow rate of 2.0 g/10 min measured at 190°C under 2.16 kg according to ISO 1133-1:2022 position SABIC LLDPE 218BJ as a butene-based LLDPE for low-to-medium gauge flexible packaging. The following application scenarios present process parameters, formulation boundaries, test methods, and failure modes specific to industrial conversion of this grade.

Heavy-Duty Sack Film at High BUR: Melt Pressure and Gauge Control in Grooved-Feed Extruders

On single-screw grooved-feed blown-film lines with screw diameters from 50 mm to 75 mm and L/D 30:1, 218BJ is typically dry-blended with 20–30 wt% LDPE having a melt flow rate of 0.25–0.7 g/10 min to increase melt strength and stabilise the bubble at BUR values from 2.0:1 to 3.5:1. The LDPE addition raises the zero-shear viscosity and shifts the onset of strain-hardening to lower Hencky strain, which permits a high-stalk bubble configuration with a stalk height of 6–9 die diameters. Die gaps are set between 1.6 mm and 2.2 mm; barrel temperatures are profiled from 175°C in the feed section to 205–215°C in the metering zone, with the die maintained at 210–220°C. Process conflict exists at the lower end: a melt temperature below 190°C improves film dart impact retention but can increase die pressure above 30–35 MPa on high-output 60 mm lines, producing shark-skin melt fracture at the die lip. Raising the melt temperature above 230°C reduces die pressure but increases the concentration of gel particles from oxidative chain scission, visible as optical defects in the finished sack web. Terminal products include industrial shipping sacks for granulated resins, fertiliser bags with a gauge range of 80–150 µm, and e-commerce mailers where the dart impact requirement is commonly specified at ≥120 g per ASTM D1709A on 100 µm film.

For agricultural silage and clamp cover films, gauge reduction below 40 µm changes the critical mechanical requirement from puncture resistance to tear initiation and tear propagation, especially on rough concrete silage clamps exposed to UV radiation and liquid manure. The butene molecular architecture of 218BJ yields a broader molecular weight distribution than metallocene LLDPE; this provides lower optical clarity but higher tolerance for recycled edge trim. In a typical formulation, 85 wt% 218BJ is combined with 10 wt% LDPE and 5 wt% carbon-black masterbatch containing a hindered amine light stabiliser at 2–3 wt% additive loading. Extrusion through a 250 mm die with a die gap of 2.0 mm and a BUR of 2.8:1 produces a 1200 mm layflat cover. The film is welded into 10–25 m sheets on high-frequency PVC welding tables; overlap welds require a minimum seal width of 30 mm and a seal strength above 40 N/50 mm when tested in accordance with ASTM D882 tensile conditions. EU Regulation 10/2011 is generally not activated for non-food silage covers, but REACH Regulation 1907/2006 Article 33 imposes a documentation duty only if the carbon-black masterbatch introduces a candidate-list substance above 0.1% w/w; this is uncommon for standard carbon black but must be verified in the supply chain. Field failure occurs most often at fold lines where the film has been stretched beyond the yield point during storage; the use of a 2.0 g/10 min LLDPE rather than a fractional-MI LDPE reduces stiffness-related cracking but requires more careful bubble cooling to prevent blocking.

How Does Low-Temperature Dart Impact Retention Shift in Freezer-Grade Lamination Films?

The substitution of a 2.0 g/10 min butene LLDPE in a freezer laminate changes the fracture mechanics of the PE web at −18°C because the glass transition of the amorphous phase is broad and the tie-chain density is strongly influenced by short-chain branching distribution. In extrusion-laminated freezer pouches, 20–30 µm of 218BJ is melt-extruded between a PET or BOPP outer web and a low-density sealant layer; the LLDPE functions as the internal bonding and puncture layer rather than the sealant itself. The process uses a 90 mm single-screw extruder at 180–220°C with a T-slot die and a nip pressure of 2–4 bar on the chilled roll. For the LLDPE web, impact resistance is determined by ASTM D1709A on the unsupported film; low-temperature performance is compared using ISO 7765-1 at −20°C conditioning, although published data for this specific 218BJ configuration under that exact conditioning is limited. The main formulation constraint is the addition of slip and anti-block masterbatch: a primary erucamide addition of 500–1000 ppm reduces coefficient of friction but can migrate to the lamination interface and lower adhesion to PET by 10–20% in peel tests. The terminal product is a stand-up freezer pouch for vegetables and seafood; control of chill-roll temperature at 15–20°C is necessary to prevent crystallisation haze greater than 30% when measured by ASTM D1003.

In liquid pouch inner webs, the critical seal-performance variable is not the base resin density alone but the concentration of soluble waxes and primary amides that migrate from adjacent layers during heat sealing. When 218BJ is used as a 60–80 µm inner ply in a three-layer coextruded film for bag-in-box liquid liners, the recommended extrusion temperature profile is 180–210°C on the barrier screw sections and 220°C at the die, with a die gap of 2.0 mm and a BUR below 2.2:1 to limit molecular orientation. The heat-seal specification is commonly set at a minimum platen pressure of 0.35 MPa for 1.0 s at 160°C, producing a seal strength of ≥10 N/15 mm when tested per ASTM F88. The choice of 218BJ at 2.0 g/10 min offers a compromise between seal strength and extrusion amperage: a lower-MI LLDPE would yield higher seal strength but would require a barrier screw with a mixing element to prevent unmelts at screw speeds above 120 rpm. For aqueous food products, migration testing must be conducted under the intended temperature and time conditions specified in EU Regulation 10/2011 Annex III, with overall migration limited to 10 mg/dm². For non-food detergent liners, the primary compatibility concern is stress-cracking; a typical surface-active agent in liquid detergents can produce environmental stress cracking, and ESCR testing per ASTM D1693 on the inner web is specified at ≥1000 h in a 10% Igepal CO-630 solution at 50°C.

When a 2.0 g/10 min Butene LLDPE Replaces LDPE in High-Output Carrier Bag Lines

The conversion of a carrier-bag line from a high-pressure LDPE to 218BJ requires a shift in screw design and bubble configuration, because the LLDPE exhibits higher shear viscosity and lower melt strength under extension. On a 60 mm grooved-feed extruder at 120–180 kg/h, the LLDPE may raise the motor load by 8–15% relative to LDPE at the same screw speed if the screw has no barrier section. The recommended replacement is a barrier screw with a Maddock mixer and an internal bubble cooling system, allowing a BUR of 2.5:1 to 3.5:1 and a film gauge of 15–25 µm. A typical blend for high-stalk bubble stability is 70 wt% 218BJ with 30 wt% LDPE; this blend maintains a stable stalk over a die diameter range of 150–200 mm while preserving tensile properties. The dry-blending step itself requires no elaboration beyond a low-shear tumble mixer running for 10–15 min. The terminal bags are tested for tensile strength per ASTM D882 at 500 mm/min, with MD and TD elongation values used to control orientation balance. Dart impact is a secondary test because the bags are often perforated for ventilation; blocking resistance becomes a primary quality parameter, with an anti-block addition of 5,000–10,000 ppm of silica in the masterbatch required for rolls stored above 30°C. Compliance for carrier bags carrying food without direct contact is limited to REACH and heavy-metal restrictions under Packaging Directive 94/62/EC; lead, cadmium, mercury and chromium VI total concentration must not exceed 100 mg/kg.

Because 218BJ contains only butene as the short-chain branching comonomer, its strain-hardening behaviour in the melt phase is lower than that of a hexene LLDPE at equivalent density, and neck-in on cast-film lines is correspondingly greater than with high-pressure LDPE. The molten web is run at 230–250°C on a 75 mm extruder with a 1200 mm coat-hanger die; a reduced die-to-chill-roll air gap of 25–40 mm and vacuum-box edge pinning are used to limit edge bead and width loss. Film gauge is typically 20–35 µm. A fluoropolymer process aid at 300–600 ppm is added only when melt fracture appears at high output, and its presence must be documented for food-contact primary packaging. Terminal products include hygiene packaging backsheet lamination where the key control test is Elmendorf tear per ASTM D1922 in both MD and TD; an MD/TD imbalance greater than 30% is considered out of specification on high-speed lines. Published data for this specific grade in high-output cast-film configurations is limited, and line trials are required to establish the exact neck-in value for a given die width, melt temperature, and air gap.

Reclaim Blending Limits in Non-Food Flexible Packaging

Post-industrial edge trim and bubble scrap generated from 218BJ film can be reincorporated into the same blown-film process, but the amount is constrained by gel accumulation and melt-pressure instability. In a heavy-duty non-food liner, converters may run up to 25 wt% of pelletised post-industrial reclaim without changing the screw temperature profile, provided the scrap is screened through a 100–150 µm melt filter. Above 25 wt%, the residence time distribution broadens and the melt pressure at the screen pack rises by 10–20% over a production week, with a corresponding increase in gel counts greater than 0.5 mm per square metre. The use of reclaim in food-contact films is governed by EU Regulation 2022/1616 on recycled plastic materials and articles; only reclaim streams produced under a suitable decontamination process and behind a functional barrier may be used, and 218BJ as a base layer behind a virgin food-contact layer is validated by the converter. A typical three-layer coextruded structure places the reclaim in the core at 30–40 wt%, with virgin 218BJ skins at 30–35 wt% each. The terminal products are non-food industrial liners, construction films, and waste sacks. Testing includes the Charpy impact test of the fabricated film structure, gel count visual inspection, and ash content per ISO 3451-1 to confirm that anti-block levels remain below 2,500 ppm in the final film.