Braskem LF218/21 is positioned as a butene-copolymer linear low-density polyethylene for cast and blown film extrusion with a nominal density of 0.918 g/cm³ per ASTM D1505 and a melt flow index of 2.1 g/10 min per ASTM D1238 at 190 °C/2.16 kg. The butene branch architecture and controlled molecular weight distribution give the grade a balance between thin-gauge drawdown and bubble stability that places it in applications where film thickness spans 8 µm to 220 µm. Because the standard additive package does not include UV stabilizers, cling agents, or anti-fog concentrates, the scenarios below specify where those functional additives must be introduced during converting. Where numerical data are quoted, they represent converter-side processing and film-performance ranges typical for butene-copolymer LLDPE of this density and melt flow index; they are not a guarantee or a product specification. Published data for LF218/21 in a specific end-use structure is limited; in those cases, the limitation is stated rather than extrapolating from laboratory-scale data.

Machine stretch film operations running at line speeds of 450 m/min on 1,800 mm cast dies process LF218/21 in an A/B/C three-layer configuration. The core layer consumes 70–80 wt% of the resin, with the balance typically a metallocene-catalyzed LLDPE or a higher-molecular-weight butene LLDPE to lift puncture resistance. Chill roll temperature is maintained between 18 °C and 24 °C, die gap is set to 0.6–0.8 mm, and melt temperature at the die lips ranges from 245 °C to 260 °C. The grade sustains drawdown to 8 µm without edge tear when the extrusion temperature profile is flat within ±3 °C across the die width. Puncture resistance measured as high-speed puncture under ASTM D5748 typically increases from 1.0 kg to 1.6 kg when the core layer is coextruded with 15–20 wt% mLLDPE. Ultimate stretch values above 250% are observed on powered pre-stretch carriages set at 200–250%, provided film gauge does not exceed 23 µm. Cling is imparted by a skin layer containing 1–3 wt% polyisobutylene tackifier, not by the LF218/21 base resin. Edge curl failures on high-speed wrappers have been traced to chill roll temperature differentials greater than 1.5 °C and to inconsistent air knife impingement across the web. Winder taper tension is maintained at 12–18 N/m to prevent telescoping rolls; core collapse at the start of winding is managed by increasing contact pressure on the lay-on roller within the first 10% of roll diameter. Cling force measurement per ASTM D5458-95(2020) is used to verify that pre-stretched film retains sufficient layering adhesion on pallet loads after 24 h of storage at 20–25 °C.

Where Does a 0.918 g/cm³ Butene Copolymer Fit on High-Stalk Blown Film Lines?

On monolayer and coextruded blown film towers producing produce bags, frozen food films, and carrier films, LF218/21 is run at melt temperatures of 195 °C to 220 °C, with die gaps of 1.8–2.5 mm and blow-up ratios of 2.0–2.8:1. The high-stalk configuration is preferred, with frost line height maintained at 7–9 times the die diameter to reduce quench-related orientation imbalances. Under these conditions, 25 µm monolayer film typically exhibits a dart drop impact value within the 90–130 g range under ASTM D1709-16a Method A and an Elmendorf tear value in the machine direction above 60 g under ASTM D1922-15. Heat seal initiation temperature measured under ASTM F88/F88M-21 at 0.5 s dwell and 2.75 bar jaw pressure falls between 100 °C and 110 °C, with plateau seal strength above 10 N/25 mm between 120 °C and 150 °C. Blown film edge folds and gauge bands are minimized when internal bubble cooling pressure is kept constant to ±0.2 mbar and ambient air flow into the tower is not allowed to vary more than 0.5 m/s. The grade can operate in coextruded structures with LDPE skins for high gloss or with mLLDPE skins for low-temperature seal performance. Food contact compliance rests on FDA 21 CFR 177.1520(c) 3.1a/3.2a and EU Regulation (EU) No 10/2011, including overall migration below 10 mg/dm² under aqueous, acidic, alcoholic, and fatty food simulants.

Converters running cast film lamination for diaper backsheet and adult incontinence outer covers at line speeds above 250 m/min use LF218/21 as a 12–20 µm tie or label film that is corona-treated to 42–46 dyn/cm before adhesive lamination to nonwoven substrates. The secant modulus at 1% strain is typically 15–25% lower than that of hexene-copolymer LLDPE of the same density and melt flow index when measured under ASTM D882-18, which reduces bending stiffness in laminated hygiene panels. The grade still retains sufficient melt strength to allow a stable web between the die and chill roll on 2,400 mm dies. Low gel content is critical in this application because gel particles above 150 µm generate visible bumps in laminated hygiene panels and are rejected by camera inspection systems. Batch-to-batch melt flow index variability within ±0.15 g/10 min under ASTM D1238 is necessary to hold basis-weight deviation below ±0.8 g/m² on automated die-bolt control systems. The coefficient of friction after corona treatment and winding is influenced by slip additive migration, and converters typically target 0.25–0.45 under ASTM D1894-14 without excessive erucamide that would interfere with adhesive bond strength. At unwind tensions above 150 N/m, thin cast films of this type may show blocking in the roll if slip additive bloom is incomplete, which is why finished rolls are stored for at least 24 h at 20–25 °C before slitting.

Greenhouse Film Service Life Is Controlled by Stabilizer Masterbatch Addition, Not by Base Resin Density

Agricultural blown film lines converting LF218/21 into 150–200 µm greenhouse cover and silage films operate with die diameters from 150 mm to 350 mm, blow-up ratios of 2.0–2.4:1, and twin-lip air ring cooling. Because LF218/21 is not UV-stabilized as supplied, a HALS-based UV masterbatch at 5–8 wt% is metered into the main feed before extrusion to achieve outdoor service beyond 12 months; insufficient masterbatch distribution produces localized transmittance loss and premature film embrittlement within 6–9 months in high-UV environments. The base resin contributes film tensile yield in the machine direction above 10 MPa and elongation at break above 600% when tested under ISO 527-3:2018 on 150 µm blown film. Impact resistance after 1,000 h QUV exposure is dominated by stabilizer formulation rather than by the polyethylene backbone, and published data for this specific configuration is limited; field validation on protected and exposed racks is required before specifying service life. Processing boundaries include avoiding pellet surface condensation at relative humidity above 60%, which causes bubble instability and microvoid defects in finished film when hopper warming is absent. For silage wrap, the film is evaluated for stretch retention and oxygen transmission, but LF218/21 itself does not provide high oxygen barrier; multilayer structures with EVOH or polyamide are required only when oxygen transmission below 100 cm³/(m²·day·atm) is specified.

Tubular blown-film lines producing heavy-duty form-fill-seal sacks of 160–220 µm for resin and fertilizer packaging run LF218/21 at output rates limited mainly by bubble cooling capacity rather than by melt fracture. On a 250 mm die with internal bubble cooling and a single-screw extruder equipped with a 30:1 L/D barrier screw, output reaches 400–450 kg/h; below that rate, film tensile properties depend less on screw speed than on frost line geometry and film thickness consistency. Dart drop values for 180 µm film are typically above 400 g under ASTM D1709-16a Method A, while machine-direction tear strength remains above 15 N under ASTM D1922-15. Thickness variation across the web is held below ±5% by stable internal bubble stabilization, and bubble instability appears when ambient air temperature fluctuates more than 5 °C during a single shift. FFS sack drop failures are often attributed to heat seal contamination or gauge bands rather than to film impact properties, which is why seal verification under ASTM F88/F88M-21 is performed at 130–150 °C jaw settings and 0.8–1.2 s dwell. The resin should not be processed at melt temperatures below 185 °C in thick films because unmelted gel-like domains from the high-molecular-weight tail can create surface roughness on polished nip rolls.

When Lamination Sealant Webs Are Specified for Hot-Fill Pouch Structures

Extrusion lamination of LF218/21 as a 20–30 µm sealant web in hot-fill stand-up pouch structures requires coextrusion with a lower-melting sealant resin or blending with 10–20 wt% LDPE to shift seal initiation downward. The sealant layer is processed on a cast line at 245–255 °C with a die gap of 0.7–0.9 mm and subsequent lamination to oriented PET or BOPP at nip pressures of 2–4 bar. Heat seal strength measured under ASTM F88/F88M-21 on 25 µm laminated film increases from 4 N/25 mm at 105 °C to a plateau of 12–16 N/25 mm at 130–150 °C. Hot tack measured under ASTM F1921-12(2018) remains above 3 N/25 mm between 120 °C and 150 °C, which prevents seal creep during vertical form-fill-seal filling of hot-filled liquids at 85–90 °C. The sealant film must be corona-treated on the outer surface for adhesive lamination only after the web has cooled below 35 °C; treating while above that temperature induces surface oxidation variability and uneven adhesive wetting. A sharp drop in interlayer adhesion at the laminate may occur if the chill roll temperature is below 18 °C and the web absorbs moisture from ambient humidity before secondary lamination. When the structure is used for liquid pouch filling, seal bar contamination from low-molecular-weight fractions is reduced by keeping die-lip buildup controlled and by avoiding melt temperatures above 260 °C, where oxidative degradation generates polar low-molecular-weight species.

Frozen Food Packaging and Sub-Ambient Dart Impact Verification

Blown film for frozen vegetable and seafood packaging uses LF218/21 in 40–70 µm monolayer or coextruded structures where low-temperature film toughness is evaluated after conditioning at −18 °C for 24 h under ASTM D1709-16a. At these temperatures, stiffness increases but the butene copolymer retains sufficient impact resistance to withstand sharp frozen product edges when the film gauge is above 50 µm and the blow-up ratio is kept between 2.2:1 and 2.6:1. Tear propagation resistance measured under ASTM D1922-15 is typically 40–70 g after sub-ambient conditioning; the lower range is associated with high frost-line hazing and excessive orientation in the transverse direction. Sealing windows for frozen food bags are specified at 130–160 °C with dwell times of 0.5–1.0 s, because seal strength below 8 N/25 mm at 140 °C leads to opening failures during automated packing. The additive package does not contribute odor or taste under ice-cold contact, but converters must verify organoleptic neutrality under the specific film structure per EU Regulation (EU) No 10/2011 or FDA 21 CFR 177.1520 before final approval. Frozen food films made from this grade are not intended for microwave reheating unless the structure is specifically designed and tested for that condition, including seal integrity after thermal exposure.