The conversion of Braskem LL218/21 into cast hand stretch wrap is centred on a 3-layer coextrusion line equipped with a 2,500 mm die width, 0.6–0.8 mm adjustable lip gap, and a polished primary chill roll maintained at 18–24°C. Melt temperature at the feedblock is held at 240–260°C. The lower limit reduces oxidative degradation during prolonged runs and the upper limit improves gauge uniformity at line speeds above 450 m/min. Edge trim generated at 5–8% of web width is reintroduced at 10–20 wt%. Recycled content above 25 wt% produces gel particles larger than 200 µm that are visible on laser inspection and that accumulate on the die lip after 48–72 hours of continuous production.

The nominal density of this cast-film grade is generally reported between 0.917 g/cm³ and 0.920 g/cm³ under ASTM D792. Melt-flow rate measured to ISO 1133-1:2022 at 190°C/2.16 kg is commonly in the range 1.8–2.2 g/10 min. The exact certificate value should be verified for each lot before process parameters are locked. The cling force of a 23 µm cast stretch film is adjusted with a polyisobutene masterbatch at 1–3 wt% and measured by ASTM D5458; the accepted peel cling range on a standard steel panel is 1.5–3.0 N/25 mm for machine-wrap and hand-wrap grades. Erucamide slip is dosed separately at 300–800 ppm to modify the coefficient of friction measured by ASTM D1894, but a coefficient below 0.15 increases roll telescoping during transit.

Pre-stretch at 200–250% on powered hand dispensers requires the film to retain a machine-direction elongation at break above 400% when tested by ASTM D882. Dart impact of a 20 µm film measured by ISO 7765-1 method A typically exceeds 100 g, but the value falls rapidly when chill-roll temperature is raised above 30°C or when die-lip deposit roughness exceeds 0.5 µm. Gauges below 10 µm approach the melt-fracture boundary; the die temperature is increased by 5–8°C or the lip gap is narrowed to 0.5 mm to stabilize the web. Narrow gaps raise backpressure and require backwash screen monitoring at 72-hour intervals. Chill-roll condensation below 10°C creates transverse optical bands, so the water circuit is kept at or above the plant dew point rather than cooled to the lowest permitted temperature.

Is direct food contact permitted for mono-layer cast produce film?

When LL218/21 is converted into a 20–35 µm mono-layer film for overwrapped leafy produce or baked goods, the completed film formulation must satisfy FDA 21 CFR 177.1520(c)3.1a and EU 10/2011 as amended. Overall migration is determined under EN 1186-1:2002 using 95% ethanol and isooctane simulants; the limit is 10 mg/dm². Base resin compliance is not sufficient because slip and antiblock masterbatches must also carry food-contact approvals and must be listed in the declaration of compliance.

Erucamide slip above 600 ppm creates visible bloom that reduces heat-seal strength and may produce roll blocking. The coefficient of friction measured by ASTM D1894 is generally specified between 0.15 and 0.30. Impulse sealing at 130–150°C and 0.3 MPa dwell must produce a seal force of at least 4 N/15 mm when tested to ASTM F88; values below this level lead to produce bag leakage at distributor level.

When the cast web is corona-treated as a pressure-sensitive adhesive carrier

Surface protection films for stainless steel, anodized aluminium profiles, and furniture-grade MDF are produced from LL218/21 at 25–45 µm thickness. The web is corona-treated inline to 38–42 mN/m measured by ASTM D2578. Treatment above 50 mN/m creates low-molecular-weight oxidation products that reduce anchorage of water-based acrylic coatings; peel adhesion on stainless steel measured by ASTM D3330 may fall below 2 N/25 mm after 7 days at 40°C. Migratory additives such as erucamide are excluded above 200 ppm because warehouse aging accelerates bloom into the adhesive layer.

The cast line is run at 230–245°C and 150–250 m/min to limit gel formation. Trim recycling above 15 wt% increases die-lip deposits; the die is cleaned every 7–10 days when producing clear protection film. Machine-direction elongation at break is specified above 500% under ASTM D882 to permit removal at 180° without tearing. For electronic component protection, surface resistivity is controlled below 10¹² Ω/sq by IEC 61340-5-1. Amine-based antistatic additives are incompatible with long-term clarity and should be replaced with non-amine esters when the film is stored in closed containers above 35°C.

Extrusion lamination onto 12–18 g/m² spunbond nonwoven is a cast-process variant in which Braskem LL218/21 forms the impermeable layer in diaper backsheets and sanitary pads. Die melt temperature is set at 290–315°C. Fibre penetration fails below 280°C, and thermal degradation with visible smoke begins above 330°C. At a coat weight of 23 g/m², the calculated polymer thickness is approximately 25 µm using a density of 0.918 g/cm³.

Online optical inspection rejects defects larger than 50 µm; the accepted pinhole count is 1/m² maximum because the backsheet must withstand a water penetration test at 50 mbar for 2 min. Skin-contact compliance is assessed under REACH 1907/2006 and, where specified, STANDARD 100 by OEKO-TEX class I. The film is also edge-trimmed at 6–10% and the trim can be reused in the core layer only; reuse in the skin layer above 10 wt% increases gel-related pinholes.

Stretch hood film and low-temperature drop impact in coextruded polyethylene layers

Stretch hood structures use LL218/21 in the core of a 3-layer to 5-layer coextruded film with total thickness 80–150 µm. The core layer is 40–60% of the total structure. The skins are generally a metallocene-catalyzed C6-LLDPE. Machine-direction tear strength measured by ASTM D1922 is maintained above 20 N/mm in the finished film. Cold-storage pallets at -20°C require a dart drop impact of at least 2.5 J at 100 µm when tested by ISO 7765-1 method A.

Heavy-gauge cast extrusion is heat-transfer limited. Line speed is held at 80–150 m/min, and the primary chill-roll wrap angle is set between 240° and 300° to reduce curl. Wrap angles below 180° produce asymmetric surface cooling and web curl that cannot be corrected at winder tension below 120 N/m. Printed films are treated to 36–40 mN/m; overloaded treatment above 44 mN/m increases the seal initiation temperature by 5–8°C, which narrows the sealing window when hoods are welded at 140–160°C. Published comparative data for LL218/21 in this specific coextruded structure is limited; the acceptance ranges above are industrial process targets and should be confirmed against the supplier lot certificate.

Agricultural silage bale wrap requires a two-part UV stabilizer package

When LL218/21 is modified for agricultural silage bale wrap, the converter compounds carbon black at 3–5 wt% and a hindered amine light stabilizer at 2,000–4,000 ppm. The film is produced at 25–40 µm thickness. Accelerated weathering to ISO 4892-2 cycle 1 for 1,000 hours must retain at least 50% of the initial tensile elongation measured by ASTM D882. Black pigmentation increases chill-roll release temperature by 2–4°C because of higher radiant absorption; line speed is reduced by 5–10% or the water circuit temperature is lowered to maintain gauge stability. Silage acids and ammonia in storage require the exclusion of amine-based antistatic additives because those compounds accelerate yellowing and reduce UV stabilizer efficiency.