On pallet-wrapping lines running at 45–60 wraps/min, machine stretch film based on Braskem LH218 is extruded at 10–23 µm gauge and supplied in 400–500 mm wide rolls for hand and machine application. LH218 enters at nominal density 0.918 g/cm³ according to ASTM D792 and nominal melt mass-flow rate 2.0 g/10 min according to ASTM D1238 at 190°C/2.16 kg. The cast line is typically a 2,000–3,500 mm external-deckle die equipped with a 100/150/100 mesh screen pack and a barrier single screw with 30:1 L/D. Melt temperature at the feedblock is held at 235–260°C, die gap is set to 0.8–1.3 mm, and primary chill roll temperature is 20–28°C with a 6–10°C secondary roll differential to control web flatness and blocking tendency.

Formulation for machine stretch webs uses 80–90 wt% LH218, 5–10 wt% metallocene plastomer, 2–5 wt% polyisobutylene tackifier, 500–1,200 ppm erucamide slip, and 0.5–1.5 wt% synthetic silica antiblock. The tackifier is concentrated in the outer layer of a three-layer coextrusion, leaving the core layer tougher and the inner surface smoother for consistent roll release. Cling force is measured by ASTM D5458, and tensile elongation at break is measured by ASTM D882. In machine-applied pallet wrap, a minimum elongation at break of 300% in both machine and transverse directions is commonly specified. The processing conflict is that excess tackifier above 5 wt% raises outer-roll blocking force, and film telescoping occurs at the winder when cling force exceeds unwind tension during acceleration. Coefficient of friction is monitored by ASTM D1894 to maintain controlled unwind without shedding layers in transit.

Edge trim regrind is returned at 10–20 wt%. Above 20 wt% regrind, gel defects become visible in 10 µm film as unoriented inclusions, and draw resonance appears as periodic gauge bands if haul-off speed exceeds 400 m/min while melt strength is low. Pre-drying is not required, but standing wet resin exposed to relative humidity above 60% should be avoided because surface water on pellets creates voids that weaken thin-gauge webs. Industrial pallet wrap is not food-contact; EU shipments require REACH SVHC documentation under Article 33 when the final article contains candidate-listed additives. Terminal products include hand rolls, machine rolls, and perforated pallet wrap for automated depalletizing lines.

What Limits Calcium Carbonate Loading in Cast Extrusion of Breathable Hygiene Backsheets?

Breathable cast precursor films for diaper backsheets are compounded from LH218 and calcium carbonate masterbatch at loadings of 45–60 wt% CaCO3. The calcium carbonate is 1.0–2.0 µm median particle size with stearic acid surface coating to reduce agglomeration. The precursor is produced as a cast web at 20–35 µm, then uniaxially oriented on a machine-direction orientation unit with draw ratios of 2.5:1–3.5:1 at preheat roll temperatures of 55–80°C and annealing roll temperatures 80–100°C. The drawing step creates microvoids around the mineral particles; water vapour transmission rate is measured by ASTM E96/E96M at 38°C and 90% RH. Typical hygiene backsheet specifications fall between 1,500 g/m²/day and 5,000 g/m²/day, depending on CaCO3 loading and final oriented gauge.

The limiting loading of CaCO3 is not extruder torque alone but orientation stability after the MDO unit. At 60 wt% CaCO3, the web becomes sensitive to pinhole formation and edge fibrillation when the draw ratio exceeds 3.0:1. Below 45 wt% CaCO3, void formation is insufficient for typical MVTR requirements above 1,500 g/m²/day. The cast film die gap is widened to 1.5–2.0 mm because the mineral-filled melt has lower melt strength and higher die swell. Screw speed is lowered 10–20% relative to unfilled cast film, and melt temperature is limited to 210–240°C to reduce degradation of the surface treatment on the mineral. Processors monitor die pressure and screen-pack pressure drop because published data for this specific configuration is limited. Skin-contact hygiene materials are assessed under ISO 10993-5 and ISO 10993-10; the final backsheet must be non-cytotoxic and non-irritating. Terminal products include diaper backsheet, adult incontinence waistbands, and feminine hygiene outer covers.

For fresh-cut produce and tray-sealed modified-atmosphere packs, a 25 µm cast lidding web is coextruded with LH218 as the sealant skin over a PP or PET rigid tray. The formulation for the sealant skin contains 85–95 wt% LH218, 5–15 wt% LDPE or metallocene plastomer, 0.3–1.0 wt% food-grade anti-fog agent, and 500–1,000 ppm slip. The anti-fog reduces condensed droplets under 4°C refrigerated display; light transmission and haze are measured by ASTM D1003, while seal strength is measured by ASTM F88/F88M after 0.4–0.6 s dwell at 1.8–2.2 bar. The cast line uses a 1,500–2,000 mm die, 0.7–1.1 mm die gap, melt temperature 230–255°C, and primary chill roll 18–25°C.

The most critical non-conformance is migration of erucamide slip to the seal interface. At slip levels above 1,000 ppm or after 14 days of ambient ageing, heat seal strength measured by ASTM F88/F88M can fall below the packaging line’s minimum acceptable burst value. On high-speed tray lines running 60–80 packs/min, seal initiation must remain below 110°C; excessive slip or heat history shifts seal initiation upward. The anti-fog additive must be listed in EU Regulation 10/2011 Annex I for EU sales. US food-contact status is covered under FDA 21 CFR 177.1520, with use conditions in 21 CFR 176.170(c) for aqueous, acidic and low-alcohol foods up to the specified temperature-time profile. Oxygen transmission rate is crop-specific and is measured on the finished lidding web by ASTM D3985 at 23°C and 0% RH. Gauge variation above ±5% across the web creates uneven sealing and tray leakers at the corners. Terminal products include lidding film for mushroom trays, fresh-cut salad packs, and berry punnets.

When LH218 is Extruded Below 15 µm as a Masking Web for Polished Metals and Glass

Surface protection webs below 15 µm are run under low-shear screw configurations and low backpressure because shear heating narrows the processing window. Melt temperature is held at 210–240°C, die gap at 0.4–0.8 mm, and primary chill roll at 15–22°C with a polished or matte finish. The film is corona-treated in line to 40–42 mN/m wetting tension measured by ASTM D2578, then coated with a pressure-sensitive adhesive or coextruded with an acid-modified polyolefin skin. Low-tack protective articles are specified by peel adhesion measured on stainless steel by ASTM D3330/D3330M, with production ranges from 0.05 N/cm for high-gloss PMMA to 1.5 N/cm for textured aluminum.

Neck-in and edge bead are the dominant process failures below 10 µm. The extrudate is pinned at the die edges with electrostatic edge pinning, and the draw ratio is set to 10:1–25:1 from die gap to final film gauge. Below 8 µm, draw resonance produces transverse thickness bands that interfere with uniform peel force. Gauge variability is measured by a non-contacting capacitance gauge and controlled to ±5% of nominal. Reclaimed edge trim is blended at 5–15 wt%; higher levels introduce gel and optical defects that become visible on polished substrates. Electronics protection articles require RoHS Directive 2011/65/EU compliance and customer-specific halide-free specifications. Terminal products include protection films for stainless steel appliances, glass sheets, polycarbonate panels, and coated metals during laser cutting or UV printing.

High-Speed HFFS Sealant Thermodynamics in LH218-Based Cast Webs

When LH218 is employed as the sealant skin in a three-layer cast film for horizontal form-fill-seal lines running 80–120 packs/min, the processing focus shifts from optical haze to seal initiation and hot tack under short dwell. The sealant skin is blended with 10–30 wt% metallocene plastomer with density 0.902–0.910 g/cm³ to lower seal initiation below 110°C. The core layer uses 0–20 wt% reclaimed edge trim and may include HDPE for stiffness if gauge exceeds 45 µm. The cast line uses an internal deckle die of 1,200–2,000 mm, 0.7–1.2 mm die gap, melt temperature 230–255°C, and a chill roll with matte texture to prevent air entrapment.

Hot tack is measured by ASTM F1921 at 0.3 s dwell and 0.5–2.0 bar seal pressure, while final seal strength is measured by ASTM F88/F88M. The technical boundary is additive migration: erucamide slip loads above 1,000 ppm and long roll ageing can reduce seal strength at dwell times below 0.3 s because bloom transfers to the sealing interface. Processors therefore split the slip additive, placing 200–600 ppm in the sealant skin and the balance in the outer layer. Coefficient of friction is measured by ASTM D1894 and maintained at 0.20–0.40 kinetic, while haze is measured by ASTM D1003 and kept below 8% for clear overwrap. Oxygen barrier is provided by lamination to PET, BOPP, or aluminum foil; the cast sealant web is not the barrier layer.

Food-contact grades for HFFS structures require FDA 21 CFR 177.1520 and EU Regulation 10/2011 compliance with overall migration tested by EN 1186 at the intended processing and shelf conditions. Terminal products include snack-bar flow packs, confectionery cold-seal overwrap, frozen seafood pouches, and zipper bags, where the sealant must be compatible with resealable zipper profiles without loss of seal force at the zipper interface.

Agricultural silage wraps produced from LH218 are extruded at 25–35 µm gauge and 500–750 mm width for round and square bale wrapping machines. The formulation includes 1–4 wt% polyisobutylene tackifier, 0.05–0.20 wt% hindered amine light stabilizer package, and 0.3–1.0 wt% UV absorber. Since the film is stretched on the baling machine at 55–70% pre-stretch, tensile behaviour under high-speed stretch is the first release criterion. Elongation at break measured by ASTM D882 commonly exceeds 400% in the machine direction, but the application force at 50% pre-stretch is also recorded with a bale-wrapper load cell to ensure compatibility with the machine.

The primary field failure is loss of cling due to dust accumulation and UV embrittlement at the film edges after 12–18 months. Accelerated weathering by ASTM D4329 or ISO 4892-2 is used to verify ultraviolet resistance, but published data for LH218-specific UV formulations is limited. Pre-drying is not required, though wet pellets from outdoor silos can introduce voids. The cast film conditions are similar to stretch film: melt temperature 240–270°C, die gap 0.8–1.2 mm, primary chill roll 20–25°C, and edge trim return at 10–20 wt%. Terminal products include round bale silage wraps, haylage films, and maize silage bale covers.

A 70 µm Cast Web for Frozen Food Withstands Dart Impact at −40°C

Vertical form-fill-seal lines for frozen vegetables and seafood demand cast webs with low-temperature ductility down to -40°C. The structure uses 80–90 wt% LH218 with 10–20 wt% ethylene-vinyl acetate or ULDPE to reduce brittle failure and improve dart impact. The final film thickness is 40–80 µm to resist ice-crystal puncture and seal-bar pressure. Dart impact is measured by ASTM D1709 Method A after conditioning at -40°C; tear resistance is measured by ASTM D1922 and tensile elongation by ASTM D882. The cast line runs a 1,500–2,500 mm die, 0.8–1.5 mm die gap, melt temperature 235–260°C, and primary chill roll 18–25°C.

The operational boundary is regrind return. Frozen food web is often coloured white or printed, so gels and charred trim from regrind above 20 wt% become visible and reduce seal integrity. Extruder screens of 80/120/120/80 mesh and a gear pump are recommended to stabilize output and reduce melt-temperature variation to ±3°C. Food-contact status is covered under FDA 21 CFR 177.1520 and EU Regulation 10/2011; cold-temperature performance is not a regulatory requirement but is set by distribution risk assessment. Terminal products include frozen vegetable pillow packs, seafood pouches, and ice cream overwrap.