High-stalk tubular film conversion of LyondellBasell HDPE L4550 for retail T-shirt carrier bags is specified around a nominal density of 0.945 g/cm³ measured under ISO 1183-1:2019 and a melt flow rate of 0.45 g/10 min measured under ISO 1133-1:2022 at 190 °C and 2.16 kg. On production lines fitted with 65 mm to 90 mm single-screw extruders at 30:1 to 36:1 L/D and barrier screws, the grade is processed at a melt temperature of 190–215 °C through a spiral mandrel die of 250–450 mm diameter and 1.2–1.8 mm die gap. Blow-up ratio is maintained between 2:1 and 3.5:1, and the frost line is held at 8–12 die diameters above the air ring; output is typically 0.8–1.5 kg/h/mm of die circumference. Formulation addition ratios for T-shirt bag stock are set at 2–4 wt% color masterbatch, 1,500–3,000 ppm silica antiblock, 500–800 ppm erucamide slip, and 200–400 ppm fluoropolymer processing aid. Regrind reincorporation is limited to ≤20 wt% to avoid batch-to-batch die swell drift and bubble instability in the upper stalk. Compliance for carryout bags used with food contact is referenced to FDA 21 CFR 177.1520 paragraph (c) for high-density polyethylene and, for the European Union, to (EU) No 10/2011 with overall migration testing under EN 1186-1:2002 to the 10 mg/dm² limit. Non-food retail bags are assessed against EU 94/62/EC Annex II and CONEG heavy metal limits with total lead, cadmium, mercury, and hexavalent chromium not exceeding 100 mg/kg combined. Terminal finished products include side-weld T-shirt bags, bottom-seal merchandise bags, produce roll bags, and thin-gauge carryout bags in the 12–25 µm range.

Does cast film extrusion of L4550 require a rebalanced melt-temperature and chill-roll protocol compared with high-stalk blown film?

Cast film conversion places L4550 under a shorter quench window than tubular film; the molten web exits a flexible lip die at 220–250 °C and is pinned to polished chrome chill rolls maintained at 20–40 °C. On a 90 mm extruder with 30:1 L/D and a Maddock mixing section, edge bead thickness variability is held below ±2% when the die gap is set at 0.5–1.0 mm and output is limited to 0.6–1.2 kg/h/mm die width. The formulation for industrial can liners incorporates 1.0–2.5 wt% additive masterbatch containing slip and antioxidant, 2,000–4,000 ppm silica antiblock, 200–500 ppm fluoropolymer processing aid, and for exterior storage duty 0.25–0.75 wt% hindered amine light stabilizer. Non-food industrial liner compliance is anchored to REACH (EC) No 1907/2006 SVHC screening, EU 94/62/EC Annex II total lead, cadmium, mercury, and hexavalent chromium limit of 100 mg/kg combined, and CONEG heavy metal restrictions. Terminal finished product types are compactor bags, drum liners, garment bags, and industrial waste liners from 18 µm to 60 µm. The principal process threshold appears at thicknesses below 12 µm, where edge thinning exceeds 5% unless die bolt distribution and air-knife impingement pressure are retuned; published data for L4550 in sub-12 µm cast liners is limited.

In coextruded cereal-liner webs where L4550 is placed as the central stiffness layer, the melt stream is combined with LDPE or LLDPE skins in a three-layer spiral mandrel die, and the layer distribution is maintained at 60–70 wt% L4550 core with 15–20 wt% skin layers on each side. Food-contact status of the structure is governed by FDA 21 CFR 177.1520 paragraph (c) for high-density polyethylene and by (EU) No 10/2011, with overall migration under EN 1186-1:2002 constrained to the 10 mg/dm² limit; organoleptic transfer is evaluated with ASTM E1870-22 or equivalent internal sensory panels. Core-layer formulation uses 0.5–1.5 wt% white masterbatch; erucamide slip is restricted to skin layers at 500–1,000 ppm, and antiblock is added to skins at 2,000–5,000 ppm, while the L4550 core is maintained without migrating slip to preserve interlayer adhesion. Coextrusion blown film processing runs with spiral mandrel dies at 1.8–2.5 mm die gap, 2:1–3:1 blow-up ratio, and 195–225 °C melt temperature; air-ring chill air is cooled to 5–12 °C, and internal bubble cooling is introduced above 1.0 kg/h/mm die circumference to control frost line oscillation. Terminal products include cereal liners, cracker liners, dry snack liners, and carton inner bags for free-flowing dry foods in the 16–40 µm gauge band. The limiting process window is the core fraction: above 75 wt% L4550 core, interlayer gauge nonuniformity above 4% and a measurable dart impact reduction have been observed on a 3-layer 80 mm line; published data for this specific configuration is limited.

When L4550 replaces a 0.948 g/cm³ HDPE in low-stalk heavy-duty sack film, the stabilizer and film-gauging profiles must be reset before extrusion begins

Heavy-duty sack conversion of L4550 is performed in low-stalk blown film geometry with a short frost line at 4–6 die diameters, blow-up ratio 1.5:1–2.5:1, and die gap 1.5–2.0 mm. The nominal density of 0.945 g/cm³ is lower than the 0.948 g/cm³ grade historically used on the same line; this shift alters tear propagation and dart impact, so blade, air-ring, and die settings are not directly transferable. Formulation for UV-exposed agricultural and construction sacks adds 2–4 wt% carbon black masterbatch to reach 800–1,200 ppm carbon black in the final film, with 0.20–0.50 wt% hindered amine stabilizer masterbatch, 500–1,000 ppm slip, and 1,000–2,000 ppm antiblock. Compliance for non-food industrial sacks references REACH (EC) No 1907/2006, EU 94/62/EC Annex II heavy metal limits, and filled-sack drop testing under ISO 7965-2:1996; weatherability of UV-stabilized film is assessed by ISO 4892-2:2013 and dart impact by ASTM D1709-22 or ISO 7765-1:2012. Extrusion is performed on 90–120 mm grooved-feed single-screw extruders with 25:1 to 30:1 L/D and barrier screws; melt temperature is maintained at 190–210 °C because overheating produces gel specks and lowers bubble stability. Terminal products are heavy-duty sacks, fertilizer bags, animal feed bags, and construction debris bags from 50 µm to 100 µm. A production-scale limitation is that carbon black masterbatch let-down above 4 wt% on this grade increases melt pressure and reduces output, while below 2 wt% accelerated weathering data may show rapid loss of elongation; converters must verify each masterbatch carrier resin compatibility.

On 100 mm to 130 mm high-output cast film lines running L4550 for agricultural chemical inner liners, the critical adaptation is the avoidance of amine-based antifog concentrates due to known interactions with erucamide slip packages that generate plate-out on chill rolls. The film is formulated with 1.0–2.0 wt% white or colored masterbatch, 0.15–0.40 wt% antistatic additive, 500–1,200 ppm slip, 1,500–3,000 ppm antiblock, and 200–400 ppm fluoropolymer processing aid. Cast film equipment uses die gaps of 0.8–1.2 mm, chill roll temperatures of 15–25 °C, melt temperatures of 205–230 °C, and line speeds of 80–220 m/min. Regulatory compliance for agricultural chemical inner liners is anchored to REACH (EC) No 1907/2006, EU 94/62/EC Annex II heavy metal limits, and chemical resistance screening according to ASTM D543-20; permeation and seal-strength validation for aggressive formulations must be performed on a case-by-case basis because published data for specific agrochemical compositions is limited. The finished product types include pesticide inner liners, fertilizer pouch stock, and chemical drum liners in the 20–50 µm gauge band. At film thickness below 20 µm, the operational boundary is set by permeation of low-viscosity active-ingredient carriers, which requires downgauging trials under full pack testing rather than resin-only laboratory screening.