In agricultural blown film extrusion, SABIC LLDPE 218WM is compounded into monolayer and three-layer greenhouse film structures at a polymer fraction of 65–75 wt% with 25–35 wt% LDPE, while a UV stabilizer masterbatch is dosed separately at 8–12 wt% based on the masterbatch carrier and target service life. The grade is processed on single-screw extruders with L/D 30:1 barrier screws and spiral mandrel dies, with melt temperature held between 190 °C and 220 °C, die gap set at 1.4–1.8 mm, and blow-up ratio controlled at 2.2:1–2.8:1. Under these conditions, the 2.0 g/10 min melt flow rate measured by ISO 1133-1:2022 and the 0.918 g/cm³ density measured by ISO 1183-1:2019 permit stable bubble formation on 70 mm dual-lip air ring dies, while film tensile properties are evaluated under ISO 527-3 and tear propagation under ASTM D1922. Production-scale lines using 218WM above 65 wt% exhibit lower melt-pressure fluctuation at the screen changer, whereas dropping below 60 wt% reduces machine-direction dart impact; the operational boundary is therefore set around 65 wt% for load-bearing greenhouse film. Compliance for agricultural covering films is referenced to EN 13206:2017, which addresses thermoplastic films for agriculture, and the resin is not selected for high-clarity greenhouse glazing where haze below 12% is required because the slip and antiblock additives in 218WM increase surface light scattering. Terminal finished product types include greenhouse covers, low-tunnel films, silage stretch films, and black or white mulch films.

When 218WM Is Diluted Below 50% in Heavy-Duty Sack Film

Heavy-duty sack film formulations add 218WM at 35–50 wt% into LDPE-rich blends, with LDPE at 50–60 wt% and optionally HDPE at 5–10 wt% to raise modulus and block resistance. The HDPE component must remain below 10 wt% because higher addition reduces dart impact and increases gel accumulation on 90 mm extruder screws. Downstream film production uses blown film extrusion on a single-screw extruder with L/D 28:1–30:1 and a spiral mandrel die, melt temperature between 200 °C and 230 °C, die gap of 1.8–2.2 mm, and high-stalk bubble geometry with a blow-up ratio of 2.0:1–2.5:1. On 80 mm dies, bubble pumping is observed when air ring pressure exceeds 5.0 kPa and is corrected by reducing cooling air velocity rather than increasing melt temperature, since melt temperature above 240 °C introduces oxidative gel defects. Dart impact resistance is tested under ASTM D1709/D1709M-15a, tear resistance under ASTM D1922, and tensile properties under ISO 527-3; these mechanical evaluations are used to qualify the film for mineral and construction product sacks rather than food contact. REACH SVHC screening applies when the film enters the European market, and the converter must verify that the final article does not exceed 0.1 wt% for any candidate-list substance in the dried film. Terminal finished product types include heavy-duty shipping sacks, building-materials bags, resin pellet bags, and woven-laminated sack alternatives where the 218WM-rich layer supplies puncture resistance and seal strength.

Collation shrink film lines running 218WM-rich blends at 65–80 wt% with 20–35 wt% LDPE produce thin-gauge webs in the 40–70 µm range for bottle and can multipacks. The film is extruded on 50–70 mm single-screw extruders with barrier screws and internal bubble cooling, using die gap of 1.0–1.5 mm and blow-up ratio of 3.0:1–3.5:1 to shift orientation toward the transverse direction, which governs shrink force in the final overwrap. A typical 60 µm collation shrink formulation uses 70 wt% 218WM and 30 wt% LDPE; additional slip or antiblock masterbatch is not required because 218WM already contains slip and antiblock additives, but a process stabilizer masterbatch may be added at 2–4 wt% when regrind content exceeds 20 wt%. Compliance for food-contact collation shrink where the film may contact outer food surfaces is assessed under FDA 21 CFR 177.1520(c) and EU Regulation 10/2011, with overall migration testing conducted according to EN 1186-1:2002; specific end-use migration depends on food type, temperature, and contact time, so each final structure requires its own extraction study. Downstream production includes tubular blown film extrusion, inline slitting, and shrink tunnel operation at 140–160 °C with a minimum dwell time of 3 s for film above 70 µm; shorter dwell times cause intermittent shrink-back inconsistency and loose package appearance. Terminal finished product types are multipack shrink sleeves for beverage bottles and cans, paper ream overwrap, and overwrap for household goods; 218WM is not recommended for high-shrink display films where gloss retention and contact clarity are critical because the slipping additive migrates to the film surface during shrink tunnel exposure.

Why Does Low-Temperature Seal Integrity Hold in Blown Freezer Film Sealant Layers?

Blown freezer film sealant layers based on 218WM are run at 50–70 wt% of the sealant layer, with 30–50 wt% LDPE, and the outer layer may use metallocene LLDPE for higher seal strength. The 0.918 g/cm³ density and butene comonomer content reduce the low-temperature brittleness of the polyethylene film and help maintain seal integrity at freezer temperatures down to −25 °C, although published data for this specific configuration is limited and low-temperature impact resistance is benchmarked under ASTM D1709/D1709M-15a after conditioning at −20 °C for 24 h. The film is produced by coextrusion blown film equipment, with the sealant layer fed by a 50 mm smooth-bore extruder at 180–210 °C, die gap of 1.0–1.4 mm, and blow-up ratio of 2.4:1–2.8:1; gel counts increase when melt temperature exceeds 240 °C, and the line must be purged with LDPE before shutdown to prevent resin hang-up in the die lip. Compliance for frozen food contact is assessed under FDA 21 CFR 177.1520(c) and EU Regulation 10/2011, supplemented by EU 2017/752 overall migration limits; specific migration testing is required for the finished multilayer film because the sealant layer is not a food-contact article alone. The formulation addition ratio above 70 wt% 218WM can reduce seal initiation temperature but may lower hot-tack strength, so converters running high-speed vertical form-fill-seal equipment typically cap 218WM at 70 wt% in the sealant layer. Terminal finished product types include frozen vegetable bags, ice cream pouches, fish fillet bags, and premade bag stock for vertical form-fill-seal machines; the grade is not recommended for retort or boil-in-bag applications because the butene LLDPE softening point is below retort process temperatures.

Blown Stretch Hood Film: BUR, Puncture Resistance, and Air Ring Configuration

Blown stretch hood film uses a polymer matrix with 218WM added at 65–75 wt% of the total polymer fraction, LDPE at 20–30 wt%, and metallocene plastomer at 5–10 wt% to increase elastic recovery; the 2.0 g/10 min melt flow rate of 218WM supports stable bubble formation at high blow-up ratios of 3.0:1–3.5:1 on 100 mm spiral mandrel dies. Downstream processing is monolayer or three-layer blown film extrusion with die gap of 1.4–1.8 mm and melt temperature of 190–220 °C, followed by inline surface treatment to 38–42 dyn/cm for pallet hood application; production-scale lines fitted with internal bubble cooling and high-deck frames require iterative air ring pressure tuning because the slip additive in 218WM reduces bubble surface friction at the frost line. Formulation addition above 75 wt% 218WM without plastomer reduces puncture resistance and causes stress whitening at gusset creases, while below 65 wt% 218WM the stretch hood loses elastic recovery after repeated cycles. Mechanical compliance is measured using ISO 527-3 for tensile modulus and yield stress, ISO 6383-2 for tear resistance, and ASTM D5748 for puncture energy, while the finished pallet hood film is validated by a stretch force test at 10–15% elongation during palletizing. The resin is not recommended for ultra-high-cling hand wrapping because tackifier migration is not optimized and the slip additive can reduce cling force after storage. Terminal finished product types are industrial pallet stretch hoods, heavy equipment dust covers, and construction pile covers.

Bin Liner Extruders Shift to 218WM-Rich Regrind Streams

On high-output bin liner lines, 218WM is added at 50–70 wt% with post-industrial regrind at 30–50 wt% to maintain blown film processability, because the 2.0 g/10 min melt flow rate and 0.918 g/cm³ density allow blending with LDPE and LLDPE scrap of variable melt index without excessive melt-pressure drift. A 65 mm extruder with L/D 30:1 barrier screw and die gap of 1.4–1.8 mm runs 218WM-rich regrind streams at melt temperatures between 180 °C and 210 °C; as regrind content exceeds 50 wt%, gel particles from degraded scrap increase and film appearance degrades, so the operational boundary is set at 30% post-industrial regrind for printed refuse sacks and 50% for black non-critical liners. Compliance for refuse sacks is evaluated under EN 13592:2017, with tensile strength at yield and elongation at break measured under ISO 527-3; REACH SVHC declarations and RoHS Directive 2011/65/EU screening apply when the finished liners are sold into electrical and electronics waste handling operations. Downstream converting includes blown film extrusion, gusseting, perforation, and roll winding, with printed bags made by flexographic or rotogravure lines using polyamide-based inks; 218WM with slip and antiblock requires corona treatment at 40–42 dyn/cm before printing because the migratory slip additive reduces ink adhesion on untreated film. Terminal finished product types include household refuse sacks, commercial bin liners, carrier bags, and industrial waste bags; 218WM is not recommended for compostable or biodegradable sack requirements because it is not a compostable polymer.