In blown film plants converting ambient and chilled food-contact packaging, SABIC LLDPE 118WJA is processed as a butene-grade linear low-density polyethylene with a nominal density of 0.918 g/cm³ (ISO 1183-1) and a melt flow index of 1.0 g/10 min (ISO 1133-1, 190 °C/2.16 kg). The resin is specified in monolayer and coextruded structures where converters balance coefficient of friction, haze, and seal initiation temperature. On production-scale blown film lines equipped with smooth-bore barrier screws at 25:1–30:1 L/D, die gaps are maintained between 1.8 mm and 2.3 mm because narrower gaps raise shear stress at the die lip and produce melt fracture at outputs above 50 kg/h per die circumference metre. Blow-up ratio is held at 2.0–2.5, and the frost line height is positioned at 6–9 times the die diameter to control crystallinity and haze for clear produce applications. Addition ratios in this segment range from 70 wt% to 100 wt% 118WJA, with LDPE let down from 0 wt% to 30 wt% when bubble stability or melt strength must be increased; slip and antiblock concentrates, only when the selected 118WJA version lacks the target additive package, are dosed at 1–3 wt% until the coefficient of friction falls between 0.20 and 0.40 (ASTM D1894). Melt temperature is normally limited to 190–215 °C; excursions above 225 °C promote oxidation by-products that can raise overall migration under food-contact protocols. The downstream process is blown film extrusion with optional internal bubble cooling and corona treatment at 38–42 mN/m for print adhesion. Terminal finished products include fresh produce bags, bakery bread bags, chilled dairy overwrap, and thin-gauge grocery bags intended for direct food contact.

Migration compliance in this segment is not limited to the base resin; the full formulation including slip, antiblock, and polymer processing aids is assessed under the intended food-contact time-temperature profile. High-clarity structures are typically produced with a dual-lip air ring and internal bubble cooling to keep gauge variation within ±5%; when gauge variation exceeds ±7% at the winder, film roll telescoping occurs in downstream bag converting. The seal initiation temperature is evaluated on a hot-tack instrument rather than inferred from differential scanning calorimetry, because vertical form-fill-seal packagers require repeatable heat-seal dwell time and peel force under production-speed cycling. Food-contact layers exclude post-consumer recyclate unless the recycled material is authorised under the applicable food-contact reuse framework and traceable to the packaging source.

Why Do Heavy-Duty Sack Lines Using 118WJA-Rich Blends Show Gauge Bands When Post-Industrial LDPE Exceeds 30 wt%?

Heavy-duty sack and liner production differs from thin-gauge food film in that final thicknesses typically exceed 100 µm, and the gauge profile must survive filling with granular polymer powders, mineral fillers, and construction chemicals without splitting at crease lines. SABIC LLDPE 118WJA is used in the skin layers at 70–100 wt%, while the core layer carries 20–40 wt% post-industrial LDPE recycled feedstock. This structure keeps low-temperature impact and puncture resistance at the surface while allowing cost and bubble stiffness adjustment in the core. The coextrusion process is run on 3-layer blown film lines with die diameters from 250 mm to 400 mm, die gaps 1.8–2.5 mm, melt temperatures 200–220 °C, and blow-up ratios limited to 2.0–2.4 to preserve tear-propagation resistance. When post-industrial LDPE content exceeds 30 wt%, converters observe gauge bands and die-lip gel accumulation if the screen pack is not stepped from 40/60/80 mesh to 60/80/100 mesh; the resulting melt pressure fluctuations produce thickness variation above ±8% at the winder. Compliance in this segment is managed through packaging recycling obligations under 94/62/EC, REACH registration under EC 1907/2006, and mechanical property verification using ASTM D1709 for dart impact and ISO 527-3 for tensile elongation. Dangerous goods sacks are certified only when the filler mandates UN packaging codes; otherwise acceptance thresholds are set between filler and converter. Terminal finished products include heavy-duty sacks for polymer resin pellets, FIBC liners, construction chemical bags, and mineral filler liners. The table below summarizes a representative three-layer structure used in this segment.

Screen pack build-up in the core layer is not a cosmetic issue; gel particles accumulated at the die lip produce machine-direction streaks that reduce dart impact and increase sack failure at top seam welds. Lines running 300 kg/h or more often insert a gear pump between the adapter and die to dampen pressure pulsation from recycled LDPE, stabilising thickness to ±4%. The inner seal layer is formulated with a higher 118WJA level because dust contamination from filled products tends to reduce seal robustness; the seal layer must remain free of filler dust at the seal bar interface. Incoming 118WJA lots are checked by melt flow index before line start, and moisture condensed on the resin surface during high-humidity storage is removed with warm air at 60–70 °C for 1–2 h only when surface moisture is visible; routine bulk drying is unnecessary for this non-hygroscopic polyolefin.

When Agricultural Greenhouse Films Require a UV-Stabilized 3-Layer Construction

When agricultural greenhouse covers are coextruded with three layers, 118WJA functions as the structural layer that carries light stabilizer masterbatch and contributes tear resistance under wind fatigue. The addition ratio in the interior layer is typically 70–85 wt%, with LDPE at 20–30 wt%, UV stabilizer masterbatch at 8–15 wt%, and anti-drip concentrate at 1–3 wt% when condensation control is specified. Skin layers are formulated with 60–80 wt% 118WJA and higher UV masterbatch loadings to protect the polymer-air interface. Processing is performed on 3-layer blown film lines with die gaps 1.8–2.5 mm, melt temperatures 200–230 °C, and blow-up ratios 2.0–3.0; high blow-up ratios in this segment improve transverse tear resistance but increase gauge scatter on wide widths. Edge trim is recycled in-line at up to 15 wt%; above that threshold, dispersion of the UV stabiliser package becomes uneven and gel speck count rises. The applicable product standard is EN 13206 for thermoplastic films for agricultural and horticultural use, with artificial weathering evaluated under ISO 4892-2 and tensile preservation measured before and after exposure. Service life in high-UV tropical climates still requires outdoor validation on the specific greenhouse structure because artificial weathering does not fully reproduce thermal cycling and wind-driven film fatigue. Terminal finished products include greenhouse roof replacements, low tunnel covers, and temporary crop protection sheets. Converters using 118WJA in this segment without UV additives must limit service to short-season applications; the base grade is not a UV-stabilised agricultural film by itself.

Artificial ageing under ISO 4892-2 provides comparative data but does not directly read across to field performance in sandy, high-altitude, or high-UV tropical sites. Greenhouse converters therefore retain border samples from each production batch and measure tensile elongation at intervals after installation; if retained elongation falls below 50% of the initial value, the cover is scheduled for replacement before the next planting cycle. Anti-drip concentrate dosing above 3 wt% should be avoided because excessive surfactant bloom reduces corona adhesion and causes flexographic ink delamination on printed greenhouse covers. The base 118WJA resin is not UV-stabilised; short-season crop protection films without stabilizer are limited to a single growing cycle to avoid brittle failure during wind gust loading.

Retail Carrier Bag and Refuse Sack Line Modification for 118WJA-Rich Blends

Retail carrier bag and refuse sack lines operate with rapid gauge changes from 12 µm to 80 µm, requiring a resin capable of stable gauge retention under different draw and blow-up ratios. 118WJA is used at 70–100 wt% for carrier bags, and at 60–80 wt% in refuse sacks where post-consumer recyclate is added at 20–40 wt% to comply with recycled content obligations. The production process is single-layer or 2–3-layer blown film extrusion; die gaps are set between 1.5 mm and 2.5 mm, melt temperatures are held at 180–210 °C, and blow-up ratios range from 2.0 to 3.5 depending bag width. Slip and antiblock masterbatches are typically dosed at 1–2 wt% to avoid film blocking in roll form, and line operators wind film only after the surface temperature drops below 35 °C; higher winding temperatures produce blocking and uneven unwind tension. Compliance for refuse sacks in the EU is evaluated under EN 13592, while packaging recycling and recovery obligations follow 94/62/EC; mechanical acceptance is checked by ASTM D882 for tensile strength at break and ASTM D1922 for Elmendorf tear. When recycled content is introduced above 30 wt%, melt filtration with a 60–80 mesh screen pack is used to prevent die-lip gel accumulation and inconsistent film thickness. Terminal finished products include T-shirt carrier bags, produce bags, drawstring refuse sacks, and bin liners for institutional service.

Line modifications for 118WJA-rich blends in this segment include adjustments to the collapsing frame angle. Because butene LLDPE exhibits lower melt rigidity than high-pressure LDPE, bubble flapping near the frost line is controlled with a low-friction collapsing surface and balanced air-ring flow rather than by increasing melt temperature. Slip masterbatch dosing is adjusted only after coefficient-of-friction measurements on printed and unprinted film; over-dosing above 2 wt% can reduce ink adhesion and make the film surface too soft for automatic bag stackers. When post-consumer recyclate is used, converters typically add a 60–80 mesh screen pack and replace it at fixed pressure differential intervals to avoid gel-induced thin spots in the film.

At temperatures below −20 °C, the selection of butene LLDPE 118WJA is based on its retention of dart impact and seal integrity in frozen food packaging films. The addition ratio is 80–100 wt%, with LDPE added at 0–20 wt% only when the converter needs higher melt strength for deep-draw corners on irregular frozen product. The production process uses blown film extrusion with a deliberately lower frost line height, typically 5–7 times die diameter, to limit crystallinity development and preserve low-temperature impact; melt temperature is maintained at 190–210 °C, die gap at 1.8–2.3 mm, and blow-up ratio at 2.0–2.8. For food-contact compliance, the finished structure is assessed under FDA 21 CFR 177.1520(c) and EU Regulation No 10/2011, with migration testing conducted at the intended frozen or refrigerated filling temperature; converters must avoid melt temperatures above 215 °C in this segment because oxidation by-products formed at higher temperatures may raise sensory taint in frozen food. The film is often corona-treated to 36–40 mN/m before flexographic printing. Terminal finished products include frozen vegetable bags, frozen seafood liners, ice cube packaging film, and frozen dough bag-in-box liners.

Low-temperature seal strength is evaluated after conditioning sealed pouches at −20 °C for 24 h; failure at the fold line rather than the seal interface indicates excessive frost line crystallinity or excessive transverse orientation. Frozen food packagers also test for pinhole resistance after repeated flexing, because perforations in the film lead to freezer burn and product weight loss. When 118WJA is blended with LDPE above 20 wt% in this segment, the film may lose some low-temperature dart impact and become stiffer at sub-zero storage conditions. The frost line height must therefore be lowered when the LDPE fraction increases, and the line speed reduced to keep the bubble stable.

Stretch Hood Film Elastic Recovery Is Governed by Comonomer Branching and Cooling Rate

Stretch hood extrusion trials with 118WJA use the grade as a blending component at 50–80 wt% with LDPE or metallocene LLDPE to balance elastic recovery and puncture resistance for pallet unitization. The production process is blown film extrusion on lines with internal bubble cooling, die diameters from 200 mm to 400 mm, die gaps 1.5–2.5 mm, melt temperatures 190–215 °C, and blow-up ratios 2.0–3.0; film thickness in this segment normally ranges from 50 µm to 120 µm. Elastic recovery is measured by ASTM D5459, while tensile properties are determined by ISO 527-3; impact resistance is commonly checked with ASTM D1709 on finished film. There is no single harmonised EU standard governing stretch hood mechanical performance, so converter and machine builder specifications govern load retention and stretch ratio limits. Published data for 118WJA in this specific stretch hood configuration is limited, and plant trials are required to fix the optimum blend ratio because comonomer branch spacing and cooling rate interact with film stiffness. The formulation boundary is operationally important: above 80 wt% 118WJA the film may lose elongation and form pinholes on corner stress, while below 50 wt% the blend may not develop sufficient elastic recovery to hold load shifts during transport. Terminal finished products include stretch hood films applied by automatic rotary arm and loop-type stretch hood machines, petrochemical pallet covers, and construction material pallet containment.

The automatic stretch hood process applies the film by converting machine-specific stretch ratios into pallet containment force; neck-on at the hood corners is influenced by die gap, blow-up ratio, and the cooling profile. Converters test each reformulation on a small batch of pallets because the coefficient of friction against packaged goods determines film slip during the hood application cycle. The base 118WJA grade is not pre-formulated for high-tack stretch applications; when cling properties are required, a cling agent masterbatch is dosed only after the applicator machine supplier confirms compatibility. Additional film edge thickness profiling may be needed on thick 100–120 µm hoods to avoid uneven stretching and localized thinning at the pallet base.