In blown-film food-contact packaging at 25–40 µm, the 0.918 g/cm³ density and 1.0 g/10 min melt flow rate of 118ZJ measured under ISO 1133-1:2022 define the processing window. On a 50 mm single-screw extruder with a 30:1 L/D barrier screw and a 150 mm spiral mandrel die, melt temperature is maintained between 190–215 °C, die gap is set at 1.8–2.4 mm, and blow-up ratio is held at 2.0–2.8:1. Because linear low-density polyethylene exhibits lower melt tension than long-chain-branched LDPE, bubble flutter occurs when frost-line height exceeds 750 mm at output rates above 140 kg/h; dual-lip air rings supplied with 10–15 °C chilled air and a shortened stalk are used to re-stabilise the bubble. Backpressure on this line typically remains below 250 bar when the barrel profile rises from 170 °C at the feed throat to 210 °C at the die adapter; feed-zone temperatures above 180 °C reduce solids conveying and increase specific energy demand beyond 0.25 kWh/kg.

Regulatory positioning for direct food contact relies on FDA 21 CFR 177.1520(c) 3.1a for olefin polymers in contact with aqueous, acidic, and dry foods, subject to extractive limits in §177.1520(d). Under EU Regulation 10/2011, overall migration must not exceed 10 mg/dm² when tested per EN 1186-1 in simulant D1 for 10 days at 40 °C; fatty-food simulant D2 is applied for high-fat contact, and specific migration of 1-butene-derived oligomers is typically below 0.01 mg/kg under standard bubble cooling. The additive package must be verified against the Union List and national measures; no statement in this section substitutes for end-article compliance testing under EU 10/2011 Annex I.

Heat-sealing on vertical form-fill-seal machines is governed by jaw temperature, dwell, and film surface treatment. Neat 118ZJ film shows seal initiation at 102–108 °C; blending with 15–20 wt% autoclave LDPE lowers seal initiation to 96–100 °C and widens the seal plateau. Seal strength above 6 N/15 mm is obtained at 115–125 °C jaw temperature and 0.3–0.6 s dwell when measured under ASTM F88-21; hot-tack strength above 2 N/15 mm at 110–120 °C is required for high-speed vertical bagging. Corona treatment should be limited to the outer lamination side because surface oxidation on the sealant side raises the required seal temperature by 3–5 °C and reduces seal-through-contamination performance.

What limits thickness uniformity in 150 µm heavy-duty sack film?

Heavy-duty sacks for 25 kg resin pellets, sand, and dry chemicals use 118ZJ at gauges from 100–180 µm. On a 70 mm extruder with 30:1 L/D and internal bubble cooling, the resin is processed at 200–230 °C with die gap 2.2–2.8 mm and blow-up ratio 1.8–2.5:1. At 150 µm, frost-line height is held between 650–850 mm; deviations above 900 mm produce a visible long-wavelength gauge band linked to molten-web oscillation. Field data from production lines indicate that the primary process boundary is not melt pressure but bubble geometry: as die output exceeds 220 kg/h, the film enters a region of low-frequency oscillation at 0.2–0.5 Hz, which can be corrected by increasing internal bubble pressure by 10–15% or reducing air-ring venturi velocity.

The incorporation of 20 wt% post-consumer HDPE is common to reduce resin cost; however, the difference in melt flow rate creates a low-shear viscosity ratio above 3:1 when the recycled fraction is below 0.45 g/10 min under ISO 1133-1:2022. In spiral mandrel dies, this mismatch appears as chevron flow marks and dart-impact variability exceeding ±15% across the web. Dart impact measured under ASTM D1709-22 Method B falls substantially relative to neat resin at constant gauge, especially below 0 °C, where post-consumer HDPE domains act as stress concentrators. Elmendorf tear under ASTM D1922-19 in the machine direction follows a similar decline, while transverse tear remains within 10–20% of the neat resin value. Producers restrict recyclate content to 15–25 wt% for sacks that require ISO 7965-1:2022 drop-test performance at 1.2 m flat drop.

Sealing of heavy-duty sacks often uses impulse sealers rather than constant-heat jaws. The seal cycle must be extended by 0.2–0.5 s relative to LDPE-rich film because the linear backbone of 118ZJ relaxes more slowly; insufficient dwell produces delamination of the seal under fill-weight load. Sacks filled with 25 kg of granular product and closed with a bottom gusset seal should be tested with ISO 7965-1:2022 vertical drop and ISO 7965-2:1993 horizontal impact. Published data for this specific SABIC grade in recycled-heavy formulations is limited; plant-level qualification is therefore required before reducing virgin content below 70 wt%.

Tackifier migration and UV stabiliser loading in agricultural silage wrap

Silage wrap produced at 25–35 µm in widths of 500 mm or 750 mm uses 118ZJ as the base resin in a three-layer coextruded construction with polyisobutylene tackifier in the cling layers. The resin’s 0.918 g/cm³ density provides lower modulus than 0.924 g/cm³ LLDPE, which permits higher pre-stretch on bale wrappers without film fracture. At 1.0 g/10 min melt flow rate, the resin maintains melt pressure below 300 bar on a 60 mm extruder with 24:1 L/D. Blown-film lines configured with die gap 1.5–2.0 mm and blow-up ratio 2.5–3.2:1 produce balanced machine-direction and transverse-direction elongation above 600% under ISO 527-3:2018.

Tackifier migration is the dominant quality risk. Low-molecular-weight polyisobutylene added at 2–5 wt% migrates to the film surface over 24–72 h; below 2 wt%, cling force under ASTM D5458-17 is insufficient for multi-layer bale wrapping on rough terrain. Above 5 wt%, migration saturates the outer layer and produces roll blocking, especially when ambient storage exceeds 35 °C. The tackified layer should be placed only in the outer plies of the coextrudate; if polyisobutylene is distributed into the core layer, tackifier return to the surface is retarded and cling performance becomes dependent on winding tension.

Weathering resistance for silage films stored outdoors for 12–18 months requires UV stabiliser loading of 0.3–0.8 wt% hindered amine light stabilizer and 0.1–0.2 wt% UV absorber. Accelerated weathering under ASTM G154-23 Cycle 1 is used for formulation screening, but the correlation to field life is nonlinear; a 20% loss of tensile elongation in accelerated testing does not uniformly predict failure in pasture-stored bales. Silage wrap produced without carbon black is exposed to UV on both film faces, so coextruded layers must incorporate stabiliser at sufficient concentration to prevent surface cracking. The outer surface should not be corona treated because oxidation accelerates HALS consumption and shortens outdoor life.

When 118ZJ is deployed as a core layer in stretch hood film coextrusions

Stretch hood pallet films at 50–120 µm are typically produced on five-layer blown-film dies with diameters of 250–400 mm. In this structure, 118ZJ is placed in the core layer at 40–60 wt%, while skin layers use ultra-low-density polyethylene or plastomer with density 0.902–0.910 g/cm³ to provide cling and puncture resistance. The die gap is set to 1.8–2.4 mm, blow-up ratio to 2.5–3.5:1, and melt temperature to 195–220 °C. Internal bubble cooling is necessary above 250 kg/h output; without IBC, the core layer retains heat and causes the bubble to sag, generating gauge variation above ±8%.

Elastic recovery after 100% extension is the critical functional property. Under ASTM D5459-17, 118ZJ-rich formulations show lower recovery than long-chain-branched LDPE; at core contents above 60 wt%, the film retains only 60–70% of the applied extension after 30 s relaxation. Below 40 wt%, the film’s holding force on pallets decreases enough to allow load shifting in transit. The processing window for this balance is narrow; core-layer melt temperature deviations greater than ±5 °C around 210 °C produce measurable changes in stretch recovery and holding force.

When the skin layer contains migratory cling agents, the core must remain free of slip additives that can migrate outward and compete with tackifier. Silica antiblock in the core at 2,000–5,000 ppm reduces roll blocking but increases haze above 10% under ASTM D1003-21. Film producers therefore minimise antiblock to 2,000 ppm when optical clarity is specified. The boundary condition for pallet wrapping in cold storage is not gauge but puncture propagation: films below 60 µm are more susceptible to protrusion puncture under ASTM D5748-19, and 118ZJ core blends with plastomers show improved energy absorption at -20 °C relative to butene-only LLDPE of equivalent density.

Seal initiation shifts when EVA is blended into 118ZJ lamination webs

In multi-material laminate structures, 118ZJ is used as a 20–40 µm sealant web laminated to PET, BOPP, or aluminium foil. The layer must achieve high seal strength without damaging the reverse-printed outer web. Differential scanning calorimetry of this butene LLDPE shows a melting peak between 122–126 °C at 10 °C/min under ISO 11357-3:2018; the seal initiation temperature is therefore higher than that of EVA-rich sealants but lower than that of high-density polyethylene. On a flat-bar heat sealer, a jaw temperature of 115–135 °C, dwell of 0.4–0.8 s, and pressure of 0.2–0.4 MPa produce seal strengths above 8 N/15 mm under ASTM F88-21.

Hot-tack performance is the limiting factor on high-speed pouch lines. At 120 °C and 0.3 s dwell, hot-tack strength above 2.5 N/15 mm under ASTM F1921-18 is required before the seal cools; 118ZJ achieves this only when blended with 15–25 wt% EVA containing 9–18% vinyl acetate. The EVA reduces seal initiation by 5–8 °C and extends the hot-tack plateau. Without EVA, neat 118ZJ sealant webs exhibit a narrow hot-tack plateau between 118–128 °C; below 115 °C, cohesive failure occurs inside the film rather than at the interface.

Surface treatment must be asymmetric. The lamination side receives corona treatment to 38–42 mN/m under ASTM D2578-17 for solvent-free or waterborne adhesive anchorage; the sealant side should remain untreated because surface oxidation raises the seal initiation temperature by 3–5 °C and reduces hot tack. Laminates exposed to aggressive foods may require inner sealant film without slip additives; if slip is necessary to prevent reel blocking, erucamide migration into the sealant surface after 48–96 h can lower seal strength by 20–30%. In such cases, a non-migratory slip approach based on high-molecular-weight silicone or controlled particle size silica is preferred, but this modifies coefficient of friction under ISO 8295:1995 and must be validated on the filling line.

E-commerce mailer film at 50–90 µm is produced as a three-layer all-polyethylene structure with 118ZJ in the outer layers and post-industrial recyclate in the core. On a 75 mm extruder with 30:1 L/D and internal bubble cooling, melt temperature is held at 200–225 °C; die gap is 2.0–2.6 mm, and blow-up ratio is 2.0–2.8:1. The outer surface is corona treated inline at 40–44 mN/m under ASTM D2578-17 for flexographic or digital printing. The core layer commonly contains up to 30 wt% post-industrial recyclate without extrusion line shutdown; above that level, viscosity heterogeneity in the melt stream produces visible gel-like inclusions and reduces edge-seal consistency on high-speed mailer converters.

Puncture resistance under ASTM D5748-19 is the main performance gate for mailer film because package corners and external transit loads generate concentrated protrusion stress. Tear propagation from the peel-off strip must be limited; Elmendorf tear is measured under ASTM D1922-19, and machine-direction tear is the primary control parameter when the structure contains recycled core material. Seal initiation is adjusted to 98–104 °C by blending 10–20 wt% LDPE into the outer layers; this supports seal dwells below 0.5 s on e-commerce fulfilment lines without sacrificing hot-tack strength under ASTM F1921-18.

Blocking is a production-level failure mode in large-diameter rolls stored at 35–45 °C. The outer layer should contain an antiblock concentration of 3,000–6,000 ppm synthetic silica while keeping coefficient of friction within 0.20–0.35 under ISO 8295:1995; lower coefficient of friction values reduce reel blocking but may impair film tracking on inclined filling sections. Since the construction remains all-polyethylene with density below 1.0 g/cm³, sorting and mechanical recycling compatibility follows the design guidance for mono-material PE flexibles, but end-of-life recyclability must be confirmed at the converter level under the applicable ISO 15270 mechanical recycling framework.