Outdoor Exposure Mechanics in Silage Bale Wrap and Agricultural Stretch Film

Chevron Phillips Marlex® 7109DJ LLDPE blown film resin, specified with nominal density 0.918 g/cm³ (ASTM D1505) and melt index 1.0 g/10 min (ASTM D1238, 190°C/2.16 kg), is processed for silage bale wrap as a three-layer coextruded film. The core layer carries 60 wt%–80 wt% of the resin, with 15 wt%–25 wt% lower-melt-index hexene LLDPE or metallocene LLDPE to raise dart impact and low-temperature puncture resistance, 3 wt%–5 wt% white UV-reflective masterbatch, 1.0 wt%–1.5 wt% HALS-based UV stabilizer masterbatch, and 0.5 wt%–1.0 wt% cling additive in the outer skin. Regulatory compliance for agricultural silage film is referenced against EN 13207:2018 for silage barrier and mechanical requirements; tensile properties after weathering are measured under ASTM D882-18, and edge tear is measured under ASTM D1922-15. Carbonate-filled formulations are excluded because they reduce tear resistance below the 400 g/25 µm threshold commonly required for wrapped grass silage.

Production-scale conversions observed on a 75 mm grooved-feed extruder with 30:1 L/D barrier screw use a 250 mm three-layer annular die with 2.0 mm die gap, 2.5:1–3.0:1 blow-up ratio, and frost line height 8–10 die diameters. Melt temperature at the die is held at 200°C–215°C, with output 250 kg/h–350 kg/h and internal bubble cooling engaged to maintain thickness variation below ±4%. Winding is configured with taper tension 0.5 N/mm–1.0 N/mm to prevent edge wrinkles at 750 mm × 1500 m finished rolls. Terminal finished products are silage bale wrap, haylage wrap, and maize silage wrap, applied on balers at 55%–70% pre-stretch. The resin itself does not provide UV stabilization; storage exposure beyond 12 months requires increased HALS concentration or secondary sleeve protection.

In frozen-food packaging lines operating at 25 µm–60 µm sealant-gauge targets, 7109DJ is blended at 80 wt% with 15 wt% high-pressure LDPE and 5 wt% synthetic silica antiblock masterbatch for monolayer printed bags, or used as the sealant layer at 20 wt%–25 wt% of total structure in a coextruded construction with EVOH or polyamide core. Food-contact compliance rests on FDA 21 CFR 177.1520(c) 3.2a and 3.2b for olefin polymers, EU Regulation (EU) No 10/2011 Annex I with overall migration limit 10 mg/dm², and China GB 4806.7-2016 for food-contact plastic articles. The blown film process uses a 45 mm–65 mm extruder with 24:1–30:1 L/D barrier screw, die gap 1.8 mm–2.2 mm, blow-up ratio 2.0–2.3, and melt temperature 190°C–210°C.

On high-speed vertical form-fill-seal lines at 45 m/min–80 m/min, seal bar temperature is maintained at 115°C–135°C with dwell 40 ms–80 ms and sealing pressure 0.3 MPa–0.6 MPa. Terminal types include frozen vegetable pillow bags, IQF fruit pouches, frozen seafood bags, and ice-cream overwrap. Seal strength under ASTM F88/F88M-21 typically exceeds 12 N/25 mm for 50 µm film at 125°C seal-bar temperature. The operational boundary is that antiblock loading above 8 wt% raises seal initiation temperature by approximately +5°C and reduces dart impact, so the combined additive masterbatch should remain below 6 wt%.

What Differs in High-Dart Heavy-Duty Sack Film Compared with General-Purpose Liner Applications?

Heavy-duty sack lines operate with film gauges from 70 µm to 150 µm and target high dart impact, tear propagation resistance, and low water vapour transmission for hygroscopic polymer shipments. A typical formulation uses 70 wt%–85 wt% 7109DJ, 15 wt%–30 wt% LDPE to enhance bubble stability, and for outdoor storage specification, 1.0 wt%–2.0 wt% carbon black masterbatch with 0.2 wt%–0.5 wt% polymer processing aid to suppress melt fracture at high throughput. Compliance is anchored to ASTM D1709-16a for dart impact, ASTM D1922-15 for Elmendorf tear, ASTM D882-18 for tensile properties, and ASTM D2103 for polyethylene film dimensional tolerance; FIBC liner insertion uses gusseted tube dimensions consistent with ISO 21898:2004 packaging requirements.

A 300 mm–600 mm annular die with 2.0 mm–2.5 mm die gap, 2.0:1–3.0:1 blow-up ratio, internal bubble cooling, and 8 m–12 m frost line height yields gauge variation below ±5%. Melt temperature at the die is 195°C–220°C. On a 90 mm grooved-feed extruder with 30:1 L/D screw, screw speed is limited so that post-screen pressure remains below 450 bar. Terminal products include polymer pellet shipping sacks, mineral and cement liners, fine chemical bulk liners, and FIBC liners. Field failure mode is bubble side-wall instability when blow-up ratio exceeds 3.0:1 without internal bubble cooling; the resulting gauge bands reduce dart impact by more than 20% relative to stable gauge film.

Lamination sealant webs for stand-up pouches and bag-in-box liners impose a narrow heat-seal initiation window because downstream packaging speeds exceed 60 m/min. The sealant layer is formulated at 70 wt% 7109DJ with 30 wt% lower-density LDPE or metallocene LLDPE, and 1 wt%–2 wt% slip/antiblock masterbatch. It is converted into 15 µm–30 µm blown film and adhesive-laminated to PET or oriented nylon; total laminate thickness ranges from 70 µm to 120 µm. Food-contact compliance follows FDA 21 CFR 177.1520(c) 3.2b, EU Regulation (EU) No 10/2011 including specific migration provisions for multilayer laminates, and GB 9685-2016 for additives in food-contact polymers. Non-food bag-in-box uses, such as liquid detergent liners, are assessed under REACH 1907/2006 Annex XVII restrictions for phthalates and heavy metals.

The blown sealant film is produced with a 60 mm extruder, 28:1 L/D barrier screw, 2.0 mm die gap, 2.2:1 blow-up ratio, and melt temperature 195°C–205°C. Surface treatment by corona discharge is set to 38 mN/m–42 mN/m; below 38 mN/m, lamination bond strength measured under ASTM F904 may fall below 2.5 N/15 mm. Terminal products include stand-up pouches for tomato paste, bag-in-box liners for cold-chain dairy, wine bag-in-box sealant plies, and liquid detergent refill pouches. The operational boundary is that continuous service temperature above 70°C or retort sterilization at 121°C exceeds the softening range of this resin.

When Blown Film Replaces Cast Extrusion for Hand-Applied Pallet Wrap

Hand-applied pallet wrap produced from blown tube uses a formulation of 90 wt% 7109DJ, 8 wt% metallocene LLDPE, and 2 wt% cling additive masterbatch, at thickness 12 µm–20 µm. Performance data are reported under ASTM D882-18 for tensile properties and ASTM D1894-14 for coefficient of friction; cling is evaluated by unwind force and peel adhesion methods specific to stretch-film converters. The blown process uses a 200 mm–350 mm annular die, 2.0 mm die gap, 2.0:1–2.8:1 blow-up ratio, melt temperature 190°C–210°C, and output per die circumference 0.8 kg/h/mm–1.5 kg/h/mm.

On pallet wrapping machines, elongation is limited to 100%–200% for hand wrapping; blown film typically retains higher machine-direction tensile strength but lower ultimate stretch than cast film. Terminal products are hand wrapper rolls at 450 mm × 300 m–600 m for appliance bundling, furniture protection, and mixed-pallet shipment. The limitation is that power pre-stretch above 250% is not recommended because neck-in and inconsistent cling may occur; published data for this specific configuration is limited, and cast-grade LLDPE remains the standard for high-speed machine pallet wrap.

Construction Vapour Retarder and Temporary Containment Film Property Requirements

Under-slab vapour retarder and temporary containment film use 7109DJ at 85 wt% with 15 wt% LDPE and 2 wt% carbon black masterbatch for UV-stabilized black sheeting; film thickness ranges 100 µm–250 µm. Compliance is governed by ASTM E1745 for flexible water vapour retarders, ASTM E96/E96M-21 for water vapour transmission, ASTM D4397 for polyethylene sheeting in construction, and ASTM D1709-16a for puncture impact. The resin provides the base polymer for a Class A vapour retarder only when thickness and lamination are specified appropriately; the actual permeance must be verified under ASTM E96/E96M-21 desiccant method.

Blown-film conversion for this gauge employs a 400 mm die, 2.5 mm die gap, 2.5:1–3.5:1 blow-up ratio, internal bubble cooling with thickness control ±5%, and melt temperature 200°C–225°C. Gusseted film is folded to 3 m–6 m layflat widths for slab placement. Terminal products include under-slab vapour barriers, wall vapour retarder membranes, dust containment sheeting, lead abatement barriers, and temporary weather protection films. The operational boundary is that contact with bitumen or solvent-based adhesives may plasticize the film; compatibility must be tested before specification.