Cast pallet-wrapping lines configured with 3,000–5,000 mm slot dies and chilled rolls at 18–25°C typically run film-grade LLDPE with density 0.917–0.919 g/cm³ (ASTM D1505) and melt index 2.0–3.5 g/10 min at 190°C/2.16 kg (ASTM D1238). Pre-stretch sections set at 250–300% require low gel counts and monotonic stress–strain response. Cast film producers meter 2–5 wt% LDPE of melt index 1.8–2.5 g/10 min into the extruder to stabilise the web and reduce edge neck-in. Polyisobutylene cling agent at 0.5–1.2 wt% is added to the core or skin layer; addition above 1.5 wt% increases unwind force and produces telescoping rolls at winding tension 15–25 N/m. Machine-direction tensile stress at break under ASTM D882 for 20 µm film is typically 25–40 MPa, with elongation at break 350–500% in the machine direction and 500–700% in the transverse direction. Puncture resistance measured under ASTM D5748 is used to reject film with inconsistent gauge bands; field data from automatic wrappers show that coefficient of friction below 0.15 (ASTM D1894) leads to roll telescoping, while values above 0.45 cause film tears at pre-stretch rollers. Blown stretch film lines running the same resin at blow-up ratio 3.0:1–3.5:1 and die gap 1.8–2.4 mm produce higher dart impact but lower machine-direction elongation; gauges below 12 µm are generally shifted to metallocene-catalysed LLDPE to survive pre-stretch above 250% without burst-through. Terminal products include machine pallet wrap, hand stretch film, and pre-stretched ancillary wrap. Edge trim is recycled at 10–20 wt%; higher regrind levels create gels and reduce puncture retention by more than 10%.

How Does UV Stabilizer Dose and BUR Control Season-Long Silage Film Integrity?

Silage bale wrap and greenhouse covering are produced on three-layer blown film lines from LLDPE with density 0.918–0.921 g/cm³ (ISO 1183) and melt index 0.5–1.0 g/10 min (ISO 1133-1). Outer layers receive hindered amine light stabiliser at 0.20–0.45 wt% and benzotriazole or triazine UV absorber at 0.10–0.25 wt%. Black silage covers use carbon black at 2.0–3.5 wt%; white greenhouse films use titanium dioxide at 4.0–8.0 wt% to retain reflectance and reduce infra-red load. Blow-up ratio is held at 2.5:1–3.5:1 with frost line height 600–900 mm above the die and die gap 1.8–2.4 mm. Raising blow-up ratio above 3.5:1 improves transverse tear resistance but introduces bubble instability and gauge variation up to ±12% on thin silage film. Oxygen transmission rate of 25 µm black film at 23°C and 0% RH under ISO 15105-2 is 2,500–4,000 cm³/(m²·day·bar); moisture vapour transmission rate under ISO 15106-2 at 38°C and 90% RH is 15–25 g/(m²·day). Weathering validation is conducted under ISO 4892-2 xenon-arc or ASTM G154 UVA 340; black formulations retaining more than 60% of original machine-direction elongation after 3,000 h exposure are often accepted for multi-season use. Low levels of liquid polybutene at 0.5–1.0 wt% provide bale-wrap self-adhesion; overdosing reduces oxygen barrier and can transfer tackifier to silage. Anti-block silica above 1,000 ppm destroys cling and is avoided in silage wrap. Terminal products include bale wrap, silage cover, greenhouse side sheet, and mulch film. In greenhouse service, the film must maintain tensile retention under ASTM D882 and tear resistance under ISO 6383-2 after 12–24 months of solar load.

Heavy-Duty Shipping Sacks and Form-Fill-Seal Resin Blends

In heavy-duty shipping sacks, film-grade LLDPE copolymers with hexene or octene comonomer are specified at melt index 0.4–1.0 g/10 min and density 0.920–0.924 g/cm³ (ASTM D1505). Three-layer coextrusion structures typically use HDPE-rich skins and an LLDPE-rich core; a skin ratio of 20/60/20 across the layers is common. Internal bubble cooling and die gaps of 1.8–2.4 mm are used with blow-up ratio 2.0:1–3.0:1. Open-mouth bags are converted at 80–180 µm; form-fill-seal film is supplied at 60–150 µm. Dart drop impact under ASTM D1709 for 100 µm FFS film on a 38 mm diameter dart is commonly specified at not less than 300 g for butene-based LLDPE and not less than 500 g for hexene or octene types. Tensile break stress in the machine direction under ASTM D882 is 25–35 MPa; secant modulus at 1% strain is 180–250 MPa. Seal strength under ASTM F88 at 140–160°C, 1.5 N/mm² seal pressure, and 0.5 s dwell is 10–20 N/15 mm. Seal initiation for hexene LLDPE begins at 105–115°C, which permits high line speeds on FFS spouts. Creep is evaluated under ASTM D2990 at 23°C and 20% of yield stress; published data for stacked-sack creep in tropical warehouses is limited, but field audits indicate that storage above 40°C can produce visible deformation when LLDPE content falls below 50 wt% of the total structure. Terminal products include open-mouth sacks, valve sacks, and FFS gusseted bags for resins, fertilisers, and construction chemicals.

When a Three-Layer Coextrusion Line Produces Collation Shrink at Line Speeds Above 120 m/min

Three-layer collation shrink film processed at line speeds above 120 m/min requires melt temperature 195–215°C and die pressure below 350 bar to avoid shark-skin texture. Skin layers contain 20–40 wt% hexene LLDPE with density 0.917–0.920 g/cm³ and melt index 0.9–1.2 g/10 min; the core uses LDPE with melt index 0.3–0.5 g/10 min. The line uses die gap 1.8–2.2 mm, blow-up ratio 3.0:1–3.5:1, and frost line height 700–1,000 mm. Output per 1,200 mm die is typically 120–180 kg/h. Film thickness is 25–35 µm for bottle and can multipacks. Free shrink under ASTM D2732 at 120°C is 50–70% in machine direction and 0–10% in transverse direction; shrink force under ASTM D2838 is 0.15–0.35 MPa. Slip and anti-block masterbatch in the skin layers at 2–4 wt% maintains coefficient of friction at 0.20–0.35; values above 0.45 cause misaligned bands on collation drums. When line speed exceeds 120 m/min, polymer processing aid below 300 ppm results in melt fracture, while addition above 800 ppm can plate out on the die lip. Seal initiation temperature for the structure is 105–115°C at 1.5 N/mm² and 0.5 s dwell under ASTM F88. Seal strength is 8–14 N/15 mm. Terminal products include shrink wrap for canned food, water bottle multipacks, and promotional packs. A blown film line with L/D 30:1 and a barrier screw is used; feed zone temperatures are kept below 120°C to avoid pellet bridging from premature melting.

Frozen food lamination films require seal initiation temperatures below 100°C to protect low-melting tie layers and prevent scorch. A cast coextruded sealant web based on hexene LLDPE with density 0.916–0.920 g/cm³ and melt index 1.0–2.0 g/10 min is blended with 10–20 wt% LDPE of melt index 2.0 g/10 min. The food-contact layer is controlled under FDA 21 CFR 177.1520 and EU 10/2011. Overall migration remains below 10 mg/dm² under EU 10/2011 test conditions. Seal strength is measured by ASTM F88 at 115–125°C seal bar temperature, 1.5–2.5 N/mm² pressure, and 0.5–1.0 s dwell; values are 8–14 N/15 mm. Water vapour transmission rate for 25 µm film under ASTM F1249 at 38°C and 90% RH is 15–25 g/(m²·day). The film is produced on cast lines at 180–300 m/min with die gap 0.8–1.2 mm, chill roll temperature 18–22°C, and winding tension 8–15 N/m. Gauge variation is held within ±4% to avoid seal bar gaps. Erucamide slip additive is dosed at 500–1,000 ppm and silica anti-block at 1,000–2,500 ppm; coefficient of friction above 0.35 causes misfeed in vertical form-fill-seal equipment, while below 0.10 creates rewind drift. The LLDPE sealant web is laminated to oriented polyester or biaxially oriented polypropylene; laminating bond strength after cure is 1.0–3.0 N/15 mm under ASTM F904. Terminal products include frozen vegetable pouches, ice cream wrap, cheese packaging, and liquid pouch film. Moisture barrier of LLDPE is insufficient for oxygen-sensitive products; EVOH or metallised films are used for extended shelf life. Regulatory compliance and barrier targets are summarised below.

Geomembrane Service Life Is Governed by Stress-Crack Resistance in Direct Leachate Contact

In secondary containment liners, film-grade LLDPE with density 0.932–0.940 g/cm³ and melt index 0.5–1.0 g/10 min is used for sheet thicknesses of 0.5–2.5 mm. The resin is processed on single-screw extruders with L/D 30:1 and barrier screws at melt temperature 190–210°C. Stress-crack resistance under ASTM D5397 or ISO 6252 is measured in a 10% Igepal CO-630 solution at 50°C; failure times above 400 hours are commonly required for liner-grade LLDPE, but comonomer type, density, and cooling rate create wide variance. Tensile break stress under ISO 527-3 is typically 25–40 MPa; elongation at break is 600–800%. Hot wedge welding is performed at 280–350°C with seam peel strength under ASTM D6392 above 80% of parent sheet yield strength. Chemical resistance is evaluated with site-specific leachate because municipal waste leachate composition varies; the material is not recommended for continuous contact with aromatic solvents above 5% by volume or with strong oxidising acids. Field deployment on subgrade with moisture content above 10% creates wrinkles and prevents intimate contact with compacted soil. Welding below 5°C lowers peel strength and increases seam failure risk. Terminal products include lagoon liners, floating covers, secondary containment basins, and methane barrier membranes.