On a 2.0 m blown film line configured with a 75 mm grooved-feed extruder at 30:1 L/D and a 250 mm spiral mandrel die with a 2.0 mm die gap, Braskem FG31D is processed into heavy-duty industrial liners and bulk shipping sacks at thicknesses from 100 µm to 250 µm. The resin is supplied with a nominal density of 0.918 g/cm³ and a melt flow rate of 1.0 g/10 min measured at 190 °C under 2.16 kg in accordance with ASTM D1238. The butene-copolymer linear low-density polyethylene has a narrower molecular weight distribution than high-pressure LDPE, which creates a more abrupt onset of sharkskin melt fracture when extruder output pushes die-lip shear stress beyond the critical level. Die gaps below 1.8 mm are generally unsuitable for thick-gauge FG31D because the reduced die land length increases shear rate at the lip and produces visible surface roughness on the inner bubble surface. Melt temperature is held between 190 °C and 220 °C; below 190 °C, screw torque and melt pressure rise, while above 220 °C, the bubble becomes difficult to stabilize at high blow-up ratios because the zero-shear viscosity drops. Production-scale instability appears as edge weave and sagging between the collapsing frame hips. Blow-up ratio is set between 2.0:1 and 2.8:1, with the lower end favoring MD tear and the upper end improving TD impact. Frost line height is adjusted between 700 mm and 1,100 mm from the die face. Raising the frost line increases MD orientation and machine-direction tensile modulus, but reduces dart impact retention under ASTM D1709 Method A. The necked bubble geometry produced by a high frost line also improves bubble stability, which is necessary when the film is used in unsupported liners for FIBCs and drum liners that must withstand two-person handling. The critical qualification matrix for these structures is defined by the test methods shown in Table 1.

Why does frost line height govern dart impact retention in agricultural covers?

Agricultural film converters blend FG31D with 10–20 wt% high-pressure LDPE and a UV stabilizer masterbatch let down at 2–4 wt% to produce silage clamp films and greenhouse side-sheets at 150–200 µm. The LDPE fraction modifies bubble stability, but the higher melt strength contribution does not compensate for orientation losses if the frost line is raised beyond the point where the spherulitic structure is quenched. Accelerated weathering is evaluated under ISO 4892-2 using UVA-340 lamps at 0.76 W/m² irradiance and a black panel temperature of 60 °C; film exposed without adequate hindered amine light stabilizer loses elongation at break rapidly, and field failure occurs as wind-induced flex cracking at fold creases. The addition of HALS at 0.15–0.35 wt% active content is typical for multiseason performance in temperate climates, although regions with solar loads above 120 kLy/yr may require a higher stabilizer package or coextruded surface layers. The frost line in the agricultural process window is set at 2–3 die diameters for high TD tear; raising it to 8–10 die diameters increases MD tensile modulus but reduces dart impact retention measured by ASTM D1709. The failure mode in silage clamps is multi-axial puncture followed by tear propagation; therefore TD Elmendorf tear is used as the primary field failure predictor. In LLDPE blown film, TD tear is typically two to three times MD tear, with the exact ratio depending on blow-up ratio and frost line height. Gauge uniformity across the layflat is controlled with a capacitive profile sensor to within ±5 % of nominal thickness. Sections below −5 % are prone to propagation tearing when the film is stretched over silage pile edges.

When frozen food converters replace cast LDPE sealant webs with FG31D blown film in a three-layer structure, re-qualification of seal-bar pressure and dwell time is required because the broader melting distribution retains more residual heat at the seal interface. The frozen food film is typically blown at 40–80 µm total thickness with a layer ratio of 20/60/20 and a BUR of 2.2:1; the inner sealant layer is FG31D-rich, while the core may contain metallocene or C4-LLDPE to raise hot-tack. Seal initiation is evaluated on flat jaw laboratory sealers in accordance with ASTM F88. The plateau for butene LLDPE emerges between 100 °C and 130 °C, with a hot-tack window measured under ASTM F1921 that narrows when the film is run above 80 m/min on vertical form-fill-seal equipment. Low-temperature impact resistance after conditioning at −18 °C is the critical property; dart impact under ASTM D1709 Method A shows that FG31D retains a greater proportion of ambient-temperature impact strength than cast LDPE at the same gauge, which is the reason converters select it for ice cream pouches and frozen vegetable bags. However, frost line fluctuations during production alter this low-temperature performance because quench rate affects crystal size distribution. The objective of the converter is to keep frost line height within ±10 % of the set point; deviations produce localized crystal size differences that create high-stress points along crease lines. Food-contact compliance for the resin is established under 21 CFR 177.1520 for olefin polymers and under EU 10/2011 with overall migration limits of 10 mg/dm². Specific migration of primary aromatic amines is not applicable because the resin does not contain aromatic diisocyanate residues; however, each finished structure must be verified by the converter using a migration testing program tailored to the final food type and storage duration. The compliance matrix is summarized in Table 2.

Coextruded hygiene overwrap and tissue bundling film structures

Tissue bundling operations running at 120 packs/min require a blown film with low coefficient of friction and stable gauge that can withstand the sudden acceleration of the wicket packer. In a five-layer line, FG31D is used in the core or surface layer at 25–45 % of the structure, with LDPE or plastomer skin layers selected to adjust hot tack and seal through residual tissue dust. The film is produced at 25–35 µm, with a BUR of 2.5:1 and a die gap of 1.6–2.0 mm; the narrower die gap is acceptable because the lower film gauge does not generate the same lip shear stress as heavy-duty liners. Slip and antiblock additives are incorporated at 500–1,000 ppm to achieve a kinetic coefficient of friction below 0.25 when measured by ASTM D1894. Higher antiblock levels can increase haze and reduce heat-seal strength; therefore the formulation is adjusted against optical measurements using ASTM D1003. The main processing failure observed on automatic bundlers is film flutter caused by thickness variation above ±5 %; this can be corrected by rotating the die and air ring more frequently when processing FG31D at high output. Weld integrity at the overwrap tail is evaluated with ASTM F88 after sealing at 115–130 °C; welds that fail at the interface before film yield indicate contamination from paper dust or an excessive slip additive concentration.

Extrusion lamination sealant webs operate in the plateau region between seal initiation and hot-tack failure.

Adhesive lamination lines use FG31D blown film as the sealant web for PET/foil/PE and OPP/PE laminates. The film is blown at 30–50 µm and then adhesively laminated; corona treatment is applied upstream of the lamination nip to raise surface energy to 38–42 dyn/cm as measured by dyne solutions conforming to ASTM D2578. If surface energy falls below 38 dyn/cm, the adhesive wets unevenly and laminate bonds fail during subsequent pouch forming. The sealant web’s heat-seal performance is determined by ASTM F2029 for hot-tack and ASTM F88 for seal strength; converters target a seal bar temperature window that avoids seal-through of the laminated foil while achieving hermetic seals on high-speed pouching machines. Because FG31D has a melt flow rate of 1.0 g/10 min, the web contributes enough melt strength to prevent burn-through at high seal-bar temperatures. Package integrity is verified by ASTM F2338 vacuum decay; laminate structures that show channel leaks along the seal edge commonly have a surface energy defect or a gauge depression from collapsing frame misalignment. The processing conflict in extrusion lamination is that high line tension can stretch the FG31D web prior to nip lamination, causing MD neck-in and reducing finished laminate width. Tension control is therefore maintained within ±3 % of setpoint to prevent permanent elongation of the sealant web. Published data for this specific configuration is limited, and pouch converters are required to qualify final seal strengths against their own fillet and closure geometry.

In collation shrink overpackaging for canned goods and bottled water, FG31D is processed in a three-layer high-stalk bubble configuration where the outer layers provide sealing and slip properties while the core layer carries the mechanical load. The film is produced at 50–80 µm with a BUR of 2.0:1 to 2.5:1; melt temperature is held at 190–210 °C. Shrink values are evaluated by ASTM D2732 at 150 °C; the actual TD and MD shrink percentages depend heavily on the blend ratio with LDPE and on the high-stalk frost line height, and published data for this specific configuration is limited. The key processing conflict is that higher stalk height increases MD shrink but reduces bubble stability; the operator must balance the effect against the requirement for sufficient shrink force to hold cans on a corrugated tray during distribution. Shrink force is measured on a strain gauge sample holder after immersion in an oil bath; the resulting force must exceed 0.5 N/15 mm to secure the pack, although this limit will vary with pack geometry and gauge. The main field failure is TD splitting at the tray bottom, which arises when the film is over-shrunk or when gauge variation along the collapsing frame exceeds ±6 %. The corrective action is to reduce frost line height and operate at the lower end of the BUR range, sacrificing some MD shrink while retaining TD tear strength.