On rotary stretch-wrap lines converting 23 µm machine film at pre-stretch ratios of 200–270%, Braskem FG31 is specified as the core layer in a three-layer A/B/C coextrusion where the outer skins carry cling and puncture response. The resin is supplied with a nominal density of 0.918 g/cm³ under ASTM D1505 and a melt index of 1.0 g/10 min under ASTM D1238 at 190 °C/2.16 kg. These values place the core melt in the high-viscosity region needed for bubble stability at thin gauges. Single-screw extruders from 45 mm to 75 mm with 24:1–30:1 L/D barrier screws and die diameters between 200 mm and 350 mm operate at melt temperatures of 195–215 °C. Die gap is held at 1.0–1.5 mm; blow-up ratio is maintained between 2.5:1 and 3.0:1. Frost line height is positioned 600–900 mm above the die face. The outer layers are typically metallocene-catalyzed ethylene-hexene copolymers or EVA compounded with polyisobutylene tackifier at 0.5–1.5 wt%. In this configuration, FG31 contributes load-holding stiffness to the 12–25 µm film while the skins control cling and unwind noise. At output rates above 350 kg/h, the process window narrows. If the frost line is too low, transverse direction tear increases. If the frost line is too high, haze rises and pre-stretch recovery declines. Operators adjust dual-lip air ring chiller temperature to 7–12 °C and maintain die land pressure drop below 180 bar to avoid melt fracture. Stretch-film performance is validated according to ASTM D5458 for cling, ASTM D882 for tensile elongation, and ASTM D5748 for puncture resistance. In pallet wrapping, the film must survive 250–300% power pre-stretch at 35–45 wraps/min. Film produced with FG31 in the core generally achieves this when total gauge is not below 20 µm and core layer fraction is controlled at 60–75 wt%. On high-speed rotary arms, edge fold-over and core telescoping are controlled by winding taper tension between 2–6 N per 500 mm width.

How Does Frost Line Height Influence Agricultural Silage Film Stability?

Agricultural film converters running 3-layer blown lines with 70–90 mm extruders and 250–400 mm dies produce silage wrap at 25–75 µm total film thickness. FG31 is usually placed in the core at 45–55 wt%, while the outer layers combine LLDPE or metallocene plastomer with carbon black masterbatch at 3–6 wt% and UV stabilizer masterbatch at 2–4 wt%. The processing conflict is the relationship between blow-up ratio and dart impact retention. Blow-up ratio is set between 2.2:1 and 2.8:1 to balance machine-direction and transverse-direction tear propagation. Frost line height is maintained at 8–12 times the die diameter for stable neck geometry. If the frost line is raised beyond 1,100 mm, bubble oscillation increases and film enters the collapsing frame with uncontrolled thickness asymmetry. If the frost line is lowered below 700 mm, film shows higher tensile strength but also excessive transverse-direction shrinkage and poor layflat. Terminal products include round bale wrap, silage bag tubes, and bunker silo cover sheets. For bale wrap, puncture resistance is tested per EN 14932 or ASTM D5748. Tensile properties follow ISO 527-3. In silage cover applications with 150–200 µm thickness, the film must survive contact with silage effluent and ammonia vapor without pinholes. Converters often coextrude a black inner layer containing 2.5–3.0 wt% carbon black for UV blocking and a white outer layer to reflect solar load. The FG31 core supplies melt strength during high-output conversion at 300–500 kg/h. Post-consumer recyclate should be limited to 15–25 wt% because higher levels can reduce sub-zero dart impact below reusable film thresholds. At ambient relative humidity above 70%, batches containing hygroscopic fillers or rework require hopper drying at 60–70 °C for 2–3 hours to prevent melt-phase hydrolysis of silane-based coupling agents present in some UV masterbatch carriers. Film friction is reduced with slip masterbatch at 500–1,200 ppm erucamide to allow bale wrapping at 20–40 rpm without surface blocking.

Below −25 °C storage temperatures, vertical form-fill-seal packaging of IQF vegetables, frozen fish fillets, and meat portions requires a blown film that retains seal strength and puncture resistance after frozen distribution. In this application, FG31 is dry-blended or compounded with a plastomer at 15–25 wt% and processed into 40–85 µm monolayer or 3-layer film on lines with 45–65 mm extruders. Melt temperature is limited to 180–205 °C because higher heat history increases gel formation and degrades seal initiation consistency. Seal jaws on vertical FFS machines are set between 115 °C and 145 °C, with dwell times of 40–80 ms. FG31 provides the stiffness necessary for high-speed bag forming at 80–110 pouches/min; the plastomer lowers seal initiation temperature by approximately 8–12 °C relative to a 100% FG31 film. Film produced with this structure is tested for seal strength according to ASTM F88/F88M, dart impact per ASTM D1709 Method A, and low-temperature brittleness via ASTM D1790 or ISO 8570. Converters serving the EU market target overall migration below 10 mg/dm² under EU 10/2011; US food-contact compliance relies on FDA 21 CFR 177.1520 olefin polymer requirements. Terminal packaging includes pillow pouches for frozen corn, bottom-gusset bags for seafood, and resealable zipper packs. A processing limitation occurs on vertical FFS mandrels with high film tension: FG31-rich film exhibits higher coefficient of friction than EVA-rich sealant. Slip agent masterbatch is therefore added at 1,000–2,000 ppm erucamide and 500–800 ppm silica to maintain kinetic coefficient of friction below 0.30 when measured per ISO 8295. Excess slip reduces zipper seal integrity and can transfer to seal jaws, so loading must be validated across the full reel width and at 38–42 °C seal jaw surface temperature.

When Heavy-Duty Industrial Liners Require 40% Recyclate Incorporation

Coextruded heavy-duty films in 100–250 µm thickness are manufactured for flexible intermediate bulk container liners, construction debris sacks, and chemical drum liners. The converter incorporates 30–40 wt% post-industrial in-house reclaim with FG31 as the dilution resin in the core layer. Because reclaim lowers melt viscosity and introduces gels, the extruder configuration shifts from a smooth-bore extruder to a grooved-feed section with 25:1–33:1 L/D and a continuous melt filter using 80–120 mesh screen packs. Barrel temperatures are profiled from 160 °C at the feed throat to 210 °C at the die adapter. Die gap widens to 2.0–3.0 mm to limit melt fracture at throughputs of 400–600 kg/h. Blow-up ratio remains low at 2.0:1–2.5:1 to maximize transverse-direction tear resistance. Frost line height is set at 5–8 times the die diameter. FG31-rich skins, typically 25–30 wt% of total film mass, provide dart impact and surface quality. The recyclate core controls cost and raises modulus. Heavy-duty film is tested for tensile yield and break per ISO 527-3, Elmendorf tear per ASTM D1922, and puncture resistance per ASTM D5748. For chemical drum liners, stress-crack resistance is evaluated according to ASTM D1693, with notched specimens in 10% Igepal CO-630 at 50 °C. The most significant process conflict is an extruder pressure ceiling. Recycled fractions above 40 wt% typically lower melt pressure but increase screen pack change frequency due to gel buildup. A 120-bar head-pressure limit is maintained by adjusting screen pack mesh and reclaim pellet size. Published data for FG31 specifically in high-reclaim chemical drum liner structures is limited; converters validate incoming reclaim melt flow rate per ASTM D1238 at 190 °C/2.16 kg and ash content per ASTM D5630 before line start-up. Drum liner drop testing at −18 °C is performed on filled containers to confirm dart impact retention after reclaim addition.

Adhesive lamination converters running blown film sealant webs at 20–35 µm use FG31 as the inner heat-seal layer in duplex and triplex structures for frozen fruit pouches, salted snack packs, and pet food bags. The blown film line is configured with a 50–75 mm extruder, 1.2–1.8 mm die gap, 2.5:1–3.0:1 blow-up ratio, and a frost line positioned 5–7 times the die diameter. Melt temperature is held between 190 °C and 205 °C. Corona treatment is applied in-line at 1.5–2.5 kW to achieve surface energy of 38–42 dynes/cm, measured using ASTM D2578 dyne solutions. The treated film is laminated to oriented polyester or biaxially oriented polypropylene with solventless polyurethane adhesives at 1.5–2.5 g/m². Seal strength of the laminate is measured per ASTM F88/F88M; the sealant film must maintain consistent seal initiation above 110 °C and survive flex-crack testing per ASTM F392. For food-contact laminates, the EU declaration of compliance follows EU 10/2011 Annex I and II; US compliance follows FDA 21 CFR 177.1520. Terminal packaging includes stand-up pouches with bottom gussets and zipper closures for nuts and snack mixes. A processing boundary occurs with solventless lamination. Unaged films may retain residual slip additives that alter adhesive wetting. Film is therefore released to lamination only after 24–48 hours of post-treatment aging at 20–25 °C and 40–50% RH. If treated film is stored beyond 90 days, surface energy decay below 36 dynes/cm can occur, causing delamination in high-stress pouch corners. For higher-speed flexographic printing, antistatic masterbatch is added at 3–5 wt% to reduce ink dry-back variability on the outer web.

In vapor barrier and temporary containment film production, FG31 is used in 150–300 µm multilayer films for below-slab vapor retarders and hazardous material enclosure. The process uses a 90–120 mm grooved-feed extruder, 2.5–3.5 mm die gap, and 1.8:1–2.2:1 blow-up ratio to limit orientation-induced shrinkage. Films are tested per ASTM E1745 for water vapor permeance with Class A limits below 0.1 Perm. Tensile properties follow ASTM D882. Puncture resistance follows ASTM D1709 and ASTM D5748. FG31 is blended with 10–20 wt% LDPE and 5–15 wt% calcium carbonate masterbatch to improve stiffness and reduce tear sensitivity during staple attachment to framing. The main process conflict is bubble instability at large blow-up ratio with high filler loading. Operators hold frost line below 4 times the die diameter and use internal bubble cooling to maintain gauge uniformity across 1,200–1,800 mm wide layflat. Terminal products include 3-meter-wide under-slab vapor retarders, temporary enclosure films for lead paint abatement, and dust containment barriers. Because wide-web gauge variation above ±5% creates folded edge memory, die bolt adjustment and air ring velocity must be logged per reel. Published data for FG31 in ASTM E1745 vapor retarder structures is limited; converters determine water vapor permeance at 38 °C and 90% RH on finished film rather than on resin correlates. At 10 °C installation temperature, the film must retain tensile elongation above 300% to survive framing movement and foot traffic before slab placement.

Protective Film Backing Layer Toughness and Static Decay Control

Surface-protection films in 30–60 µm thickness are produced as multilayer structures where one skin is a low-tack pressure-sensitive adhesive layer and the opposite skin is an FG31-based backing. The backing layer is typically 50–65 wt% FG31, 15–25 wt% LDPE for bubble stability, and 5–10 wt% of a conductive compound to address static discharge during peeling. Blown film process conditions include 1.5–2.0 mm die gap, 1.8:1–2.4:1 blow-up ratio, and melt temperatures of 180–200 °C to minimize odor and volatile release. Static decay is measured at 12% RH and 23 °C per FTMS 101C 4046 or MIL-PRF-81705D. A decay from 5,000 V to 500 V in under 2.0 seconds is required for clean removal from automotive painted panels. The backing film is tested for elongation at break per ASTM D882 and Elmendorf tear per ASTM D1922. The adhesive layer usually contains 20–35 wt% EVA or ethylene-octene plastomer to produce peel adhesion between 0.05 N/25 mm and 1.5 N/25 mm when tested per ASTM D3330. Terminal applications include masking films for coil-coated metal, ABS appliance panels, and automotive body parts during assembly. A technically limiting factor is high unwind static on fast peeling lines above 100 m/min. FG31 backings without conductive additive can generate surface charges above 15 kV. The conductive compound must be dispersed without raising haze above 25%, requiring a twin-screw compounding pass at 190–210 °C before film extrusion. Published data for conductive FG31-based protection film is limited; converters verify surface resistivity per ASTM D257 and adjust conductive masterbatch loading in 2 wt% increments. Blocking is controlled with low-migration antiblock masterbatch at 800–1,500 ppm loaded in the backing layer only, preventing transfer to the pressure-sensitive adhesive skin during roll storage at 30–40 °C.