On a vertical form-fill-seal line running a 25 µm monolayer cast film at 80 cycles/min, the heat seal is formed against a heated jaw while the packaging line indexes the film over a forming collar. Revode 101 cast film high heat-seal polylactic acid resin is dried in a desiccant hopper with a dew point below -40 °C for 4–6 h at 80 °C, because pellet moisture above 250 ppm causes hydrolytic chain scission during extrusion and produces bubble defects and a measurable drop of 5–15% in dynamic viscosity before pellet melting is complete. The extrusion profile on a 90 mm single-screw extruder with an L/D ratio of 30:1 and a barrier screw is set from 180 °C at the feed throat to 210 °C at the die, with a gear pump holding melt pressure between 12 MPa and 18 MPa before a 0.6–0.8 mm coat-hanger die gap. The melt is pinned to a 22–26 °C chill roll by an air knife at 30–40 m/s, then passed through a corona treater set to deliver 38–42 mN/m surface energy measured by ASTM D2578. Seal jaws on the form-fill-seal unit are set to 95–115 °C with a dwell of 0.3–0.6 s and a jaw pressure of 0.4–0.6 MPa. Finished pillow packs for dry grains, rice, tea, pulses, and portioned snack powders are sealed on a 15 mm-wide seal; seal strength measured according to ASTM F88/F88M at 300 mm/min jaw separation after 24 h conditioning at 23 °C and 50% RH generally falls from 5 N/15 mm to 12 N/15 mm, depending on film thickness, seal bar temperature, and quench roll temperature. The packaging line must not be run with seal jaw temperatures above 120 °C because molten PLA residue accumulates on the jaw face and produces seal defects; if residue appears, the jaw temperature is reduced and the seal bar surface is cleaned with a non-abrasive tool. For food-contact compliance in the European Union, the film must meet the overall migration limit under Regulation EU 10/2011, and compostability claims are linked to EN 13432 certification when the finished bag is marketed as compostable. Plain PLA cast film replaces conventional LDPE in dry-food VFFS lines only when the mechanical strength and moisture barrier are matched to the short shelf life of the packaged product; long-term storage of hygroscopic goods in high-humidity distribution chains is outside the operational boundary of a plain PLA cast film.

What Limits the Difference Between Seal Initiation Temperature and Blocking Onset in Thin Cast Film?

The dominant variable in cast PLA film is not the extruder melt temperature but the quench-roll thermal history. Revode 101 is designed for high heat-seal response, which means the resin’s higher amorphous fraction must be preserved during quenching; if the chill roll is run too warm or if the film is annealed, the seal initiation temperature rises and the advantage is lost. On a pilot cast line with a 450 mm-diameter chill roll, 300° wrap contact, and an air knife velocity of 35 m/s, quench roll temperatures below 20 °C produce films with almost no measurable crystal fraction by differential scanning calorimetry under ISO 11357-3, and seal initiation temperatures of 80–90 °C are recorded at 0.4 MPa seal pressure and 0.5 s dwell when tested by ASTM F88/F88M. The same films, however, begin to block after 24 h at 40 °C under a surface pressure of 0.1 MPa, because the amorphous surface has a low softening point and a high contact area. Raising the quench roll to 24–28 °C reduces blocking but shifts seal initiation to 90–100 °C, narrowing the practical seal window on high-speed machinery. Post-extrusion enthalpy relaxation measured as an endothermal peak in the 55–65 °C region by ISO 11357-3 raises seal initiation by a further 2–5 °C within 48 h at ambient temperature, which is why master rolls aged for more than two days must be re-qualified before the packaging line speed is fixed. The plant must also control the outer skin temperature; the air knife that pins the film to the chill roll cools the surface faster than the core, creating an amorphous skin that is beneficial for sealing but vulnerable to blocking if wound too tightly or stored above 30 °C. In practice, adding antiblock is not a complete solution because silica particles at the seal interface create stress concentrations; converted-film trial data typically show a 20–40% reduction in ASTM F88/F88M seal strength when the antiblock loading exceeds 3,000 ppm. The conversion path for this reason is usually a 20–25 µm cast film wound at reduced tension onto 76 mm cores and shipped within 24 h to vertical form-fill-seal or horizontal form-fill-seal converters, where the seal jaw temperature is locked after an initial mapping of seal initiation and blocking onset.

When Revode 101 is converted as a thin sealant web in a compostable dry-food laminate, it is typically coextruded as an 8–12 µm layer against a thicker PLA core and then adhesive-laminated to a reverse-printed metallized PLA or cellulosic substrate. The cast line must hold the sealant layer thickness within ±0.5 µm because thin spots below 6 µm produce variable seal strength and premature delamination at the seal interface. The heat-seal layer is exposed to the seal jaw while the outer web provides print protection and barrier; seal initiation on the laminate is tested with a 15 mm-wide specimen according to ASTM F88/F88M after sealing at 95–105 °C, 0.5–0.7 MPa, and 0.5 s on a flat bar sealer. Measured seal forces are typically 6–12 N/15 mm, and the accepted failure mode is delamination of the sealant layer from the laminate rather than cohesive failure through the sealant, because cohesive failure indicates that the sealant layer was overheated and degraded. If the sealant layer is thicker than 12 µm, the laminate may curl after cooling due to differential shrinkage between the PLA sealant and the outer web; the converter compensates by balancing the gauge and the corona-treatment level on both sides. Terminal structures are used for organic dry snacks, granola sachets, and portioned powdered beverages with short shelf life and dry-fill conditions. The laminate is not qualified for liquid filling, alcohol-containing products, or high-moisture pet food because the PLA sealant layer softens above 55 °C. The outer substrate may supply barrier, but the sealant layer itself does not provide high moisture barrier; moisture vapor transmission rate should be determined by ISO 15106-3 for the full laminate rather than for the sealant film alone.

Fresh Produce Overwrap and Modified Atmosphere Packaging

Thin cast films in the 15–25 µm range serving as high-clarity breathable bags for leafy greens impose oxygen transmission and anti-fog additive compatibility constraints. PLA has a much higher oxygen transmission rate than polyethylene; the value measured on a 25 µm film at 23 °C and 0% RH under ASTM D3985-17 is typically in the range 500–700 cm³/(m²·day·atm), while carbon dioxide permeability is typically 3–5 times higher, which can be used to maintain a modified atmosphere for cut leafy greens when the bag area and film gauge are calculated for the respiration rate of the packed produce. The high heat-seal layer is critical because the vertical bag is sealed through condensation and produce juice contamination; seal jaws must be set at 95–110 °C with a dwell of 0.4–0.7 s to drive contamination out of the seal interface. Anti-fog treatments based on glycerol fatty acid esters are added at 0.5–2.0 wt% masterbatch dilution, and the treated film is conditioned for 72 h at 23 °C before haze and anti-fog performance are judged; the anti-fog additive must not reduce ASTM F88/F88M seal strength by more than 15% relative to the untreated control. The finished bags are used for cold-chain distribution of whole-leaf spinach, mixed salad, and fresh herbs in compostable packaging programs, but the film is not suitable for hot-fill or for produce that is packed above 40 °C because PLA begins to shrink and distort near its glass transition temperature. For cold storage at 4 °C, seal strength retention is tested after 7 days to verify that no crystallization-induced embrittlement occurs; if the film is stored at temperatures above 30 °C before packing, the seal initiation temperature may increase by 3–6 °C and the packaging line must be re-qualified.

If Confectionery Flow Wrap Requires Dead-Fold Retention, the Seal Layer Must Be Kept Below 30 µm

Because PLA retains dead-fold without the addition of polyolefin waxes, Revode 101 cast film enters confectionery and bakery flow-wrap lines as a replacement for cellophane or OPP in small-format biscuit and candy wraps. On a horizontal fin-seal wrapper, the film is run at 20–30 µm because thicker gauges reduce folding precision and increase unwinding tension. The fin seal is set at 100–110 °C with a rotating sealing wheel or a flat bottom seal bar, a dwell of 0.3–0.5 s, and a pressure of 0.4–0.7 MPa; seal strength is checked on-line by sampling every 30 min using a tensile tester configured to ASTM F88/F88M. Twist-wrap formats are also sold without a heat seal, relying on the inherent dead-fold of PLA, but the same cast film can be used when a heat seal is preferred to prevent unwrapping. The film surface must be treated to 38–42 mN/m according to ASTM D2578 for cold-seal adhesive registration or printing. If a cold-seal cohesive is applied, the heat-seal side must remain free of adhesive, because cold-seal residue on the seal jaw elevates the required temperature and creates volatile deposits that degrade seal consistency. Cast film for confectionery should have a static coefficient of friction no greater than 0.40 when measured by ASTM D1894 to prevent blocking on the unwinding spindle; slip masterbatch addition must be limited because migratory slip agents can reduce seal strength if they bloom to the surface. Dead-fold retention is evaluated by measuring the angle of unwrap after 24 h at 23 °C and 50% RH; an unwrap recovery of less than 20° is considered acceptable for a twist-wrapped sweet. The wraps are not used for hot-filled confectionery or for packs exposed to sustained temperatures above 45 °C, because the dead-fold property declines and the film may distort in the folding track.

For compostable tray lidding of chilled ready-to-eat meals and cut fruit, the sealant web is a cast film of 30–50 µm sealed to a PLA, bagasse, or coated paper tray flange at temperatures between 100 °C and 120 °C. The tray sealer must use a heated platen with a seal pressure of 0.3–0.5 MPa and a dwell of 0.5–1.0 s, and the flange must be flat within ±0.2 mm to prevent local seal gaps. Seal strength measured by ASTM F88/F88M on a 15 mm strip cut perpendicular to the flange must exceed 4 N/15 mm for a peelable seal and 8 N/15 mm for a lock-up seal, depending on the tray flange material and the application. The difference between peelable and lock-up behavior is set by the seal temperature and the surface roughness of the tray flange, not by the cast film alone; if peelability is required for consumer opening, the seal temperature is kept at the low end of the range and the sealing time is not extended above 0.8 s. For chilled products stored at 4 °C, seal strength retention and leak-tightness are verified using a vacuum decay leak tester with a sensitivity of 0.005 cm³/min. The lidding is used for cold-chain ready meals, cut fruit, and dry snack trays, but is not suited for microwave heating above 60 °C, for retort, or for high-pressure processing because the PLA film loses dimensional stability near its glass transition. If a print-receptive surface is required, the top side is corona treated inline to 38–42 mN/m; treatment must not be applied to the sealant surface because oxidation raises the seal initiation temperature and causes inconsistent peel force.