In ready-meal tray converting, ECOPLAN -DURA EN100 enters the line as a compounded PLA grade that must be dried below 250 ppm residual moisture before any heat exposure above 170 °C begins. On a single-screw sheet extrusion line with a barrier screw of 36:1 L/D and a grooved feed section, a desiccant dryer with a dew point of -40 °C or lower is used for 4–6 h at 70–80 °C, and residual moisture is confirmed by Karl Fischer titration according to ISO 15512:2019. In plants where ambient relative humidity exceeds 60%, opened bulk bags should be returned to conditioned storage within 2 h or transferred to a hopper loader with dry-air purge. The barrel profile rises from 170 °C at the feed throat to 205 °C at the adapter, while the melt temperature is maintained between 190 °C and 210 °C. Melt temperatures above 220 °C are linked to hydrolytic chain scission, lactide regrowth, yellowing, and loss of melt elasticity; melt temperatures below 185 °C produce unmelts, flow lines, and localised thickness variation. The sheet die uses a choker bar and a lip gap of 0.3–0.6 mm, and the polishing roll stack is held at 40–60 °C to retain an amorphous sheet with controlled frozen-in stress. Edge nicks, melt surging, and viscosity drift in the feed block are the earliest line-side indicators of insufficient drying or excessive residence time.

Thermoforming of the amorphous sheet is carried out at a sheet surface temperature of 95–110 °C, measured by infrared pyrometer, before plug-assisted forming into a heated mould at 95–105 °C. The mould-hold time is the throughput-limiting variable because the compound must undergo cold crystallisation while the part is restrained; at wall thicknesses of 0.8–1.5 mm, a cavity hold time of 15–30 s is generally required, but this range must be re-established after every revision of sheet gauge or nucleating additive lot. If the part is ejected too early, the tray rim shows dimensional recovery and dome collapse during microwave reheating at 100–110 °C; if the hold time is too long, corner cracking and brittleness appear after cooling. Heat deflection temperature is verified on crystallised tray sections according to ASTM D648-18 Method B at 0.45 MPa, and a target of no less than 90 °C is typically required for ready-meal trays that are filled at 80 °C and reheated in an 800 W microwave. For microwave performance, a finished-article test is run with distilled water or a starch-water simulant for 5 min at 800 W, after which rim deformation and base warp are recorded; published data for this specific configuration is limited, so the converter evaluates crystallised-wall fraction by differential scanning calorimetry according to ISO 11357-3:2018. Food-contact suitability for the finished tray is not assigned by the polymer supplier alone; the tray is tested for overall migration into aqueous and fatty food simulants under Regulation (EU) No 10/2011 using EN 1186-1:2002 and specific migration methods in EN 13130-1:2004. In the United States, the converter confirms the additive and colourant package against the applicable Food Contact Notification in the FDA FCN database because 21 CFR 177.1520 does not cover PLA, and residual monomer content must remain below the applicable specific migration limit before commercial release.

Injection Moulding of Reusable Bowls Requires a Mould Temperature Above the Glass Transition

Because the flexible heat-resistant formulation contains a biodegradable copolymer modifier, the crystallisation kinetics in injection-moulded bowls are slower than those of nucleated rigid PLA; the tool must therefore be operated above the amorphous-phase glass transition for the entire cavity residence. The melt is delivered through hot runner drops and valve gates at 190–205 °C, and pack pressure is set between 600 bar and 900 bar, with holding time adjusted from 8 s to 15 s depending on wall thickness and gate size. The mould is maintained at 85–105 °C using oil or pressurised-water tempering, not plain tower water, and temperature tolerances of ±2 °C across the mould halves are required. Cavity-to-cavity variation above 3 °C produces non-uniform shrinkage and rim ovality after conditioning. At mould temperatures below 80 °C, the skin freezes before cold crystallisation reaches the core, leaving a low-crystallinity layer that softens during microwave reheating. At mould temperatures above 110 °C, ejection is compromised because the flexible compound has reduced hot modulus; the bowl rim may tear at the stripper ring or stick on the core. Clamp force is calculated from projected area and a cavity pressure limit of 300–500 bar rather than from shot weight alone, and insufficient clamp force is detected as flash at the parting line and gate blush around the hot sprue.

When annealing is used to raise heat deflection temperature, bowls are placed on restraining plug fixtures in a forced-air oven at 80 °C for 30–60 min and cooled slowly; free-standing annealing without restraint causes uneven radial shrinkage. Shrinkage is determined after 48 h at 23 °C and 50% RH according to ISO 294-4:2018, and the measurement is taken on the bowl rim, sidewall, and base because flow orientation creates anisotropic shrinkage. The finished bowl is tested for microwave resistance by heating with water at 100 °C for 5 min; lid fit, rim flatness, and inner-wall surface crazing are recorded, and the bowl is re-checked for heat deflection temperature according to ASTM D648-18 Method B at 0.45 MPa. Migration kinetics of the additive package are temperature-dependent and must be evaluated by specific migration testing on the moulded article under Regulation (EU) No 10/2011; in the United States, the converter confirms food-contact status through the applicable FCN for the additive and colourant package, as PLA itself is not covered by 21 CFR 177.1520.

Steam-in-bag lidding produced from ECOPLAN -DURA EN100 requires a different thermal history than rigid thermoforming; the film is purposely quenched rather than crystallised so that a low seal initiation temperature remains available on vertical form-fill-seal machines. Cast film extrusion is performed at a melt temperature of 185–210 °C and a chill-roll temperature of 15–25 °C. This thermal history suppresses the crystalline fraction and permits heat-seal initiation near 85–95 °C, provided jaw pressure and dwell are adjusted for film gauge. On a VFFS line, seal strength is measured according to ASTM F88/F88M-21; a typical acceptance limit for a 25 µm lidding film is 8 N/25 mm after a 0.5 s dwell at 120 °C and 2 bar jaw pressure, but the converter must revalidate after each gauge change because seal strength does not scale linearly with thickness for plasticised PLA compounds. If the film is not quenched quickly enough, the seal layer develops haze and the seal initiation rises above 100 °C, which then damages the substrate tray during sealing. Amine-based antifog masterbatches should not be assumed compatible; amine migration can accelerate ester hydrolysis and premature film embrittlement, so the additive must be verified by oven-ageing at 50 °C for 7 days before line trials.

Blown-film processing of the same compound for pouches is performed with a die gap of 0.8–1.2 mm, a blow-up ratio of 2.0:1–3.0:1, and a frost-line height of 4–6 die diameters. The bubble is susceptible to draw resonance when melt strength is depleted by excess moisture; the same 250 ppm moisture limit applies, and dryer uptime becomes a direct production metric. Pinholes are evaluated with a water-bath leak test under internal pressure, and oxygen transmission is measured according to ASTM D3985-05 at 23 °C and 0% RH; PLA films are not high-barrier structures, so steam-in-bag formats usually require an additional barrier coating or lamination layer. Water vapour transmission is measured according to ASTM F1249-20 at 38 °C and 90% RH, and the result is used to determine shelf life for frozen or chilled products. Compostability claims are verified separately under EN 13432 or ASTM D6400-21.

When Clamshell Foam Extrusion Lines Move from Talc-Filled PP to PLA

In clamshell foam extrusion, the processing window narrows because the gas-loaded PLA melt has lower elongational viscosity than talc-filled polypropylene. The line is configured as a tandem extruder with a 36:1 L/D primary screw and a 28:1 L/D cooling screw; physical blowing agent injection, typically carbon dioxide or nitrogen, is located after the melt seal at approximately 24:1 L/D on the primary barrel. Melt temperature must be maintained between 180 °C and 200 °C at the die, which is 10–20 °C lower than the melt temperature used for dense sheet; above 205 °C, cell coalescence and prefoaming inside the die produce surface defects and density variation. Below 175 °C, the gas-laden melt exhibits high head pressure and melt fracture at the die lips. The die gap is set between 0.2 mm and 0.5 mm, and the forming temperature is maintained in a narrow band of ±3 °C across the sheet because the flexible PLA compound has a lower cold-crystallisation onset than rigid PLA and therefore a narrower thermoforming plateau. Density reduction is verified according to ASTM D792-20, and foam cell size is measured according to ASTM D3576-15.

Post-extrusion trim and guillotine cutting are more sensitive to blade temperature; ambient slitting of PLA foam at speeds above 20 m/min can generate microcracks along the hinge area. Clamshell hinges made from foam are the main failure zone during repeated microwave reheating; a hinge flex test after 10 open/close cycles at 23 °C and after heating at 100 °C for 3 min identifies crack initiation. Published data for this specific configuration is limited, so converters should generate a fractional factorial design including melt temperature, gas injection rate, and cooling roll temperature before committing to long-run production. Food-contact evaluation follows Regulation (EU) No 10/2011 and applicable FDA FCN requirements, with particular attention to blowing-agent residuals and print adhesion.

What Causes Pinhole Formation in Extrusion-Coated Paperboard During Microwave Reheating?

Extrusion coating of ECOPLAN -DURA EN100 onto paperboard for microwavable cups and bowls creates a failure mode that is not visible at the coating line but appears after steam pressure is generated under the PLA layer during reheating. The melt curtain is delivered from a slot die at 200–220 °C and drawn into a nip at 80–120 m/min. If the paperboard contains more than 9% moisture at the nip, the vaporising water disrupts the melt web and leaves latent pinholes. Paperboard is conditioned to 7–9% moisture and the chill roll is held at 15–25 °C to freeze the amorphous PLA surface before crystallisation can produce pinholes or adhesion loss. Coating thickness below 12 µm is not recommended for microwave steam release because pinhole probability increases as the melt web is drawn to lower thickness; 15–25 µm is the typical product window. Adhesion is checked by a 90° peel test after 24 h conditioning, and pinholes are detected with a solvent-based dye penetrant test before and after microwave reheating.

The second source of pinhole failure is melt-temperature drift at the die lip. If the die lip temperature falls below 195 °C, the melt curtain develops edge thickening and folds, creating air entrapment at the web edges; if the die lip temperature exceeds 225 °C, oxidative degradation at the lip increases and the coating surface becomes turbid. These defects are monitored by recording die lip temperature at 6 points across the width and by measuring the coating weight profile with a beta gauge before the chill roll. For cups and bowls, the coated paperboard is die-cut, folded, and heat-sealed; the seal area is tested according to ASTM F88/F88M-21 after being filled with water and heated in a microwave at 800 W for 5 min. Food-contact verification of the finished cup is performed under Regulation (EU) No 10/2011 using EN 1186 and EN 13130 test protocols, and the converter confirms that the paperboard, coating, and printing system are covered by the applicable FDA FCN or 21 CFR section for the complete construction.

A separate class of application is the direct food-contact pouch for frozen vegetables that is transferred from freezer storage at -18 °C to microwave reheating at 100 °C steam. Flex-crack resistance at -18 °C is evaluated according to ISO 527-2:2012 after conditioning the film for 48 h at 23 °C and 50% RH, then chilling for 24 h at -18 °C. The compound's flexible modifier shifts the low-temperature brittle point downward relative to unmodified PLA, but the exact value depends on the additive lot; converters should therefore run a gel permeation chromatography check of molecular weight before converting return regrind above 15% because hydrolytic degradation caused by residual moisture concentrates in film scrap. At the blown-film die, a die gap of 0.8–1.2 mm, a blow-up ratio of 2.0:1–3.0:1, and a frost-line height of 4–6 die diameters are used to balance machine-direction and transverse-direction tear resistance; the bubble is run with a collapsing frame that is pre-heated to 30–40 °C to reduce blocking and wrinkle writing. Seal initiation is measured on a gradient sealing jig according to ASTM F88/F88M-21, and the heat-seal window is defined as the range between the minimum seal strength of 8 N/25 mm and the temperature at which the film shrinks or wrinkles on the tray flange.

After the pouch is sealed, a steam-in-bag test is conducted with frozen food simulant or vegetable mix; the seal is inspected for channel leaks, and the film is visually rated for whitening, delamination, and pinholing after 5 min at 800 W. Because the polymer is not a high-barrier material, the package design uses a laminated or coated structure when oxygen-sensitive vegetables are packed, and the oxygen transmission rate is measured according to ASTM D3985-05 at 23 °C and 0% RH. Compostability claims for the finished pouch are verified separately under EN 13432 or ASTM D6400-21 and are not granted by the PLA resin supplier without complete article testing. The film handler must also confirm that the antifog and slip additives used in the formulation do not raise water vapour transmission beyond the limit set for frozen-to-microwave use, which is measured according to ASTM F1249-20 at 38 °C and 90% RH.