Sheet extrusion for fresh-cut salad MAP trays starts with L100-H granules dried in a desiccant-wheel dryer at 80 °C for 4 h and a dew point below −40 °C, producing residual moisture below 250 ppm as measured by ISO 15512. A single-screw extruder with 38:1 L/D and a double-flighted barrier screw feeds a melt pump and a flat die; melt temperature is held between 195 °C and 205 °C, while die temperature is set 5–10 °C below melt temperature to reduce die-lip deposit. The extruded web is quenched on polished chill rolls at 35–50 °C to suppress crystalline haze and retain a sheet thickness of 350–500 µm. Thermoforming is performed on a plug-assisted continuous machine with sheet surface temperature 90–105 °C and mould temperature 110–120 °C; infrared pyrometry is used to hold surface-temperature variance within ±3 °C. Cavity venting must be maintained below 0.2 mm slot width because PLA releases condensable oligomers that deposit on unheated tool surfaces. The resulting MAP tray is matched with a peelable lidding film; oxygen transmission of the tray is governed by ASTM D3985 and cold-chain performance is checked at 4 °C for 7 days under packhouse-specific abuse protocols. Compliance for direct food contact is established under EU No 10/2011 and FDA 21 CFR 177.1520. Because hydrolysis accelerates above 60% RH, opened resin bags must be re-dried before extrusion, and regrind content above 30 wt% should not be used without verifying melt flow rate per ISO 1133-1:2022.

Resin lot acceptance for this application also requires measurement of melt flow rate per ISO 1133-1:2022 at 210 °C and 2.16 kg, verification of pellet moisture below 250 ppm by ISO 15512, and a differential scanning calorimetry check per ISO 11357-3 to confirm that the cold crystallisation peak remains inside the supplier-specified range. D-lactide mass fraction above 1.5% reduces the maximum attainable crystallinity and lowers heat deflection temperature after thermoforming; high-crystallinity extrusion grades therefore require optical purity control and separation from mixed-PLA regrind streams. In continuous production, sheet edge trim is ground and reintroduced at 15–25 wt%; before raising regrind content, the MFR shift relative to virgin pellets is measured and limited to 2 g/10 min. Static drying at 80 °C without desiccant airflow is insufficient above 60% RH; dryer hopper bed height should not exceed 1.5 m and air flow speed is maintained at 0.5–1.0 m/s to reach the required dew point.

Why Does Extruded Sheet for Bakery Clamshells Require Impact Modification?

Unmodified L100-H sheet has a notched Izod impact below 25 J/m when tested per ASTM D256 at 23 °C, which is insufficient for repeated hinge flexing on a bakery clamshell. Dry compounding with 3–5 wt% PBAT or 2–4 wt% core-shell acrylic impact modifier before sheet extrusion raises the Izod value to 45–70 J/m, but it also reduces light transmission measured by ASTM D1003 from 92% to 85–88%. The blend is processed on a co-rotating twin-screw extruder with 32:1 L/D at barrel temperatures 175–195 °C, followed by a flat die at 190 °C; melt pressure at the die lip should remain below 12 MPa to avoid shear-induced crystallisation that creates die-lip build-up. Impact-modified sheet is then thermoformed at sheet surface temperature 88–100 °C; bottom plug temperature is kept at 70–80 °C and plug assist speed is reduced to 100–150 mm/s to avoid whitening at the hinge. Hinge endurance is evaluated by repeated flexing to 90° at 23 °C; converter-reported data from commercial lines place failure between 20,000 and 50,000 cycles depending on additive package, but published data for this specific L100-H configuration is limited. The finished bakery clamshell is compliant with EU No 10/2011 and FDA 21 CFR 177.1520, and impact-modified formulations are tested for overall migration below 10 mg/dm² under aqueous and acidic simulants.

Processors must set the extruder screw speed to maintain specific mechanical energy input between 0.15 kWh/kg and 0.20 kWh/kg; below that range, dispersion of the impact modifier is poor, while above it, molecular weight loss generates free lactide that condenses on vacuum calibration ports. The chill-roll stack is run with a roll gap of 0.25–0.40 mm and a downstream roll temperature of 30 °C to stabilise sheet flatness; static pinning is avoided because high-crystallinity PLA accepts charge unevenly above 40% RH. Regrind from trimmed web is limited to 20 wt% unless the MFR increase per ISO 1133-1:2022 is less than 2 g/10 min relative to virgin pellets. The hinge area should be cooled separately from the body cavity to maximise orientation while avoiding excessive crystallinity at the fold line; hinge whitening is a primary failure signal because it predicts crack initiation under drop loading from 1 m.

For refrigerated dairy portion packs requiring a 30-day shelf life at 4 °C, L100-H is used as the outer structural layer in a five-layer cast sheet, with barrier and tie layers comprising the core. A typical structure is PLA high-crystallinity cap layer / maleated PLA tie / ethylene vinyl alcohol copolymer barrier / maleated PLA tie / PLA high-crystallinity cap layer; total thickness is 700–900 µm, with EVOH at 5–8% of total thickness. The coextrusion feedblock requires matched melt viscosities at 200 °C and a shear rate range of 100–500 s⁻¹, otherwise interfacial instability appears as wavy line defects across the sheet. Individual extruders for cap and tie layers are set at 185–195 °C, the EVOH extruder at 190–210 °C, and the flat die at 200 °C; layer distribution is verified by cross-sectional microscopy against a tolerance of ±1% for the EVOH layer. The sheet is quenched on a three-roll stack at 40 °C, then thermoformed into portion cups on a form-fill-seal line. During thermoforming, the sheet surface is held at 95–110 °C and forming air pressure is set to 4–6 bar; the EVOH layer reduces the oxygen transmission rate to below 2 cm³/(m²·day) at 23 °C and 0% RH when tested per ASTM D3985. The dairy pack is filled at 4–8 °C; high-crystallinity PLA caps resist deformation at filling temperatures because the crystalline fraction developed during thermoforming raises the heat deflection temperature under ASTM D648 to 85–95 °C. Food-contact compliance is assessed under EU No 10/2011 with the assigned dairy simulant and FDA 21 CFR 177.1520; the EVOH layer requires a functional barrier assessment under the relevant migration model if its thickness exceeds the accepted barrier threshold. Moisture ingress into EVOH remains a process risk: if the sheet is stored above 50% RH for more than 24 h before thermoforming, the EVOH layer absorbs water and delamination may occur at the tie interfaces during heating.

Cold-Beverage Lid Thermoforming Demands Tight Crystallization Control

The drinking-lip geometry on a cold-beverage lid requires the sheet to maintain detail reproduction without exceeding the heat-seal initiation temperature of the lid stock. L100-H sheet is thermoformed at a surface temperature of 95–110 °C; the upper limit is set 5 °C below the temperature at which cut edge welding and plug sticking occur on contact-heat tooling. Mould temperature is maintained at 115 °C and dwell time is adjusted to 5–8 s; this produces a crystalline fraction of 25–35% as measured by differential scanning calorimetry in accordance with ISO 11357-3. Below 20% crystallinity, the lid will curl and lose stacking stiffness after filling at 4 °C; above 40%, the skirt becomes brittle and edge cracking occurs during automatic capping. The indexing interval on a roll-fed thermoformer is therefore controlled by a pyrometer array with ±2 °C zone accuracy. Pre-stretch plug temperature is set at 80 °C and plug material is selected from syntactic epoxy or PEEK to reduce heat extraction from the sheet; metal plugs cause premature sheet quenching at the plug contact area and produce aperture thinning below 150 µm. Tool venting channels of 0.1–0.2 mm width are degreased every shift because PLA oligomers deposit and reduce air evacuation, causing incomplete rim formation at the skirt base.

The sheet entering this process is produced from L100-H with 2–4 wt% acetyl tributyl citrate or a polymeric plasticizer to lower the glass transition temperature to 52–58 °C measured by dynamic mechanical analysis at 1 Hz; the exact concentration is adjusted so that the notched Izod impact exceeds 40 J/m per ASTM D256 at 10 °C. If the plasticiser is omitted, lid puncture resistance under ASTM D732 or EN 14477 drops, and cold fracture occurs during palletising. The final lid is tested for migration under EU No 10/2011 with simulant A for cold aqueous beverages and FDA 21 CFR 177.1520; residual lactide content is monitored by GC-headspace and kept below 0.5 wt% to prevent off-taste in the beverage. The process window is classified as a critical control point because a ±2 °C sheet-temperature deviation at the forming station can move the part from ductile to brittle from one cycle to the next.

Industrial Compostable Food Service Trays and EN 13432 Compliance

L100-H is converted into industrial compostable food service trays where the end-of-life claim requires certification under EN 13432 and ASTM D6400. The extrusion and thermoforming conditions follow the fresh-produce tray profile, but the tray design removes undercuts and sharp radii below 3 mm because high-crystallinity PLA has limited elongation and will crack during industrial sorting. Additive package is restricted to substances listed in the certifying body positive list; a typical formulation includes 1–2 wt% talc nucleating agent and 1–3 wt% white masterbatch if opaque trays are produced. Disintegration behaviour is assessed according to ISO 16929 under pilot-scale composting at 58 °C for 12 weeks; high crystallinity retards initial hydrolysis by 7–14 days relative to amorphous PLA, so the tray must remain below 1.5 mm wall thickness to meet disintegration limits without requiring pre-hydrolysis. Aerobic biodegradation is measured by ISO 14855-1 and must reach 90% absolute or relative to cellulose within 180 days; the lag phase observed in respirometric data is typically 10–20 days longer for a nucleated L100-H tray than for an amorphous PLA tray. Food-contact compliance for the serviceware tray remains under EU No 10/2011; if the tray is used for fatty foods, overall migration testing with simulant D2 is required and the result must remain below 10 mg/dm². The compliance checklist matrix below links the relevant standards to the measurement endpoint.

When High-Crystallinity PLA Replaces PET in Transparent Consumer Clamshells

In non-food consumer packaging, L100-H is introduced as a renewable replacement for PET in transparent clamshells only when the distribution chain remains below 35 °C and the contained product mass does not exceed 500 g. The critical replacement boundary is dictated by the heat deflection temperature of the PLA clamshell: after thermoforming and in-mould crystallisation to 25–30%, the HDT per ASTM D648 at 0.455 MPa is 85–95 °C, whereas PET clamshells typically exceed 120 °C. The sheet is extruded at 190–200 °C and thermoformed at a surface temperature of 90–100 °C; recycled-content claims are not made unless a mass-balance chain-of-custody certificate covers the specific extrusion lot. Tooling for PET is not directly transferable because PLA shrinks less and requires lower plug-assisted stretch ratios; cavity depths above 25 mm need plug redesign to avoid sidewall thinning below 200 µm. A transparent PLA-compatible antistatic masterbatch at 1–2 wt% is applied when the clamshell is used for electronic accessories, with surface resistivity measured per IEC 61340-2-3. The finished clamshell is assessed for total migration under EU No 10/2011 if it may contact food service accessories, and for REACH and RoHS Directive 2011/65/EU restrictions in electronics packaging; PLA grades often meet RoHS lead and cadmium limits because polymerisation catalysts are not antimony-based. Moisture absorption remains a limitation: at 23 °C and 50% RH, PLA takes up 0.3–0.5 wt% water over 24 h, which is higher than PET and reduces dimensional stability in humid coastal warehouses.

Production trials on a PET thermoforming line reveal that the lower melt strength of L100-H sheet relative to PET causes sag differences above 100 °C; sag rails and infrared heating profiles must be rebalanced to avoid webbing. Trimming and punching stations require blade clearances below 0.02 mm to reduce microcracks at cut edges, which propagate under drop testing at 1 m when the packaged product mass approaches 500 g. Because this application is non-food, the relevant material declarations under REACH and RoHS Directive 2011/65/EU are applied, and food-contact use is not inferred without EU No 10/2011 migration testing.