Luminy LX175U High Viscosity Amorphous Transparent PLA is a polylactide homopolymer supplied by TotalEnergies Corbion BV. The grade is identified by three converting-relevant characteristics: high melt viscosity, amorphous solid-state morphology, and optical transparency. These characteristics separate it from low-viscosity injection-molding PLA and from nucleated semicrystalline PLA. The product is intended for sheet extrusion, thermoforming, and rigid packaging where melt strength and optical clarity are required. The technical profile below defines the measured property envelope, the production-scale processing window, and the operational boundaries that apply to the grade. The values given are typical or recommended processing values and are not specification limits unless stated.

What Defines the Amorphous, High-Viscosity Profile of LX175U?

Under ISO 1133-1:2022 at 190 °C and 2.16 kg, the typical melt mass-flow rate of LX175U is 3 g/10 min. This value is the primary rheological boundary between this grade and high-flow injection-molding PLA, which commonly exhibits melt mass-flow rates above 10 g/10 min. The solid density is reported as 1.24 g/cm³ under ISO 1183-1:2019. The amorphous character is verified by differential scanning calorimetry according to ISO 11357-3; a conventional heating scan at 10 K/min shows a glass transition in the range 55–60 °C and does not display a significant melting endotherm. The low crystallinity of the rapidly cooled resin permits total luminous transmittance values typically above 90% and haze values below 2% for a 2 mm plaque measured under ASTM D1003-21.

The thermal boundary associated with amorphous PLA is often misread as a defect. Because LX175U does not form a high-crystallinity network during rapid quench, the heat deflection temperature under 0.45 MPa is approximately 55 °C (ISO 75-2/B), and the Vicat softening temperature is near 57 °C (ISO 306/B50). These values preclude hot-fill packaging and retort exposure but enable a wide post-extrusion thermoforming window. During cooling from the die, the resin remains optically clear at chill roll temperatures between 25 °C and 35 °C; higher roll temperatures, particularly above 40 °C, allow spherulitic growth and increase haze. The absence of a melting endotherm therefore does not represent thermal instability; it means the load-bearing limit is controlled by the glass transition rather than by a crystalline reinforcement phase.

Capillary rheometry under ISO 11443:2021 is required to resolve the high-shear behavior relevant to flat die extrusion. The low-shear melt mass-flow rate alone does not predict die pressure because LX175U is pseudoplastic; its apparent viscosity decreases with increasing shear rate. Converting lines equipped only with melt-flow indexers should not extrapolate flow length or die pressure. When process simulations are performed, the supplier’s viscosity curves at 190 °C, 200 °C, and 210 °C should be used rather than a single viscosity point.

Sheet Extrusion Conditions and Moisture Control on Production Lines

Hydrolysis is the primary process failure mode on production-scale equipment. Residual moisture above 250 ppm depolymerizes PLA at melt temperature, producing a measurable loss of melt viscosity and surface splay. The material must be dried in a desiccant dryer at 80 °C for 4 h with a dew point no higher than −30 °C; final moisture content should be verified by ISO 15512:2019 and held below 250 ppm. On single-screw sheet lines with an L/D ratio of 28:1 to 32:1, barrel temperatures are typically set from 170 °C in the feed zone to 200 °C at the metering zone, with adapter and flat die temperatures between 195 °C and 210 °C. The melt temperature measured at the die should remain at 190–210 °C. A screen pack of 60/100/60 mesh is common for flat die sheet; finer filtration below 150 mesh can raise backpressure and shear heating. Polished three-roll stacks are used with roll temperatures from 25 °C to 35 °C to quench the sheet into an amorphous state. On production lines with L/D ratios below 28:1, uneven plastication has been observed as transverse thickness variation greater than 8% at widths above 600 mm; the defect appears when the screw cannot complete melting of the high-viscosity feed. Gravimetric dosing is preferred because pellet bulk density variation of ±2% can shift volumetric feeder output by several percent.

Melt bank size on the polishing stack is a process conflict. Excessive bank volume creates stagnant material, extended residence time, and gel or discoloration; insufficient bank volume causes draw marks and edge waviness. The die lip gap is normally set 10–15% above the target sheet thickness to allow controlled draw-down. Excessive draw-down of more than 20% induces molecular orientation that can increase shrinkage during reheating.

When High Viscosity Is Preferred Over Standard Injection-Molding PLA

The primary functional difference between LX175U and standard injection-molding PLA is melt strength. In sheet extrusion, low-viscosity grades with melt mass-flow rates above 10 g/10 min produce draw resonance, edge neck-in, and poor transverse thickness control at sheet widths above 300 mm. LX175U at 3 g/10 min maintains a more stable melt web at die gaps from 0.3 mm to 3.0 mm, and the extruded sheet retains sufficient strength during sag tests. In thermoforming, plug-assisted forming of cups and trays is possible at sheet surface temperatures of 85–95 °C; under these conditions the sheet remains above the glass transition but below the rapid crystallization temperature range. Nucleated PLA grades are different: they are formulated with talc or organic nucleants to increase heat deflection temperature above 90 °C after annealing, but they typically show haze values above 10% under ASTM D1003-21 and require heating above 110 °C for full crystallization. The amorphous grade therefore serves transparent rigid packaging where cold-fill or ambient-fill conditions are acceptable.

The viscosity advantage is also a limitation. The same chain length that stabilizes the melt web increases injection pressure and reduces flow length. LX175U is not suitable for thin-wall injection-molded parts with a flow length to wall thickness ratio greater than 150:1, and should not be processed in hot-runner systems with long residence times above 210 °C because lactide reformation increases and melt strength declines. In extrusion coating or lamination configurations, high melt strength reduces draw resonance but may require higher backing-roll pressure to achieve adhesion; published data for this specific configuration is limited.

Application usage is concentrated in transparent food and non-food sheet. Documented converter-grade uses include cold-fill dairy cups, produce containers, bakery clamshells, transparent lids, blister packs for consumer goods, and display packaging. The recommended formed article wall thickness is generally between 0.2 mm and 1.5 mm after thermoforming. Thinner sections require sheet pre-blowing or plug assist to prevent webbing; thicker sections may cool slowly and develop haze unless chilled with cooled molds. Since the material has a glass transition near 55–60 °C, post-forming handling at ambient temperatures is dimensionally stable, but storage in closed vehicles above 50 °C can distort finished parts. Direct contact with high-fat foods may require migration testing under EU Regulation 10/2011 because lactide migration is both time- and temperature-dependent.

Transparency Is Maintained Only Below a Critical Cooling Rate

Transparency in LX175U is not an additive effect; it is controlled by suppressing crystallinity during rapid quench. The critical cooling rate for this grade is determined by the die-to-chill-roll gap and roll temperature. If the sheet contacts the first chill roll at a temperature above 60 °C and is then cooled slowly through 80–100 °C, spherulites grow and haze increases beyond 5%. On polished three-roll stacks, the first roll must therefore be maintained below 35 °C, and the air gap should be minimized. In thermoforming, the sheet is reheated from ambient to 85–95 °C for forming. At this temperature the material is rubbery and transparent; it does not crystallize rapidly, so cycle times up to 10 s in the mold are typically possible without opacity. However, if the sheet is held at 100 °C for longer than 2 min, optical haze in the final part can exceed the specification of 3%. Infrared ovens with a center-to-edge sheet surface temperature difference greater than 5 °C can also produce uneven wall thickness and webbing. Compared with amorphous polyethylene terephthalate, LX175U offers lower processing temperatures but a lower continuous-use temperature; it cannot be sterilized by superheated steam or hot air above 60 °C without dimensional change.

Regulatory conformity for food-contact use is covered under EU Commission Regulation 10/2011 and applicable national provisions; the supplier’s declaration of compliance should be consulted for the specific additive package and monomer migration. The grade is not formulated with halogenated flame retardants and is outside the scope of RoHS restrictions under Directive 2011/65/EU. Storage before processing requires sealed moisture-barrier packaging at warehouse temperatures below 30 °C and relative humidity below 60%. Opened material should be transferred to a desiccant dryer immediately; exposure to ambient air at relative humidity above 60% for more than 2 h can raise pellet surface moisture above 500 ppm. Alkaline cleaning solutions, concentrated aqueous ammonia, and certain solvent-based inks can attack the amorphous PLA surface; compatibility must be evaluated against the specific chemical formulation because published data for this configuration is limited. Dried material returned to ambient should be processed within 2 h unless held under dry air at a dew point no higher than −30 °C.