Ingeo Polylactic Acid (PLA) 6100D is a thermoplastic aliphatic polyester produced by NatureWorks through lactide ring-opening polymerization of plant-derived sugars. The model designation 6100D identifies the resin within the Ingeo extrusion series and should not be confused with Ingeo 6201D or 6202D, which are fiber-spinning grades. The resin is supplied as cylindrical pellets with a bulk density of 0.80 g/cm³ to 0.88 g/cm³ and a specific gravity of 1.24 when tested according to ASTM D792. The 6100D grade is intended for sheet extrusion and downstream thermoforming rather than high-speed injection molding. Its controlled melt flow rate, nominal 6.0 g/10 min at 210 °C and 2.16 kg per ASTM D1238, provides the melt strength needed to reduce sheet sag and edge weave between the die and the three-roll stack. The grade is used in cold-fill rigid packaging, clear cups, lids, and clamshell trays, although final suitability for food-contact or mechanical service must be confirmed on the finished article under the relevant standards.

What Are the Published Property Limits for Ingeo 6100D?

A representative Ingeo 6100D data sheet lists the following typical values at 23 °C and 50 % RH after conditioning according to ASTM D618. These values are not lot-specific guarantees; pigment, regrind fraction, and thermoforming orientation can shift the results.

The tensile modulus of 3.6 GPa indicates a rigid, glassy polymer under standard room-temperature loading. The notched Izod value of 16 J/m is lower than that of many polyolefins; sharp corners and gate remnants in thermoformed parts therefore act as stress concentrators. The 0.45 MPa heat distortion temperature of 55 °C restricts hot-fill and dishwasher exposure unless annealing or nucleation raises crystallinity. Vicat softening at 57 °C provides a second reference for short-term surface deformation under load, but it is not a long-term service limit. The D-lactide content is not listed as a routine property in every commercial data sheet, but it is a release parameter that controls crystallization rate. A higher D-lactide fraction reduces crystallinity and heat resistance, while a lower fraction increases crystallization but can embrittle the sheet if cooling is too rapid.

Drying is the first critical control. Ingeo 6100D must be dried to a moisture content below 250 ppm before extrusion. On humid production lines where ambient relative humidity exceeds 60 %, a desiccant dryer with a dew point of -40 °C or lower is recommended. A drying schedule of 80 °C for 4 h in a desiccant dryer is a common starting point, with hopper residence not exceeding 8 h to limit pellet bridging and discoloration. Moisture above 250 ppm drives hydrolytic chain scission in the melt, reducing intrinsic viscosity and producing bubbles at the die lip, melt fracture, and irregular sheet gloss. The reaction is autocatalytic because the carboxylic acid end groups generated by hydrolysis further accelerate ester cleavage.

Sheet extrusion on single-screw extruders with 24:1 to 30:1 L/D and barrier screws is standard. Melt temperature should be held between 200 °C and 230 °C. Above 230 °C, lactide reformation and color development accelerate. Below 200 °C, excessive screw torque and unmelted granules may appear. Screen packs of 40/60/80 mesh are installed before the gear pump or die to trap gels and char particles. Die zones are usually maintained within 5 °C of the melt temperature. The polishing stack roll temperatures are commonly set from 20 °C to 40 °C; lower temperatures can create stress whitening in high-draw regions, while higher temperatures extend cycle time and can cause sticking to aluminum or chrome rolls.

Thermoforming operations generally reheat sheet to 90 °C to 110 °C depending on sheet thickness and tool geometry, but published data for specific tooling configurations is limited. Plug-assisted forming with POM or syntactic foam plugs is used to redistribute material before pressure or vacuum forming. Mold temperatures below 20 °C increase cooling stress and notch sensitivity, while mold temperatures above 40 °C increase cycle time and may require a release agent on uncoated aluminum tools.

Gauge uniformity in sheet is influenced by die gap, air gap, and roll gap. A typical die gap is set 10 % to 20 % wider than the target sheet thickness to compensate for sag and neck-in. Air gap is kept short, often 50 mm to 150 mm, to minimize melt relaxation and edge deformation. The polishing stack roll gap is set slightly below the desired sheet thickness to apply contact pressure and reduce surface haze. Edge pinning is required to prevent sheet movement on the rolls.

Sheet produced from 6100D is largely amorphous after rapid cooling but can develop crystallinity during thermoforming or annealing. Differential scanning calorimetry of PLA typically shows a glass transition near 55 °C to 60 °C and a cold crystallization exotherm near 100 °C to 110 °C under ASTM D3418. Heat setting of thermoformed parts in the mold at 90 °C to 110 °C can increase crystallinity and improve dimensional stability, but the rate and final level depend on D-lactide content and nucleating additives.

When Ingeo 6100D Is Compared with Injection Molding and Film Grades

The primary difference between Ingeo 6100D and other Ingeo grades is rheological. Ingeo 6100D has a nominal melt flow rate of 6.0 g/10 min at 210 °C under 2.16 kg load. Ingeo 3052D, an injection molding grade, has a typical flow of 14 g/10 min. Ingeo 3251D is typically 30 g/10 min to 40 g/10 min. Ingeo 4032D for biaxially oriented film is in a comparable viscosity range, but its stereochemical purity, additive package, and surface treatment are optimized for orientation and heat sealing rather than thick-sheet sag resistance. Ingeo 6201D and 6202D for staple and spunbond fibers are supplied with higher flow values, typically 15 g/10 min to 30 g/10 min, and are not interchangeable with 6100D in sheet lines.

The lower flow of 6100D correlates with higher melt strength and less draw resonance in thick sheet, but it also increases melt residence time and shear heating in narrow runner channels. It is not suitable for high-flow injection molding or thin-wall parts with flow length-to-thickness ratios above 200:1. Conversely, injection grades such as 3052D cannot maintain sheet gauge uniformity at the low shear rates encountered in flat-die extrusion because they sag and draw excessively.

Thermoformed containers from Ingeo 6100D are used in cold-fill dairy, produce, bakery, and deli packaging. The stiffness of the resin allows down-gauging in cups and trays, but the notched Izod impact of 16 J/m and the 0.45 MPa heat distortion temperature of 55 °C define service boundaries. Cold-chain use below 4 °C raises modulus but can intensify brittle failure at sharp corners if regrind content exceeds 20 wt% or if the part design includes abrupt wall-thickness transitions. The resin is not recommended for hot-fill above 50 °C or conventional oven reheating unless the part is crystallized in the mold and the package is validated by thermal migration testing.

Production-scale sheet lines return edge trim and skeletal scrap as dried regrind at levels not exceeding 20 wt% in the main feed. Higher regrind fractions lower melt strength and increase yellowness index; the loss gradient depends on prior thermal history and drying. Batch-to-batch variation in melt flow rate is typically reported on the certificate of analysis and should be tracked because a shift of ±1.0 g/10 min may require adjustment of barrel zone temperatures and die gap.

Drying, Hydrolytic Degradation, and Boundary Conditions

Hydrolytic degradation is the primary failure mode during processing. Water attacks the ester linkages of the PLA backbone, reducing molecular weight and generating carboxylic acid end groups that further catalyze chain scission. The practical moisture boundary is 250 ppm; above this limit, sheet haze, edge tear, and die-lip buildup increase. Melt should not be held above 230 °C for more than 10 min. Longer residence times produce lactide monomer and oligomers that plasticize the melt and lower the glass transition temperature. A purge with LDPE or an acrylic-based purge compound is recommended when shutting down or transitioning between materials.

Surface energy of PLA sheet is approximately 38 mN/m to 42 mN/m, which is lower than that of corona-treated polyethylene terephthalate and can require corona or plasma pretreatment before printing or lamination. Aqueous alkaline cleaning solutions etch the sheet surface and should be avoided in washdown environments. Solvent-based inks and coatings require adhesion pre-testing because some carriers can induce stress cracking in amorphous PLA. The resin is not formulated with amine-based additives; unauthorized masterbatch carriers containing amines may promote ester aminolysis and should not be introduced without technical review.

Stock conditions are also a boundary. Unopened bags should be stored at or below 50 °C and 60 % RH to preserve molecular weight. Re-drying is required when bags are exposed beyond 8 h or when the pellets reach the 250 ppm moisture threshold.

Food Contact Compliance Is Tested on the Finished Article, Not the Pellet

Under European Union Regulation (EU) No 10/2011, PLA is evaluated as a polymer in food-contact applications. The overall migration limit of 10 mg/dm² applies to the finished article, and specific migration of lactic acid is assessed according to Annex I, Table 1 restrictions. Because high-molecular-weight PLA has low diffusion and 6100D is supplied without plasticizers, migration risk is generally low for cold-fill and room-temperature contact, but the converter must still demonstrate compliance by testing the thermoformed article under EN 1186 and EN 13130. Thermoforming orientation, regrind fraction, label adhesives, and sealing layers can alter migration behavior.

In the United States, food-contact status depends on the specific Ingeo grade and the conditions of use, with evaluation under 21 CFR Parts 174–179 and applicable Food Contact Notifications. The pellet alone is not a finished food-contact article; the converter is responsible for confirming that the final package meets the relevant FDA clearance for the intended food type, temperature, and contact time.

For industrial applications not involving food, the grade should be assessed for REACH registration and RoHS compliance if the article enters the EU or electrical/electronic waste streams. PLA is not classified as hazardous under CLP Regulation (EC) No 1272/2008, but processing fumes and lactide dust should be controlled through local exhaust ventilation.