Polylactide resin Ingeo™ Biopolymer 2500HP High Viscosity Crystallizing Extrusion PLA is a semicrystalline poly(L-lactic acid) grade designed for cast sheet, thermoforming, and downstream crystallization where high melt strength and heat deflection after annealing are required. It is supplied in pellet form and is characterized by a melt flow rate of 8 g/10 min at 210 °C under a 2.16 kg load when measured according to ASTM D1238-23 or ISO 1133-1:2022. Specific gravity is approximately 1.24 g/cm³ under ASTM D792 or ISO 1183-1:2019. The resin is intended for conventional single-screw sheet extrusion lines with 24:1 to 36:1 L/D ratios, provided that pellet drying and residence-time control are enforced.

The Semi-Crystalline PLA Chain Controls the Crystallization Window

The enantiomeric composition of 2500HP governs its crystallization response. In semicrystalline PLA, D-lactide units act as stereochemical defects that reduce spherulite growth rate; therefore, 2500HP maintains a D-lactide fraction below 1.0 % to preserve an accessible crystallization window. Differential scanning calorimetry using ASTM D3418-21 or ISO 11357-3:2018 typically records a glass transition temperature between 55 °C and 60 °C and a crystalline melting endotherm between 155 °C and 180 °C, with the upper value dependent on thermal history. Isothermal crystallization of unmodified PLA exhibits a maximum rate near 105 °C–110 °C; below 90 °C segmental mobility is insufficient, and above 130 °C the thermodynamic driving force declines. In production, chilled-roll quenching at 25 °C–40 °C arrests crystallization in thin amorphous sheet, while heated molds or annealing at 80 °C–120 °C drive the development of crystalline morphology.

These thermal boundaries create a narrow processing window. If the sheet leaves the die above 220 °C, adhesion to the roll stack increases and the quench may retain orientation; if the roll temperature exceeds 50 °C, premature crystallization can create haze and embrittlement. Conversely, if the mold temperature is below 40 °C, crystallization is too slow to achieve heat deflection above the glass transition within normal cycle times.

Moisture control is the primary processing constraint. Hydrolytic chain scission in PLA becomes significant when pellet moisture exceeds 250 ppm, and the resulting viscosity loss reduces melt strength and sheet toughness. Pellets are therefore dried at 80 °C for 4 h in a desiccant dryer with a dew point no higher than -40 °C; pellet temperatures must remain below 100 °C to prevent agglomeration and sticking. At ambient relative humidity above 60 %, dried pellets should be conveyed with dried air or consumed within a narrow hold-time window. Published moisture-regain kinetic data for this specific grade is limited, but hydrolysis during open hopper storage is a well-documented industrial failure mode. Melt temperatures should normally be held at 200 °C–210 °C; sustained operation above 240 °C or residence times above 30 min increase lactide reformation, yellowing, and molecular weight degradation. The combination of high moisture and high temperature is particularly damaging and must be avoided.

What Extrusion Screw Geometry and Melt Pressure Profiles Are Required?

High-viscosity PLA grades respond best to gradual compression and low shear heating rather than to aggressive mixing screws. A single-screw extruder with an 24:1–36:1 L/D ratio, a compression ratio of 2.5:1–3.5:1, and a barrier or double-flighted screw is commonly used. Barrel set points from feed throat to adapter are often 180 °C, 200 °C, 210 °C, 210 °C, and 205 °C, with the die at 190 °C–210 °C. Because PLA viscosity is shear-rate dependent, screw speeds above 100 rpm on smaller extruders can generate local melt temperatures above the set point even when barrel heaters are reduced; a melt pressure at the screen changer below 20 MPa is therefore a practical control limit. Gear pumps reduce pressure pulsation and improve sheet gauge stability to ±1.0 % or better under steady conditions. Filtration through 60/80/100 mesh stacked screens protects the die from carbonized particles; finer filtration increases back pressure and residence time without proportional quality improvement.

Sheet surface temperature during thermoforming is normally controlled at 90 °C–110 °C with ceramic or quartz infrared heaters. Below 85 °C, the forming window narrows and sheet fracture occurs; above 115 °C, sag and local thinning become process risks. Mold temperature is the main control for crystallinity. Molds held below 40 °C produce high-clarity amorphous articles with heat deflection near the PLA glass transition; molds held at 80 °C–120 °C promote crystallization and can raise heat deflection temperature above 120 °C, although haze increases and impact strength decreases. Plug-assisted forming with heated composite or polymer-coated aluminum plugs improves material distribution in deep-draw containers; plug temperatures below the sheet surface temperature can generate cold spots and microcracks. Sidewall thickness variation below 0.25 mm–0.35 mm is a practical target for thin-wall food packaging, but published data for this specific grade and mold configuration is limited.

Typical values reported for Ingeo 2500HP are summarized in the following table. These values are not batch-specific specifications and must be verified against the supplier’s certificate of analysis.

When Post-Forming Annealing Is Used to Raise Heat Deflection Temperature

When post-forming annealing is used to increase heat deflection temperature, the formed article is held at 80 °C–100 °C for 10 s–5 min depending on wall thickness and tooling. At 100 °C, thin-wall articles can develop haze within seconds; thicker sections require longer soak to achieve uniform crystallinity. Inadequate annealing leaves amorphous regions that soften near 55 °C; excessive annealing causes warpage unless constrained. Dimensional change during crystallization is anisotropic and must be accounted for in tooling. For parts requiring dimensional stability within ±1.0 %, annealing fixtures should constrain edges and flat surfaces. Thermoforming-induced orientation accelerates crystallization but increases shrinkage; therefore, sheet orientation should be minimized for articles destined for high-temperature use.

Relative to injection molding PLA grades with melt flow rates of 30–40 g/10 min, 2500HP has a lower melt flow rate and higher melt strength, which reduces sheet sag and permits wider die gaps. Relative to amorphous extrusion grades that lack a controlled crystallization response, 2500HP is intended for applications in which post-forming crystallization or elevated heat deflection is required. The grade is not a drop-in replacement for high-clarity amorphous sheet used in cold-drink cups, because the crystallization potential must be suppressed by rapid quenching; otherwise, nonuniform haze may appear. In comparison with PET, 2500HP has lower density, lower continuous-use temperature unless crystallized, and different drying and melt filtration requirements. Compared with PP, it has a higher tensile modulus, typically near 3.5 GPa under ASTM D790, and lower moisture vapor barrier. Industrial compostability under EN 13432 or ASTM D6400 applies only to defined industrial composting conditions and is not a claim of home compostability or marine degradation.

Regulatory Compliance Status and Boundary Conditions

In the European Union, plastic food contact materials are evaluated under Regulation (EU) No 10/2011; migration testing for PLA follows the EN 1186 series and EN 13130 series using the intended food simulant, contact time, and temperature. In the United States, food contact use is normally approved under a food contact notification rather than a single generic 21 CFR citation, and the supplier’s conditions of use must be confirmed for the specific article. REACH compliance under Regulation (EC) No 1907/2006 requires verification that monomers are registered and that substances of very high concern are below 0.1 % by weight. RoHS compliance under Directive 2011/65/EU concerns only the restricted substances listed in Annex II and should be documented by lot-level certificate. The grade is not recommended for continuous high-moisture service above 60 °C, and steam autoclave sterilization is unsuitable.

Operational boundaries include avoidance of alkaline or amine-based additives and high-peroxide masterbatches, which accelerate chain scission and discoloration. Residual polyvinyl chloride on shared extrusion lines must be purged thoroughly because hydrogen chloride release during purging can degrade PLA. The grade is not intended for retort, microwave, or oven use unless post-crystallized and validated under end-use conditions; even then, hydrolysis rate increases with temperature and moisture. Processing above 240 °C or at pellet moisture above 250 ppm is outside the intended processing envelope.