FC 60020 Crystallized Compostable Injection Molding Polylactic Acid is a nucleated poly(L-lactic acid)-based compound supplied in pellet form for rigid injection-molded articles that require industrial compostability under EN 13432:2000 or ASTM D6400-23. The designation “crystallized” refers not to a pre-crystallized pellet morphology but to the grade’s capacity to develop a crystalline superstructure during heated mold residence, thereby raising the heat deflection temperature above the 55–60 °C plateau typical of amorphous PLA. Bio-based carbon content, where required, is normally verifiable by ASTM D6866-22 or ISO 16620-2:2019. Published data for this specific configuration is limited; values in this document are class-level representative ranges unless labeled as grade-specific.

Moisture control is the primary pre-processing constraint. Hydrolytic degradation in PLA accelerates rapidly above 250 ppm residual moisture. When ambient relative humidity exceeds 60%, pellets should be dried at 80 °C for 4–6 h in a desiccant dryer with a dew point below -40 °C, and hopper residence should not exceed 1 h without dry-air purge. Drying above 100 °C risks pellet agglomeration and should be avoided. Residual moisture is best determined by ASTM D6980-17 or Karl Fischer titration, not by visual inspection.

What Distinguishes FC 60020 from Amorphous PLA in Injection Molding?

Amorphous PLA solidifies without significant spherulitic growth; the molded part retains a heat deflection temperature near 55–65 °C under 0.45 MPa (ISO 75-2:2013 Method B) and may deform in hot-fill or direct sunlight. FC 60020 is formulated with a nucleating system that shortens the isothermal crystallization half-time at 110 °C to a class-level range of 30–60 s, compared with 180–300 s for unmodified PLA. In a mold held at 100–120 °C, the part develops sufficient crystallinity to achieve a heat deflection temperature in the range of 95–120 °C under the same load. This is not simply a resin substitution; it changes mold temperature control, gate design, shrinkage allowances, and ejection force requirements.

The difference from other nucleated PLA grades lies primarily in the balance of flow length and crystallization rate. Some crystallizable PLA products require a post-mold annealing step at 100–120 °C for 30–60 min; FC 60020 is intended to crystallize in the mold, eliminating the annealing cycle for many geometries. However, the in-mold crystallization route demands mold temperature uniformity within approximately ±5 °C of the nominal set point. When steel surface temperatures vary more than 10 °C across the cavity, differential shrinkage produces warp and post-demolding dimensional drift that cannot be corrected by pressure adjustment alone.

Melt Temperature Does Not Compensate for Low Mold Temperature

Injection molding operators sometimes raise melt temperature to improve fill when mold temperature is below the crystallization threshold. For FC 60020 this strategy is ineffective and accelerates degradation. The recommended melt temperature is 190–220 °C measured at the nozzle. Barrel zone settings should be reverse-profile or flat, with the feed throat at 35–50 °C and the compression/metering zones increasing to 190–210 °C. At melt temperatures above 230 °C, lactide reformation, yellowing, and molecular weight loss occur rapidly; total residence time at 230 °C should remain below 5 min. Below 180 °C, viscosity is high and freeze-off at the gate can occur before the cavity is packed.

The mold temperature boundary is the controlling variable. If the cavity surface is below 90 °C, crystallization is too slow for practical cycle times, and the part surface remains amorphous, producing heat deflection values no better than standard PLA despite the nucleating package. Mold temperatures above 120 °C increase cycle time and can cause part sticking, gate stringing, and dimensional overshrinkage. The practical nominal mold temperature is 100–120 °C, with 110 °C as a starting point. This requires a mold temperature control unit capable of maintaining a set point within ±5 °C, not a standard chiller or ambient-cooled tool.

Production-scale experience with comparable nucleated PLA grades shows that mold temperature variation of more than 10 °C between fixed and moving halves creates measurable warp in flat parts with wall thickness below 2 mm. The problem is not immediately visible at ejection; dimensional drift appears after 24–48 h at 23 °C/50% RH as secondary crystallization continues. Parts should be inspected after conditioning, not packed immediately after demolding.

Injection velocity should be sufficient to fill the cavity before the melt front drops below 180 °C. For wall thickness 1.5–2.5 mm, flow-front velocity of 100–300 mm/s is a starting range; thin-wall parts may require 300–500 mm/s. Holding pressure is typically 50–70% of peak injection pressure and should be maintained until gate freeze. Cooling time is not merely the time to ejection stiffness; it must include sufficient time at the crystallization temperature. A part can be stiff enough to eject but still have low crystallinity if ejection occurs too early. The recommended cooling time for a 2 mm wall at 110 °C mold is typically 20–35 s, compared with 10–15 s for amorphous PLA at low mold temperature. These values are class-level and must be confirmed by thermal analysis of the ejected part.

Screw geometry for FC 60020 should be a general-purpose or low-shear metering profile with L/D 20:1–24:1 and compression ratio of 2.5:1–3.0:1. High-shear screws with mixing sections can generate sufficient frictional heat to push melt temperature above the degradation boundary even when barrel set points remain within limits. Back pressure should be maintained at 5–10 bar hydraulic; excessive back pressure extends residence time and increases shear heating. Screw speed should be set so that recovery completes 1.5–2.0 s before cooling time ends, not at maximum rpm. Shot size should occupy 40–70% of barrel capacity to minimize dead time and maintain melt quality.

Rheological behavior is pseudoplastic. Apparent viscosity at 190 °C and shear rate 1000 s⁻¹ for injection molding PLA typically lies between 50 and 150 Pa·s; FC 60020 class materials may be at the lower end if MFR is elevated. Melt density is approximately 1.10–1.15 g/cm³ at processing temperature, while solid density is approximately 1.24–1.26 g/cm³. The density difference between melt and solid contributes to sink marks if packing pressure is released before gate freeze. Crystallization increases density further; this is why holding pressure and gate seal are critical.

When High-Cavity Hot Runner Systems Are Operated with FC 60020

When a hot runner is used, the manifold and nozzle set points should remain within 190–210 °C and be balanced across drops to limit shear heating at valve gates and small orifices. Hot runner temperature above 220 °C can cause local viscosity loss, drooling, and gate blush. Thermal uniformity of the manifold should be held within ±2 °C; individual nozzle controllers should not deviate more than 10 °C from the manifold set point. Valve gate sequencing should prevent filling of one cavity before others; imbalance exceeding 5–10% of shot mass causes inconsistent crystallization because residence time under pressure varies. Hot sprue bushings and cold runners are less sensitive, but cold runner diameters below 3 mm may freeze prematurely and require high injection velocities that generate shear heat above the degradation limit.

Gate location determines weld line strength and flow-induced crystallization. For FC 60020, direct hot-tip gates or wide edge gates are preferred; pinpoint gates below 1.0 mm can restrict flow and generate shear heat. Weld lines in amorphous PLA may retain 70–80% of nominal tensile strength; in crystallized PLA, weld lines can be more noticeable and may retain 50–70% depending on melt temperature and mold temperature. This is a key difference from other products and must be considered when placing gates for load-bearing features.

Dimensions, Shrinkage, and the Post-Demolding Growth Defect

Crystallization during molding reduces the post-mold shrinkage drift that affects amorphous PLA, but it increases total mold shrinkage. Typical mold shrinkage for FC 60020 class materials is 0.8–1.2% parallel to flow and 0.6–1.0% perpendicular to flow, depending on wall thickness and mold temperature. Shrinkage anisotropy must be accommodated in tool design; amorphous PLA values near 0.4–0.7% are not applicable. Parts ejected before sufficient crystallinity is achieved may continue to shrink after 24 h by an additional 0.1–0.3%. This is the post-demolding growth defect: the part dimensionally drifts after packing and can fall out of specification. The mitigation is not longer packing pressure alone; it requires sufficiently high mold temperature and holding time to reach a stable crystalline fraction.

Ejection force may be higher because crystallized PLA contracts onto cores. Draft angles of 1–2° are recommended; textured surfaces require additional draft. For amorphous PLA, 0.5–1° is often sufficient. Ejector pins should be placed over rigid ribs and bosses, not thin unsupported regions that can puncture while the part is still above the heat deflection temperature.

Compared with talc-filled PLA injection molding compounds, FC 60020 class material has lower density and lower abrasive wear on screws and molds, but lower stiffness and lower heat deflection under load if mineral content exceeds 10 wt%. Compared with amorphous PLA/impact-modifier blends, crystallized PLA has higher thermal stability but lower notched impact resistance. The selection between these products depends on whether thermal resistance or impact resistance controls the application.

FC 60020 is intended for single-use and repeated-use rigid articles where industrial compostability is required. Conformity with EN 13432:2000 requires assessment of the final article, including disintegration, biodegradation, ecotoxicity, and heavy metal limits; resin certification alone is not sufficient. Under ASTM D6400-23, the equivalent requirements apply. The base polymer is typically suitable for food-contact applications when supported by the relevant Food Contact Notification or FDA 21 CFR 175.300 clearance, but specific migration testing must be performed on the final part. Compliance with REACH and RoHS heavy-metal restrictions is generally documented by the resin supplier; additives, colorants, and processing aids require separate verification.

This grade is not formulated for transparent thin-wall applications; spherulitic crystallization produces opacity. It is incompatible with prolonged contact with boiling water above 85–90 °C unless the part is specifically designed for hot-fill and tested under the intended load. Combinations with amine-based additives, strong bases, or high-acid concentrates should be avoided without compatibility testing because they can accelerate hydrolytic degradation. Storage should be in sealed, moisture-barrier packaging below 30 °C; opened bags should be consumed within 8 h under high-humidity conditions or re-dried before processing.