Ecopond PLA-873 Modified Compostable High Impact Polylactic Acid is supplied as a pelletized compound based on polylactic acid (PLA) with a non-styrenic impact-modifier package intended for injection molding, sheet extrusion, and thermoforming operations where unmodified PLA fracture energy is insufficient. The grade carries a nominal melt flow index of 6 g/10 min at 210 °C under 2.16 kg load in accordance with ISO 1133-1:2022, and a solid-state density of 1.24 g/cm³ measured by ISO 1183-1:2019. Compounding on a co-rotating twin-screw extruder with 44:1 L/D and closed-loop vacuum devolatilization below -0.08 MPa yields a pellet moisture content below 0.04% as shipped and a lot-to-lot melt viscosity variation of ±4% at constant screw speed and throughput. The impact modifier is selected to preserve disintegration and biodegradation behavior under EN 13432:2000/AC:2005, which distinguishes this product from PLA compounds modified with non-compostable styrenic or acrylic elastomers.

Capillary rheometry at 200 °C reveals a power-law response that differs from unmodified PLA. Apparent melt viscosity at 1000 s⁻¹ is 180–220 Pa·s, and the power-law index between 100 s⁻¹ and 1000 s⁻¹ is 0.55–0.65, indicating stronger shear thinning than unmodified PLA with a power-law index near 0.70–0.75. This rheological response permits lower injection pressure in thin-wall cavities but also increases the tendency for gate blush if the gate shear rate exceeds 50,000 s⁻¹. Capillary data was generated according to ISO 11443:2021 with Bagley correction.

How Does PLA-873 Retain Compostability After Impact Modification?

In an impact-modified PLA, compostability depends on whether the discontinuous modifier phase permits hydrolytic attack of the continuous PLA matrix. Aerobic biodegradation of milled powder must exceed 90% relative to cellulose within 180 days under ISO 14855-1:2012. Disintegration of 2 mm sheet must show no fragments larger than 2 mm after 12 weeks in a controlled composting test at 58 °C, as specified in EN 13432:2000/AC:2005. The impact-modifier loading is kept below the phase-inversion threshold observed in PLA/aliphatic polyester compounds; above that threshold, co-continuous hydrophobic phases reduce hydrolysis rate by more than 40% and delay disintegration beyond the 12-week window. Published data for this specific modifier configuration is limited, but grade-specific certificate of analysis should be requested for each batch.

Notched Impact, Tensile Behavior, and Thermal Deflection Data

For unfilled natural-color pellets, indicative lot-specific values appear in Table 1. Specimens are conditioned at 23 °C and 50% RH for 40 h before mechanical testing.

Because PLA esters are hydrolytically sensitive, drying before processing is required when ambient humidity exceeds 60% RH. Pellets should be dried in a desiccant-wheel dryer with a supply dew point of -40 °C or lower, at 80 °C for 4 h, to a residual moisture level below 250 ppm (0.025%) measured by Karl Fischer titration per ISO 15512:2019. If the return-air dew point rises above -25 °C, hydrolysis during plastication reduces melt viscosity by more than 8% and produces visible splay on molded surfaces. Reported production-scale behavior for high-impact PLA compounds indicates that undried resin exposed to 70% RH for 6 h generates a 15–20% loss in notched Izod impact compared with dried controls. The same data shows no measurable loss in elongation at break when the hopper is blanketed with dry air below -30 °C dew point.

When High-Shear Injection Molding Demands Lower Viscosity

When thin-wall parts below 1.2 mm require faster cavity filling, the barrel profile must balance shear thinning against thermal degradation. A five-zone reciprocating screw barrel is set from rear to nozzle at 165 °C, 180 °C, 195 °C, 200 °C, and 200 °C, with the hot runner or nozzle held at 200–205 °C. Mold temperature is maintained at 20–30 °C for standard wall thickness; for sections below 1.2 mm, mold temperature is raised to 40 °C to prevent premature skin freezing before the cavity is packed. Injection velocity is profiled so that 90–95% of the cavity volume is filled before transfer to pack pressure at 600–800 bar hydraulic pressure. Screw recovery speed is kept below 80 rpm to limit shear heating to 10 °C or less above the set melt temperature. Total melt residence time above 200 °C is specified below 5 min. Exceeding this window increases melt flow index by 1–2 g/10 min and lowers tensile strength by 5–10% due to chain scission, a failure mode confirmed by gel permeation chromatography shifts in PLA molecular weight distribution.

Gates and runners must be sized for shear rates below 50,000 s⁻¹. For a cold-runner edge gate, this corresponds to a gate diameter of at least 1.0 mm for a 2 mm wall thickness, based on a volumetric flow rate of 20 cm³/s. If the gate shear rate exceeds this threshold, visual gate blush and localized reduction in tensile elongation at break of 10–15% have been observed. Hot-runner systems should use unheated gate tips with a thermal separation length of 3–5 mm to prevent thermal soak at the gate. Published data for this specific configuration is limited for hot-runner performance, so tool trials are recommended.

At -10 °C, low-temperature impact behavior separates PLA-873 from unmodified extrusion-grade PLA. An unmodified extrusion-grade PLA with a similar melt flow index typically exhibits notched Izod impact of 2.5–3.5 kJ/m² at 23 °C and 1.5–2.0 kJ/m² at -10 °C under ISO 180/A:2019. PLA-873 maintains 12–18 kJ/m² at 23 °C and 6–9 kJ/m² at -10 °C, while tensile elongation at break remains above 70% instead of the 5–8% typical of unmodified PLA. Compared with PLA/PBAT blends having similar elongation, PLA-873 exhibits a higher tensile modulus of 2.4–2.8 GPa, which reduces sheet sag on extrusion thermoforming lines. Published data for oxygen barrier properties specific to this modified grade is limited; packaging structures requiring high barrier must be tested under ISO 15105-2:2023 and should not assume equivalence to unmodified PLA films.

For additive dosing in PLA-873, the ester groups in the polylactic acid matrix are susceptible to alkaline and amine-catalyzed degradation. Free amine-based slip agents should be avoided above 0.5 wt%, because ester aminolysis raises melt flow index by more than 3 g/10 min during compounding and reduces notched Izod impact by more than 20%. Silicone-based mold release agents at 0.2–0.5 wt% do not produce measurable loss in notched Izod impact. If colorant masterbatches are required, the carrier resin must be a similar PLA or certified compostable aliphatic polyester; non-compostable carriers at 2 wt% can reduce disintegration performance below the 90% biodegradation threshold. Pre-production trials on the intended dosing equipment are required because published data for this specific configuration is limited for additive interactions.

Regulatory Documentation Is Grade-Specific

Documentation for compostability must be tied to the specific formulation, colorant package, and wall thickness. The absence of non-compostable styrenic modifier simplifies the documentation for industrial composting but does not automatically confer food-contact or home-compostability status.

In sheet extrusion and thermoforming, a separate viscosity strategy is required. For flat sheet die widths of 600–900 mm, melt temperature at the die lips is controlled to 195–205 °C, with chill rolls set to 30 °C on the top roll and 25 °C on the bottom roll to limit crystallinity below 10%. The extruder is typically a single-screw machine with 30:1 to 36:1 L/D and a barrier screw designed for low-shear PLA plastication; vented barrels must maintain vacuum below -0.06 MPa to remove residual moisture and lactide monomer. Thermoforming of PLA-873 sheet is performed at 90–105 °C surface temperature, below the heat deflection threshold, with plug assist using syntactic foam plugs coated with a non-stick surface. Because PLA-873 has lower melt strength than petroleum-based high-impact polystyrene sheet, draw ratios above 3:1 may produce wall-thickness variability above 0.15 mm. Continuous processing above 210 °C for more than 30 min is outside the documented operating boundary.