Eco Solution GP335C Biodegradable Injection Molding Polylactic Acid/PBS Alloy

Eco Solution GP335C is a biodegradable injection molding compound based on polylactic acid and polybutylene succinate. The alloy is intended for thin-wall rigid packaging, disposable consumer goods, and non-durable technical parts where disposal routes require industrial compostability under EN 13432:2000 or ASTM D6400-21. The melt flow index is specified at 12 g/10 min under 2.16 kg load at 190 °C using ISO 1133-1:2022, placing the grade in a high-flow class for nominal wall sections from 0.8 mm to 2.5 mm. Density is 1.26 g/cm³ under ISO 1183-1, tensile strength at yield is 45 MPa under ISO 527-2/1A, and elongation at break is 160%. These values differ from unmodified PLA, where elongation at break is typically below 5%, and from PLA/PBAT compounds, where tensile strength is commonly below 32 MPa and flexural modulus falls below 1.0 GPa. The PBS phase in GP335C raises impact toughness without eliminating the rigidity required for injection molded sidewalls, closures, and generic rigid articles.

How does the PBS co-polyester phase modify notched impact behavior relative to neat PLA?

In polylactic acid homopolymer, the glass transition near 60 °C and the low crack-propagation resistance of the amorphous matrix produce brittle failure under notch loading. Polybutylene succinate has a glass transition near -30 °C and a melting point near 115 °C. When dispersive mixing is applied in a corotating twin-screw extruder with L/D 44:1 and 12 barrel sections, the PBS phase forms low-modulus domains that blunt crack tips and increase the notched Izod impact strength to 8 kJ/m² under ISO 179-1/1eA. The same test on representative injection molding PLA with 1.5 mol% D-lactide content yields approximately 3 kJ/m². Flexural modulus remains at 2.4 GPa under ISO 178, whereas a PLA/PBAT compound containing 30 wt% PBAT can exhibit flexural modulus below 0.9 GPa and heat deflection temperature below 65 °C at 0.45 MPa.

Dynamic mechanical analysis under ISO 6721-1 shows a secondary loss peak associated with the PBS phase near -30 °C and the PLA glass transition between 60 °C and 65 °C. The storage modulus at 25 °C is approximately 2.1 GPa, falling to 0.3 GPa at 60 °C. This temperature dependence explains why thin-wall parts retain stiffness at ambient temperature but become compliant above the PLA glass transition. The difference from neat PLA is therefore not a simple increase in toughness; it is a redistribution of mechanical response across the service temperature range.

The increased impact performance is accompanied by a reduction in heat deflection temperature compared with neat PLA. Continuous service above 55 °C in humid conditions is not recommended for GP335C. The property profile places the grade between rigid PLA and highly ductile PLA/PBAT materials for injection molding, with lower notch sensitivity than PLA and higher stiffness than common PLA/PBAT blends.

Predrying, melt temperature, and screw configuration boundaries

Processing of GP335C requires moisture removal before plastication. The resin is dried at 80 °C for 4 h in a desiccant dryer with a dew point not higher than -40 °C. Residual moisture must remain below 0.025 wt% as measured by ISO 15512. If moisture content exceeds 0.08 wt%, hydrolysis during melt processing reduces molecular weight and produces splay, surface roughness, and reduced melt strength. This is especially visible on 0.8 mm wall sections where gate blush and flow hesitation occur at lower melt viscosity. In production environments where ambient relative humidity exceeds 60%, granulate exposed to open air for more than 30 min can exceed 0.04 wt% moisture. Central drying systems should maintain dew point below -40 °C and use sensors calibrated at least annually. Hopper inlet temperature should not exceed 45 °C to prevent pellet bridging.

Barrel temperatures are set between 170 °C and 190 °C, with a nozzle temperature from 185 °C to 195 °C. The mold temperature is maintained between 20 °C and 35 °C. At melt temperatures above 195 °C, the PBS phase undergoes thermal degradation; the resulting acid species can accelerate PLA hydrolysis and transesterification. A maximum barrel residence time of 8 min above 190 °C is specified. On a 40 mm general-purpose screw with L/D 25:1 and compression ratio 2.5:1, screw speed is typically limited to 80 rpm to 150 rpm. Back pressure is maintained at 0.3 MPa to 0.5 MPa. Higher back pressure above 0.7 MPa extends screw recovery time and increases shear heating, which can exceed the safe melt temperature before the shot accumulates.

Injection molding trials on 1200 kN hydraulic toggle-clamp machines with single-phase AC drives have shown that screw recovery time increases by approximately 18% when back pressure is raised from 0.3 MPa to 0.7 MPa, without a corresponding improvement in part surface quality. Low-shear screws designed for neat PLA may not distribute PBS uniformly. Trials on 60 mm barrier screws with L/D 28:1 and a mixing section of 1.5 D provided consistent impact values; screws without distributive mixing produced notched Izod values as low as 5 kJ/m² in the same mold.

On hydraulic toggle-clamp machines with clamp force between 1200 kN and 1800 kN, thin-wall containers with nominal wall thickness of 0.8 mm are molded with short hold-pressure times because the alloy releases from core surfaces more readily than neat PLA. Post-mold shrinkage under ISO 294-4 is 0.6% to 0.9% parallel to flow and 0.7% to 1.1% perpendicular after 24 h at 23 °C and 50% relative humidity. Gate freeze time is approximately 15% lower than that of neat PLA at the same melt temperature, which permits shorter packing profiles and reduces cycle time. Mold temperature below 20 °C increases shrinkage anisotropy and can create warp in rectangular lids. Above 35 °C, the cycle penalty is not offset by significant crystallinity development because the PLA phase in GP335C remains largely amorphous under normal injection molding conditions.

When filler loading is increased beyond 10 wt%, processing and compostability require re-validation

The base GP335C grade is unfilled. In downstream compounding, adding talc or calcium carbonate above 10 wt% raises flexural modulus by approximately 0.6 GPa to 1.0 GPa but reduces elongation at break to below 50% and increases melt viscosity. The higher viscosity shifts the minimum injection pressure upward by 10 MPa to 15 MPa on 80 mm axisymmetric screws. Filler addition also changes the compostability evaluation because inorganic fillers do not mineralize under ISO 14855-1; the reported percentage of biodegradation is calculated on total dry solids, and a high filler fraction may require correction for ash content. Therefore, any filled derivative must be re-validated under EN 13432:2000 and ASTM D6400-21 as a separate formulation, not by reference to the unfilled GP335C data.

Compostability verification is not identical to food-contact approval

Under EN 13432:2000, GP335C is assessed by ISO 14855-1 for aerobic biodegradation, ISO 16929 for disintegration, and OECD 208 for ecotoxicity. Biodegradation must reach at least 90% relative to a positive control within 180 days. Disintegration requires at least 90% of material fragments to pass a 2 mm sieve after 12 weeks of controlled composting. Ecotoxicity requires plant germination and biomass not lower than 90% of the blank compost reference. Heavy metal limits follow EN 13432:2000 Annex E; lead must remain below 50 mg/kg dry solids, cadmium below 0.5 mg/kg, mercury below 0.5 mg/kg, and hexavalent chromium below 50 mg/kg.

Food-contact status is separate. No FDA 21 CFR 177.1520 clearance is claimed for GP335C unless a complete migration study under EU Regulation 10/2011 or FDA conditions of use is completed for the finished article. The presence of PBS does not automatically confer food-contact compliance. Converters must verify overall migration, specific migration of 1,4-butanediol and succinic acid, and organoleptic acceptance before use with food. Published data for this specific configuration is limited; lot-specific migration testing is required.

Compared with starch-filled PLA compounds, GP335C exhibits lower water uptake in ISO 62 testing at 23 °C over 24 h because the PBS phase is hydrophobic. Relative to PLA/PHA alloys, the PBS-containing system provides a broader injection molding melt-temperature window and lower sensitivity to nucleant concentration. The principal limitation is thermal resistance: continuous service above 55 °C in humid environments is not recommended, and the material is not compatible with prolonged exposure to strong bases or strong acid solutions because both PLA and PBS undergo chain scission. This limitation is below the heat deflection temperature of neat PLA and is relevant in applications such as hot beverage lids, dishwasher-exposed articles, and components exposed to hot-water rinsing.