INZEA F28 Rigid 75%+ Renewable Compostable Polylactic Acid is supplied as a pelletized rigid PLA-based compound with a renewable carbon fraction above 75% when measured in accordance with ASTM D6866-21 Method B or EN 16640:2017. The material is formulated for injection molding, sheet extrusion, and thermoforming of single-use and durable articles where industrial compostability under EN 13432:2000 or ASTM D6400-23 is required. The grade is not intended for home compost conditions unless specifically certified by the supplier. Because exact melt volume-flow rate and mechanical data are lot-dependent, the controlling values appear on the supplier certificate of analysis; class-level rigid PLA data are used here only for processing context.

What distinguishes this grade from lower-renewable PLA or starch compounds?

Renewable carbon fraction is not the same as total dry mass. Under EN 16640:2017, bio-based carbon content is determined by ¹⁴C analysis; inorganic fillers and mineral additives do not contribute to the renewable carbon result. This grade therefore satisfies a 75%+ renewable carbon specification while retaining a rigid mechanical response typical of unplasticized polylactic acid. In comparison, starch-filled compostable compounds may show lower continuous-use stiffness after moisture uptake; their tensile modulus can fall below 1.5 GPa at 50% relative humidity, whereas rigid PLA compounds typically remain above 3.0 GPa under ISO 527-2:2012.

Thermoplastic starch blends also exhibit higher equilibrium moisture content, commonly 2-5 wt% at 50% RH, while dried PLA-class resins are processed below 0.025 wt% residual moisture. That difference imposes stricter pre-drying discipline but also reduces the risk of screw slip and melt-pressure fluctuation on vented barrels when the drying sequence is maintained.

Rigid PLA compound property windows reported across producer datasheets and peer-reviewed literature place tensile yield strength in the 45-65 MPa range when measured at 23 °C and 50% RH according to ISO 527-2:2012 specimen type 1A. Tensile modulus values of 3 000-4 000 MPa and flexural modulus values of 3 000-4 500 MPa under ISO 178:2019 are typical for rigid unfilled PLA grades. The ductility of such grades is low: nominal strain at break commonly lies between 1.5% and 4%, which means snap-fit designs, self-tapping screw bosses, and living hinges require radiused transitions and reduced stress concentration unless impact modification is added. The heat deflection temperature of amorphous PLA under 1.8 MPa is usually below 60 °C per ISO 75-2:2013 Method A; under 0.45 MPa Method B, values between 50 °C and 60 °C are common. This limits unsupported service above 55 °C, particularly in dishwasher or hot-fill containers, unless the part is crystallized via mold-temperature control above 90 °C or post-mold annealing.

Because the grade is designated “Rigid”, the expectation is that tensile modulus is not decreased by high plasticizer or low-molecular-weight polyester content. However, the manufacturer’s lot certificate remains the only authoritative source for the exact tensile modulus, melt flow rate, and heat distortion temperature. Published data for this specific INZEA F28 configuration are limited beyond the renewable carbon and compostability descriptors used by the supplier.

Rheological behaviour under shear in 25:1 L/D single-screw extrusion

On a 25:1 L/D single-screw extruder with a 40 mm diameter screw and a compression ratio of 2.5:1 to 3:1, the compound should be processed with a flat or slightly reverse temperature profile from 170 °C at the feed throat to 190-210 °C at the metering zone and die. PLA-based melts exhibit shear-thinning behaviour; apparent viscosity can range from 200 Pa·s to 800 Pa·s at shear rates of 100-1 000 s⁻¹ depending on molecular weight, temperature, and moisture. Higher melt temperatures above 220 °C accelerate thermal degradation, increasing lactide reformation and shifting molecular weight distribution downward. Melt-pressure instability at the die above ±1.5 MPa typically indicates moisture contamination, degraded regrind, or insufficient back pressure.

Vented barrel operation is not a substitute for drying. At 0.25 wt% moisture, PLA undergoes hydrolytic chain scission during plastication; intrinsic viscosity can fall by 0.2-0.4 dL/g in a single residence time at 210 °C, reducing melt strength and causing sheet-edge tear in extrusion lines. The use of a 40/80/40 mesh screen pack is common, but pressure drop across the screen should not exceed 10 MPa at 210 °C.

Capillary rheometry data for unplasticized PLA at 190 °C show shear viscosity decreasing from approximately 1 200 Pa·s at 10 s⁻¹ to 200 Pa·s at 1 000 s⁻¹. Die design should avoid high shear regions, sharp corners, and long flow paths. Melt pressure may be higher than in semi-crystalline polyolefins with similar melt flow index, so injection pressure should be established from short-shot studies rather than from polypropylene reference settings.

Injection molding trials on 800-1 200 kN clamp-force machines have used barrel temperatures of 190-215 °C, mold temperatures of 20-30 °C for amorphous parts, and 90-110 °C for crystallized parts. Back pressure of 5-15 bar and screw rotation speeds of 60-120 min⁻¹ are adequate to maintain melt homogeneity without excessive shear heating. Pack pressure is typically set at 60-80% of injection pressure, with hold times of 3-6 s for thin-wall parts of 1.5-2.5 mm wall thickness. When the mold temperature is raised above 90 °C, cycle time increases by 15-30% because the part must be cooled below the heat deflection temperature of approximately 55 °C before ejection to avoid distortion. Hot-runner systems with valve gates are preferred over cold-runner sprues for this shear-sensitive material when runner scrap cannot be immediately dried and reused.

Field observations on production-scale injection molding of rigid PLA compounds indicate that cold slug wells, sharp runner bends, and undersized gates below 0.8 mm for thin-wall parts can increase shear heating and cause silver streaks, particularly if regrind above 20% is used without re-drying. The gate should be located in thickened sections to reduce jetting; a gate land length of 0.5-1.0 mm is typical.

When residual moisture exceeds 0.025 wt% prior to melt processing

Desiccant-bed or molecular-sieve drying is required. The recommended drying condition for rigid PLA compounds without mineral fillers is 80 °C for 4 h to reach a dew point of -40 °C or lower in the return air. Target residual moisture is ≤0.025 wt% (250 ppm). In plant environments above 60% RH, undried pellets can equilibrate above 0.25 wt% within 1-2 h after bag opening; hydrolysis then proceeds rapidly during plastication. Moisture analyzers using loss-on-drying at 105 °C may overestimate water content in PLA because lactide and low-molecular-weight degradation products volatilize; Karl Fischer coulometric titration at 160 °C is more accurate for moisture levels below 500 ppm.

The operational boundary is therefore not the resin’s drying specification alone but the plant’s material-handling configuration. Central vacuum conveying with unheated hoppers can reintroduce ambient moisture in humid weather. A heated hopper or insulated receiver is required when the ambient dew point exceeds 10 °C. If the melt pressure vibration is above ±1.0 MPa or the extrudate has surface roughness, drying should be extended rather than compensated by raising melt temperature, which increases degradation.

During compounding on a co-rotating twin-screw extruder with an L/D ratio of 40:1 to 44:1, the PLA base resin should be introduced in the main feed, with heat-sensitive nucleating agents or peroxide-based chain extenders fed downstream into a side feeder or liquid injection port to minimize residence time. Addition of amine-based lubricants or certain amide slip agents can promote transesterification or degradation and should be avoided unless specifically tested. Flame-retardant additives containing phosphoric acid derivatives can also reduce molecular weight if compounded above 210 °C. The compound should not be purged with PVC or acetal residues; acidic residues from PVC decomposition initiate PLA hydrolysis. Equipment should be purged with a low-MFI polypropylene or a dedicated PLA purge grade before shutdown to reduce carbonized material in the barrel.

Reclaim and regrind use is possible up to 20% in injection molding when the regrind has been dried to ≤0.025 wt% moisture and is free of dust and fines above 0.5 mm. Repeated regrind cycles lower intrinsic viscosity; after three cycles, the melt flow rate can increase and screw recovery time may fall, indicating molecular weight loss. This operational boundary is typical for rigid PLA compounds and should be confirmed on the production line by monitoring melt pressure and part weight stability.

Compostability certification boundaries for this rigid grade

Compostability under EN 13432:2000 requires aerobic biodegradation of at least 90% relative to a suitable reference material within 180 days under ISO 14855-1:2012 conditions. Disintegration requires 90% of the mass of test material to pass a 2 mm sieve after 12 weeks in a controlled composting test per ISO 16929:2021 or equivalent. The ecotoxicity assessment follows OECD 208 or equivalent, comparing plant germination and growth in compost containing the test material against blank compost. Heavy metal limits are specified in EN 13432:2000 Annex A, with values below 150 mg/kg for lead, 0.7 mg/kg for mercury, and 50 mg/kg for chromium VI, among others.

For the U.S. market, ASTM D6400-23 aligns with these criteria through biodegradation, disintegration, and ecotoxicity testing. A certification mark is not a guarantee of home compostability; most certifications apply only to industrial composting facilities operating at 58 °C for a sustained thermophilic phase. The product’s renewable carbon fraction is measured separately by ASTM D6866-21 Method B and does not by itself demonstrate compostability.

For food-contact use, the grade should be evaluated under EU Regulation 10/2011 as amended, particularly with respect to overall migration into simulant A, B, C, D1, or D2 according to EN 1186-1:2002 migration test methods. The presence of lactic acid as a hydrolysis product may reduce pH in high-moisture simulants; migration of monomers and additives must not exceed the applicable overall migration limit of 10 mg/dm² for food contact materials under EU Regulation 10/2011. For the U.S., FDA food-contact status should be confirmed by the supplier under applicable food contact notifications or 21 CFR clearances specific to polylactic acid; the user should not assume compliance from compostability certification alone.

This grade is not suitable for prolonged contact with strong acids or alkalis, as PLA undergoes bulk hydrolysis. At pH 2 and 60 °C, the rate of molecular weight degradation is significantly higher than at neutral pH; in alkaline conditions above pH 10, surface erosion may occur within 24-72 h. These operational boundaries are inherent to aliphatic polyester chemistry and apply to PLA-based compounds regardless of renewable carbon content.

Outdoor exposure is limited by UV-induced chain scission and embrittlement. Without UV stabilizer packages, rigid PLA compounds can lose more than 50% of initial tensile strength after 500-1 000 h of accelerated weathering under ISO 4892-2 cycle 1. Parts requiring outdoor service should be formulated with hindered amine light stabilizers and UV absorbers, but such additives may fall outside the original compostability certification and must be revalidated under EN 13432:2000.

In comparison to other INZEA compostable grades designed for film, thermoforming, or injection molding, the “Rigid” designation signals a compositional boundary: the material is not plasticized to achieve film flexibility. Therefore, it should not be evaluated as a drop-in replacement for compostable PBAT-based film resins, which may display tensile elongation above 300% and tensile strength below 30 MPa under ISO 527-3. Conversely, the rigid grade is expected to show tensile strength above 45 MPa and elongation below 5%, placing it closer to polystyrene in mechanical behaviour while retaining compostability.

The main application difference between this grade and standard petroleum-based rigid resins such as GPPS or PET is the thermal boundary. GPPS can be used continuously at 70-80 °C without distortion, whereas amorphous PLA compounds soften near 55-60 °C. The compostable rigid grade therefore is most suited to cold-fill packaging, cutlery, trays, inserts, cosmetic applicators, and single-use medical training devices where industrial compostability is required. In injection-molded cutlery, the use of 2-5% talc or highly nucleated PLA can raise cycle speed and stiffness but may reduce biodegradation to below the 90% threshold if filler content is too high; the formulator must hold the mineral filler within the certified formulation boundary.

Compared with certified compostable flexible film grades, this rigid grade lacks the high elongation and tear propagation resistance required for thin gauge film below 50 μm. It should not be used for blown film unless the supplier explicitly lists film extrusion as a validated process. It also has lower impact strength than petroleum-based polypropylene, with unnotched Charpy impact values in rigid PLA compounds typically below 25 kJ/m² per ISO 179-1:2020. Notched Charpy values commonly fall below 4 kJ/m², so impact-dominated applications require design measures rather than material modification.

Extensional viscosity and melt strength are lower than for PET, limiting draw-down in deep-draw thermoforming. For sheet extrusion, a polished three-roll stack at 40-60 °C is used to cool without crystallizing the sheet. Amorphous sheet below 500 μm can be thermoformed at 80-100 °C with an infrared oven; above 100 °C, the sheet may sag excessively and lose plug-assist control. Crystallized sheet requires higher forming temperatures and is not generally used for high-clarity applications.