INZEA F13C is a compostable polylactic acid grade supplied in pellet form for blown film extrusion and paper or paperboard coating where industrial compostability is required. The product is specified with a density of 1.24 g/cm³ when measured according to ISO 1183-1:2019, and a melt flow rate of 6 g/10 min at 190 °C under a 2.16 kg load when tested according to ISO 1133-1:2022. These properties place it in the medium-viscosity range for extrusion coating, requiring controlled pre-drying before processing. As-supplied moisture content is normally below 0.25%, but the material must be dried to below 0.025% residual moisture to avoid hydrolytic molecular-weight loss during extrusion. The supplier-recommended drying condition is 70 °C for 4 h in a desiccant dryer with a dew point of -40 °C or lower.

The primary application envelope for INZEA F13C is the replacement of petroleum-based extrusion-coating layers on kraft paper, folding carton board, and compostable film structures. In blown film converting, the grade is used for tubes, liners, and compostable packaging films in which stiffness, surface gloss, and renewable carbon content are specified. The material is not a drop-in replacement for LDPE on high-speed coating lines; its processing window is narrower and its melt temperature must be controlled within a defined band. Published data for the exact neck-in and drawdown limits of F13C on specific coaters is limited, so pilot-scale qualification is required before production line escalation.

What prevents unmodified PLA from running on high-speed paper-coating lines?

Unmodified PLA frequently fails in extrusion coating because the polymer melt exhibits low extensional viscosity. In the air gap between the coating die and the chill roll, the molten curtain is stretched at high strain rates. If the extensional response is insufficient, the curtain edges taper inward, producing neck-in and edge-bead variation. Unmodified PLA grades with melt flow rates above 10 g/10 min at 190 °C are particularly prone to curtain sagging at line speeds above 80 m/min on dies wider than 1000 mm. INZEA F13C is differentiated by a formulation that shifts the low-frequency melt elasticity upward without increasing the melt flow rate beyond 6 g/10 min. This is observable in capillary rheometry as increased melt tensile force at 190 °C and in oscillatory shear as a higher storage modulus between 0.1 rad/s and 1 rad/s. The modification is proprietary, but F13C remains a polylactic acid product and should not be assumed to contain PBAT as a dominant modifier.

For coating operations, the die gap is typically set at 0.5–0.7 mm, and the air gap is maintained between 150 mm and 250 mm. A shorter air gap improves adhesion to corona-treated paper but reduces the time available for melt-curtain stability. Chill roll temperature is held at 15–25 °C. At these settings, F13C-coated paper can be produced at coating weights of 15–30 g/m². The resulting coating contributes stiffness, heat-seal response, and compostability, but it does not provide the water-vapour or oxygen barrier of metallised film or high-barrier dispersion coatings.

Extrusion equipment configuration for blown film conversion

F13C blown film processing requires a single-screw extruder with an L/D ratio of at least 30:1 and a compression ratio between 2.5:1 and 3.0:1. A barrier screw with a metering section designed for medium-viscosity polyester melts is preferable. Barrel temperatures are profiled from 170 °C in the feed zone to 190 °C in the metering zone. The die temperature is held at 195–205 °C. Melt temperature must not exceed 210 °C. Above 220 °C, polylactic acid undergoes accelerated unzipping and lactide reformation; the volatile lactide deposits on die lips and destabilises bubble geometry.

The die gap in blown film is set between 1.0 mm and 1.2 mm, and the blow-up ratio is limited to 2.0:1–3.0:1. Frost line height should be maintained between 2 and 4 die diameters. Higher frost lines increase haze and reduce dart drop resistance because the oriented PLA network is not relaxed sufficiently before crystallisation. Melt residence time should remain below 10 min. When bubble instability occurs, the first corrective action is to lower the melt temperature and verify that residual moisture is below 0.025%, rather than increasing blow-up ratio or frost line height.

Batch-to-batch variation in moisture content is a significant converting bottleneck. If pellets are stored at relative humidity above 60%, surface moisture increases rapidly and the bubble exhibits edge tear and audible popping. Inline moisture analysers on the feed throat or vacuum vent are recommended. Edge-trim regrind should not exceed 20% of the feed stream unless the regrind is dried and the melt-viscosity variation is monitored by melt-pressure fluctuation.

When paper or paperboard replaces polyethylene in extrusion coating

Substitution of an LDPE extrusion-coating layer with F13C changes the thermal profile, the sealing window, and the mechanical response of the coated sheet. F13C has a glass transition temperature of 55–60 °C and a sharp melting endotherm between 150 °C and 160 °C. LDPE, by comparison, has a broad melting range and elongates beyond 300% before failure. The PLA coating therefore heat-seals at jaw temperatures of 130–150 °C on intermittent sealers, but the hot-tack window is narrower than that of LDPE. Hot-tack evaluation should be performed according to ASTM F1921-18 before vertical form-fill-seal conversion is transferred from LDPE.

The tensile modulus of F13C is in the range of 3200–3600 MPa, which is higher than common PBAT-modified compostable compounds. This increases paperboard bending resistance and produces a crisper coating surface. However, elongation at break remains below 10%, so the coating does not provide puncture toughness in produce bags or stretch-film applications. PBAT-rich compounds with elongation above 300% remain preferable where high deformation tolerance is required. F13C is selected when stiffness, surface cleanliness, and compostability dominate the specification.

Corona treatment of the paper or board surface is required before the molten PLA web contacts the substrate. The recommended wetting tension is 40–46 dyn/cm. Without inline corona, adhesion to sized kraft paper is inconsistent, and the coating peels under flexographic printing or creasing. The coated surface itself has a surface energy of approximately 38–42 mN/m; water-based inks and cold-seal adhesives require additional corona or primer treatment at the converter.

Compostability certification and food-contact status

Compostability claims for INZEA F13C are supported by testing under EN 13432:2000 and ASTM D6400-23. The material is intended for industrial aerobic composting systems with sustained thermophilic conditions above 58 °C. Disintegration is assessed according to ISO 16929:2021 and ISO 20200:2015. Aerobic biodegradation is measured by ISO 14855-1:2012 or ASTM D5338-15, with a threshold of 90% biodegradation relative to a cellulose reference within 180 days. Home composting certification should not be assumed for PLA-based films because degradation below 30 °C is substantially slower.

Food-contact documentation is typically available under EU 10/2011 and FDA 21 CFR 175.300. However, the final multilayer paper structure must be migration-tested at the finished coating weight because low-molecular-weight lactide and coating additives can migrate into food simulants. Migration testing under EU 10/2011 with 3% acetic acid and 10% ethanol simulants is recommended for acidic and aqueous-fatty food contact. REACH compliance is managed under Regulation (EC) 1907/2006; the polymer itself is exempt from registration under Article 2(9), but monomer and additive components require registration.

Moisture uptake above 0.025% hydrolyzes PLA within the barrel

The critical process boundary for F13C is residual moisture. At melt temperature, water hydrolyzes the polyester backbone and reduces molecular weight within seconds. A moisture content above 0.025% produces brittle film, edge tear, and a measurable drop in melt pressure at constant screw speed. The same failure occurs when the material is exposed to ambient air above 60% relative humidity after drying. Therefore, dried pellets should be conveyed to the feed throat with dried-air or vacuum loading, and hopper residence time should be limited.

F13C is incompatible with amine-based additives, high-pH fillers, and peroxide concentrates. Alkaline conditions catalyse chain scission during extrusion. Acidic or neutral processing aids are preferable when slip or antiblock is required. The material should not be purged with LDPE or PP at high temperatures unless the PLA is fully displaced, because mixed polymer residues form brittle gels and die drips. As a final operational boundary, the melt should not remain above 210 °C for more than 10 min. Exceeding this condition generates lactide vapour and accelerates molecular-weight loss even when the polymer is dry.