Bio-Flex F 1814 is a translucent blown film compound based on polylactic acid (PLA) and a biodegradable copolyester minor phase, distributed under the Bio-Flex trade name by FKuR Kunststoff GmbH. The grade is intended for tubular film extrusion at finished film thicknesses from 15 µm to 80 µm and is positioned for flexible packaging, organic waste collection bags, and agricultural films where industrial compostability is required. Melt flow rate measured per ISO 1133-1:2022 at 190°C/2.16 kg is typically 3.5 g/10 min. Density determined per ISO 1183-1:2019 is 1.24 g/cm³. Industrial compostability certification under EN 13432:2000 requires ≥90% biodegradation by organic carbon conversion within 180 days, ≥90% disintegration to fragments <2 mm within 12 weeks, and no adverse effects in the specified ecotoxicity test series. The recyclability claim is limited to closed-loop post-industrial recovery in dedicated PLA or PLA-blend streams; commingling with polyolefins or polyethylene terephthalate in the melt is incompatible and should be excluded during regranulation because phase separation reduces the mechanical continuity of the regrind.

The material is not designed for direct long-term food contact unless article-specific migration testing under Regulation (EU) No 10/2011 is completed, because PLA oligomers and copolyester degradation products may migrate at elevated temperature or in fatty simulants. Continuous service above 50°C is also not recommended, as the PLA phase undergoes cold crystallization, reducing clarity and increasing brittleness.

How Does the Copolyester Modifier Shift the Mechanical Failure Envelope Compared with Unmodified PLA?

Unmodified PLA blown film typically fails in tensile elongation between 5% and 10% under ISO 527-3, with machine-direction Elmendorf tear propagation below 10 N/mm. The copolyester modifier in F 1814 disrupts PLA crystallinity and creates a dispersed rubber-like phase that cavitates under stress. As a result, film at 30 µm thickness conditioned at 23°C and 50% RH exhibits tensile elongation at break above 300%, tensile strength at yield between 22 MPa and 26 MPa, and a secant modulus of 1,400–1,800 MPa when tested per ISO 527-3. Dart impact F50 determined per ASTM D1709 Method A is typically 400–600 g at 30 µm, compared with 80–150 g for unmodified PLA film of the same gauge. The shift from brittle fracture to ductile tearing is also evident in trouser tear testing; tear propagation resistance per ISO 6383-2 reaches 12–15 N/mm in the machine direction and 15–20 N/mm in the transverse direction.

This modification reduces tensile modulus and yield strength relative to high-crystallinity PLA, which is the principal trade-off. Flexural modulus measured on injection-moulded test specimens per ISO 178 is 2,100 MPa, Charpy notched impact at 23°C per ISO 179-1 is 8 kJ/m², and Vicat softening temperature A120 per ISO 306 is 55°C. The comparatively low Vicat temperature reflects the low-temperature flexibility imparted by the copolyester phase and imposes an upper service boundary for warm-fill packaging.

Translucency is retained because the copolyester domains are small enough to avoid strong visible scattering. Wide-angle haze at 50 µm per ASTM D1003 is typically 15–20%, and total luminous transmittance per ISO 13468-2 is 88–92%. These optical values are not water-clear PLA values, but they are sufficient for printed film where back-side graphics remain visible. The property set is summarized in the following representative datasheet values; these are typical values, not specification limits.

For blown film mechanical data, direction-dependent values should be used rather than isotropic injection-moulded data. Machine-direction elongation is typically 350–450% and transverse-direction elongation 500–600%, while tensile strength at break decreases from 30 MPa in the machine direction to 25 MPa in the transverse direction. The anisotropic spread is controlled by blow-up ratio and frost line positioning and becomes wider above BUR 4:1.

Moisture Uptake, Hydrolytic Chain Scission, and Extruder Pre-Drying Requirements

At equilibrium with 50% RH and 23°C, PLA-based granules can reach 0.4 wt% moisture. Residual moisture above 0.02 wt% at processing temperature causes hydrolytic chain scission of the PLA ester linkages, leading to molecular weight loss, melt strength reduction, and pinhole clusters in the finished film. Field observations from 45 mm single-screw blown film lines with 30:1 L/D barrier screws show that wet granules produce melt fracture at the die lip and a 10–20% reduction in bubble tear resistance; the same lines recover stable gauge when the granulate is dried to ≤0.02 wt%.

Desiccant drying is mandatory for opened bags and material stored at ambient humidity. The practical drying envelope is 70–80°C for 4–6 h with a desiccant dryer air dew point ≤-40°C. Drying above 85°C or beyond 12 h can cause granulate sticking and should be avoided. The extruder should use a moderate-shear screw with compression ratio 2.5:1–3.0:1; higher compression ratios above 3.5:1 generate excessive viscous heating. Melt filtration with a 40/60/80 mesh screen pack is typical, but the pressure before the screen pack should not exceed 180 bar because prolonged residence time in the adapter accelerates gel formation and black specks.

On a 45 mm extruder, screw speed above 120 rpm increases shear heating and reduces melt pressure. If the melt temperature exceeds 200°C, the polymer begins to generate thermal degradation products that reduce translucency and increase odour. Edge trim and start-up purge generated during such excursions should be isolated from reprocessable regrind.

When Screw Speed and Melt Temperature Exceed the Stable Blown Film Window

When melt temperature is held below 175°C, the viscosity of F 1814 remains high enough to cause bubble neck-in and low-frequency chatter. Above 195°C, thermal thinning produces gauge bands and bubble sag. The usable melt temperature window is therefore approximately 20°C wide, narrower than the 40–60°C window typical of LDPE on the same blown film line. A barrel profile of 150°C at the feed throat increasing to 185°C at the die is a practical starting point; melt temperature measured at the die exit with an infrared probe should remain between 175°C and 190°C.

Die gap of 0.8–1.2 mm and blow-up ratio of 2.5:1–3.5:1 provide sufficient transverse orientation without destabilizing the frost line. The frost line should be positioned 80–150 mm above the die face. Internal bubble cooling air conditioned to 10–15°C and aligned collapsing frames reduce gauge variation to ±10% at 30 µm. For lines with manual die lip adjustment, the higher viscosity of the PLA blend at the die lip requires a wider die gap than LDPE; die gaps below 0.8 mm create excessive shear heating at commercial output rates, while die gaps above 1.2 mm reduce transverse orientation and increase haze.

Capillary rheometry per ISO 11443:2021 at 190°C gives an apparent shear viscosity of 900–1,200 Pa·s at 100 s⁻¹ and 250–400 Pa·s at 1,000 s⁻¹. The pronounced shear thinning maintains bubble stability at the die but requires close melt temperature control because the activation energy for viscous flow of PLA at these shear rates is approximately 70–80 kJ/mol. A 5°C temperature shift can therefore alter viscosity by 15–20%.

Edge trim and post-industrial scrap may be reprocessed in the same film line if the regrind is dried to ≤0.02 wt% moisture and the addition level does not exceed 20 wt%. At addition levels above 30 wt%, gel counts and haze increase because the repeated thermal history degrades the copolyester phase. Granules stored in sealed moisture-barrier bags at 10–30°C retain processing stability for 12 months from the production date; opened bags should be re-dried before use. Published data for post-consumer recyclate retention rates in mixed PLA/PBAT mechanical recycling streams is limited; closed-loop trials should be conducted on the specific washing and regranulation line before post-consumer content is incorporated.

Film intended for organic waste collection and short-cycle retail packaging forms the primary application envelope for F 1814. At 30 µm, water vapour transmission rate per ISO 15106-2 is approximately 120 g/(m²·d) at 23°C and 85% RH, and oxygen transmission rate per ISO 15105-1 is 700 cm³/(m²·d·bar) at 23°C and 0% RH. These permeation values are higher than those of polyethylene and should be considered when designing respiring produce packaging or organic waste bags. Direct contact with alcohols, chlorinated solvents, or moist heat above 60°C is not recommended because PLA ester linkages are susceptible to alcoholysis and hydrolytic attack.

The differentiation from unmodified PLA is defined by the copolyester phase, which increases elongation and tear resistance while reducing modulus and tensile yield strength. Against starch-containing PLA compounds, F 1814 avoids the moisture uptake and viscosity variability associated with starch degradation at high processing temperatures. Against PBAT-rich flexible blown film grades, F 1814 contains a higher PLA fraction, providing higher stiffness and lower melt strength at equivalent film gauge.

For film structures requiring lamination or printing, corona treatment should be applied immediately after the collapsing frame because surface energy decays from 42 mN/m to 36 mN/m within 24 h at 50% RH. Slot-die coating with water-based primers is preferred over solvent-based adhesives because solvent absorption can swell the copolyester phase and reduce interlayer adhesion.