Bio-Flex N 45261 is a polylactide (PLA) injection molding compound supplied by FKuR Kunststoff GmbH for rigid parts that require high bending stiffness at ambient temperature. The grade is supplied as cylindrical granulate and is processed on reciprocating-screw injection molding machines. Manufacturer-reported typical physical data include a density of 1.24 g/cm³ (ISO 1183-1) and a melt mass-flow rate of 10 g/10 min to 15 g/10 min at 190 °C under 2.16 kg load (ISO 1133-1:2022). The mechanical envelope is defined by a tensile modulus near 3500 MPa, a tensile stress at break near 60 MPa, and a tensile strain at break in the 3 % to 4 % range (ISO 527-2). These values place the compound in the high-stiffness segment of biopolymer injection materials, distinct from flexible PLA/co-polyester blends with tensile modulus below 2500 MPa. Typical applications include writing instruments, cosmetic packaging, office equipment housings, and thin-wall consumer articles that require renewable carbon content but do not require high notched impact strength or sustained heat resistance above ambient temperature.

Where the Grade Fits in the Bio-Flex N Family

Within the Bio-Flex portfolio, N-type grades are compounded for injection molding. S-type sheet and F-type film grades are lower-viscosity or higher-toughness formulations and are generally not interchangeable with N 45261. N 45261 is an unfilled, high-stiffness PLA compound. It does not incorporate mineral fibers or impact-modifying elastomers in significant concentration; therefore density remains near 1.24 g/cm³, while glass-filled PLA alternatives commonly exceed 1.35 g/cm³. The melt is pseudoplastic, and the processing window is narrower than that of polypropylene or ABS because melt temperature, moisture content, and residence time must be controlled together. Processors using open-loop barrel machines should instrument the nozzle and use a needle pyrometer to verify that the melt does not exceed 200 °C during normal cycling.

On a 600 kN hydraulic toggle-clamp machine with a 35 mm screw, shot weights between 40 % and 80 % of barrel capacity minimize residence time. Field experience on PLA injection compounds indicates that oversized barrels induce progressive yellowing and loss of weld-line strength even with correctly dried granulate. Published data for Bio-Flex N 45261 under oversized-barrel conditions is limited; processors should perform a residence-time study in which melt is held at 190 °C for 5 min, 10 min, and 15 min, then measure the melt mass-flow rate and visual color. A flow-rate increase greater than 15 % relative to fresh material suggests chain scission and requires a smaller barrel, lower nozzle temperature, or shorter cycle interruption.

Moisture, Melt Temperature, and Residence-Time Boundaries

Moisture content must be reduced to below 0.025 wt% (ISO 15512) before melting. The minimum equipment requirement is a desiccant dryer with air dew point not higher than -30 °C, drying temperature 80 °C, and residence time 2 h to 4 h. At 23 °C and 50 % relative humidity, PLA compounds can absorb water from the immediate environment. Opened bags should be consumed within 8 h when ambient humidity exceeds 60 %. Insufficient drying is the dominant production failure mode, presenting as silver streaks, splay, and a measurable drop in melt viscosity. If wet granulate reaches the melt zone, hydrolytic chain scission produces lower molecular weight fractions that reduce tensile strength and notched Charpy impact. The melt temperature measured at the nozzle should remain between 180 °C and 200 °C. On a 3-zone barrel, settings are commonly 165 °C to 175 °C in the rear zone, 175 °C to 185 °C in the center zone, and 185 °C to 195 °C in the front zone, with the nozzle set at 190 °C. Prolonged exposure above 210 °C accelerates depolymerization and lactide reformation; this is outside the processing boundary for this grade. Total residence time at 190 °C should not exceed 5 min, and hold-up points in hot-runner manifolds must be minimized.

Plastication should use a low-shear general-purpose screw with L/D 20:1 to 24:1 and compression ratio 2.5:1 to 3.0:1. Screw speed for a 35 mm screw is typically 80 rpm to 120 rpm; back pressure should be set between 50 bar and 100 bar. Higher back pressure increases melt homogeneity but also raises melt temperature. Purging with polypropylene or LDPE before shutdown prevents PLA from remaining in the barrel at elevated temperature. The non-return valve should be inspected frequently because PLA compounds can build up degraded material at dead spots, causing shot volume drift and intermittent gate freeze.

What Gate Dimensions and Shrinkage Values Should Be Used?

Gate design follows amorphous, unfilled polymer practice. For wall thicknesses between 1.5 mm and 3.0 mm, edge gates of 0.8 mm to 1.2 mm or pin gates of 0.6 mm to 1.0 mm are typical. Direct sprue gates should have a minimum diameter of 1.5 mm. Full-round runners of 4 mm to 6 mm are preferred over trapezoidal runners because they reduce pressure drop and shear heating. Venting depth should be 0.02 mm to 0.03 mm at the end of fill. Mold shrinkage is reported as 0.3 % to 0.6 % parallel to flow and up to 0.7 % transverse (ISO 294-4). Because the material is stiff and lower-ductility, internal corners should use a radius not less than 0.5 mm and wall thickness transitions should not exceed 1.5:1. For a 2 mm wall-thickness part, fill time should be 0.6 s to 1.2 s. Hold pressure should be 600 bar to 900 bar hydraulic and held for 0.5 s to 1.5 s per mm wall thickness after gate freeze. Cooling time depends on wall thickness and mold temperature; because the material is amorphous under standard molding conditions, it does not require crystallization time, but ejection temperature should remain below 50 °C to avoid distortion.

Color concentrate selection affects mechanical properties. Use a PLA-based carrier with melt flow rate close to the base resin; polyolefin carriers can form immiscible inclusions that reduce weld-line strength. A loading of 2 wt% to 4 wt% is typical. Liquid colorants may plasticize the matrix; tensile modulus should be re-verified according to ISO 527-2 on colored plaques because a drop greater than 5 % indicates carrier incompatibility. Weld lines should be moved away from load-bearing features. If a weld line cannot be avoided, an overflow tab or increased injection speed can improve local melt temperature. Weld-line tensile strength in unmodified PLA can be 60 % to 80 % of bulk tensile strength; the exact retention for N 45261 is not published and should be qualified on the production tool.

Representative Property Block Reported for Bio-Flex N 45261

The values below are manufacturer-reported typical values, not specification limits. Incoming inspection should establish internal lot-acceptance criteria based on critical-to-quality properties: melt mass-flow rate, tensile modulus, and Charpy notched impact.

How Does N 45261 Differ from Standard PLA and ABS?

Compared with unmodified PLA injection grades, N 45261 is positioned in a similar density and modulus range but is flow-adjusted for thin-wall molding. Compared with flexible Bio-Flex F-grade compounds or PLA/co-polyester blends, N 45261 has a tensile modulus approximately 1.5× to 2.0× higher and a tensile elongation at break roughly one order of magnitude lower. This makes it more suitable for rigid casings, caps, and structural ribs than for snap-fit arms or living hinges requiring large permanent deformation. Compared with mineral-filled PLA, N 45261 gives lower density and generally better surface gloss, but lower heat deflection temperature and lower flexural modulus. Compared with general-purpose ABS, N 45261 provides higher tensile stiffness at similar wall thickness but significantly lower notched impact strength and lower heat deflection temperature.

The comparative ABS values are typical orientation data and vary with comonomer content, rubber loading, and supplier. A direct replacement of ABS with N 45261 should not be made without testing finished-article impact and thermal performance under the relevant end-use conditions.

If High Heat Deflection Is Required, What Alternatives Should Be Evaluated?

At temperatures above 50 °C to 55 °C, the modulus of unfilled PLA declines and the part may distort under load. Post-molding annealing at 80 °C to 100 °C for 15 min to 60 min can increase crystallinity and raise HDT B to approximately 85 °C to 95 °C, but the process adds cycle cost and causes shrinkage that must be compensated in tooling. If sustained load at 85 °C or above is required, a mineral-filled PLA grade or a nucleated PLA compound should be evaluated. Published data for the annealed performance of this specific compound is limited; therefore annealing should be qualified with prototype tools using ISO 75-2 and ISO 75-1 conditions before production release.

Regulatory Documentation Cannot Substitute for Finished-Article Migration Testing

Bio-Flex N 45261 is generally considered suitable for industrial composting under EN 13432 when final part geometry and thickness meet the standard’s disintegration requirements. The standard requires 90 % disintegration after 12 weeks and 90 % ultimate biodegradation after 6 months; specific certificates should be requested for the current lot. The grade does not automatically imply home-compost certification; the presence of a TÜV Austria OK compost HOME mark should be confirmed separately. Food-contact use must be validated under EU Regulation 10/2011 or the relevant FDA 21 CFR condition on the finished article. Migration testing is required on the production part because pigments, mold release agents, and processing aids in the value chain affect compliance. REACH and RoHS 2011/65/EU heavy metal restrictions are generally addressed by the supplier, but a full material declaration should accompany each production shipment.