Bio-Flex S 5630 Injection Molding Biodegradable PLA Blend is a polylactic acid–based polyester compound formulated for melt processing on standard reciprocating-screw injection molding machines. The grade belongs to the Bio-Flex family and is intended for rigid, short-cycle molded articles that require industrial compostability. Public datasheet values place density near 1.25 g/cm³ under ISO 1183-1:2019 and melt flow rate in the 15–30 g/10 min range at 190 °C/2.16 kg when tested to ISO 1133-1:2022. The material therefore occupies a low-to-medium flow segment that allows filling of thin-wall geometries with nominal wall stock between 1.0 mm and 2.5 mm without the excessive gate pressure characteristic of high-molecular-weight PLA film grades. The compound is supplied as cylindrical granules, is compatible with conventional single-screw recovery units, and is differentiated from unmodified PLA homopolymer by a balance of stiffness, processability, and reduced notch sensitivity in molded parts.

When Residual Moisture Exceeds 0.025 % in PLA Blends

Moisture control is the primary processing risk for Bio-Flex S 5630. Because the polyester backbone is hydrolytically unstable at melt temperatures above 180 °C, free water in the granulate accelerates chain scission. The result on production equipment is a batch-to-batch shift in melt viscosity, lower weld-line strength, gas splay on cavity surfaces, and reduced tensile elongation at break. Desiccant-wheel dryers with a supply dew point of -40 °C or lower and an insulated stainless-steel hopper are specified. Manufacturer processing guidance for PLA compounds typically recommends drying at 80 °C for 2–4 h until residual moisture falls below 0.025 % by weight, measured by Karl Fischer titration under ISO 15512:2019. Hot-air tray dryers are not recommended because they cannot achieve a sufficiently low dew point in high-humidity production rooms.

At relative humidity above 60 %, dried granulate should not remain exposed in an open hopper for more than 30 min unless the hopper is continuously purged with dry air at a dew point of -40 °C. Failure to observe this boundary produces visible silver streaks and reduced melt strength; in multicavity tools the defect first appears in the cavity farthest from the sprue. The same moisture limit applies to regrind. Sprues and runners should be collected in sealed containers immediately after ejection and should not be left on open shop-floor containers. Published hydrolysis rate constants for this specific S 5630 formulation are limited, so the residual moisture limit should not be extrapolated from neat PLA and should be verified on the target production press if high regrind fractions are used.

Batch-to-batch variation in moisture content also affects cushion stability. In production-scale trials on general-purpose machines with 20:1–25:1 L/D three-zone screws, a moisture change of 0.01 % can shift the observed melt flow rate by several grams per 10 minutes and alter the screw recovery time. Closed-loop molding therefore requires that dryer outlet moisture be logged and that the injection unit maintain a stable shot-to-shot cushion. The transfer from holding pressure to screw rotation should occur only after the cushion has been secured; otherwise the check ring tends to leak in low-viscosity portions of the molten blend.

What Limits the Melt Temperature Window in Thin-Wall Parts?

The practical melt-temperature window for Bio-Flex S 5630 is constrained by two competing failure modes. At melt temperatures below 180 °C, the viscosity is too high for complete filling of ribs, bosses, and snap-fit hooks; injection pressure rises sharply, and flow marks appear in laminar flow fronts. At melt temperatures above 210 °C, thermal degradation of the PLA phase accelerates. Residence time at 220–230 °C should not exceed 3 min in the barrel; above 240 °C, the melt can generate lactide monomer and exhibit a burnt-sugar odor. Therefore the recommended melt temperature is 190–205 °C, with an outer tolerance of ±5 °C for closed-loop controls. The narrow tolerance is necessary because thin-wall parts freeze rapidly at the gate, and any viscosity excursion changes the short-shot threshold before barrel temperature alarms are triggered.

Mold temperature is set between 15 °C and 40 °C. Chilled water at 10–15 °C is used for rapid solidification, but overcooling below 10 °C can cause condensation on the tool surface and surface blush. For parts with wall sections below 1.0 mm, injection velocity should be raised to fill the cavity before the melt freezes at the gate. Screw-forward time and holding pressure should be set so that gate freeze occurs within 1–2 s at a 2.0 mm wall and a 1.5 mm diameter edge gate. If gate freeze occurs too early, the part exhibits sink marks and post-mold shrinkage; if gate freeze is too late, the runner remains soft and cycle time increases without mechanical property benefit.

Screw, Gate, and Mold Design Requirements

A three-zone general-purpose screw with a compression ratio of 2.0:1–2.5:1 and a check ring free of dead spots is recommended. Excessive compression can over-shear the blend and reduce impact strength at the weld line. The feed throat should be cooled to prevent pellet bridging; the barrel front zone should be fitted with a shut-off nozzle because the melt can drool at low back pressure. Hot-runner systems can be used, but the manifold should have no stagnant areas and should be equipped with individually controlled nozzles. Gate locations should be placed to minimize weld lines in areas subject to bending; for snap-fit fingers, a single edge gate at the base of the finger is preferred over a center gate that directs the weld line into the flexure point.

Mold shrinkage is typically 0.3–0.6 % depending on wall thickness, gate orientation, and holding pressure. Shrinkage measurements should be made after 24 h at 23 °C/50 % RH before committing to production tooling. The material does not require high mold polish; a VDI 24 to VDI 30 cavity surface is usually sufficient for release, but undercut features should use ejection angles of at least 0.5° per side. For cylindrical parts, core pins should be cooled independently because the low melt temperature leaves a thick frozen layer that can distort thin steel sections if cooling is unbalanced.

Density and mechanical values reported for Bio-Flex S 5630 are summarized below. These are typical dry-as-molded values from public datasheets, not batch guarantees. Property retention in molded parts depends on moisture content, weld-line position, and regrind level.

Mechanical property translation to part performance is not linear. The tensile modulus near 3,500 MPa indicates that thin-walled parts will be stiff under short-term loading but will remain notch-sensitive. Weld lines in fiber-free PLA blends generally retain less than 50 % of the base tensile strength; therefore, gate positions must be shifted to move weld lines away from snap-fit flexure zones. Creep resistance is poor at temperatures above the Vicat A value; parts under continuous stress should be designed with maximum strain below 0.5 %. The notched Charpy values place S 5630 below ABS and polycarbonate in impact resistance, so sharp internal corners, molded-in stresses, and uncontrolled regrind addition are common causes of field cracking.

The Compostability Standard Chain Is Not a Single Test

Bio-Flex S 5630 is differentiated from non-degradable polypropylene and high-impact polystyrene by its certification under EN 13432:2000 for industrial composting. This standard requires at least 90 % biodegradation in a controlled aerobic composting environment within 6 months, disintegration measured under ISO 16929:2021, and absence of ecotoxicity according to OECD 208. It is not, however, a soil-biodegradable or marine-biodegradable grade; those end-of-life routes do not provide the thermophilic microbial activity required for disintegration. The material is also not autoclavable and should not be used for packaging that requires retort sterilization.

The compliance chain includes ISO 14855-1:2012 for ultimate aerobic biodegradability under controlled composting conditions. The test reports for this product family are based on a specific granulate batch and should not be interpreted as a guarantee that every molded part will disintegrate at the same rate. Part thickness, fillers, printing inks, and adhesives can delay disintegration if the article does not achieve the required surface-area-to-volume ratio. Industrial composters that screen fragments above 10 mm may retain thick molded parts longer than the 12-week disintegration window in the standard.

Compared with Bio-Flex F-series film-extrusion grades, S 5630 has a higher melt flow rate, a narrower molecular-weight distribution, and a stiffer tensile response. Film grades are plasticized or high-molecular-weight versions that maintain bubble stability and machine-direction elongation; those properties are undesirable in injection molding because they increase cycle time, drool, and post-mold warpage. Conversely, S 5630 would fail in blown-film processes because low melt strength and high neck-in produce gauge variability beyond practical limits. The product should therefore be selected only when the conversion route is injection molding or injection stretch blow molding with short residence times.

Relative to starch-rich thermoplastic starch blends, S 5630 has lower equilibrium moisture uptake, higher flexural modulus, and better dimensional stability in dry indoor environments. However, it retains a polyester backbone, so it is more sensitive to aqueous acids and alkalis than polyolefins. It also has a lower continuous service temperature than talc-filled polypropylene; sustained exposure above 50 °C under mechanical load may cause creep. Applications such as under-hood automotive parts, microwaveable trays, or exterior structural components are outside the operational envelope of this grade.

Injection unit data recorded on general-purpose machines with 20:1–25:1 L/D three-zone screws indicate that reverse barrel temperature profiles are rarely required. A practical barrel set-up is 160 °C in the feed zone, 180–190 °C in the compression zone, and 190–205 °C in the metering zone. Back pressure is typically held between 5 bar and 15 bar hydraulic; screw speed should not exceed 150 min⁻¹ unless the screw is specifically designed for low-shear PLA processing. The material is sheared by the screw at a rate that can generate frictional heat; therefore, screw recovery time is a more reliable set-point than barrel setpoint alone. Consistent shot-to-shot recovery variation below 0.1 s is generally required for stable cushion.

Processing boundaries must be communicated to tooling engineers before mold construction. The grade should not be purged with polyamide or polyethylene terephthalate at melt temperatures above 280 °C; residual nylon in the barrel can degrade the PLA phase and cause black specks. Regrind from sprues and runners may be used up to 20 wt% without drying if it is collected and sealed immediately; higher regrind levels or mixed-color scrap require re-drying and raise lot-to-lot viscosity variation. Incompatibility with amine-based processing aids or flame-retardant masterbatches containing strong alkalinity should be verified by thermal stability testing before production. Published data for this specific formulation in multi-shot overmolding is limited; therefore, trials on the target production press are required.