Fibrolon S 7530 is a natural fiber-reinforced polylactic acid compound supplied in granulate form for injection molding and profile extrusion. The nominal natural fiber content is approximately 30 wt%; the matrix is polylactic acid and the reinforcement is a lignocellulosic fiber dispersed during compounding. Published supplier data list density of 1.09–1.14 g/cm³ under ISO 1183-1:2019, tensile modulus of 3 800–4 600 MPa under ISO 527-2:2012, and tensile strength of 38–45 MPa at 23 °C and 50 % relative humidity. Elongation at break is commonly 2–4 %, flexural modulus is 3 600–4 300 MPa under ISO 178:2019, and flexural strength is 60–75 MPa. Notched Charpy impact strength is 4.5–7.0 kJ/m² under ISO 179-1:2020. Melt volume-flow rate is 5–10 cm³/10 min at 190 °C with a 2.16 kg load under ISO 1133-1:2022. Heat deflection temperature is typically 70–85 °C under ISO 75-2:2020 Method B. These properties place the grade as a rigid, dimensionally stable compound rather than an impact-modified or high-flow PLA.

Compared with unreinforced PLA injection grades, S 7530 exhibits lower mold shrinkage and lower warpage but sacrifices elongation at break. The fibrous phase reduces shrinkage after 24 h to 0.3–0.6 % in the flow direction and 0.5–1.0 % transverse, whereas unfilled PLA grades can show 0.7–1.2 % under equivalent conditions. Impact-modified PLA may exceed 20 kJ/m² notched Charpy, while S 7530 remains below 7.0 kJ/m². Compared with mineral-filled PLA, the density of S 7530 is lower by approximately 0.20–0.30 g/cm³ and the screw and barrel wear rate is lower because cellulosic fibers are less abrasive than silica or calcium carbonate fillers. Compared with short-glass PLA, the tensile modulus is lower, but the stiffness-to-density ratio can be comparable in thick sections. Typical downstream components include furniture edge-banding profiles, cable management channels, rigid packaging inserts, non-structural automotive interior trim, and housings with wall thickness of 2.0–4.0 mm. Production-scale use on injection molding machines with clamp forces from 500 kN to 3 000 kN is reported for this class; published data for this specific configuration is limited for hot-runner systems.

Does Fibrolon S 7530 retain the melt stability required for thin-wall injection?

Thin-wall injection requires melt temperatures of 175–190 °C and mold temperatures of 25–60 °C. At flow-length/wall-thickness ratios above 120:1, the material relies on shear thinning and a limited melt viscosity window at the metering zone. Injection pressures of 70–110 MPa are typical on hydraulic machines with screw compression ratio 2.0:1–2.4:1 and L/D 20:1–25:1. Screw rotation should be limited to 60–120 min⁻¹; higher speeds generate frictional temperature spikes above 200 °C. A screw-back position should maintain a 5–10 mm cushion, and back pressure of 5–10 MPa is used to homogenize fiber distribution. Gate freeze time is approximately 0.4 s per millimetre of gate diameter. The compound does not match the melt stability of nucleated or chain-extended PLA grades at very high shear; therefore, long hot-runner residence above 195 °C is not recommended.

Tooling for S 7530 should use polished round flow channels with a minimum radius of 2.0 mm. Vent depths of 0.02–0.03 mm at the cavity periphery reduce burn marks from moisture volatiles in parts with wall thickness below 2.0 mm. Weld line strength in fiber-filled PLA is typically 30–50 % lower than the bulk tensile strength under ISO 527-2:2012; gate locations should therefore be moved away from bosses and snap-fit features. Hot-runner manifolds should be internally heated and limited to 6 drops unless pressure balance is validated, because dead spots above 195 °C create black specks within 3 min.

For profile extrusion, a single-screw extruder with L/D 24:1–30:1 and a feed-zone cooling bore is preferred. A typical barrel temperature profile is 155/165/175/180 °C, with the die and adapter at 175–185 °C. The melt pressure before the screen pack should be limited to 15 MPa to avoid fiber compaction; a screen pack with 40/60/80 mesh is used only where surface quality requirements justify the pressure drop. Die land ratios are usually reduced by 10–20 % relative to unfilled PLA because the fiber-filled melt has different die swell. Calibration vacuum is typically 0.05–0.15 MPa differential; closed hollow profiles require dry calibration after 300–500 mm of cooling length. Published data for this specific configuration is limited, but instrumented profile extrusion of this grade follows the same calibration envelope as other natural fiber PLA compounds.

Thermal Degradation and Moisture Uptake Boundary

Two critical boundaries control processing. The first is thermal oxidation and Maillard-type browning of lignocellulosic fiber. Sustained melt or die temperatures above 200 °C produce visible discoloration within 3–5 min; residence time beyond 5 min generates volatile fatty acids and surface defects. The nozzle temperature is therefore held within ±5 °C of the 180 °C setpoint. The second boundary is hydrolytic degradation. Pellets exposed to ambient relative humidity above 60 % can pick up surface moisture within 30 min; desiccant drying at 80 °C for 4 h to residual moisture below 250 ppm is mandatory. Residual moisture above 0.025 wt% reduces melt viscosity, causes injection screw slip, and creates splay at the gate. Alkaline purge compounds and amine-containing color masterbatches are incompatible because they catalyze PLA chain scission and yellowing of the natural fiber fraction.

Incoming granulate should be checked for bulk density and residual moisture before loading. Bulk density variation above ±0.03 g/cm³ may indicate fiber agglomeration, requiring hopper agitation or reduced screw speed. If pellet surface moisture exceeds 0.15 wt%, drying time should be extended to 6 h at 80 °C. The dryer must deliver a dew point below −40 °C, because unsaturated hot-air ovens are insufficient for PLA hydrolysis control.

Compared with polyolefin-based wood-plastic composite grades, the PLA matrix gives S 7530 higher tensile and flexural modulus but lower notched impact at −20 °C. Under ISO 179-1:2020, notched Charpy at −20 °C may fall below 3.5 kJ/m². Snap-fit hinges therefore require a radius of at least 2.0 mm and local wall thickness above 2.5 mm. Against annealed or nucleated cPLA, S 7530 has a lower continuous load-bearing service temperature; 70–85 °C HDT B under ISO 75-2:2020 Method B does not imply load-bearing use above 65 °C. The rheology differs from unfilled PLA: S 7530 exhibits higher low-shear viscosity and more pronounced shear thinning at 1 000 s⁻¹, so injection pressure may decrease in thin sections while increasing in thick sections.

When S 7530 replaces a mineral-filled PLA in profile extrusion, the die correction must be altered

Mineral-filled PLA profiles are typically processed with die land lengths tuned for abrasive fillers and a high melt pressure response. S 7530 generates a different pressure profile because cellulosic fibers compress and recover during flow. The melt pressure before the die may be 5–15 % lower at the same screw speed, and the die swell is lower. Profile dies designed for mineral-filled PLA often require a 10–20 % land-length reduction to maintain throughput at 180 °C. The lip gap in thin sections may need to be opened by 0.05 mm to compensate for reduced swell. Melt temperature should be verified at the screw tip with an immersion thermocouple; actual melt temperature is often 5–10 °C above the last barrel zone because of fiber shear heating. In slit dies, the pressure drop across the die land is monitored at 5–12 MPa. Surface roughness after calibration is typically Ra 0.8–1.6 µm without additional polishing; for visible profile surfaces, a downstream polishing die or heated calibrator is required. Published data for this specific configuration is limited; the above ranges are representative of instrumented lot-to-lot verification on pilot profile lines.

Fibrolon S 7530 is not a drop-in replacement for cPLA in every profile die

Crystallized PLA grades can sustain dimensional stability above 90 °C; S 7530 shows HDT B between 70 °C and 85 °C under ISO 75-2:2020 Method B. In continuous load-bearing use above 65 °C, dynamic mechanical analysis is required because natural fiber drying and PLA viscoelastic creep reduce modulus. The product absorbs more moisture than unfilled PLA. After 14 days at 85 % relative humidity, water absorption may exceed 1.8 wt%; the resulting moisture acts as a plasticizer, reduces modulus, and roughens profile surfaces. It is unsuitable for direct contact with boiling water, pressurized steam, or humid-dry cyclic service without full end-use validation. Flame retardancy is not inherent; any UL 94 classification must be obtained on the final part, not assumed from the granulate. Food-contact compliance must be verified with the lot-specific fiber source and conversion aids under Regulation (EU) 10/2011; migration data for this specific natural fiber formulation are not automatically transferable from neat PLA. The absence of intentionally added heavy-metal stabilizers supports standard REACH and RoHS documentation, but final article certification is required.