● Dead-zone-free flow paths: Avoid polymer degradation hot spots.
● High viscosity compatibility: Common polymers include PI and PSf; require large channels and strong pressure capability.
● Dry–wet compatibility: Often requires longer air gaps (5–20 cm) to form a dense skin.
● High temperature materials: PI spinning may require >200°C.
● Flow-path structure → formation: Manifold/equalization design governs dope distribution, avoiding “streaky” multi-orifice output.
● Material → stability: Insufficient wear resistance enlarges orifices; poor chemical compatibility causes corrosion—both degrade quality over time.
● Sealing and flow resistance → continuity: Leaks and unequal resistance cause breaks or lumen closure, reducing yield.
● Film-formation dynamics: At the outlet (NIPS/TIPS), extrudate swell and initial bore/shell interface set the stage for phase separation, impacting pore size, distribution, and porosity.
● high temperature: Nickel alloys, titanium alloys, SUS630 (17-4PH) for TIPS (100–260°C), with higher hot strength and wear resistance.
● Corrosion-resistant: Hastelloy and ceramic-coated materials for aggressive solvents (DMF, DMSO) and strong acids/bases.
● Auxiliary coatings: PTFE or polysiloxane coatings on orifice walls to increase hydrophobicity and reduce deposition.
● Complete degassing: Purge bubbles before start to prevent breaks or bubble defects.
● Low speed start: Ramp slowly; observe fiber and then increase.
● Synchronous bore/shell start: Avoid dry extrusion or lumen collapse.
● Coagulation bath matching: Maintain composition, temperature, level; precisely control air-gap length.
● Pressure/flow tuning: Begin low and ramp; keep pressure ripple ≤3%; stabilize bore/shell flow ratio (e.g., UF often ~1:1.2).
● Dope pretreatment: Verify filtration (≤5 μm) and viscosity spec (variation ≤5%) to avoid clogging/nonuniform extrusion.
● Flow control: Match supply to outflow to maintain multi-orifice uniformity.
● Real-time monitoring: Watch pressure/flow/temperature; stop and troubleshoot if abnormal.
● Record parameters: Maintain SOPs for reproducibility and optimization.
● Melt spinning (e.g., PP, PE): Typically 180–300°C (PP ~200–260°C).
● Wet spinning (NIPS for PVDF/PSf): Room temperature to ~90°C; control aims at viscosity stability.
● TIPS: Most stringent; control above the polymer–diluent binodal, typically 150–250°C within a narrow window.
● Core principle: Set temperature to ensure optimal, stable rheology without thermal degradation (too high) or clogging (too low).
● Ultrasonic cleaning: Disassemble and sonicate with compatible solvent.
● Unclogging: Do not scrape micro-orifices; use high-pressure inert gas to blow through.
● Dry and store: Oven dry or nitrogen blow; store sealed in a dry, clean environment.
● Routine inspection: Check O-rings, threads, orifices for wear/deformation; replace consumables.
● Avoid dry firing: For TIPS, ensure dope or protective gas is present before heating to prevent oxidation.
● Precision: Higher demands on orifice size and concentricity for uniformity and performance.
● Materials: May require higher corrosion/temperature resistance for membrane dopes.
● Applications: Hollow fibers for water treatment/biomedical; conventional spinnerets for polyester/nylon, etc.
● Process conditions: hollow fiber spinning is more demanding in temperature, pressure, and cooling control.
● Maintenance: More complex due to structure and tighter tolerances.
● Rheology: Appropriate, stable viscosity/MFI for smooth, stable extrusion.
● Viscosity stability: Batch-to-batch variation ≤5%; match viscosity to orifice size (high μ → larger orifices).
● Chemical compatibility: Solvent compatibility with hollow fiber membrane spinneret material (e.g., stainless vs. nickel alloy).
● Thermal stability: No decomposition/crosslinking/charring at process temperature.
● Pretreatment: Dry hygroscopic resins (PET, PA) to prevent bubbling or hydrolysis.
● Bore fluid: Immiscible with shell dope; flow stability variation ≤3% for consistent lumen size.
● Capillary wear: Prolonged high pressure enlarges orifices → thicker fibers beyond spec.
● Eccentric spinning: Reduced concentricity or pressure imbalance → uneven wall thickness.
● Leakage: Seal failure and exposure to DMAC/NMP/DMF causes seal attack; poor assembly leaks at interfaces.
● Precision drift: Long-term heat/chemical attack causes deformation; diameter/concentricity drift, quality fluctuations.
● Concentricity: Bore and shell channel concentricity ≤0.003 mm.
● Hole pitch tolerance: Inter-orifice pitch deviation ≤0.01 mm for multi-orifice plates.
● Surface roughness: Orifice inner-wall Ra ≤0.8 μm to minimize deposition/clogging and ensure smooth extrusion.
● Orifice roundness: ≤0.002 mm; no axial scratches.
● Multi-hole array pitch tolerance: ±0.01 mm to prevent fiber sticking.
● Flow pulsation: Metering pump wear/faults cause flow oscillations (“thick–thin” segments).
● Temperature instability: Temperature dips raise viscosity, increasing resistance and diameter.
● System pulsation: Gear/screw pump cyclic flow ripple.
● Entrained bubbles: Bubbles intermittently disrupt extrusion.
● Take-up instability: Winder slip or speed variations.
● Maldistribution: Poor manifold design causes near-inlet holes to run rich, far holes lean.
● Uneven pressure field: Unstable extrusion pressure or non-level installation.
● Supply/pump issues: Under- or over-supply affects uniformity.
● Process control: Temperature/pressure/speed nonuniformity → viscosity differences → flow differences.
● Environment: Nonuniform temperature/humidity/airflow disturbs formation across holes.
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