● Excessive viscosity: Slow flow increases deposition; residual dope solidifies upon stops.
● Untimely/insufficient cleaning: Failure to flush hot with solvent; lack of ultrasonic cleaning leaves orifice contamination.
● Process temperature too low: Dope solidifies prematurely in the capillary.
● Raw-material impurities: Gels, mechanical debris, undissolved particles.
● Degradation/crosslinking: Overheating or long residence causes hardened species.
● Temperature miscontrol: Too low → high viscosity; too high → charring.
● No purge at shutdown: Residual dope solidifies or scales after solvent loss.
● Filter failure: Damaged or underspecified filters allow contaminants through.
● Flow-path dead zones: Stagnant volumes cause solidification.
● Dope viscosity nonuniformity: Undissolved polymer causes local resistance differences and uneven extrusion speeds.
● Installation misalignment: hollow fiber spinneret not vertical to line causes flow skew.
● Unstable melt/solution flow: Viscosity fluctuation; pump discharge nonuniformity.
● Poor filtration: Particles hang at orifice edges, disturbing uniform outflow.
● Bore/shell flow or pressure mismatch: Insufficient bore pressure/flow fails to uniformly open the lumen.
● Coag bath disturbance or unsteady take-up: Early-stage fibers deviate before setting.
● Multi-orifice plates: Under- or over-supply can cause eccentricity and nonuniformity.
● Dope condition: Viscosity, solids content, solvent ratios may vary; even with the same formulation, batch-to-batch dissolution uniformity impacts spinning.
● Raw materials: Polymer molecular weight, viscosity, additive content differ.
● Bore–shell matching: Bore fluid flow/pressure/temperature and compatibility with dope directly affect geometry and morphology.
● Environment: Ambient temperature/humidity affect cooling/solidification of filaments.
● Operations and equipment: Operator habits; condition of gear pumps, filters, etc.
● High viscosity dope: Requires larger flow channels to reduce resistance, ensure stable extrusion, and enable stable hollow fiber formation. Larger orifices also reduce residence time, mitigating thermal degradation.
● Gen 4: Stepped needle with dowel-pin positioning.
● Gen 5: Independent spinning insert, pinless; ~80% lower maintenance cost.
● Gen 6: Independent feed control per channel.
● Gen 7: Screwless and pinless; size reduced by ~50%.
● Gen 8: On-line, non-stop insert changeover.
● Flow-path design: TIPS emphasizes insulation and anti-freezing/solidification, often with heating jackets; NIPS emphasizes precise bore/shell flow control and mixing.
● Bore fluid needs: NIPS usually requires a bore fluid (e.g., water or non-solvent) to support the lumen; some TIPS systems can self-support without a bore fluid.
● Orifice and finish: TIPS handles higher viscosity dopes; orifices are often larger with higher surface finish to reduce hang-up.
● TIPS (thermally induced phase separation): Melt or high-concentration solution cooled to form membrane; suitable for high temperature polymers (PP, PE, PVDF).
● Dry–wet spinning: Combines air gap (dry zone) with coagulation bath (wet zone) for enhanced structure control.
● Co-extrusion composite spinning: Produces multilayer or functional hollow fibers (e.g., liner-reinforced).
● Melt spinning: Polymer pellets melted and extruded through the hollow fiber spinneret, solidifying in air to form fibers.
● Alignment: Precisely align the hollow fiber spinneret with coagulation bath and take-up to ensure vertical fiber fall.
● Connect lines: Correctly connect bore fluid and shell dope (or single dope) feeds; ensure leak-free seals.
● Preheat and degas: Preheat to process temperature before feeding and purge all trapped air.
● Trial run and tuning: Start at low flow; observe filament formation (breakage, eccentricity, bubbles), then gradually adjust bore/shell flow ratio, temperatures, and take-up speed to stable operation.
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