射流先导与旋风拉伸协同离心纺丝制备聚丙烯超细纤维OA

Objective Unstable melt feeding,severe splashing,and insufficient fiber stretching during centrifugal spinning of high-viscosity polymers consid-erably limit fiber quality and process continuity.To address these issues,this study proposes a hybrid technique combining a jet-guided feeding flange with cyclone-assisted aerodynamic stretching.The jet-guided flange was designed to stabilize melt injection by increasing the initial melt velocity,while the cyclone-induced airflow provides secondary stretching of the semi-solid fibers.The effects of spinning temperature(190 ‒230℃)and centrifugal acceleration(20 000‒60 000 m/s2)on fiber morphology,diameter distribution,crystallinity,and mechanical properties were systematically investigated to identify the optimal processing conditions and elucidate the synergistic mechanism between flow control and aerodynamic stretching. Methods Transient melt flow on an enclosed rotating disk was simulated using ANSYS Fluent with a volume-of-fluid(VOF)multiphase model.The melt viscosity was set to 10 000 g/(m·s)at 230℃.Two feeding modes,conventional gravity feeding and jet-guided injection,were compared under an identical disk rotation speed of 6 000 r/min.The simulation domain was discretized using hexahedral meshes,with local refinement near the disk surface.Based on the simulation results,spinning experiments were conducted using a custom-built centrifugal spinning apparatus.Poly-propylene(PP,MFI=26.2 g/10 min)was dried at 50℃for 8 h,melted in an extruder(60 r/min;feed rate=1.0 Hz),and injected into the spin-ning disk through a jet-guided flange with an exit diameter of 2.00 mm.The spinning temperature and centrifugal acceleration were varied from 190 to 230℃and from 20 000 to 60 000 m/s2,respectively.A cyclone ring was mounted around the disk to generate an external airflow of 10 m/s for secondary stretching.The collected fibers were characterized by scanning electron microscopy for morphology,differential scanning calorim-etry(DSC)for crystallization behavior,and single-fiber tensile testing for mechanical properties. Results and Discussions Simulation results were used to compare the melt distribution behavior under two feeding modes:with and without jet-guided injection.Without jet-guided injection,the high-viscosity melt accumulated unevenly on the disk surface and exhibited severe splashing when feeding was interrupted.Within 0.007 s after feeding stopped,numerous melt droplets detached from the main body and were thrown to-ward the disk edge,resulting in significant thickness variations along the circumferential direction.In contrast,with jet-guided injection,the melt maintained a continuous and uniform film along the disk perimeter,with substantially less droplet detachment and splashing.The increased initial velocity imparted by the guiding flange effectively suppressed the rod-climbing effect and stabilized melt feeding,resulting in a more uniform melt distribution across the disk surface. Experimental spinning revealed that spinning temperature and centrifugal acceleration significantly influenced fiber morphology and diameter distribution.At the lowest temperature(190℃),the fibers exhibited irregular,ribbon-like morphologies and poor diameter unifor-mity at all tested centrifugal accelerations.The diameter distribution was broad,with some fibers reaching the nanometer scale while others exceeded 20 μm,indicating highly nonuniform melt stretching.As the temperature increased to 210℃,the fiber morphology transitioned from ribbon-like to more cylindrical,and the diameter distribution narrowed considerably,although a small fraction of particulate material remained. At 230℃,uniform cylindrical fibers with smooth surfaces were consistently obtained,and the diameter distribution closely followed a Gaussian profile.The effect of centrifugal acceleration on fiber diameter exhibited a nonmonotonic trend at all temperatures.Increasing the accel-eration from 20 000 to 40 000 m/s² promoted melt thinning and effectively reduced the fiber diameter.However,a further increase to 60 000 m/s2 caused fiber breakage and re-entanglement of broken segments,resulting in a larger average diameter and the formation of agglomerated par-ticles.Among all tested conditions,230℃and 40 000 m/s2 consistently produced the finest and most uniform fibers. DSC analysis of the as-spun fibers revealed an upward shift in the crystallization temperature relative to that of the raw PP pellets,indicating that molecular chain orientation was induced by the elongational flow during spinning.The highest crystallization temperature was observed at 40 000 m/s2,suggesting degree of molecular chain alignment.In contrast,excessive acceleration at 60 000 m/s2 resulted in reduced crystallinity,which may be attributed to frequent fiber breakage and subsequent relaxation of the molecular orientation. The introduction of cyclone-assisted stretching further improved fiber quality.Fibers subjected to the external airflow exhibited more uni-form diameters and smoother surfaces than those produced without aerodynamic stretching.The additional aerodynamic drawing force enhanced molecular orientation along the fiber axis,while the rapid cooling induced by the airflow helped preserve the oriented chain configuration,thereby improving the mechanical performance of the resulting fibers. Conclusions This study demonstrates that the synergistic combination of jet-guided feeding and cyclone-assisted stretching effectively addresses key challenges in centrifugal spinning of high-viscosity polymers.The jet-guided injection flange stabilizes melt delivery by mitigating the rod-climbing effect and suppressing splashing,while the cyclone-induced airflow provides an additional aerodynamic drawing force that reduces fiber diameter and enhances molecular orientation.Under optimized conditions(230℃and 40 000 m/s2),uniform ultrafine PP fibers with an average diameter of 1.1 μm were successfully produced.Cyclone-assisted stretching further reduced the average diameter to 1.0 μm and increased the single-fiber tensile strength by 2.4-fold.These findings demonstrate that controlled melt feeding and aerodynamic stretching can effectively over-come rheological limitations associated with high-viscosity polymer processing.The proposed approach offers a scalable pathway for producing high-performance ultrafine fibers and provides insights into the role of flow engineering in regulating fiber morphology and enhancing mechani-cal properties.