Research On Preparation And Characteristics Of Fibrillated Ultrafine-fiber Media

Modern air filtration technology requires filter media with better filtration properties andexcellent processability. To achieve this requirement, the ultrafine fibers with diameter under5μm—especially those under1μm—are utilized by advanced filter media. With theultrafine-fiber structure, the fibrillated ultrafine-fiber can be applied to produce the highperformance filter media via wet-laid process. It's a new field for high performance filtermedia.The research of this paper is based on high performance air filtration application. Theforming process of fibrillated ultrafine-fiber and its wet-laid filter media will be studied. Andthe relation between structure and performance of media will be illustrated. The research willalso theoretically model the optimal double-layer media which laminated with fibrillatedultrafine fiber mixed layer. This research shows that:1. The forming of fibrillated ultrafine-fiber is a complicated process during which thefibers transform from large to fine, straight to curl and monodisperse size to polydisperse size.2. The fibrillated ultrafine-fiber FL₅with the highest filtration efficiency, surfacefiltration properties and uniformity can be obtained by classifying. And the average fiberdiameter of FL₅is0.24μm.3. With the rising of fibrillation intensity, the beating degree of fibrillated ultrafine-fiberkeeps increasing and the uniformity of its handsheet becomes better and better, while thewet-laid formability of the fibrillated ultrafine-fiber becomes worsen as a result that it isn'tsuitable for sheet forming alone.4. With the rising of fibrillation intensity, the permeability and pore size of the fibrillatedultrafine-fiber handsheet keeps decreasing and the peak of its pore size distribution shiftstowards smaller value.5. Compared with single-layer structure, double-layer structure greatly improves thefiltration properties of media which is composed of fibrillated ultrafine-fiber. In the samecontent of fibrillated ultrafine-fiber, the highest filtration efficiency for0.3-0.5μm particles ofdouble-layer structure media is93.2%, while single-layer structure is only38%.6. The fibrillated ultrafine-fibers bridge the surface pores of substrate in a dispersedfashion leads to better filtration performance. While fibrillated ultrafine-fibers intertwist ortangle with the substrate fibers lead worse.7. Better filtration performance can be obtained by further optimizing the surface layerstructure of the fibrillated ultrafine fiber laminated media: Intermediate-layer or fibrillated ultrafine-fiber mixed layer are applied to improve the filtration efficiency of media withoutincreasing pressure drop significantly. When the basis weight of mixed layer is only1.00g/m²,mixed ratio is6:4(MGF₃:FL₅), the filtration efficiency for0.3-0.5μm particles of the mediaincreases from25.8%to61.1%and acquires the highest quality factor.8. The modeling and verification of the optimal double-layer media laminated withfibrillated ultrafine-fiber mixed layer suggest the calculation model is reliable which isestablished by the filter media structure and single fiber filtration theory.