Abstract:

Objective At present, the development of water treatment technology is a global task,because of the water pollution and the shortage of pure water faced by mankind. In consideration of its superior performance, nanofiber composite filtering materials are widely used to efficiently filter micron sized particulate pollutants in sewage. However, how to increase the filtering efficiency and the adhesion between nanofiber layers and how to evaluate the adhesion are crucial. Therefore, this work is set out to prepare the multilayer materials with high filtering efficiency and adhesion between nanofiber layers and to set up test method for the adhesion.

Method In this work, a firmly bonded multilayer nanofiber composites was prepared by putting five types of low melting point polymer fibers, which are polyethylene oxide (PEO), polyvinylidene difluoride(PVDF), polystyrene (PS), polymethyl methacrylate(PMMA), metallocene linear low density polyethylene(mLLDPE), together with polyamide 6 (PA6) nanofibers on industrial filter fabrics through eletrospun technology pressed with glass fiber at a designed temperature. Meanwhile, a tensile test method was established to measure the bonding strength of multilayer nanocomposites. The effects of the content of PA6 nanofibers of the materials and initial turbidity value of PS microspheres with a diameter of 1μm solution on the filtration efficiency and filtration flux were also studied.

Results The low melting point polymer fibers containing PEO, PVDF, PS, PMMA and mLLDPE were made to have different fiber diameters, which are 0.27, 0.36, 0.42, 1.29 and 35.31 μm, respectively(Tab. 1). The multilayer nanocomposite material was successfully prepared by hot pressing the industrial filter cloth spun with low melting point polymer fiber and glass fiber, and the adhesion between nanofiber layers of the multilayer nanocomposite material was significantly improved compared with the common sandwich materials, increasing from 2.6 N/cm² to 8.2 N/cm². When the concentration of PS microsphere suspension with a diameter of 1 μm was 80 NTU, the filtration efficiency of multilayer nanofiber composite materials enhances with the increase of the surface density of the PA6 nanofibers(Fig. 5). When the surface density of PA6 nanofibers was constant, the filtration efficiency of the multilayer nanofiber composite materials increaseds with the increase of initial turbidity value of PS microspheres solution, and the filtration efficiency was up to 97.75%. When the initial turbidity of the solution was 160 NTU and the PA6 nanofiber membrane density was 2.5 g/m², the filtration efficiency of materials on PS microspheres with a diameter of 1μm reached 98.9%, the flux recovery rate was 76.3%, and the interception rate reached above 98%(Tab. 2). With the increase of the surface density of the PA6 nanofiber, the filtration flux of the material to PS microsphere filtrate gradually decreased (Fig. 6). Moreover, a tensile test method was designed to measure the adhesion between nanofiber layers of the multilayer nanocomposite material(Fig. 2).

Conclusion In conclusion, after the addition of low melting point polymer fiber, a firmly bonded multilayer nanofiber composite was prepared, and a test method for the adhesion of nanofiber composite was established. The multilayer nanofiber composite was found to have high interlayer adhesion, which is significantly higher than the common sandwich purification material, and the composite has good filtration performance for PS microspheres with a diameter of 1 μm. It would have broad application prospects in the field of sewage filtration.

Key words: electrospinning, nanofiber, polyamide 6, polystyrene, metallocene linear low density polyethylene, multilayer nanocomposite, filtration efficiency