Studies on fabrication, morphology and performances of bi-layer electrospun nanofibre membranes

摘要

The current study investigated the fabrication and characterization of homogeneous and heterogeneous bi-layer membranes using electrospinning technique. The membranes were fabricated from four polymers: hydrophilic polymers such as polyamide 6 (Nylon 6) and polyvinyl Alcohol (PVA) and hydrophobic polymers such as polyacrylonitrile (PAN) and copolymer poly(vinylidene fluoride)-Hexafluoropropylene (copolymer PVDF)) polymers. A preliminary study was carried out to determine the optimal conditions of electrospinning for each of the above polymers. The optimal conditions for each polymer were different and were determined based upon uniform cylindrical fibres, large coverage area and uniform membrane structures. The study demonstrated that the resultant average fibre diameters for electrospun Nylon 6, PVA, PAN and copolymer PVDF were 109 + 16, 259 + 39, 677 + 205 and 570 + 105 nm, respectively. From the FTIR analysis, the electrospinning was found to transform crystal phases of polymers such as Nylon 6 and PVDF. Changes in the crystal phases were confirmed by the wide angle X-ray diffraction (WAXD) diffraction peaks. The optimal conditions for each polymer were then used to fabricate bi-layer membranes. The bi-layer membranes were fabricated as: homogeneous bi-layer membranes (membrane composed of two identical polymers) and heterogeneous bi-layers membranes (membrane composed of two different polymers, hydrophobic and hydrophilic). The bi-layer membranes were characterized for membrane thickness and surface wettabilities. The membranes were also tested for tensile properties and adhesion strength. The tensile properties for homogeneous bi-layer could be affected by the membranes pore sizes and bonding between fibres in the membrane. For heterogeneous bi-layer membranes, the tensile properties were different depending on the combination of polymers used. For adhesion strength, bi-layer PVA/PVA showed far higher adhesion highest adhesion strength at about 78 mN/mm2 compared to others. For other membranes, the adhesion strengths were lower than 7 mN/mm2. In addition, a modified 180° peel test was developed to evaluate adhesion strengths between the top and bottom layers of the bi-layer membranes. A support system (glass slide) was introduced in order to prevent unnecessarily movement of the sample during the test. The application of homogenous and heterogeneous bi-layer electrospun membranes for the removal of contaminants in textile effluent was investigated. The fine pore sizes of homogenous bi-layer Nylon 6/Nylon 6 exhibited the best performance with the highest effluent removal of 99%. The large pore sizes of commercial membrane gave a much lower performance of improving 33 to 35% of the effluent turbidity. Poor quality of permeate was also observed for the large pore sizes of homogenous bi-layer PAN/PAN and homogenous copolymer PVDF/PVDF membranes. However, the accumulation of suspended solid particles over the homogenous bi-layer Nylon 6/Nylon 6 surface exhibited the lowest flux for the membrane as compared to the commercial membrane and homogeneous bi-layer membranes. For heterogeneous bi-layer membranes, the membranes were found to give a lower flux due to the presence of electrospun Nylon 6. However, the presence of electrospun Nylon 6 in the membranes was found to give an excellent removal of suspended solids from liquid.