Effects of relative humidity, particle hygroscopicity, and filter hydrophilicity on filtration performance of hollow fiber air filters

The aims of this study are to fabricate hollow fiber air filters with different hydrophilicity and investigate their filtration performance against different particles under different relative humidity. In this study, three types of hollow fibers were prepared: a hydrophilic PAN hollow fiber, a hydrophobic PVDF hollow fiber, and a dual layer PAN/PVDF hollow fiber. The three hollow fibers were used to filtrate nano-sized NaCl (hygroscopic) and Al2O3 (non-hygroscopic) particles at RH 80% and 40%. The results showed that the filtration efficiency was not affected by RH, particle hygroscopicity and filter hydrophilicity whereas the pressure drop across membranes was influenced significantly. When filtrating NaCl particles at RH80%, a RH higher than deliquescent point of NaCl, the PAN hollow fiber had a quick pressure drop increase initially whereas the pressure drop of the PVDF hollow fiber only increased dramatically at a later stage. In contrast, the PAN/PVDF hollow fiber always displayed the lowest pressure drop increment. When filtrating Al2O3 particles at RH 80%, the PAN hollow fiber showed a higher pressure drop increment than PAN/PVDF and PVDF hollow fibers. For the filtration at RH 40%, the pressure drops of all hollow fibers were independent of particle hygroscopicity and filter hydrophilicity. Overall, the PAN/PVDF dual layer hollow fiber had the best filtration performance at all experimental conditions. The mechanisms of particle deposition at different filtration conditions have been elucidated. These findings may provide useful insights to design next-generation air filters suitable for filtrating various aerosol particles in a wide range of RH.