Effect of electrospinning conditions on β-phase and surface charge potential of PVDF fibers

Electrospun polyvinylidene fluoride (PVDF) fibers, can act as electrets in filtration applications. Relevant to this is the extent at which electrospinning conditions affect the beta-phase content of PVDF fibers. The beta-phase content is a strong factor in measured charge potentials on PVDF fiber mats. PVDF fiber mats were electrospun from three different polymer solution concentrations (10, 14 and 18 wt%) to fabricate mats of three average fiber diameters (328, 780, 1167 nm) respectively and of five different basis weights (10, 20, 30, 40, and 50 g/ m2). Furthermore, fiber mat samples were electrospun at varying conditions of applied voltage (21, 24, 27 and 30 kV), solution flow rates (2, 5 and 8 ml/h), needle-tip to collector distances (12, 15, 18, 22 cm) and collector drum rotation speeds (5, 45, 100 rpm) while holding constant the 10 wt% solution concentration and 20 g/m2 mat basis weight. SEM images and FTIR spectra were analyzed to estimate the average fiber diameter and amount of beta-phase content. The apparent surface charge potential was measured using a custom-made Faraday Bucket. The solution compositions, flow rates, and needle-tip distance had moderate effects on fiber diameters and on the beta-phase content. The measured surface potential was found to be directly proportional to beta-phase content. The rotation rate of the drum collector had negligible effect on fiber diameter but did affect the beta-phase and surface potential. The measured surface charge potential was directly proportional to the basis weight and inversely proportional to the fiber diameter.