Estudos sobre a produção de nanofibras de PVA via electrospinning e sua aplicação em filtração de nanoaerossóis

Abstract

Poly(vinyl alcohol) nanofibers for air filtration were produced by electrospinning using citric acid and different concentrations of Triton X-100 surfactant. Filtration tests with nanoparticles (5.94–224.7 nm) and tests of resistance to humid air streams were performed. It was found that there was an optimum concentration of surfactant (0.25% wt.) that provided the highest quality factors for nanofiltration. The median fiber size, filter porosity, thickness of the filter medium, and the Darcyan permeability constant were strongly dependent on the concentration of Triton X-100 in the polymer solution. The filters were resistant to humidity, with a maximum 4.1% change of the pressure drop after 60 min exposure to an air stream at ~15 cm/s with 90% R.H. In this work, theoretical studies were also carried out: theoretical expressions of viscous flow of gas relative to fibers were applied for the evaluation of the enhanced efficiency of a micro-fibrous filter medium after coating it with electrospun nanofibers. An extended form of the Kuwabara hydrodynamic factor was used to cover the particle size range considered (5.94–224.7 nm). A Boltzmann particle charge distribution (as applied in the experiments) was assumed and the effects of the main particle deposition mechanisms were considered. The absolute errors in the efficiency were ±5% for particles in the size range 50-200 nm, which confirmed the better fits obtained with the assumptions adopted in this work. The collection efficiency was greatly enhanced by the addition of nanofibers (increasing from 6.39 to 94.2% for 200 nm NaCl particles), due to predominance of the diffusional mechanism and interception due to diffusion for particles with sizes up to 150 nm, while interception of particles flowing with the air streamlines was most important for larger particles. Also, theoretical and semi-empirical models of air permeability of packed beds and fibrous beds were used in order to obtain the porosity of micro-fibrous and nano-fibrous mats. Porosity values using Davies’ correlation provided the best accuracy for experimental data of collection efficiency of >100 nm NaCl particles. The models were also used to compare the porosities obtained according to this technique with the porosities obtained from the grammage, providing accordance between the results (deviation up to 0.07% for 94 nm fibers using Davies’ equation and the lowest deviation of -0.02% using Pich’s model when 15 μm fibers were evaluated). Design of an HVAC (Heating, Ventilation and Air Conditioning) system was also performed, allowing the application of the produced PVA nanofibers in the retention of viral particulate emitted in a room and PM2.5 coming from the outside. It was verified that the most economical configuration achieved after 167 minutes the concentration below the threshold value recommended by the World Health Organization.