A material capable of filtering the air and retaining even particles as small as the new coronavirus, which is around 100 nanometers in size, was developed by researchers at UFSCar (Federal University of São Carlos) with fibers produced from recycling PET bottles.
The work was carried out during the PhD of Daniela Patrícia Freire Bonfim, a student of the Postgraduate Program in Chemical Engineering at UFSCar, with support from FAPESP and guidance from Professor Mônica Lopes Aguiar. The results were published in the journals Polymers and Membranes.
The work is part of a line of research conducted since the 1990s at DEQ-UFSCar (Laboratory of Environmental Control of the Department of Chemical Engineering). The group now intends to develop new filtering materials impregnated with biocide and virucidal additives, such as metallic nanoparticles or essential oils – these considered more sustainable and less risky to human health.
In addition to helping to prevent covid-19 and other respiratory and infectious diseases, which are also caused by bacteria and fungi, filter media are essential in tackling another important current problem, air pollution. According to the World Health Organization (WHO), air pollution kills about 7 million people a year around the world and, in Brazil, the estimate is 50 thousand deaths per year. Therefore, the materials can be applied in PPE (personal protection equipment) – such as masks, lab coats and others – and in systems for filtration and air conditioning in environments such as hospitals, schools and other buildings.
“When we started, in 1992, we were the only laboratory working with gas filtration in Brazil, under the coordination of Professor José Renato Coury. Since 2000, our attention has been focused on particles in a little-studied size range, in which microorganisms are found. Now, we have a boom, because of the pandemic”, says Lopes.
One of the main challenges faced in the research concerns the combination of different parameters in the electrospinning process – in which an electric field is applied to a drop of polymer solution (PET dissolved in a solvent) at the tip of a syringe needle, resulting in in solvent evaporation and fiber production, deposited on a fixed or rotating collector. The concentration of the solution, the diameter of the needle, the intensity of the applied field and the distance between the tip of the needle and the collector are just some of the parameters to be defined, combined and then associated with the different characteristics found in the resulting material.
“These parameters interfere, each in a different way, in the final result. The concentration of the solution, for example, interferes with the fiber diameter. Other parameters interfere with how the fiber is deposited in the collector, which interferes with the permeability which, in turn, establishes how the air flow passes through the material and, thus, determines the pressure drop”, exemplifies Bonfim, in an interview with the Coordination of Social Communication of UFSCar.
“In other words, these parameters will determine the morphology of the fibers, which, in turn, interferes with collection efficiency and pressure drop. And you need to monitor them all together. So, the initial challenge was, based on the desired filtration, to go on combining the various parameters to arrive at the fiber as we wanted”, says the doctoral student.
From the tests, the researchers arrived at a web of nanofibers that does not require a substrate, that is, it does not need to be applied on another more resistant or structured material, being itself the filter and the support. The product achieves up to 100% efficiency in collecting particles between 7 and 300 nanometers, with very low pressure drop.
“The particles stick to the fibers and, in this way, the space for air to pass is reduced, and it is this obstruction that we call pressure drop. If it is high, it means that the obstruction happens quickly and you need to use more energy for the air to pass”, explains Bonfim.
.With information from UFSCar’s Social Communication Coordination