  Citation: Gul, A.; Hruza, J.; Dvorak, L.; Yalcinkaya, F. Chemical Cleaning Process of Polymeric Nanofibrous Membranes. Polymers 2022, 14, 1102. https://doi.org/10.3390/ polym14061102 Academic Editor: Subramanian Sundarrajan Received: 14 February 2022 Accepted: 8 March 2022 Published: 9 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Chemical Cleaning Process of Polymeric Nanofibrous Membranes Aysegul Gul , Jakub Hruza, Lukas Dvorak and Fatma Yalcinkaya * Institute for Nanomaterials, Advanced Technology and Innovation, Technical University of Liberec, Studentska 1402/2, 46117 Liberec, Czech Republic; aysegul.gul@tul.cz (A.G.); jakub.hruza@tul.cz (J.H.); lukas.dvorak@tul.cz (L.D.) * Correspondence: fatma.yalcinkaya@tul.cz Abstract: Membrane fouling is one of the most significant issues to overcome in membrane-based technologies as it causes a decrease in the membrane flux and increases operational costs. This study investigates the effect of common chemical cleaning agents on polymeric nanofibrous membranes (PNM) prepared by polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyamide 6 (PA6) nanofibers. Common alkaline and acid membrane cleaners were selected as the chemical cleaning agents. Membrane surface morphology was investigated. The PAN PNM were selected and fouled by engine oil and then cleaned by the different chemical cleaning agents at various ratios. The SEM results indicated that the use of chemical agents had some effects on the surface of the nanofibrous membranes. Moreover, alkaline cleaning of the fouled membrane using the Triton X 100 surfactant showed a two to five times higher flux recovery than without using a surfactant. Among the tested chemical agents, the highest flux recovery rate was obtained by a binary solution of 5% sodium hydroxide + Triton for alkaline cleaning, and an individual solution of 1% citric acid for acidic cleaning. The results presented here provide one of the first investigations into the chemical cleaning of nanofiber membranes. Keywords: nanofiber; PAN; membrane; microfiltration; cleaning; chemical agents 1. Introduction Today’s rapid urbanization and industrialization cause a rapid depletion of limited resources. Water is one of the most valuable resources on Earth, but has come seriously under threat from contaminants due to undesirable human activities such as marine dumping, as well as domestic, industrial, and agricultural practices. Approximately 40% of the world’s population lives in areas with water issues. Al- though 70% of the earth is covered with water, the proportion of freshwater is low. Only 3% of the water on the planet is considered suitable for human consumption. It is known that 1.2 billion people do not have access to clean drinking water; however, this number may reach 3.5 billion by 2025 [1]. Taking this into consideration, one of the biggest challenges today is the development of highly efficient and cost-effective water treatment technologies. The most widely used water treatment technologies today are pressure-driven membrane filtration processes (including microfiltration (MF), ultra-filtration (UF), nanofiltration (NF), and reverse os- mosis (RO)). These systems have certain advantages and disadvantages and are open to development. For example, while the thermal stability and durability of ceramic MF are relatively good, they have lower permeability and higher costs than other processes [2]. Nowadays, researchers are focusing more on studying how nanotechnology may be integrated into membrane systems to improve membrane stability, where water treatment is gaining tremendous importance. The most common techniques used in nanofiber production are two-component extrusion, phase separation, template synthesis, drawing, melt blowing, electrospinning, and centrifugal spinning [3,4]. Of these, electrospinning Polymers 2022, 14, 1102. https://doi.org/10.3390/polym14061102 https://www.mdpi.com/journal/polymers