Citation: Patrichi, C.A.M.; Cioroiu Tirpan, D.R.; Aljanabi, A.A.A.; Trica, B.; Gifu, I.C.; Dobre, T. Extraction of Cellulose from Ulva lactuca Algae and Its Use for Membrane Synthesis. Polymers 2023, 15, 4673. https:// doi.org/10.3390/polym15244673 Academic Editor: Francisco Javier Manzano-Moreno Received: 20 October 2023 Revised: 8 December 2023 Accepted: 9 December 2023 Published: 11 December 2023 Copyright: © 2023 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 Extraction of Cellulose from Ulva lactuca Algae and Its Use for Membrane Synthesis Claudia Ana Maria Patrichi 1, * , Doinita Roxana Cioroiu Tirpan 2, *, Ali A. Abbas Aljanabi 3 , Bogdan Trica 1,4 , Ioana Catalina Gifu 1,4 and Tanase Dobre 1 1 Chemical and Biochemical Engineering Department, University Politehnica of Bucharest, 1-6 Gheorghe Polizu, 011061 Bucharest, Romania; trica.bogdan@gmail.com (B.T.); gifu_ioanacatalina@yahoo.com (I.C.G.); tghdobre@gmail.com (T.D.) 2 Chemistry and Chemical Engineering Department, Ovidius University of Constanta,124 Mamaia Street, 900527 Constanta, Romania 3 Al Mussaib Technical College, Al-Furat Al-Awsat Technical University, Babylon P.O. Box 51006, Iraq; dr.ali.aljanabi@atu.edu.iq 4 National Research & Development Institute for Chemistry and Petrochemistry, ICECHIM, Splaiul Independentei No. 202, 6th District, 060021 Bucharest, Romania * Correspondence: patrichi.claudia@gmail.com (C.A.M.P.); tirpanroxana@gmail.com (D.R.C.T.); Tel.: +40-762521058 (C.A.M.P.); +40-721901272 (D.R.C.T.) Abstract: Green algae are a sustainable source of biopolymers for the global demand due to their high photosynthetic efficiency. This article describes the extraction of cellulose from plant systems represented by Ulva lactuca species. In order to extract various substances, algae were finely ground with the help of solvents (liquid media). This was carried out to achieve the necessary conditions that help reduce the resistance this phase shows in regard to the transport and transfer of the species being extracted. The highest yield of extracted cellulose (20,944%) was obtained for the following factors: S/L = 1/20; conc. ethanol = 90%, conc. salts = 4 g/L. Hydrogel membranes are a unique class of macromolecular networks that contain a large fraction of aqueous solvent within their structure. With the cellulose extracted from algae, we obtained membranes which underwent the process of swelling in liquid media (ethyl alcohol) of different concentrations. The swelling of biocellulose membranes in alcoholic solutions of high concentrations was investigated. It was observed that the process of absorption of the alcoholic solution by the membrane occurred rapidly in the first part. After stabilization, the membranes continued to absorb at a slower rate until stabilization or saturation concentration was reached. Keywords: swelling; membrane; cellulose; algae; diffusion of swelling layer 1. Introduction In present, synthetic polymers began to widen their fields of use and they are find practically in all branches of the economy due to their excellent mechanical properties and competitive price. There are no limits regarding the use of polymer materials in the age of advanced technologies. Nevertheless, the particularity of these synthetic polymers obtained from monomers is their non-biodegradable behavior that affects the quality of the environment. Therefore, scientists focused their attention to biodegradable biopolymers, a current field of research with great ecological and economic importance. Due to their structure, biopolymers have unique properties that can be adapted for different uses [1,2]. Organisms like bacteria, plants and animals produce through biosynthesis biopoly- mers which could be separated by chemical or enzymatic treatment [3,4]. In recent decades, chemically synthesized fibers have been replaced by a wide range of biopolymers leading to the development of the bio-composite materials industry [5–11]. Seaweed represents a sustainable feedstock for the global demand of biopolymers. In nature, algae produce ten times more organic matter and release five times more oxygen Polymers 2023, 15, 4673. https://doi.org/10.3390/polym15244673 https://www.mdpi.com/journal/polymers