Citation: Seciureanu, M.; Nastac, S.-M.; Guiman, M.-V.; Nechita, P. Cellulose Fibers-Based Porous Lightweight Foams for Noise Insulation. Polymers 2023, 15, 3796. https:// doi.org/10.3390/polym15183796 Academic Editor: Selestina Gorgieva Received: 22 August 2023 Revised: 12 September 2023 Accepted: 14 September 2023 Published: 17 September 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 Cellulose Fibers-Based Porous Lightweight Foams for Noise Insulation Mihai Seciureanu 1 , Silviu-Marian Nastac 1,2, * , Maria-Violeta Guiman 2, * and Petronela Nechita 1, * 1 Engineering and Agronomy Faculty in Braila, “Dunarea de Jos” University of Galati, 810017 Braila, Romania; mihai.seciureanu@gmail.com 2 Faculty of Mechanical Engineering, “Transilvania” University of Brasov, 500024 Brasov, Romania * Correspondence: snastac@ugal.ro or silviu.nastac@unitbv.ro (S.-M.N.); violeta.guiman@unitbv.ro (M.-V.G.); petronela.nechita@ugal.ro (P.N.) Abstract: This paper examines effective and environmentally friendly materials intended for noise insulation and soundproofing applications, starting with materials that have gained significant attention within last years. Foam-formed materials based on cellulose fibers have emerged as a promising solution. The aim of this study was to obtain a set of foam-formed, porous, lightweight materials based on cellulose fibers from a resinous slurry pulp source, and to investigate the impact of surfactant percentage of the foam mixtures on their noise insulation characterisitcs. The basic foam-forming technique was used for sample assembly, with three percentages of sodium dodecyl sulphate (as anionic surfactant) related to fiber weight, and a standardised sound transmission loss tube procedure was used to evaluate noise insulation performance. Results were obtained as observations of internal structural configurations and material characteristics, and as measurements of sound absorption/reflection, sound transmission loss, and surface acoustic impedance. Based on the findings within this study, the conclusions highlight the strong potential of these cellulosic foams to replace widely used synthetic materials, at least into the area of practical noise insulation applications. Keywords: cellulose fiber; foam-forming; surfactant; noise insulation; sound absorption; sound transmission loss 1. Introduction In the past 10 years, the potential of foam-formed materials based on cellulose fibers (CF) has been harnessed in the pursuit of sustainable and environmentally friendly materi- als and has gained significant attention [1–6]. Indeed, foam-formed materials based on CF have emerged as a promising solution. By combining the inherent properties of CF with the unique characteristics of foam-forming, these materials offer a wide range of applications and demonstrate great potential in various industries [7–11]. The use of CF in noise insulation and soundproofing (NISp) applications combines their natural properties, sustainability, and cost-effectiveness, providing an attractive solu- tion for creating quieter and more comfortable environments [1,2,5–7,10,12–17]. Below is a brief description of the advantages of using foams, particularly those based on CF, for NISp applications. (i) Foams with excellent sound absorption, including CF-based foams, possess a porous structure that effectively absorbs sound waves, reducing noise transmission; the interconnected void spaces in foams allow for the dissipation of sound energy through friction and air resistance [15,16]. (ii) Lightweight foams, including CF-based foams, are easy to handle and install; this characteristic is particularly beneficial for NISp applications as it minimizes additional weight on structures and systems [2,3]. (iii) Sustainable and en- vironmentally friendly, CF-based foams are derived from renewable sources such as wood, making them a sustainable choice; these foams are biodegradable and can be produced from recycled materials, reducing environmental impact [1,4]. (iv) CF-based foams are typically non-toxic and safe for human health; they do not release harmful chemicals or Polymers 2023, 15, 3796. https://doi.org/10.3390/polym15183796 https://www.mdpi.com/journal/polymers