materials Article Sustainable Lightweight Insulation Materials from Textile-Based Waste for the Automobile Industry Zengxiao Cai 1 , Md Abdullah Al Faruque 1 , Alper Kiziltas 2 , Deborah Mielewski 2 and Maryam Naebe 1, *   Citation: Cai, Z.; Al Faruque, M.A.; Kiziltas, A.; Mielewski, D.; Naebe, M. Sustainable Lightweight Insulation Materials from Textile-Based Waste for the Automobile Industry. Materials 2021, 14, 1241. https:// doi.org/10.3390/ma14051241 Academic Editor: Philippe Boisse Received: 11 February 2021 Accepted: 1 March 2021 Published: 5 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 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/). 1 Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia; z.cai@deakin.edu.au (Z.C.); malfaruq@deakin.edu.au (M.A.A.F.) 2 Research and Innovation Center, Ford Motor Company, Dearborn, MI 48121, USA; akizilt1@ford.com (A.K.); dmielews@ford.com (D.M.) * Correspondence: maryam.naebe@deakin.edu.au Abstract: Globally, automotive manufacturers are looking for ways to produce environmentally sustainable and recyclable materials for automobiles to meet new regulations and customer desires. To enable the needs for rapid response, this study investigated the feasibility of using waste and virgin wool fibres as cost-effective and sustainable alternatives for automotive sound and heat insulation using a chemical-free approach. Several properties of the currently available commercial automotive insulators were investigated in order to facilitate the designing of green wool-based needle-punched nonwoven materials. The effect of fibre diameter, nonwoven surface, layer structure, thickness, and area density on sound absorption and thermal resistance was investigated. The results suggested that the wool nonwoven materials, fabricated using waste and virgin wool fibres, possessed extremely efficient acoustic and thermal insulating properties comparable with the currently used commercial synthetic insulating materials. Besides, the wool nonwoven materials showed identical antibacterial and antifungal properties with a greater biodegradation rate (50%) than that of the commercial synthetic insulating materials. Hence, this study showed that natural wool fibres have the potential to be used as green, lightweight, and sustainable materials in the automobiles, while they qualify for Reuse–Recycle and Reuse–Recover purposes at the end-of-life of vehicles. Keywords: wool; recycling; nonwoven; sound and thermal insulator; biodegradation; antimicrobial 1. Introduction In this modern era of environmental awareness, manufacturers and consumers are mainly focusing on the production and consumption of nature-based biodegradable, bio- compatible and recyclable products [1–4]. The automobile industry is not exempt from this and seeks to fabricate various automobile parts derived from natural and renewable raw materials rather than traditional synthetic fibres (glass, carbon, aramid fibres etc.) and petroleum-based oils for polyurethane foams [5–8]. Besides, it has been found that every year, in the European Union, end-of-life vehicles (ELV) generate around 8–9 million tonnes of waste [9]. Moreover, as of 1 January 2015, the Directive 2000/53/EC on end- of-life vehicles set detailed quantified targets, which state that 85% of the vehicle must qualify for Reuse–Recycle and 95% for Reuse–Recover purpose [9]. This has pushed car manufacturers to consider the use of sustainable manufacturing materials such as natural fibres especially for the noise and heat insulation. The ability to isolate the mechanical noise, vibration, heat, and thermally insulate the interior of the vehicle leads to comfortable driving, and significant energy savings from the air-conditioning usage perspective. These insulation materials can be used for floor coverings, under the seat cover, door trim, pack panels, engine compartment, and on the ceiling [6,10]. Nonwovens, which can be easily made into different densities, thickness, and forms, have been applied in the car interior owing to their light weight, simple processing, flexibility, porosity, and sound insulation properties [11]. Needle-punching, a large-scale nonwoven manufacturing method using Materials 2021, 14, 1241. https://doi.org/10.3390/ma14051241 https://www.mdpi.com/journal/materials