A flexible nanofibrous aerogel with laser-cut perforations was developed for effective sound absorption and insulation. Polyethylene terephthalate (PET) waste bottles were turned into uniform nanofibers (NFs) via an electrospinning technique that were subsequently processed to create a 3D porous network through a freeze-drying method. Reinforcing the aerogel with glutaraldehyde-cross-linked poly(vinyl alcohol) (PVA) allowed mechanical flexibility resulting in a Young's modulus of 2.28 × 10 −2 MPa. The highly tortuous pore structure produced by the densely packed nanosized fibers permitted a noise reduction coefficient (NRC) of 0.37 (at areal density of 465 g m −2 ). Likewise, the overall transmission loss is increased as nanofibers are used instead of microfibers. In terms of sound insulation performance, a standard transmission class (STC) of 6.1 dB, which is about 10 times that of a commercial polyurethane-based acoustic foam, is displayed by the PETNF aerogel. Moreover, the creation of perforations further enhanced the material's sound absorption such that an NRC of 0.54 (at areal density of 930 g m −2 ) was obtained, which is similar to or greater than that of most fiber-based acoustic materials previously reported. By changing the perforation diameter, one can tune its overall acoustic performance. In addition, utilizing a waste-derived material for noise pollution control alleviates the generation of plastic waste that is detrimental to the environment.

Highly porous aerogels are greatly anticipated for multifunctional utilization, including building insulators, sound absorbers, filters, energy storage devices, etc. Currently, most aerogels are usually resourced from fossil fuels and nonrenewable materials and often require an additional step to provide multifunctionality. In this work, a facile strategy is presented to fabricate a multifunctional scaffold valorizing polypropylene mask filters intercalated by calcium alginate (CAP) through an ice templating method to generate a dual-pore structure with fibrillated networks. The exploitation of the enhanced porous cell wall and the intrinsic properties of the constituting materials provided a platform for multifunctionalities such as sound absorption, thermal insulation, and fire retardant properties. The dual-pore attribute implemented an effective broadband frequency sound absorption. The outstanding acoustic performance can be ascribed to the structural integrity of the dual-pore microchannels that dissipate the sound within the interconnected fiber wall resonating the sound in different directions. This structural orientation also endows excellent thermal transport properties for a broad range of temperature conditions depleting energy transport. Moreover, the resultant material exhibited flame retardant properties without any further functionalization but through its structural attributes and innate nature of the compounding material. Upon pyrolysis, the structure networks form a char layer that acts as a fire-repellent barrier to induce fire propagation. Without further modification, the generated aerogel can serve as a base platform for sustainable multifunctional scaffolds. This strategy is realized to be a universal technique to prepare highly porous allotropic aerogels with various functionalities.

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A multifunctional composite fibrous sound-absorption panel was acquired via sustainable fabrication from milling corrugated cardboard box wastes to unleash its fibrous property, creating a high-porosity material. Here, a multifunctional composite fibrous panel from the milled fibers of corrugated cardboard boxes reinforced by cross-linked polyvinyl alcohol as a biodegradable binder is generated. It is designed to have a dual-pore structure with a low density of 0.04 g/cm3, which can withstand a load of 5000 times its weight and is effective for the dissipation of sound at a wide range of frequencies. The prepared material demonstrates an excellent average absorption coefficient of 0.83 at wideband frequency, which is about 280–6300 Hz. The outstanding sound absorption performance of the material is primarily ascribed to its dual-pore architecture, the anisotropic pores interconnected by the random pores formed from the collection of cardboard box fibers within the architecture of the porous material, its thickness, and the concentration of corrugated box fibers. Furthermore, the prepared material manifests a unique porous morphological structure, favorable thermal properties, excellent mechanical stability and sustainability, and superhydrophobic properties. The successful fabrication of this riveting material endowed a promising result that may be applicable for various types of applications.