Durability of Recycled and Natural Fibrous Acoustic Materials Undergoing Long‑term Indoor Ageing

ABSTRACT Sustainable fibrous materials are increasingly used as sound absorbers in building applications; however, their long-term acoustic durability still requires further documentation. This study presents a long-term acoustic ageing case involving thermobonded fibrous materials that were designed some years ago for sound absorption applications. Thirty-two fibrous material formulations manufactured from recycled polymers, recycled textiles and natural fibres were originally characterised approximately sixteen years and six months ago and have now been re-evaluated using identical experimental procedures. These materials have been subjected to temperature and relative humidity gradients and exposed to ambient air conditions. Normal-incidence sound absorption coefficients and airflow resistivity were measured using an impedance tube in accordance with international standards. The original and current results were directly compared using different indicators to quantify the deviation of these parameters. The comparison between different material families shows that synthetic materials exhibit the highest stability, while natural and mixed materials are more sensitive to environmental and structural changes. Optical microscopy was also used to assess the current condition of the samples. Fibre diameters were determined and representative porosity values were obtained. The results show that the materials have largely retained their original acoustic properties after the period of natural ageing. Although the materials have not been subjected to real service conditions in buildings, they have been exposed to ageing factors comparable to those found in indoor environments which is relevant for applications in the field of construction materials. These findings are relevant for building applications, as they provide insight into the long-term acoustic stability of fibrous materials under indoor environmental conditions.