Hygroscopic effects on sound absorption of multiscale bio-based porous materials

Hygroscopicity is the tendency of a material to absorb moisture from the surrounding environment. This work investigates hygroscopic effects on the sound absorption properties of multiscale bio-based materials. It is shown how moisture can significantly alter their acoustic performance as well as how to recover their original dry-material performance by means of heat treatment, akin to thermal reactivation commonly used in the chemical engineering industry. The results of an experimental campaign, conducted over an extended period of time, is reported. Possible theoretical explanations on the reduced acoustic performance of activated carbons by hygroscopic effects and the achieved improvement, obtained after heat treating the material, are also presented. The results of this work provide useful insights on the long-term acoustic behaviour of multiscale bio-based materials for noise control applications.