Sound-absorbing materials are used to reduce noise in, e.g., indoor spaces, cars, or aircraft. Often, foams made from synthetic polymers are used in sound absorbers. Biodegradable, sustainable alternative materials that are easy to fabricate and absorb sound efficiently would be useful.

C. Chandraprakash, Indian Institute of Technology Kanpur, Uttar Pradesh, India, and colleagues have developed seaweed-derived agar-based composite films that can be used as sound absorbers. Agar is a mixture of polysaccharides that can be obtained from seaweed and is used, e.g., as a plant-based alternative to gelatin. The team prepared agar films via a solution casting method, using different concentrations of agar powder as well as glycerol and nanocrystalline cellulose as optional additives. Porous films were prepared using a freeze-drying step, while nonporous films were obtained by drying under hot air.

The sound absorption of the resulting films was measured using a brass sound tube outfitted with a speaker at one end, the sample film at the other, and microphones in the middle that measure the reflected sound. The researchers found that the non-porous films absorbed only small parts of the incoming sound energy. The porous films, however, were efficient broadband sound absorbers. Glycerol improved the sound absorption properties, while nanocrystalline cellulose did not change the acoustic properties of the resulting composite material. According to the team, the simple fabrication, biodegradability, and mechanical stability could make agar-based porous films promising sound-proofing materials.

• Agar-Based Composite Films as Effective Biodegradable Sound Absorbers,
  Surendra Kumar, Kousar Jahan, Abhishek Verma, Manan Agarwal, C. Chandraprakash,
  ACS Sust. Chem. Eng. 2022, 10, 8242–8253.
  https://doi.org/10.1021/acssuschemeng.2c00168