An evaluation study of pressure-compressed acoustic absorbers grown on agricultural by-products

This research examines the use of a novel new renewable resource in acoustic absorption applications. The new material being tested is based on a fungi that is grown on semi-hydrophobic agricultural by-product substrates such as cotton burs, switch-grass, rice straw, sorghum stalks, corn stalks and kenaf; to form a light-weight all-natural bio-composite board. The study examines the impact of a new post-processing technique that converts the raw light-weight board into a much higher density compressed board that requires no additional glue or binder. The material traits of interest to this study are the acoustical absorption properties of this new high density variant. The study tested the boards over a range of compressed densities that resulted by increasing the compression force in a laboratory board press with a fixed temperature of 205° Celsius for the following applied pressures {0, 2644, 3051, 3661, 4678 N/m2} to achieve the following five density levels that were tested, {0.042 (uncompressed), 0.057, 0.086, 0.120, 0.169 g/cc}. Also included in the study were three reference materials {commercial acoustic ceiling tile, a cork flooring under-layment and birch plywood}. The acoustic properties of the material were characterized for acoustic absorption, in reflection and for through-transmission. The results of the study indicate this new class of densified mycelium based boards are a promising bio-based composite alternative for through-transmission acoustic shielding boards. Results show a progressive increase in sound shielding up to 0.087 g/cc after which further increases in density are statistically insignificant. This new material provides an all-natural, sustainable alternative to modern composite boards such as medium density fiber boards, “MDF” and oriented strand boards, “OSB”.