Algal Biomatter Metamaterials for Acoustic Insulation Applications

The increasing consumption of plastics has led to a significant environmental pollution problem. Synthetic polymer foams end up in landfills after short service lives and degrade into micro/nanoplastics that now permeate our environment. As a result, there is a critical need for new foams that are sustainably sourced and biodegradable. One type of foam that needs more study is acoustic foams, which are used to dampen room reverberations. Metamaterials allow for the unique control over wave propagation and mechanical properties and can be used to engineer materials with exceptional utility. Here, we show that sustainable biomatter building blocks can be assembled in a metamaterial composite design for use in sound dampening applications. We show that different species of algae can be lyophilized to create foams with different sound absorption properties as measured by an impedance tube. Rheology and small-angle X-ray scattering (SAXS) of the pre-lyophilized algae is studied to gain insight into the final microstructure of the materials. Compression is used to understand the static and dynamic mechanical properties of the lyophilized foams. Scanning electron microscopy (SEM) and micro computed tomography (micro-CT) are used to determine the morphological differences between each material caused by differences in processing, density, and species of algae. Finite Element Modeling (FEM) is used to better understand the acoustic and dynamic behavior of the materials, which allows for the design of metamaterial assemblies with exceptional acoustic absorption and transmission loss properties. These metamaterial composites show target frequencies common to built environments, highlighting the ability for biomatter to be used in sustainable engineered materials.