Geyandraprasath Karunakaran: Biodegradable Earplugs

Interest in biobased materials is rapidly increasing as society moves towards more sustainable, environmentally friendly future. This study focuses on biobased sound-absorption materials particularly earplugs, which are typically made from polyurethane (PU) foams and polyvinyl chloride (PVC) derived from petroleum-based fossil fuels, whose production contributes to environmental pollution. 

TEMPO-oxidized hardwood cellulose and chitosan are used to fabricate porous cryogels earplug applications. TEMPO-oxidized cellulose is chosen for its high content of carboxylic groups facilitates cross-linking with other biopolymers, whereas chitosan acts as an elastomer and enhances the mechanical properties of the material. A chitosan solution in acetic acid is mixed with TEMPO-oxidized cellulose and then freeze-cast and freeze-dried to obtain porous, anisotropic-structured cryogels. 

The cryogels are optimized by varying the molecular weight of chitosan, the blending ratio of the two biopolymers, and the concentration of acetic acid. The surface morphology of the resulting structures is characterized using scanning electron microscopy. 

Acoustic properties are evaluated by measuring the sound absorption coefficient (SAC) and transmission loss (TL) for both the whole cryogels and the squeezed (to mimic earplugs) cryogels configurations. The fabricated cellulose-based cryogels exhibit near-perfect sound absorption, with SAC values ranging from 0.95 to 1 in the frequency range of 1500–6000 Hz, outperforming conventional commercial products such as polyurethane and melamine foams. The squeezed cryogels have transmission loss up to 60 dB.