Carbon Nanotubes/Polyurethane Foam for Noise Passivation at 4000 Hz

Abstract

Occupational noise-induced hearing loss prominently occurs due to unavoidable sound frequencies mainly in the range of 3000 to 6000 Hz. This frequency region thus holds great importance for acoustic insulation. Polymeric foams with open cellular frameworks are mostly employed for sound absorption in these frequency regions. To enhance their sound-absorbing ability, nanofillers are integrated with the polymeric matrix. However, the majority of the incorporation methods result in a single-phased porous structure, which limits their potential. Herein, an altered method of modification of multiwall carbon nanotubes (MWCNTs) is explored for the preparation of modified polyurethane foam via a simple one-pot immersion-hydrothermal-evaporation method. A unique self-assembled nanolayered structure with nanopores was fabricated through optimized experimental conditions resembling a double three-dimensional form. This gave rise to an additional resonating-type structure within the porous-type matrix. Thus, a hybrid-type sound-absorbing material with distinctive structure was fabricated which could help achieve focused sound absorption ability at the desired frequency. The sound pressure level evaluated at a frequency of 4000 Hz was found to improve through incorporation of 0.5 wt % modified CNTs. The mean percentage enhancement in sound isolation for treated foam in comparison to untreated foam is 15 to 20% at 4000 Hz. The development of distinctive structures within the polymeric framework opens up a plethora of horizons that could be employed at the industrial level as well, and such structures could be engaged for achieving other eccentric properties, which would further enhance their applicability.