Optimization and Characterization of Polyurethane Electro-Spun Nano-Membranes Used for the Surfaces of Sound Absorbent Multi-Layer Sheets

Abstract

With more and more attention paid to the quality of life, noise pollution has been ranked the third in environmental pollution. In this study a symmetrical multi-layer sheet was designed for a sound absorbent material. Needleless electro-spinning nano-membranes of polyurethane (PU) were used as the surfaces of the sound absorbent multi-layer sheets. The effects of the PU concentration, solvent ratio, membrane thickness and solvent additives on the surface morphology of the nano-membranes and the sound absorption coefficient of the sound absorbent sheets were carefully investigated by scanning electron microscopy and sound absorption measurements. The results showed that the optimal spinning solution was 10 wt.% PU and the solvents ratio of N,N-dimethylformamide (DMF) and tetrahydrofuran (THF) at 1:1. Under this condition, the average sound absorption coefficient of the multi-layer sheets increased from 0.29 for the 0 mm nano-membranes to 0.57 for the 1.2 mm nano-membranes (spinning time 240 minutes). For the nano-membranes in the range of 0.2–1.2 mm, it was noted that the average sound absorption factor of the multi-layer sheets increased with the increasing of the nano-membranes’ thickness and the absorption frequency for which the highest sound absorption coefficient occurred moved to lower frequencies with the increasing of the membranes’ thickness. By adding sodium dodecyl sulfonate (0.5 wt.%) and sodium chloride (1.0 wt.%) into the optimal solution, a nano-membrane with a nano-cobweb structure of 100% coverage rate was formed. Under the spinning condition of 10 wt.% PU, 1.0 wt.% NaCl, 0.5 wt.% SDS, 1:1 DMF/THF and 240 minutes, a nano-cobweb multi-layer material with an average sound absorption factor of 0.63 was obtained. Although not a large increase from the sound absorption coefficient for the nano-membrane multi-layer sheet material of 0.57, the results showed that the multi-layer sheet with nano-cobweb layer had a great improvement of sound absorption in the range of 500–2000 Hz relative to the nano-membranes. Therefore, a good sound absorption sheet with multi-layer structures was obtained successfully.