Fiber-based flexible composite with dual-gradient structure for sound insulation

Abstract Sound insulation materials in the traditional sense are rigid, which are usually dense and bulky, while common porous materials have almost no sound insulation ability. Herein, a fiber-based flexible porous composite is presented as sound insulator fabricated via single-sided coating finishing on the one side of a nonwoven framework and has been demonstrated for high performance noise reduction. The enhanced acoustic insulation is identified to be structure dependent of the area density and microstructure of the sound insulator and the type of filler. The flexible sound insulator exhibits ≈100% enhancement in broadband acoustic insulation over the whole frequency range compared to the bare nonwovens. And the most sound transmission loss (STL) of at the peak is up to 37 dB, which is about 30 times that of bare nonwovens. Furthermore, the novel sound insulator has an admirable dual-gradient structure in which the concentration gradient of coating finishing agent is opposite to the pore gradient. Therefore, sound insulation capacity of the sound insulator exhibits obviously anisotropy according to the incident direction of sound waves. This flexible porous material for broad-band sound insulation has an easy and inexpensive scalable production, demonstrating its great potential for lightweight requirements for specific applications.