Ultralight and degradable polylactic acid bimodal fibrous sponges by direct electrospinning for effective acoustic absorption

Noise pollution is increasingly threatening human health and causing economic damage on a global scale. Current acoustic absorption materials predominantly rely on non-renewable resources, encountering dual challenges of inadequate noise absorption efficiency and lack of sustainability. This study proposes a scalable strategy for directly fabricating ultrafine PLA fibrous sponges with a bimodal diameter distribution through humidity-assisted electrospinning to improve acoustic performance. By adjusting the electrical conductivity of the spinning solution to regulate jet stretching, a bimodal fiber diameter can be achieved using a single nozzle. The stable physical entanglements between micro/nano fibers construct a "rigid-soft" network, endowing the sponge with robust mechanical properties, which can withstand 600 compression cycles with almost no plastic deformation. The dual-scale fiber network enhances the tortuosity of porous pathways and expands the contact area between the sound wave and absorbers, thereby achieving efficient acoustic energy dissipation. The noise reduction coefficient of the resulting sponge reaches 0.53 at the low areal density of 360 g m-2, which can be capable of reducing air compressor noise by 27.1 dB and decreasing white noise by 12.1 dB. Moreover, benefiting from the dual-scale structure with high specific surface area, the soil degradation ability of the bimodal fibrous sponge has been significantly enhanced. Compared to PLA sponges with uniform fiber diameters, the degradation rate of the dual-scale PLA fibrous sponges increased by 54.1%. The controllable fabrication of biodegradable fibrous sponges opens up a new avenue for lightweight sound-absorbing materials in the pursuit of sustainable solutions.