Pore-Gradient, Flexible, and Fully-Degradable Foam with Outstanding Noise Absorption and Thermal Insulation

With the increasing frequency of extreme cold conditions and emphasis on sustainable economic development, there is an escalated demand for the eco-friendly fabrication of thermal insulation and noise absorption materials. These materials must strike an optimal balance, effectively minimizing the excessive loss of heat from internal spaces while simultaneously mitigating the intrusion of noise from external industrial activities. The existing uniform cellular structures exhibit limited capabilities. Herein, inspired by natural gradient structures, a robust and biodegradable gradient foam that integrates continuous gradient cell structure and excellent thermal insulation and noise absorption is directly designed via a pioneering Pre-N₂ foaming strategy. Through the modulation of the physical blowing agent type in the first stage and the incomplete adsorption time of the gas in the second stage, a concentration gradient of the gas can be established, facilitating the formation of gradient foams. The lightweight and biodegradable gradient foam achieves a remarkable noise absorption coefficient of 0.83. In comparison to the uniform foam, the gradient-structured foam shows a 74% improvement in ball rebound resilience. Notably, its biodegradability is 600% higher than that of the uniform structure. The controllable synthesis of biodegradable gradient foams opens a promising avenue for the development of multifunctional materials.