Toward controllable micropores in aerogels via response surface methodology: recycled PET/chitosan aerogels with a gradient structure for superior thermal insulation

Thermal insulation materials play a critical role in enabling energy conservation and sustainable development. While emerging micro-nanofiber-based porous insulation materials have attracted significant attention due to their remarkably lower thermal conductivity compared to traditional counterparts, their widespread application has been hindered by complex manufacturing processes and high costs. This study pioneers a novel pathway to address these challenges through the high-value transformation of waste polyethylene terephthalate (PET) bottles into cost-effective, high-performance materials. To overcome the difficulty of controllably constructing micropores within aerogels, we developed an innovative approach combining electrospinning with vapor-induced phase separation (VIPS), optimized via response surface methodology (RSM) to precisely engineer nano-pores on fiber surfaces. This strategy successfully produced recycled polyethylene terephthalate (rPET)/chitosan (CS) composite aerogels featuring a hierarchical “macro–meso–micro” porous architecture. Furthermore, by uniquely regulating tert-butanol concentration to control ice crystal dimensions, we constructed aerogels with a distinctive “dense-sparse-dense” gradient structure. The resulting material demonstrates exceptional comprehensive performance, with outstanding thermal insulation properties exhibiting an ultralow thermal conductivity of 0.040 W/(m K). This work, therefore, holds dual significance: it offers a viable solution for sustainable waste management and establishes a robust theoretical and technical foundation for the development of high-performance aerogels with customizable hierarchical and gradient structures. Graphical abstract