Polyimide Reinforced Silica Composite Aerogels with High Mechanical Properties and Low Thermal Conductivity for Thermal Insulation

Organic–inorganic hybridization is an effective strategy to enhance the mechanical properties of silica aerogels. However, their fabrication typically relies on supercritical or freeze-drying methods, which result in high production costs. In this study, polyimide-hybrid reinforced silica composite aerogels were successfully fabricated via a simple ambient pressure drying method. A controlled variation of polyimide content (5–30 wt %) enabled the transformation of the composite aerogels from transparent monoliths to white structures. Experimental results demonstrate that increasing the PI content promotes the formation of extended linear polyimide chains within the silica network, markedly enhancing the compressive strength and Young’s modulus of the composite aerogels. Meanwhile, the thermal conductivity of these composite aerogels remained low. Most notably, the composite aerogel with 5 wt % PI exhibited a thermal conductivity of 22.34 mW·m–1·K–1, visible light transmittance exceeding 70%, a limiting oxygen index of 42.6%, and a compressive strength of 0.7 MPa, demonstrating its potential as an excellent transparent and thermal insulation daylighting material. The composite aerogel SP30 exhibited a compressive strength and Young’s modulus of 2.15 and 8.55 MPa, respectively, outperforming previously reported SiO2/PI composites. Finally, an in-depth analysis of the growth mechanisms and structures of composite aerogels with varying PI contents was conducted. This study provides a promising technical route for the low-cost fabrication of high-performance organic–inorganic composite aerogels. The proposed composite aerogels hold considerable promise for next-generation building energy-saving materials, especially in transparent insulation and thermal management applications.