Eco-friendly fabrication of a delignified wood‑calcium alginate aerogel with improved mechanical properties for efficient thermal insulation and flame retardancy.

Wood based composites with low density and great flame retardancy are increasingly required as sustainable and low-carbon building materials for energy conservation. In this work, the symbiosis between bio-based calcium alginate (CaA) and delignified wood was fabricated to form delignified wood-CaA aerogel composites. The density of the delignified wood@CaA sample was dropped to only 89 kg/m from 120 kg/m of the control wood. In addition, its tensile strength, elongation at break, and bending strength reached 16.9 MPa, 4.6 %, and 40.2 MPa, which was increased by 128.4 %, 109.1 %, and 31.8 %, respectively compared to that of control wood. During either heating or cooling, the delignified wood@CaA sample always showed better thermal insulation than the control wood, moreover, it can be developed as an infrared stealthy material. Furthermore, the delignified wood@CaA aerogel reached the limiting oxygen index of 59.2 %, and it was self-extinguished immediately after leaving ignitor in the vertical burning test. In the cone calorimeter test, the total heat release and total smoke production of delignified wood@CaA aerogel decreased by 27.6 % and 71.4 % compared to that of the control wood, respectively. In summary, the light-weighted delignified wood@CaA aerogel composite with superior performance is an ideal material used in sustainable and low-carbon building.