Novel phosphorus-containing polyborosiloxane synergistic fireproof layer: A multifunctional emergency barrier for building window fire protection

Building windows, as vulnerable areas in the wildland-urban interface fires and building facade fires, often crack due to external flames, leading to fire spread indoors and significant loss of life and property. Thus, a multifunctional fire-resistant adhesive layer (PAMSPB) was designed, integrating siloxane, phosphate, ammonium, and borate structures, and combined with SiO₂ aerogel felt to create an emergency fire-resistant curtain. Results show PAMSPB exhibits excellent thermal stability and high-temperature charring capacity, with a T_1 % (temperature at 1 wt% weight loss) of 277 ℃, 176 ℃ and 131 ℃ higher than PAMS and PAMSP, respectively. Its char residue at 800 ℃ reaches 37.57 wt%, significantly higher than PAMS (1.17 wt%). In fire-resistance tests, the composite curtain drastically reduces the backside temperature of glass, effectively preventing cracking and flame penetration. Compared to pure aerogel felt, which burns through, PAMSPB maintains the structural integrity of the aerogel felt and reduces the backside temperature by 310 ℃. Mechanistic analysis reveals that outer PAMSPB layer forms a dense, high-temperature ceramicized char under flame impact, enhancing fire resistance and thermal insulation. The inner layer tightly adheres to glass surface under high-temperature exposure, ensuring curtain remains securely attached during fires. The unique elemental composition and high-temperature reaction mechanisms (inert gases to dilute combustibles, inorganic barriers) not only delay flame spread but also provide critical protection through multilayer synergy. The outer layer blocks high-temperature heat flow, while inner layer suppresses thermal stress accumulation. This creates an efficient fire barrier for building windows, preventing fire spread and reducing disaster losses.