Mechanical and Fireproof Behaviors of Ammonium Polyphosphate Particles-Filled Shear-Stiffening Gels

The threats posed by flame burning and falling debris during fires are immense, making the development of flame-retardant and impact-resistant protective devices an urgent necessity. By employing particle reinforcement technology, ammonium polyphosphate (APP) particles were introduced into the shear-stiffening gel (SSG). The results of rheological experiments demonstrate that the SSG filled with APP particles (SSG@APP) can significantly enhance the storage modulus (G′) of the matrix SSG. The Prony series model effectively predicted SSG@APP’s storage modulus-frequency curve (R2 > 0.99). The shear stress–strain curve of SSG@APP demonstrates a high degree of consistency with the rate-dependent Cowper-Symonds model. Regarding impact protection, SSG@APP can dissipate 82% of the impact force under the condition of an impact height reaching 20 cm, which mainly stems from the shear-stiffening effect. When SSG is filled with 40% APP particles, the material can meet the V-0 vertical burning standard and has a measured limiting oxygen index (LOI) value of 30%. The total heat release (THR) values of SSG and SSG@APP were measured as 81 and 54 MJ/m2, respectively, indicating that SSG@APP exhibits superior flame-retardant properties. Therefore, SSG@APP is not only highly suitable for manufacturing wearable protective devices but also effective in safeguarding fragile/flammable items.