Integration of safety and energy storage: Experimental study on thermal and flame-retardant properties of ammonium polyphosphate/polyvinyl alcohol/modified melamine foam as a composite phase change material

Organic phase change materials pose a risk of flammability in practical applications, and composite materials prepared after encapsulation also face the problem of high thermal resistance when in contact with equipment. In this study, a new type of flexible composite phase change material with flame retardancy and insulation was prepared. Melamine foam (MF) was also physically modified with flexible long-chain polymer polyvinyl alcohol (PVA) to improve tensile property, leading to the preparation of one porous material, denoted as PMF. Subsequently, ammonium polyphosphate (APP), an intumescent flame retardant, was incorporated to formulate the composite phase change material APP/PEG@PMF. The mechanical properties of melamine foam were assessed using the universal material testing machine both before and after modification and the optimal amount of PVA, determined to be 15 %, was selected. The experimental results show that the composite materials have a high latent heat (both higher than 160 J/g). After 100 heating and cooling cycles, the material demonstrates excellent shape stability, proficiently preventing PEG leakage during phase transformation. Additionally, it exhibits prominent shape memory attributes, thereby reducing the contact thermal resistance when integrated within equipment. The oxygen index meter and vertical combustion test show that when the APP content is higher than 10 %, the oxygen index of the composite material reaches 22.6 %, while the thermal conductivity decreases to 0.13 W/(m·K). It not only improves the safety of PCMs in practical application scenarios, but also broadens the potential application spectrum of this composite material within the thermal insulation domain.