A green, durable and effective flame-retardant coating for expandable polystyrene foams

Expandable polystyrene (EPS) foam, one of the most widely used thermal insulation of building materials, is highly flammable, while its traditional flame-retardant coating has been severely restricted by the low efficiency and the use of toxic formaldehyde adhesive. Herein, we demonstrate a formaldehyde-free phosphorus-containing polysiloxane coating that acts as both an adhesive and a flame retardant for EPS foams. In this design, on one hand, the high adhesion of the polysiloxane can evenly and tightly bind the EPS beads and expandable graphite (EG, a flame-retardant synergist filler) at a relatively low additive loading, thus leading to durable thermal insulation even under high humidity conditions. On the other hand, the functional coating can promote the formation of P/Si-containing graphited char layers during the combustion of the EPS composite, which can effectively isolate oxygen, heat, combustible compounds, and smoke particles. As a result, the EPS composite showed excellent flame retardancy with a high limiting oxygen index of 36%, a UL-94V-0 rating, and a significantly reduced peak heat release rate (−76%), while the smoke release can be greatly suppressed both in cone calorimetry and smoke density tests. This work provides a new strategy for the design of environmentally friendly coatings, which can give EPS foam high fire safety and excellent comprehensive performance.