Enhanced flame retardancy of polyurethane foam with alginate-based flame-retardant coating.

Polyurethane (PU) foam is widely used in industrial and civil fields, but it is highly flammable. An eco-friendly flame-retardant coating has been fabricated from sodium alginate (SA) and mica powder, it has been applied to PU foam using a facile direct dip coating method, followed by crosslinking with Ca and modification with polydimethylsiloxane (PDMS), respectively. The original porous network structure is maintained in the coated PU (SMPU) foam with a porosity of 90.51 %, and exhibits good thermal stability, hydrophobicity and excellent flexibility. Moreover, the as-prepared SMPU foam exhibits reduced flammability, e.g., the limiting oxygen index (LOI) for combustion of SMPU foam is 30.5 %, whereas that for unmodified PU foam is 16 %. The SMPU foam also exhibits a self-extinguishing effect without melt dripping and passes UL-94 V-0 rating. A significant reduction in the release of heat as well as total smoke and CO formation during combustion was noted using cone calorimetry. These improvements in combustion behavior may be ascribed to a physical barrier formed by non-flammable mica powder, SA and PDMS which displays char forming ability. A facile strategy for improvement of the fire safety of PU foam using a green and efficient flame-retardant coating has been demonstrated.