Boron-Containing Polyelectrolyte Complex for Self-Extinguishing Polyurethane Foam

Polyurethane foam (PUF) is used in a variety of cushioning applications due to its comfort and flexibility, but it is very flammable. PUF releases a large amount of heat, dense smoke, and toxic gases and leads to fire propagation with melt dripping. To reduce flammability, surface coatings of an environmentally benign polyelectrolyte complex (PEC) composed of polyethylenimine (PEI), sodium hexametaphosphate (PSP), and varying concentrations of ammonium pentaborate (APB) were deposited onto the foam by immersion and complexation through pH adjustment. The incorporation of APB is imperative to the reduction of flammability of the PUF, as there are 32.1% and 23.5% reductions in the first and second peak heat release rates measured from microscale combustion calorimetry, respectively, when 0.5% APB is included. As the APB loading is increased, there is further reduction in the peak heat release rate and quicker self-extinguishing behavior. The favorable compressibility of flexible PUF is maintained with this coating, and self-extinguishing behavior is maintained after conditioning. This effective flame retardant treatment primarily acts in the condensed phase, forming a thermal barrier cross-linked by boron chemistries to reduce mass and heat transfer of PUF when ignited. This study demonstrates the promising and scalable incorporation of a boron-based additive to protect highly flammable polyurethane foam.