Properties of waterborne polyurethane with phosphorus-nitrogen synergy effects

A flame retardant waterborne polyurethane (PU) was prepared by using N, N-bis(2-hydroxymethyl) aminoethyl phosphonic acid dimethyl ester and toluene diisocynate. The performance of the PU was studied with oxygen index (LOI), thermo-gravimetric analysis (TG), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The results showed that with 15% flame retardant in the PU, the LOI of the PU reached 30.2%, making the polyurethane from flammable level reduced to flame retardant level. Compared with unmodified waterborne polyurethane, the thermo-decomposition temperature of the PU was reduced, but the maximum decomposition rate dropped by 38.9% and the amount of carbon residue increased by 1075%. The surface of carbon residue was compact and smooth without holes, which would be good for separating oxygen and heat. Phase separation with increasing flame retardant content showed regular changes. With increasing content of flame retardant, tensile strength increased and elongation at break decreased.