A green flame retardant coating based on one-step aqueous complexation of phytic acid and urea for fabrication of lightweight and high toughness flame retardant EPS insulation board

• A facile and efficient coating technique to improve flame retardancy of EPS foam composites by introducing polydopamine is developed. • The phosphorus-nitrogen flame retardant coating is applied for development of light weight and high toughness flame retardant EPS . • The studied flame retardant coating displays low toxicity, high efficiency and simplicity, which is crucial to EPS industry and human health. Green flame retardants have drawn much attention because of their environmental friendliness. But for the high flame retardancy of flammable polymers, most existing green flame retardants are unsatisfactory, even the flame-retardant process can not achieve high efficiency and environmental protection. In this work, flame retardants and flame-retardant process are addressed in a two-pronged approach. An eco-friendly bio-based synergistic flame retardant (PAU) was synthesized based on phytic acid (PA) and urea (U) through simple complexation assembly in water. The designed flame retardant coating can be directly coated on the surface of any topological shape with polydopamine as an adhesive. Flame retardant expandable polystyrene (EPS-PAU) with light weight and high toughness is prepared with the designed PAU flame-retardant coating. The coated EPS plates exhibit V-0 UL-94 rating and 42.0 % of limited oxygen index and excellent smoke suppression. Moreover, the density of EPS-PAU is slightly increased only by 2.27 % on the basis of the neat EPS, and the hard shell formed using PDA as an adhesive layer is beneficial for the improvement of impact strength. This novel biomass-based PAU system provides a promising strategy for manufacturing polymer products with excellent flame retardancy, smoke inhibition and light weight.