Influence of degree of polymerization of ammonium polyphosphate on anti-aging property of waterborne fire resistive coatings

5 kinds of ammonium polyphosphate (APP) with different degrees of polymerization (DP, DP = 5, 30, 78, 125, 184) were used as acid source in fire resistive coatings. After a period of accelerated aging tests, the influences of DP of APP on the anti-aging property of the coatings were investigated in detail by XPS, TGA, XRD, SEM and fire protection test. XPS results implied that the migration speed of APP with higher DP from inside to outside of the coating was smaller during the aging process, which could prevent the loss of APP and keep the intumescent performance of the coating. TGA and fire protection test results showed that the thermal stability and fire protection of the coating using APP with high DP could still maintain the excellent intumescent performances and fire protection. XRD results proved that the remaining APP could react with TiO2 to produce more ceramic TiP2O7 to protect the char layer. SEM observation indicated that the foam structure of the coating char layer would be better kept after being aged when APP of higher DP was adopted. Besides, the anti-oxidation property of the char layer would also be maintained. Therefore, the coating using APP with higher DP would more likely to keep the fireproof property after being aged, showing better anti-aging property.