Influences of molecular weight of epoxy binder on fire protection of waterborne intumescent fire resistive coating

Epoxy emulsions with different number average molecular weight ( M ¯ n = 446, 568, 1025 and 1739 g/mol) were used as polymer binders for preparation of waterborne intumescent fire resistive coating. The influences of M ¯ n of the epoxy resin on the properties and char formation of the coatings were investigated in detail by TGA, FTIR, EDS, SEM, rheological measurement and fire protection test. The TGA, FTIR and EDS results proved that epoxy binder with high molecular weight could improve thermal stability of the coating and enhanced anti-oxidation of the char layer at high temperature. The rheological results showed that the melting viscosity of epoxy binder increased with increase of M ¯ n , and the increasing melting viscosity of epoxy binder could slow down the expansion speed of the coating and also lead to an increase of the cell size of the char layer. The coating using epoxy with M ¯ n of 1025 g/mol as binder had good fire protection. However, epoxy binder with excessive high molecular weight led to formation of loose and uneven foam structure, which could significantly reduce the fire protection of the coating.