Effects of the addition mode and amount of organic montmorillonite in soft-core/hard-shell emulsion on fire protection, water resistance and stability of fire retardant coating

[Display omitted] •A novel organic-inorganic soft-core/hard-shell hybrid emulsion was used as the film former of the waterborne intumescent fire retardant coating and greatly improved the fire resistance performance.•The optimum addition modes of OMMT in soft core hard shell emulsion was shown to be in core layer.•The performances of emulsion and coatings, such as the water resistance, fire resistance and film forming property, were improved by combining adding OMMT into soft core phase with the structure of soft core and cross-linking hard shell. In order to meet the basic demands for everyday use and construction requirements, the organic montmorillonite/poly-(Methyl methacrylate-butyl acrylate)/poly-(Methyl methacrylate-butyl acrylate −methacrylic acid) soft-core/hard-shell emulsion was synthesized and used as the film former of the waterborne intumescent fire retardant coating. The effects of addition mode and amount of organic montmorillonite in emulsion on coating properties were studied. Emulsion stability analysis, water resistance tests of films and fire resistance tests all showed the optimum addition mode of OMMT was in the core layer of soft-core/hard-shell emulsion. The reason could be that the addition of OMMT in core layer could not destroy core-shell structure and cross-linked structure, and parallel-arranged OMMT was distributed well. The result of differential scanning calorimetry (DSC) showed that soft-core/hard-shell emulsion containing OMMT in core layer had lower glass transition temperature (Tg) of core layer and higher glass transition temperature (Tg) of shell layer, which play an important role in lowering film-forming temperature and enhancing resistance to water. The results of fire protection test indicated the fire resistance of coatings were significantly improved by adding OMMT in the range of 1.0wt.% to 1.5wt.% in core layer and scanning electron microscopy (SEM) demonstrated that the well-dispersed OMMT could improve the foam structure of char layer by limiting the escape of inert gases and filling carbon layer’s tiny cracks generated at high temperature.