Polyurethane-clay nanocomposite adhesives were prepared by different synthetic routes and their microstructures were determined by X-ray diffraction measurements and from transmission electron microscopy images. The preparation method of the polyurethane nanocomposite adhesives was systematically changed, that is, condensation either in the presence or absence of catalyst, concentration and type of nanoclay, premixing order of nanoclay (nanoclay was either premixed with the polyol or isocyanate part) and by using MDI surface treated nanoclays. Depending on the polymerization conditions cluster, intercalated, and exfoliated clay structures were obtained. The flame retardant properties of the manufactured nanocomposite adhesives and the synergistic effect of clay in combination with dolomite were investigated by cone calorimeter and UL 94 vertical burning tests. The results indicate that addition of nanoclay reduces burning time and the total heat evolved (THE) at flame out, and that the type of assembled clay structure (cluster, intercalated or exfoliated) had a significant effect on the flame retardant property. Nanocomposites with 3 wt % of clay loading gave the shortest burning time, the lowest THE and also UL 94 V-2 ratings were reached, although the flame retardancy in terms of heat release rate and time to ignition was not improved.

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In this study, the effect of surface properties of three organophilic montmorillonites, i.e., the structure and concentration of organic amine surfactant modifier on the degree of dispersion in water expandable polystyrene (WEPS)-organoclay nanocomposites, was investigated. The WEPS nanocomposites were synthesized via a conventional suspension polymerization in which water droplets were finely dispersed in the polystyrene-clay matrix with the aid of a hydrophilic polymer. The combined transmission electron microscopy and wide angle X-ray scattering results showed a poor dispersion of the organoclay with high organic modifier content and thickness of surfactant layer (highest gallery distance) in WEPS matrix. Based on a simple phenomenological explanation, this was attributed to the escaping of polymer chains from organoclay galleries, i.e. inverse intercalation during suspension polymerization, after reaching a critical average length. The immiscibility between polymer and long surfactant chains is the major mechanism of inverse intercalation. On the other hand, different morphologies e.g. intercalated and exfoliated was observed in 'Corresponding author samples containing organoclays with smaller gallery distances. Therefore, the extent of exfoliation of an organoclay in WEPS matrix does not relate to the basal spacing of the organoclay. Comparing the observed results with the existing models' predictions of phase behavior of polymer melt/organoclay nanocomposites suggested the need to development a new model for the prediction of polymerization inducing phase separation in organically modified layered silicates-monomer-polymer blends.