Different formulations were designed to evaluate the effect of organically modified clay (DK4) on the combustion behavior of polystyrene (PS) containing an intumescent flame retardant, poly(4,4-diaminodiphenyl methane spirocyclic pentaerythritol bisphosphonate) (PDSPB). The results of transmission electron microscopy reveal that DK4 selectively dispersed in the PDSPB phase. An investigation of thermogravimetric analysis revealed that the thermal stability of PS resin showed no obvious change with the addition of PDSPB and DK4, but the residue increased. From the results of cone calorimetry, we observed that there were two steps during combustion. The dispersion of DK4 played an important role in improving the thermal stability and the flammability of the PS/PDSPB/DK4 nanocomposites. In the first step, DK4 was restricted in the PDSPB phase; there was no synergistic effect. A synergistic effect occurred in the second step when clay had a homogeneous distribution, in which the peak heat release rates were reduced by about 40 and 61% compared to the pure PS. A model of combustion behavior was developed according to these results. The synergistic mechanism was caused by the formation of the silicoaluminophosphate (SAPO) structure formed by reactions between PDSPB and DK4. Field emission scanning electron microscopy characterization showed that such an SAPO structure led to a ceramic-like residue after burning.

A novel modification of cyanate ester (CE) resin by epoxidized polysiloxane (E-Si) has been developed, and the modified system is coded as CE/E-Si. E-Si was prepared by the reactions among octamethylcyclotetrasiloxane, hexamethyldisiloxane, (3-aminopropyl)-methyldiethoxysilane, and diglycidyl ether of bisphenol-A resin. Six formulations were designed to evaluate the effect of the weight ratio between CE and E-Si on performance parameters. Results reveal that the addition of E-Si in CE resin cannot only significantly decrease the curing temperature of the CE resin but also improve the water resistance and toughness of original CE resin. Moreover, these positive effects increase with the increase of E-Si concentration in CE/E-Si systems. Thermal property investigation shows that the glass-transition temperature and initial degradation temperature of CE/E-Si systems are lower than that of original CE resin. For the flexural properties of the CE/E-Si systems, the E-Si concentration in the system exists a threshold, that is, when the E-Si concentration is smaller than the threshold, original CE and CE/E-Si systems have similar flexural properties, whereas when the E-Si concentration is higher than the threshold, CE/E-Si systems have lower flexural properties than original CE resin. All these changes of properties are closely correlated to the structure alteration from neat CE to CE/E-Si networks.

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