Interpenetrating vinylester/epoxy resins modified with organophilic layered silicates

Organophilic layered silicates (OLS), modified by means of cation exchange, were added in amounts of 5–15 wt.% to vinylester (VE)/epoxy (EP) hybrid resins which can form interpenetrating networks (IPN) after curing at T=150 °C. The resulting phase structure was studied by atomic force microscopy (AFM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was established that the OLS were intercalated by the hybrid resin. On the microscale silicate particles surrounded by a broad EP interphase were formed. This "encapsulation" was considered as the major cause for the reduction in both stiffness and glass transition temperature (Tg) of the resins. Irrespective to the coarse dispersion of the OLS, the fracture energy of the resins was doubled by adding 5 wt.% OLS. The fracture energy decreased, however, with increasing OLS content. This was explained by changes in the failure mode concluded from fractographic studies. The type of the organic cation modification of the OLS had no effect on either morphology or toughness. This was attributed to the coarse dispersion of the OLS and its encapsulation by the EP phase in the VE/EP hybrid resins.