Abstract

Nanoclay and a thermoplastic were incorporated into general purpose unsaturated polyesters in order to provide for toughening. The effect of each additive on physical and mechanical properties of the composite was explored to understand the advantages and drawbacks. Since, the morphology of multiphase systems plays a key role in determining the final properties, the micro- and nano-structures of the various binary and ternary systems, were evaluated by electron, optical, and atomic force microscopy.
Different mixing methods for preparing clay/polyester nanocomposites were used to explore the effect of nanostructure on characteristics such as glass transition temperature, flexural properties, and fracture toughness. The results indicated that the incorporation of nanoclay causes a slight improvement in fracture toughness and that the degree of intercalation/exfoliation did not significantly affect the properties.
Polystyrene and poly(styrene/methyl methacrylate) were synthesized by in situ free radical polymerization in the presence of Cloisite 20A to provide a toughening agent. This approach enabled the pursuit of two aims: (i) improving the degree of dispersion and the distribution of clay silicate layers, and (ii) preparing the thermoplastic additive. A second curing agent, methyl methacrylate, was included to promote the conversion of styrene inside the clay galleries as well as in the thermoplastic-rich phase. The morphological study showed that the thermoplastic additive forms a second phase, dispersed throughout the continuous thermoset-rich phase. In the ternary systems, X-ray diffraction and transmission electron microscopy (TEM) revealed a fine intercalated/exfoliated structure, where the majority of clay silicate layers were located inside the thermoplastic-rich phase. Experimental results indicated that the incorporation of the thermoplastic caused a slight improvement in fracture toughness. In contrast, a combination of the thermoplastic and the nanoclay caused a significant improvement in fracture toughness, without any reduction in glass transition temperature and elastic modulus.
The effect of the characteristics of the two phases and the microstructure on fracture toughness was explored. Results revealed that the microstructure (the size and distribution of thermoplastic-rich particles) had the greatest effect on fracture toughness. An interesting correlation between fracture toughness and the microstructure was found indicating the best particle size and spacing.