Unsaturated polyester-based hybrid nanocomposite: fracture behavior and tensile properties

In this study, unsaturated polyester (UP) resin was reinforced by using an organically-modified montmorillonite (OMMT) and toughened with poly(n-butyl acrylate)/poly(vinyl acetate-co-methyl methacrylate) core-shell rubber (CSR) particles. The effects of OMMT and CSR levels on the fracture behavior and tensile properties of UP were investigated. The results showed that the incorporation of OMMT of up to 3 wt.% increased the UP fracture toughness (K_IC) to some extent, while further addition caused the fracture toughness to reach a constant level. Furthermore, the dispersion state of OMMT platelets and CSR particles inside the UP matrix was studied by means of transmission electron microscopy (TEM). TEM micrographs showed a good dispersion of organoclay tactoids with an intercalated structure or partial exfoliation for the UP reinforced by 1 and 3 wt.% OMMT. On the other hand, addition of 5 and 10 wt.% CSR particles to the UP increased the fracture toughness much more than the OMMT. Locally clustered but globally good CSR particle dispersion inside the UP matrix was observed in toughened UP specimens. Interestingly, a synergistic effect in fracture toughness was only observed for the UP hybrid composite containing 1 wt.% OMMT and 10 wt.% CSR particles, when compared with other reinforced, toughened, and hybrid specimens. In this case, the OMMT platelets were found to act as bridges between the small rubber-particle agglomerates, which may cause alternating clay debonding/CSR particle cavitation and improve plastic deformation inside the UP matrix. The incorporation of OMMT increased Young’s modulus and also decreased the tensile strength of the neat and CSR-toughened UP specimens with increasing the amount of OMMT.