Cluster size effect in hardness of nanoclay/epoxy composites

The mechanical and thermal properties of nanoclay polymer composites have been experimentally investigated over the last decade. Most of the research has been focused mainly on the control of their interplanar structures, which govern the global properties of the composites. In reality, these structures (both exfoliated and intercalated patterns) are hardly achieved through the use of conventional manufacturing process for plastic products. Different sizes of clusters mixed by nanoclays and matrix would be easily formed, particularly in the extrusion of polymer-based components. This paper experimentally studied the hardness and interlaminar shear properties of nanoclay/epoxy composites with different amount of nanoclay content, which formed different sizes of nanoclay/epoxy clusters after mixing in an extruder. The results showed that the micro-hardness of the composites could be enhanced when a small amount of nanoclay was added into the epoxy. However, there was an optimal limit in which the hardness was dropped by continuously increasing the nanoclay content. Microscopic observation on the fracture surfaces showed that the size of the clusters varied with the amount of nanoclays used in the composites. Although previous literatures have reported that the use of nanoclays in polymer-based composites could enhance their mechanical properties, the interlaminar shear test indicated that the short beam shear strength of the composites decreased after adding the nanoclays into the matrix.