Polymer nanocomposite technology has become an important and strategic field, since Okada’s group realized the commercialization of clay/nylon-6 nanocomposites. This new family of materials exhibit outstanding mechanical properties and thermal stability with low filler contents. A lot of effort has been dedicated to the exploring of new materials with low cost and high performance for potential applications to structural materials, coatings, microelectronic devices, and packaging products. Besides mica-type silicates, many other nanostructured materials such as graphite, titania, calcium carbonate, etc., most of which are cheap and abundant, have been applied as inorganic fillers in polymer-based nanocomposites. High cost carbon nanotubes (CNTs) have also been widely investigated in dif...[ Read more ]

Polymer nanocomposite technology has become an important and strategic field, since Okada’s group realized the commercialization of clay/nylon-6 nanocomposites. This new family of materials exhibit outstanding mechanical properties and thermal stability with low filler contents. A lot of effort has been dedicated to the exploring of new materials with low cost and high performance for potential applications to structural materials, coatings, microelectronic devices, and packaging products. Besides mica-type silicates, many other nanostructured materials such as graphite, titania, calcium carbonate, etc., most of which are cheap and abundant, have been applied as inorganic fillers in polymer-based nanocomposites. High cost carbon nanotubes (CNTs) have also been widely investigated in different polymers. In the current work, epoxy-based nanocomposites with halloysite as the reinforcing phase were studied.

Halloysite, a kind of natural clay, was disclosed by SEM and TEM to consist of a lot of nanotubes, which are morphologically similar to multi-walled CNTs (MWCNTs). Considering the extremely low cost of halloysite compared to CNTs, one can imagine that halloysite may be a potential alternative to CNTs. To evaluate the role of halloysite in polymer composites, in the present work, epoxy/halloysite nanocomposites were prepared. The morphology and properties of the nanocomposites were investigated using different techniques including SEM, TEM, TGA, DMA, three-point bending test and the charpy impact test. The results suggest that the incorporation of halloysite has insignificant effects on the thermal decomposition temperature and the glass transition temperature of the epoxy. The significant finding was that the charpy impact strength of the nanocomposites exhibited a tremendous increase while the flexural modulus was almost unchanged. The increase in impact strength at a halloysite loading of 3 phr by weight reached as high as 409%, compared to that of neat epoxy.

The behind toughening mechanisms were examined. It was found that the major mechanism was the formation of large damage zones in the nanotube-rich regions, accompanying the occurrence of crack deflection. In the damage zones, numerous micro-cracks were caused by nanotube pullout, nanotube bridging, etc. Moreover, in the epoxy-rich region, nanotube pullout, nanotube/matrix debonding, and matrix cracking were observed. What is more interesting is the phenomenon of nanotube bridging with a crack width ranging from nano-scale to micro-scale was also detected, which indicates that the HNTs have a strong interface strength with the epoxy matrix.

This work suggests that halloysite, which is cheap, abundant and environmentally friendly, can act as reinforcing fillers for polymer nanocomposites to achieve a high performance, at least for epoxy systems. Through this work, we also wish to generate a picture on the future applications of halloysite in polymer composites and other areas.