Effects of Chemical Treatment and Mixing Methods on Fracture Behaviour of Halloysite-Epoxy Nanocomposites

As a naturally existing clay mineral, consisting of unique tubular particles in submicron or nano-scales, halloysite has recently attracted some research attentions as a new type of additive for strengthening and toughening epoxies [1-3]. Tubular halloysite particles, mostly halloysite nanotubes (HNTs), are readily obtainable and are much cheaper than other nanoparticles such as carbon nanotubes (CNTs). More importantly, the unique crystal structure of HNTs resembles that of CNTs in terms of aspect ratio. There are obvious advantages in using hallooysite as filler for polymer composites. First is the ease of processing, because halloysite particles are mainly discrete nanotubes with no or little surface charge. Such particles may eliminate the need for intercalation and exfoliation, as required by other two-dimensional nanoclay fillers such as montmorillonites (MMTs), to mix with polymers to produce homogeneous particle dispersion. On the other hand, halloysite belongs to the 1:1 type of the silicate clay family with a crystal lattice in each layer consisting of one aluminium octahedron sheet and one silicon tetrahedron sheet and with a monolayer of water in the interlayer positions. Certain surface modifications to halloysite may provide intercalations of halloysite layers with organic and inorganic compounds, which may provide the opportunity of exfoliation of individual layers, similar to those of organically modified MMTs. Preliminary results have demonstrated that blending epoxies with a certain amount of HNTs can noticeably increase their fracture toughness, strength and modulus, without sacrificing their thermal mechanical properties such as glass transition temperature (Tg) [2, 3]. However, achieving homogeneous dispersion of HNTs in epoxies remains a challenge due to agglomeration of large particle clusters [3].