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Title: Unique rheological behavior of chitosan modified nanoclay at highly hydrated state

item Liu, Linshu

Submitted to: Journal of Physical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2009
Publication Date: 4/15/2009
Citation: Liang, S., Liu, L.S., Huang, Q., Yan, K.L. 2009. Unique rheological behavior of chitosan modified nanoclay at highly hydrated state. Journal of Physical Chemistry B. 113(17):5823-5828.

Interpretive Summary: The technology of controlled release of active substances (CRAS) is a hundred billion dollar market, covering various areas from pharmaceuticals and cosmetics, to active packaging and agribusiness. Nanoclay can be converted to delivery vehicles for CRAS by complexation with polysaccharides or synthetic hydrocolloids. The present study evaluated the structure and properties of chitosan/clay nanoparticles to expand their industrial utilization. Furthermore, the study brings us one step closer to developing a series of intelligent packaging/wrapping/coating materials from pectin and other byproducts of agricultural processing. Eventually, the development of these new materials will expand the market for the products and byproducts from agricultural processing.

Technical Abstract: Chitosan/exfoliated clay nanocomposites (CCNs) were prepared using our newly developed method which is based on an electrostatic adsorption process and pre-exfoliated silicate clay. Atomic force microscopy, optical microscopy and rheological technology are employed to clarify the effect of the initial chitosan-clay weight ratio (m) on mesostructure and rheological behavior of CCNs. Mechanism analysis on the formation of mesostructure and the unique rheological behavior of CCNs is further performed. Our results indicate that a critical saturated adsorption ratio is observed to exist at m = 0.16. Increase of m gives rise to an interesting evolution in the mesostructure from smooth to porous network, which is attributed to the formation of a clay-connected structure at m < 0.16 and a chitosan-bridged structure at m > 0.16. Dynamic rheological tests indicate that both stress-strain behavior and moduli of CCNs exhibit a strong dependence on the initial ratio m. Shear-thinning behavior is observed and further confirmed by steady-state shear testing. Interestingly, two unique transitions, denoted as a small peak for CCNs with m > 0.06 at 10.0 < sheer rate < 30.0 s-1 and a sharp drop for CCNs with m = 0.16 at 0.2 < sheer rate < 0.5 s-1 in the shear viscosity, appear during the shearing process. Pre-shearing tests show that the mesostructure stability of CCNs has been effectively enhanced by the bridging effect of chitosan at higher m, though possessing an irreversible shearing-induced breakage. In combination with the evolution in the mesostructure, we conclude that the above rheological behaviors are mainly determined by the amount of adsorbed chitosan on clay surface through strong electrostatic interaction along with other interactions.