Location: Dairy and Functional Foods ResearchTitle: Effect of chitosan molecular weight on rheological behavious of chitosan modified nanoclay at highly hydrated state) Author
Submitted to: Journal of the Balkan Tribological Association
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/19/2010
Publication Date: 4/30/2011
Citation: Liu, L.S., Liang, S., Chen, L., Yuan, P., Huang, Q., Yam, K.L. 2011. Effect of chitosan molecular weight on rheological behavious of chitosan modified nanoclay at highly hydrated state. Journal of the Balkan Tribological Association. 17(2):247-261. Interpretive Summary: Controlled release systems (CRS) are a rapidly developed technology. The technology has been used in various areas ranging from pharmaceuticals and cosmetics, to active packaging and functional biomaterials, to agrobusiness. Nanoclay can be converted to delivery vehicles for CRS by complexation with polysaccharides or synthetic hydrocolloids. However, little knowledge on the structure-function relationship of nanoclay-polysaccharide composites has been previously obtained. The present study performed fundamental research on the structure and properties of chitosan/clay nanoparticles in the attempt to facilitate industrial utilization. The study evaluated the effect of molecular weight and molecular size of chitosan on the rheological and thixotropic properties of the composites in a highly hydrated state. Results obtained from the study are useful for the design of various nanoclay/polysaccharide composites to satisfy different applications. Furthermore, the information generated from the present study is also useful for scientists and engineers, who are involved in the design of intelligent materials from plant polysaccharides 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: Effect of chitosan molecular weight (M(cs)) on the rheological properties of chitosan modified clay (CMCs) at highly hydrated state was investigated. With special emphasis on its effect on the thixotropy of CMCs, the structure recovery at rest after underwent a pre-shearing process was further performed by the oscillatory shear measurements in the linear viscoelastic region. It was observed that both stress-strain behavior and moduli of CMCs are closely correlated to M(cs). An interesting slope transition from negative to positive in the tan delta vs log omega plot is observed at omega = 2.5 rad/s. The value of tan delta < 0.5 over the entire range of frequency suggests a strong association in CMCs and a dominant elastic response of CMCs. Small peak-like transition of the shear viscosity, which denotes the yield region of the CMCs network, shifts to high shear rate with the increase of M(cs). Remarkably, different thixotropic behavior of these considered CMCs are observed relating to M(cs). G’(After) of CMCs with high M(cs) shows a linearly monotonic increase with the increase of the testing time, which is well match the power law of G’(After) ~ t(n). G’(After) of those CMCs with low M(cs), however, is distinctly deviated from the power law and possesses an exponential increase. The deviation of G’(After) becomes more marked with the decrease of M(cs). Furthermore, the effect of the pre-shearing history on the thixotropic properties of CMCs is performed by employing a large range of the pre-shear rate. Analysis of empirical Cox-Merz rule indicates a failure of the rule in CMCs system. CMCs prepared from low M(cs) chitosan are easier to be orientated at low shear rate.