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 behaviour and moduli of CMCs are closely correlated to M cs . An interesting slope transition from negative to positive in the tan δ versus lg ω plot is observed at ω = 2.5 rad/s. The value of tan δ<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 behaviour 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 well matches 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 the 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.
|Original language||English (US)|
|Number of pages||15|
|Journal||Journal of the Balkan Tribological Association|
|Publication status||Published - Aug 1 2011|
All Science Journal Classification (ASJC) codes
- Mechanics of Materials
- Surfaces, Coatings and Films