series of chitosan samlpes with 91% deacetylation but different molecular weight were obtained by varying the time of chitosan solution in acetic acid aqueous solution at 70℃.The viscosities and flow behavior of the concentrated solutions of chitosan were investigated in 10% (vol%) formic acid aqueous solution after the solutions were prepared for two days by using RPX-705 Rheopexy Analyzer.For each chitosan sample

at the concentration of 3.5 g/100ml

the log (ηr/η0)versus lgγη0

M curves superimpose each other within the same rheogramme. Then the relationship between log nr and lgM was studied under different shear rates.For the highest M sample

the experimental data deviate from the straight lines greatly. This was because the chitosan chain degradated in acid solution during dissolving. The molecular weights were measured in acid solution after two days of dissolving

they were right on their own straight lines. However

no obvious degradation was observed after two days in the same solution for the other lower M chitosan sam-ples. In addition

the plot of nr against M was not a straight line

probaly due to particular interaction of chitosan.