Studies Of The Fundamental Physico-chemical Properties Of Chitosan In Relation To Application

Chitosan is one kind of very promising natural polymer materials, itsfundamental physico-chemical properties and related application aremainly influenced by the degree of polymerization (DP) and degree ofdeacetylation (DD). The results obtained are basic and significant for thefuture applications.By preparation of chitosans with two series, e.g. one with confirmedDD and varied DP, and another on the contrary, both characterized byFTIR spectroscopy and viscosimetry, respectively. This work studied theinfluences of these two main parameters on the surface properties,thermal stability, rheological and dissolution behavior.Utilization of the contact angle measurement and the combing rules ofvan Oss-Chaudhury-Good to study the surface properties of these twoseries chitosans, results showed that both the degrees of deacetylation andpolymerization are importantly to influence the surface free energy andrelated components for chitosans. For example, chitosans with the same of the DD, the influence from DP is that the higher the DP, the greater isthe surface free energy, the Lifshitz-van der Waals component, the Lewisacid/base ratio, the Lewis acid component and polarity, while the Lewisbase component is observed on the contrary. For chitosans with thesimilar DP, the DD has been found to be principally a dominator toinfluence the surface properties. Moreover, it was found that the influencefrom DD is that the higher the DD, the greater is the surface free energy,the Lifshitz-van der Waals component, the Lewis acid and basecomponent ass well as the polarity, while the Lewis acid/base ratio on thecontrary. Studies also found that the relationship between the DD andγsmay follow an equation as below:γs=-56．74+108．18 DD.The thermal stability of these two series chitosans was investigated byDSC and TGA. We found that the chitosan is decomposed under atemperature increasing condition in three stages. In the first stage, theresidual moisture within chitosan was removed visibly. The thermaldecomposition of chitosan was visible in its second temperature increasestage and evidenced by a sharp valley in all TG curves. Finally, thedecomposition of chitosan is less influenced by temperature due to weightloss unvisible. According to recorded DSC and TG curves for two serieschitosans, the greatest weight loss-based temperature, Tp, is influencedby both the DD and DP, for varied DP and confirmed DD, the Tp isvaried with the DP; while for similar DP series, the higher the DD, the greater is the Tp.Rheological analysis indicated under a constant temperature conditionand to confirm the DD of chitosan, both the structure-viscosity index,△η,and the zero-viscosity,η0, are increased proportional to the DP, while thenon-Newton index, n, is on the contrary. Additionally, to confirm the DPand to vary the DD, the greater the DD, the greater is the n, and thesmaller are the△ηandη0．To increase the temperature, it was found thatthe n is enhanced, but the△ηandη0 are reduced.The dissolution of chitosan in HAc and HCl was studied by dynamicconductivity measurement. Based on recorded dynamic dissolving curves,the dissolution behavior of chitosan was described by a mathematicalmodel, e.g. dC/dt=k₀ + k-1C + k₂C²ï¼ŽTo analyze the k values found thatthe constants, k₁ and k₂, are quite small, this suggests that the dissolutionof chitosan in acid solution is probably controlled by the zero rateconstant-based kinetics.