Effect of deacetylation degree and molecular weight on surface properties of chitosan obtained from biowastes

A surface characterization of two types of unmodified chitosan properties with different molecular weight (MW) and deacetylation degree (DD) was carried out in terms of polymer concentration (a concentration lower than the saturation, the saturation concentration and a supersaturated concentration). The modification of the production conditions allowed to obtain chitosan samples with different properties (MW and DD), which eventually determined its surface activity. Thus, a kind of tailor-made chitosan may be designed to be adapted to different applications. Surface activity has been analysed by mean of measurements of surface tension, dilatational and shear rheology. The results have demonstrated that chitosan possessed a good surface activity at high ionic strength. Also, the increase in the concentration of chitosan in the solution, and the increase in molecular weight (and, therefore, a decrease in the degree of deacetylation) favoured the formation of aggregates, which improved the adsorption kinetics. The latter allowed adequate elasticity values to be reached more quickly. These prop-erties are reached faster for the higher molecular weight chitosan (lower degree of deacetylation), due to the more hydrophobic character that facilitates the interactions between the adsorbed aggregates. Surface rheology revealed a predominantly elastic behaviour of chitosan film. All of these results strengthen the idea that chitosan behaves as a surface-active hydrophilic Pickering agent.