Thermal effect on the microhardness of chitosan films.

In this communication we present the results obtained from a study on the e ffect of thermal treatments of chitosan films with different molecular weig hts, but with a similar acetilation degree, carried out by microhardness. I t was found that the hardness of films prepared from both type of chitosan is similar, of approximately 190 mPa. This suggest that this property is al most independent from the molecular weight in a wide range. The hardness in creases notably with a moderate heating (60 degrees C) reaching a constant value of about 450 Mpa after 60 minutes at this temperature. This is attrib uted to the loss of water and the formation of new intermacromolecular bond s leading to a more compact network. The increase of hardness is accompanie d by an increase in the fragility of the films.