Structure and thermal properties of a chitosan coated polyethylene bilayer film

The thermal and the structural properties of chitosan coated polyethylene (PE) films were studied. The coating process did not significantly influence the thermal stability and the PE surface structure and/or composition of the polyolefin. Dehydration temperature of chitosan films reflected the strength of water/acetic acid/chitosan chains interactions. Glycerol, used as a plasticizer, formed new hydrophilic centres in the film matrix. Moreover it was better integrated in the CSEGLY than in CSAGLY network. Besides, the addition of a plasticizer in the chitosan films decreased the film degradation temperature. There were two main steps for the PE chitosan coated films degradation. The first degradation step was attributed to the chitosan coating and the second one to the additional degradation of both PE and CS. At a microscopic level, improved adhesion of the chitosan coatings on the polyethylene surface was observed. After coating processing characteristic bonds were found at the PE and chitosan side surface. In the coating layer, after drying, because of residual water and acetic acid, strong hydrogen bonds established. Finally, during drying in the presence of glycerol, acetic acid (which was bound with chitosan macromolecules) was displaced and new bonds between glycerol and N-H groups in the chitosan were formed.