Hot Melt Reactive Extrusion of Chitosan with Poly(acrylic acid)

The hot melt reactive extrusion of blends of chitosan and poly(acrylic acid) (PAA) was carried out without any process additives such as organic solvent or plasticizer. The maximum amount of chitosan in the blend during the extrusion process was kept at 40wt%, since the melt viscosity of a system containing 50wt% of chitosan exceeded the torque limitation of the equipment. The carboxylic groups of PAA interacted with the amine groups of chitosan during the melt process, and the system exhibited good melt flow. The interactions between these two polymers were explained by investigating the results obtained by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal transition behavior of PAA was altered with a decrease of more than 10 degrees C in the peak melting point after extrusion. The infrared (IR) spectroscopic data confirmed the existence of a complex formation and possible hydrogen bonding between chitosan and PAA during the melt process. Scanning electron microscopy (SEM) micrographs indicated that chitosan was well-dispersed in the PAA blends up to 30wt% chitosan, with no indication of loose particles or other disruptions on the upper and lower fractured faces. This smooth interface might have been caused by the interaction between amide bonds of chitosan and carboxylic groups of PAA.