Thermomechanical plasticization and stability characterization of different chitosan types

Thermomechanical plasticization of chitosans differing in molecular weight (1.3-2.6∙10⁵ Da) was investigated using a dual glycerol-lactic acid plasticizer system. A solvent-free processing approach was demonstrated, yielding stable thermoplastic materials. Plasticization was performed in a two-stage process using a batch mixer, followed by compression molding. The resulting materials were characterized by FTIR spectroscopy, capillary rheometry, TGA, DSC, optical microscopy, and SEM. Water absorption, solubility, volatile content, and mechanical properties were determined after 24 h and 2 months of storage to characterize long-term stability. Homogeneous, dense matrices exhibiting pseudoplastic flow behavior and good thermal stability (mass loss <10% up to 170 °C) were obtained. FTIR analysis indicates predominant protonation of amino groups and the formation of ionic interactions within the matrix. Thermal and DSC analyses indicated reduced structural order and increased chain mobility after plasticization. Material performance was influenced by the molecular weight of chitosan. Lower-molecular-weight chitosan exhibited significantly higher water absorption and solubility, while higher-molecular-weight samples exhibited improved mechanical strength and reduced deformability. Despite these differences, all systems showed comparable thermal behavior and processability. The glycerol-lactic acid system enables efficient, scalable thermomechanical processing of commercially available chitosans, providing a robust, solvent-free route to thermoplastic chitosan materials. This work provides a systematic and comparative investigation of the effect of subtle chitosan molecular-weight variations under identical glycerol-lactic acid conditions on thermomechanical plasticization, with an explicit focus on long-term stability and processability robustness.