Synthesis of chitosan/TCN nanocomposites with the carbon dioxide assisted phase inversion

The chitosan (CS)/bis(2-hydroxyethyl)methyl tallow ammonium modified montmorillonite (TCN) nanocomposites are synthesized by the phase inversion procedure via the assistance of carbon dioxide (CO₂). The viscosity of CS/formic acid solution is reduced with the incorporation of CO₂ owing to the formation of carbamic acid. However, the incorporation of TCN promotes the viscosity of CS solution due to the interaction between TCN and carbamic acid. The morphology of CS/TCN nanocomposites is studied by scanning electron microscopy (SEM), where the surface of the membrane is dense and non-porous. The microstructure of the synthesized CS/TCN composite is further investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). It is found that the incorporation of TCN without the presence of CO₂ disturbs the crystallization of CS. Interestingly, the melting enthalpy of the CS/TCN composite is notably increased with the introduction of CO₂, demonstrating that the interaction between the TCN and carbamic acid enhances the formation of CS crystals. XRD and TEM results show that this interaction is able to promote the homogeneous distribution of TCN in the nanoscale with the non-exfoliated form, enhancing the mechanical properties of the synthesized nanocomposites. In particular, the synthesized CS/TCN nanocomposites with the assistance of CO₂ present exceptional mechanical properties, where the tensile strength (65.82 MPa) and Young's modulus (3512.48 MPa) are twice as high as that of the CO₂ free system.