Preparation of Schiff Bases Derived from Chitosan and Investigate their Photostability and Thermal Stability

This study intends to synthesize Schiff bases derived from chitosan and aromatic aldehyde to investigate their photo-stability. The surface morphology and chemical structure of modified polymer were characterized using different techniques such as infrared spectroscopy (FTIR), scanning electron microscope (SEM), microscopic images, atomic force microscopy (AFM), and energy dispersive X-Ray (EDX) mapping. The thermal stability of synthesized materials was determined using thermogravimetric analysis (TGA). The modification in the chemical structure and morphology of new Schiff bases were verified using FT-IR, NMR, AFM, and SEM, whereas the thermal properties were investigated by TGA. Thus it was demonstrated that the thermal stability of chitosan has improved after the modification with the corresponding aldehyde. The decomposition temperature (Td) of pure chitosan is about 220 °C while it is between 250-256 °C for modified Schiff bases. Two approaches were applied to investigate the physical photo-stability of modified chitosan the weight loss percentage, and monitoring of the functional group by FTIR. The weight loss percentages of blank films are much higher than modified chitosan polymeric films. This is because the photo-degradation of blank chitosan is faster when irradiated by UV light. The main reason is attached aldehydes groups are aromatic moieties that absorb light in the UV region and convert it to harmless heat. Compound 3 showed the best results this might be because of the existence of the phenol group which is known as an excellent free radical scavenger. Chitosan modification with aromatic aldehydes would have an accelerating effect on thermal decomposition and they are photo-stabilizers, we used many techniques to prove that like FESEM, AFM, weight loss, EDX, TGA.