Facile fabrication of chitosan Schiff bases from giant tiger prawn shells (Penaeus monodon) via solvent-free mechanochemical grafting

Fabrication of chitosan Schiff bases (ChSB) from giant tiger prawn shells (Penaeus monodon) using an environmentally friendly method has been conducted successfully. Transformation of Prawn Shells (PS) as raw material into chitin then chitosan was executed under ambient temperature. Later, three Ch Schiff bases (ChSB-A, ChSB-S, and ChSB-V) were successfully synthesized for the first time via solvent-free mechanochemical grafting with 2-hydroxy benzaldehyde, 4-methoxy benzaldehyde, and 3-methoxy-4-hydroxy benzaldehyde, respectively. Synthesis was carried out with Shaker Mill-Ultimate Gravity equipped with a Teflon jar with zirconia balls; then the product was characterized. FTIR analysis proved the conversion of free amine to imine groups. The degree of substitution (DS) and crystallinity index (CrI) were determined by elemental analysis and X-ray diffraction. The DS values obtained were about 0.343, 0.795, and 0.055 for ChSB-A, ChSB-S, and ChSB-V, respectively. The CrI of ChSB-A, ChSB-S, and ChSB-V was 53.3, 51.7, and 46.9 %, respectively. The thermal gravimetric analysis showed that the mechanochemical grafting of Ch improves the thermal stability of ChSB. This developed method provides a novel potential technique to convert PS into ChSB products by solvent-free mechanochemical grafting.