Exploring morphological and thermal characteristics of chitosan/starch blend films derived from natural sources: incorporating thiourea and urea coupling agents with stearic acid plasticizer

Enhanced biobased polymeric films based on chitosan and starch polysaccharides were prepared and thoroughly investigated. The polymer components were coupled using thiourea and urea as crosslinking agents, with stearic acid incorporated as a plasticizer. The Fourier Transform Infrared spectroscopy (FTIR) and Energy Dispersive X-ray spectroscopy (EDX) data confirmed the successful crosslinking reaction through specific amide peak shifts and elemental distribution. Morphological investigations using Scanning Electron Microscopy (SEM) revealed that urea produced a homogeneous matrix, whereas thiourea induced a rougher morphology due to agglomeration. X-ray Diffraction (XRD) analysis revealed that thiourea-modified films achieved a significantly higher crystallinity index (43.2%) compared to urea-modified films (28.9%). Thermal behavior was analyzed using Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Differential Thermal Analysis (DTA), demonstrating that thiourea composites exhibited superior thermal stability with a residual weight of ~ 40% at 600 °C. Kinetic parameters were calculated using the Kissinger-Akahira-Sunose (KAS) model, confirming the enhanced activation energy of the crosslinked networks. The synthesized biobased polymers demonstrated thermal and mechanical stability suitable for applications in agriculture and packaging.