Structural and Thermal Properties of Agricultural Mulch Films Based on Native and Oxidized Corn Starch Nanocomposites

The current need to put an end to the accumulation of synthetic polymer waste during the cultivation and harvest of food has promoted scientific research for the development of biodegradable agricultural mulch films. Native and oxidized thermoplastic corn starch, with and without the addition of natural and modified bentonite (Bent) with an eco-friendly natural polymer such as chitosan (CS) are proposed as an alternative for this field. The hydrogen-bonding interactions affecting the structural and thermal properties of the designed films are followed and analyzed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and rheometry. Results indicate that chemical modification carried out onto starch's structure leads to a reduction in the OH polar groups, which affects their films interaction with nano-clays and glycerol. Besides, nanocomposites which present an intercalated structure demonstrate less effective intercalation when oxidized starch is used as the matrix. Additionally, a higher degree of crystallinity is observed, which could indicate a lower degree of compatibility between polymer and plasticizer. Thermal characterization confirms that the glass transition temperature of plasticized corn starch increases when oxidation is performed due to the decreased compatibility between the plasticizer agent and the oxidized corn starch.