Preparation and Characterization of Cross-Linked Starch/Poly(vinyl alcohol) Green Films with Low Moisture Absorption

The effects of incorporating different cross-linking agents into starch/poly(vinyl alcohol) (PVA) blend were examined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), mechanical characterization, dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), moisture absorption tests, and scanning electron microscopy (SEM). Different cross-linkers such as borax, formaldehyde, epichlorohydrin, and ZnO were used to cross-link the films at the same weight percent. The films were prepared by gelatinization followed by a solution casting method. SEM microstructures revealed that the destructuring of starch granules was significantly influenced by the presence of cross-linkers during the gelatinization process. The extent of cross-linking was measured through the determination of the normalized gel mass and the normalized swelling degree of the films in dimethyl sulfoxide (DMSO) solvent. Tensile strength and tensile modulus were highest in borax cross-linked film, while the highest flexibility was achieved with the epichlorohydrin cross-linked film. Damping was remarkably increased, and moisture absorption was considerably decreased in the cross-linked films. The onset of thermal degradation was lowered, but the char yield was slightly increased in the cross-linked films.