Characterization of glycerol-plasticized starch and graphene oxide extruded hybrids

• Thermoplastic starch and graphene oxide hybrids were prepared by extrusion.
• The results indicated that the filler was well-dispersed within the polymer matrix.
• The aging process was investigated at high humidity conditions.
• Graphene oxide could not inhibit starch retrogradation.
• The hybrids showed improved stiffness with the increase in the filler content.

Melt extrusion was chosen to exfoliate graphite oxide (GO) incorporated to glycerol-plasticized cornstarch, aiming to produce hybrids with improved mechanical and barrier properties. The effect of increasing GO content, from 0.5 to 2.0 mass%, on the extruded and compression-molded samples was evaluated by X-ray diffraction (XRD), capillary rheometry, and dynamic mechanical analysis (DMA). The results suggested that the polymer-intercalated filler was well-dispersed within the thermoplastic starch (TPS) matrix, and corroborated the expected interaction between the functional groups of both components. Submitted to aging tests at 80% relative humidity conditions for ninety days, XRD data revealed that GO, independently of its content, could not prevent retrogradation of the starch matrix. Tensile tests, carried out for the hybrid samples before and after the aging tests, indicated improved stiffness as the GO content was increased. Before aging, the E values increased continuously, from 16.3 ± 2.9 MPa to 60.0 ± 3.9 MPa, with the increase of GO content from 0 to 2.0 mass%. Conversely, the variation of GO content led to a complex behavior in the E values for the aged TPS/GO hybrids. Images obtained by transmission electron microscopy revealed the presence of exfoliated and aggregated GO sheets.