Starch Nanocomposites with Platelet and Fibrillar Fillers

Cast amylopectin-based nanocomposite films were prepared and characterized with focus on their structures and mechanical properties. Sodium-rich montmorillonite (MMT) clay was used as a filler together with a water-soluble polymer, poly[(isobutylene-alt-maleic acid, ammonium salt)co-(isobutylene-alt-maleic anhydride)] (PIM), that was added to enhance the compatibility and interfacial strength between the clay and the matrix. Microfibrillated cellulose (MFC) was added to investigate any synergistic effects between the clay and nanofibrous additive. When MFC, MMT and glycerol were present, their concentrations (solids content for MFC and MMT), were, respectively, 10, 4 and generally 30 wt%, with respect to the total dry mass of the film. The solids content of PIM was 30 wt% of the total mass of clay and PIM. Transmission electron microscopy and X-ray diffraction showed that the clay was well dispersed in several systems. It was found that a certain premixing procedure with the clay and PIM dispersion at elevated temperature (80 degrees C) and a film heat-treatment (150 degrees C), yielded, in relative terms, a good combination of high stiffness, strength and extensibility. Additionally, it was found that the clay dispersion was better in absence of the glycerol plasticizer. Field-emission scanning electron microscopy indicated that the distribution of MFC in the amylopectin-based films was not optimal and, in addition, the combination of clay and MFC did not seem to have any synergistic effects on the mechanical properties.