NMR relaxometry evaluation of nanostructured starch-PLA blends

Abstract

Blends formed by starch and poly(lactic acid) (PLA) are very promising from environmental and economic standpoints, because starch is an abundant and cheap natural polymer and PLA is a biodegradable polymer that has good mechanical properties. In this study, starch-PLA blends were prepared by solution casting, employing chloroform and distilled water as a solvent pair. Then, dispersions containing 1, 3 and 5% montmorillonite clay and a dispersion containing 0.1% silica were added to the starch-PLA blends. The new materials obtained were characterized by X-ray diffraction, thermal analysis and, especially, nuclear low-field nuclear magnetic resonance (LF-NMR) relaxometry to measure the proton spin-lattice relaxation. All blends composed of starch and PLA showed significant increase in relaxation time due to the homogenous mixing of both polymers as a consequence of strong intermolecular interaction between them. Addition of clays caused substantial modification of the material and a large unique domain was observed. As a consequence, the domains corresponding to pure polymers were not observed. With the addition of the clay NT25, intermediate degradation temperatures were observed at concentrations of 3 and 5%, compared to the degradation temperatures of pure polymers. The X-ray diffraction results indicated the formation of an intercalated nanocomposite. There was an increase in the organization of the material compared to previous results observed for polymeric material, indicating the formation of an intercalated structure.