The phase composition and molecular motions of plasticized wheat gluten-based biodegradable polymer materials studied by solid-state NMR spectroscopy

The water plasticized wheat gluten (WG) materials were prepared by thermal processing and studied by dynamic mechanical analysis and solid-state NMR spectroscopy. The results indicate that the materials displayed a broad distribution of molecular motions and could be divided into different phases in terms of their mobility above the Tg. The rigid phase mainly consisted of proteins and starch with enhanced interactions between the two components via hydrogen bonding with water molecules. Lipid and water formed the mobile phase, however, lipid molecules were always more mobile than water. The intermediate phase consisted of plasticized starch and proteins (mainly proline and glutamine segments). The whole plasticized WG materials were heterogeneous at a scale of 20-30 nm, but the miscibility between proteins and starch was enhanced via increasing hydrogen bonding interactions with water molecules. Such strong hydrogen bonding acted as adhesion among these multi-components/phases over a wide range of temperature thus resulting in good mechanical properties of the materials. The results demonstrated that solid-state NMR techniques can provide valuable information of quantitative composition of phase structures with different mobility in a multi-component system and the chemical nature of each phase along with the interactions among these components/phases.