¹H NMR study of amylose films plasticised by glycerol and water

Amylose–glycerol films prepared by casting from solution were hydrated to different water contents. Wide-angle X-ray diffraction analysis suggested that the films were partially crystalline and contained the B polymorph. At a given hydration level, the presence of glycerol did not affect the extent of crystallinity or polymorphism of amylose. Proton NMR relaxometry was used to study the effects of water and glycerol on the molecular mobility of amylose. Spin–spin and spin-lattice relaxation parameters suggested a step change in the mobility of amylose when sufficient plasticiser, water and glycerol, was added to decrease the glass transition temperature (T_g) such that it became equal to or smaller than the observation temperature (T), i.e. (T−T_g)≥0. The mobility of amylose probed through the properties of the rapidly decaying component of the spin–spin relaxation varied with temperature in an identical fashion for films in the glassy state regardless of their composition. In the rubbery state, the mobility of amylose increased with increasing glycerol and water contents, i.e. with increasing (T−T_g). The mobility of amylose in the glassy state was best assessed through the spin-lattice relaxation times which suggested that at a given (T−T_g), the addition of glycerol leads to a decreased mobility probably through its well documented antiplasticising role. The findings were discussed in relation to documented changes in important physical properties of amylose films such as elongation and gas permeability.