Molecular mobility glassy starch

Molecular Mobility in Glassy Starch Influence of Hydration and Sucrose... 

A polymer may show its backbone chain mobility increased because of plasticization, but this may not necessarily agree with the motions of water (or diluent) molecules, which become available to chemical reactions and microbial growth when these molecules are adequately mobile (Vittadini et al., 2001). It was reported that water, for example, has been found to be highly mobile even in a glassy state of waxy corn starch (9.3% moisture content). Hence, molecular mobility of water around reactive molecules involved in the degradation of AA into the films herein formulated is, as it was above pointed, a very important feature to be considered. Local water availability (that is at a molecular level) may be a key factor for AA stability in solid-like polymeric networks. 

Identification and characterization of domains with different mobilities were performed by C direct excitation (DE) and CP MAS, as well as by H static and MAS experiments. H spin-lattice relaxation time (within laboratory, Tj and rotating, frames) measurements were carried out (Figure 8.16) to investigate molecular motions in different frequency ranges. Experimental data show that the main components of flour (starch and gluten proteins) are in a glassy phase, whereas... 

The thermoplasticity of material proteins has been utilised to produce materials using thermal or thermomechanical processes under low hydration conditions, as already employed for starch- or polyolefin-based materials [136, 152]. According to the thermoplastic behaviour of synthetic polymers, the Tg of the proteins involves sudden variations in their physical properties (thermal, mechanical, dielectric properties and so on). The molecular response associated with the transition from the glassy to the rubbery state involves an overall increase in the free volume and macromolecule mobility [153,154]. As for synthetic polymers, the Tg of the proteins is affected by the MW, chain rigidity, size and polarity of the lateral groups, presence of intermolecular bonds or crystalline zones, and also by the plasticiser type and concentration [155,156]. 

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