Proton NMR relaxometry as probe of gelatinization, plasticization and montmorillonite-loading effects on starch-based materials

The effects of granule disruption, the addition of glycerol and montmorillonite on the granule structure of corn starch were investigated by proton NMR relaxation, through the T2*, T1 and T1ρ relaxation times. Films containing 0%, 1%, 5% and 7% (w/w) of clay were prepared by solution casting and the relaxometry data were compared with those gleaned from WAXD, TGA and SEM techniques. Starch gelatinization without glycerol or clay results in an amorphous and rigid film having a dipole coupling higher than that observed for the granule. The plasticization reduces the chains rigid fraction by more than 20% and increases the adsorption of moisture in the region of greater molecular mobility. The addition of 1% of clay reduces the adsorption of moisture and, in concentrations of 5% and 7%, the agglomerates reduce the plasticization effect. These features studied were observed by the Tube-Reptation and Renormalized Rouse models applied at low frequencies.