Abstract
The influence of bentonite nanoclay on the viscoelasticity and dynamics of potato starch (PS) and corn starch (CS) films was investigated. Free standing films were plasticized with glycerol and displayed elastomeric behavior. The addition of bentonite (up to 4 wt%) increased the glass transition temperature Tg of PS/bentonite nanocomposites, however the Tg of CS/bentonite nanocomposites was reduced. On the other hand, bentonite increased the tensile modulus E’ of both type of nanocomposites. Dynamic mechanical analysis (DMA) showed that CS film displayed two mechanical relaxations, named α and α’, whereas PS film displayed only the α relaxation. The α relaxation was associated with the glass transition whereas the α’ relaxation appears to be associated to starch-rich domains due to lower miscibility of CS with glycerol. Rheology showed that bentonite increased the rubbery modulus Ec of the nanocomposites thus explaining the mechanical reinforcement. The starch nanocomposites exhibited exfoliated and intercalated morphologies (at low and higher bentonite content, respectively). Hence, nanoconfinement and domain separation appear to drive the thermo-mechanical properties and dynamics of the starch-based nanocomposites.
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