Dynamics and viscoelasticity of potato and corn starch bio-polymers reinforced with bentonite nanoclay

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 T-g of PS/bentonite nanocomposites, however the T-g 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 alpha and alpha', whereas PS film displayed only the alpha relaxation. The alpha relaxation was associated with the glass transition whereas the alpha' 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 E-c 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.