Starch/zirconium phosphate composite films: Hydration, thermal stability, and mechanical properties

Composite films of plasticized potato starch filled with 1, 4, and 6 wt% zirconium phosphate (ZrP) particles have been prepared by casting mixtures of gelatinized starch, a gel of partially exfoliated ZrP in water, and glycerol. The XRD patterns of the composite films reveal the formation of glycerol intercalated ZrP for the highest filler loadings (4 and 6 wt%) while suggest partial filler exfoliation for the composite with 1 wt% ZrP, in agreement with TEM analysis. The presence of the filler improves the thermal resistance of the starch, both at low and, particularly, at high temperature. The composites also exhibit a significant enhancement in the Young's modulus (from ∼700 MPa for neat starch up to ∼1600 MPa for 6 wt% filler loading) and in the yield stress (from ∼17 to ∼38 MPa). The increase in stiffness is concomitant with a water uptake reduction, which is maximum at 100% relative humidity.