Key interactions in biodegradable thermoplastic starch/poly(vinyl alcohol)/montmorillonite micro- and nanocomposites

A series of thermoplastic starch/poly(vinylalcohol)(PVOH)/montmorillonite (Na-MMT) micro- and nanocomposites which exhibit intercalated and highly exfoliated structures have been developed. Fourier transform infrared (FTIR) spectra of the thermoplastic starch and starch nanocomposites showed a number or variants in H-bonding between starch chains, PVOH and Na-MMT during extrusion processing. The addition of small amounts of PVOH to the starch nanocomposite produced a very ordered intercalated structure. The relative concentrations of PVOH and Na-MMT could be directly correlated to changes in intergallery spacings. Although good dispersion of clay platelets was important in improving mechanical properties in these nanocomposites the interfacial interactions of filler and matrix played just as important a role (the more agglomerated composites) containing both Na-MMT and PVOH showed significant increases in tensile strength (up to 67% increase) and tensile modulus (up to 85% increase) as compared to the more well dispersed composites without PVOH. The improvements in properties could be attributed to both interfacial interactions and the disruption of the retrogradation (recrystallisation process).