A high-resolution solid-state NMR study on starch–clay nanocomposites and the effect of aging on clay dispersion

Abstract

High-resolution solid-state nuclear magnetic resonance (NMR) was applied as a bulk analysis method to provide an indication of clay dispersion in starch–clay nanocomposites. The starch composite containing 2.5 wt% nano-clay appeared as an exfoliated system with an average distance between clay platelets (<D̄>) of around 40 nm. Increasing the amount of nano-clay to 5.0 wt% reduced the <D̄> value to around 20 nm. Aging displayed a minimal effect on the exfoliation of starch–clay nanocomposites. However, the <D̄> value became much larger on introduction of 5 wt% polyvinyl alcohol (PVOH) into the systems because of the formation of aggregated structures, and the <D̄> value increased further after aging. The motion of PVOH molecules during the aging period could function as a driving force toward a more stable interaction between PVOH chains and clay platelets, thus resulting in a reduction in the degree of clay exfoliation in the starch matrix. The high-resolution solid-state NMR technique was applied as a bulk analysis method to provide an indication of nano-clay dispersion in starch–clay nanocomposites. The effects of having polyvinyl alcohol as additives and aging up to 105 days were also investigated.