  We envision that dispersion between two polymeric materials on mesoscales
would create new composites with properties that are much more superior to the
components alone. Here we elucidate the dispersion between two of most abundant
natural polysaccharides, starch and chitosan, which form mesoscale composites
that may promise many applications. By using X-ray microscopic imaging,
small-angle X-ray scattering, and differential scanning calorimetry, we were
able to characterize the interactions of chitosan and starch in the mesoscale
composites. The morphology of the composite is far more complex from the simple
mixture of starch granules with a nominal size of a few micrometers and
chitosan microbundles of tens and hundreds of micrometers. This unique
morphology can only be explained by the enhanced miscibility of chitosan in a
starch granular matrix. It is evidenced that there is a possible ionic
interaction between the amino group in chitosan and the hydroxyl groups in
starch granules. Despite the limited solubility of chitosan in water, this
ionic interaction allows for the disassembly of chitosan microbundles within
the starch suspension. The result is a chemically stronger and more stable
granular composite formed by two biocompatible and biodegradable polysaccharide
polymers. The mechanism of chitosan to disperse throughout starch granules has
implications for the application of chitosan in water and other solvents.
