Aspects of the preparation of starch microcellular foam particles crosslinked with glutaraldehyde using a solvent exchange technique

Starch microcellular foam (SMCF) has been produced using a solvent exchange technique with a native corn starch crosslinked with glutaraldehyde. To produce a high specific surface area for the starch particles the cooked starch solution was reacted with glutaraldehyde and then precipitated under shear with ethanol. The relationship between the crosslinking density on the void structure of the SMCF has been studied. Characterization by NMR confirmed the crosslinking reaction. An increase in the glutaraldehyde concentration from 0 to 15 g glutaraldehyde/100 g starch was accompanied by a decrease in particle size and moisture content and an increase in brightness and specific surface area. Scanning electron microscope images of the SMCF particles show that the smallest average void diameter obtained was 0.182 μm at a 7.5 g glutaraldehyde/100 g starch. Four starch materials having different viscosity were prepared by hydrolysis of the native corn starch with a 1 N HCl/methanol system for different reaction durations to investigate the relationship between starch molecular weight and void structure of the SMCF. The starches were crosslinked with 15 g glutaraldehyde/100 g starch and precipitated with ethanol to form SMCF. Decreasing the starch viscosity decreased the brightness and specific surface area, and increased the particle size, void diameter and moisture content. Increases in stirring speed during the precipitation enhanced the properties of the SMCF particles. The effect of pressing the starch particles to form a pellet caused a collapse of the foam structure at pressures above about 6000 psi. The results indicate that the structure/chemistry of the starch material and the processing conditions can be controlled in order to produce particles with morphology and properties useful for light scattering applications. In particular, higher molecular weight and intermolecular crosslinking and high shear during precipitation have been found to enhance the foam formation.