Maleimide grafting onto polysaccharides via mild condition esterification and its impact on their structure

This study proposes an innovative approach to tailor the properties of two polysaccharides, microcrystalline cellulose (MCC) and potato starch, through chemical modification in dispersion. The methodology involves the grafting of 6-Maleimidohexanoic acid (6-MHA) moieties onto hydroxyl groups of the polysaccharides without dissolving them in order to keep their native structure preserved. To overcome the slow and inefficient reaction between carboxylic acids of 6-MHA and hydroxyl groups of the polysaccharides, a vinyl ester of 6-MHA was synthesized through the transvinylation of 6-MHA acid with vinyl acetate. The resulting 6-MHA ester was employed to introduce a new functionality to polysaccharides' hydroxyl groups via transesterification, catalyzed by potassium carbonate. To enhance the reactivity, the polysaccharides were mercerized prior to modification process. The efficiency of the transesterification reaction between the vinyl ester of 6-MHA and the hydroxyl groups of the polysaccharides was confirmed using Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (NMR). Thermal behavior analysis was carried out using thermogravimetric analysis (TGA), while changes in crystallinity resulting from the modification were assessed through X-ray diffraction analysis (XRD). Finally, the impact of the modification on the morphology of polysaccharides was examined with environmental scanning electron microscopy (ESEM). Despite changes in microstructure, MCC kept its macrostructure remained morphologically unchanged while the granular structure of starch was damaged. Maleimide grafting onto MCC and starch has the potential to turn them into thermally reversible materials for various applications such as debondable adhesive or coating.