Preparation of water-soluble dialdehyde nanocelluloses by periodate oxidation under microwave irradiation

Abstract

Water-soluble dialdehyde nanocellulose was readily produced at room temperature by sodium periodate oxidation under microwave irradiation. The effect of various experimental parameters, such as reaction temperature, cellulose to periodate ratio and microwave power, on periodate oxidation of cellulose, during one to five hours of irradiation, were investigated. FT-IR spectroscopy and aldehyde content analyses revealed two stage reaction rates: an initial rapid oxidation in the amorphous region, followed by a slower second reaction across the crystalline surface. The chain-cleavage accompanying the introduction of dialdehyde groups contributed to an increase in the water solubility and a decrease in the thermal stability of cellulose nanoparticles, which reached sizes of about 200-300 nm. The five specimens prepared using three to five hours of microwave irradiation were readily dissolved in water by simple stirring at room temperature. Additional heating at 55 °C for an hour solubilized the other specimens. XRD investigation substantiated a decrease in the crystalline area by ring breakage. FeSEM analyses also verified the morphological changes that occurred in the oxidized nanocelluloses.