Green Synthesis and Fractionation of Cellulose Acetate by Controlling the Reactivity of Polysaccharides in Sugarcane Bagasse
Shiori Suzuki, Risa Yada, Yosuke Hamano, Naoki Wada, Kenji Takahashi
Abstract
A green synthetic protocol was developed to prepare cellulose acetate (CA) directly from sugarcane bagasse without using any pretreatments or corrosive reagents, such as strong acids, bases, or halogenated chemicals. The key in this method is to control the reactivities of cellulose and xylan-based hemicellulose in bagasse under mild conditions, making their solubilities in acetone different. Homogeneous transesterification was performed for bagasse at 50 °C using isopropenyl acetate as an acetyl donor and 1-ethyl-3-methylimidazolium acetate as a solvent and catalyst. By controlling the reaction temperature, the degree of substitution for cellulose was adjusted to 2.5–2.8 to maintain solubility in acetone, while the acetylation of hemicellulose was suppressed to prevent its dissolution in acetone. In the subsequent fractionation process, the hemicellulose-rich component was first precipitated in acetone and removed by filtration. The filtrate was subsequently separated into lignin- and cellulose-rich fractions by solid–liquid separation using methanol. Then, CA as the target compound was collected as the acetone-soluble and methanol-insoluble fraction, with a sufficiently high purity (∼90%), according to FT-IR and 1H NMR analyses.