Two-Step Carboxymethylation of Cellulose from <i>Halocynthia roretzi</i> Using Ionic Liquid

Water-soluble carboxymethylated tunicate cellulose (CMTC) was produced using cellulose from <i>Halocynthia roretzi</i>, known for its uniquely high molecular weight and crystallinity. Among various known methods for cellulose carboxymethylation tested in this study, only the homogeneous method using LiClO₄ yielded water-soluble CMTC. However, industrial application of this method is hindered by LiClO₄'s toxicity, explosiveness, and high cost. Therefore, we developed a two-step carboxymethylation process utilizing [Emim][Ac], effectively converting crystalline cellulose into an amorphous form and reducing both the degree of polymerization (DP) and polydispersity index (PDI). CMTC prepared by this two-step method exhibited a high degree of substitution (DS = 1.94), excellent water solubility (>100 mg/g), and superior thermal stability. Compared to the LiClO₄-based CMTC, our product contained only 5% unmodified glucose and demonstrated significantly enhanced thickening properties, with 8-fold greater viscosity in 5% aqueous solutions. Structural properties were confirmed via HPLC, ¹H NMR, XRD, FT-IR, and TGA analyses.